Spin Seebeck effect and thermoelectric phenomena in superconducting hybrids with magnetic textures or spin-orbit coupling.

PubMed

Bathen, Marianne Etzelmüller; Linder, Jacob

2017-01-31

We theoretically consider the spin Seebeck effect, the charge Seebeck coefficient, and the thermoelectric figure of merit in superconducting hybrid structures including either magnetic textures or intrinsic spin-orbit coupling. We demonstrate that large magnitudes for all these quantities are obtainable in Josephson-based systems with either zero or a small externally applied magnetic field. This provides an alternative to the thermoelectric effects generated in high-field (~1 T) superconducting hybrid systems, which were recently experimentally demonstrated. The systems studied contain either conical ferromagnets, spin-active interfaces, or spin-orbit coupling. We present a framework for calculating the linear thermoelectric response for both spin and charge of a system upon applying temperature and voltage gradients based on quasiclassical theory which allows for arbitrary spin-dependent textures and fields to be conveniently incorporated.

Spin-orbit coupling controlled ground state in Sr 2 ScOsO 6

DOE PAGES

Taylor, A. E.; Morrow, R.; Fishman, R. S.; ...

2016-06-27

In this paper, we report neutron scattering experiments which reveal a large spin gap in the magnetic excitation spectrum of weakly-monoclinic double perovskite Sr 2ScOsO 6. The spin gap is demonstrative of appreciable spin-orbit-induced anisotropy, despite nominally orbitally-quenched 5d 3Os 5+ ions. The system is successfully modeled including nearest neighbor interactions in a Heisenberg Hamiltonian with exchange anisotropy. We find that the presence of the spin-orbit-induced anisotropy is essential for the realization of the type I antiferromagnetic ground state. Finally, this demonstrates that physics beyond the LS or JJ coupling limits plays an active role in determining the collective propertiesmore » of 4d 3 and 5d 3 systems and that theoretical treatments must include spin-orbit coupling.« less

Spin-orbit coupling controlled ground state in Sr 2 ScOsO 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, A. E.; Morrow, R.; Fishman, R. S.

In this paper, we report neutron scattering experiments which reveal a large spin gap in the magnetic excitation spectrum of weakly-monoclinic double perovskite Sr 2ScOsO 6. The spin gap is demonstrative of appreciable spin-orbit-induced anisotropy, despite nominally orbitally-quenched 5d 3Os 5+ ions. The system is successfully modeled including nearest neighbor interactions in a Heisenberg Hamiltonian with exchange anisotropy. We find that the presence of the spin-orbit-induced anisotropy is essential for the realization of the type I antiferromagnetic ground state. Finally, this demonstrates that physics beyond the LS or JJ coupling limits plays an active role in determining the collective propertiesmore » of 4d 3 and 5d 3 systems and that theoretical treatments must include spin-orbit coupling.« less

Spin-orbit-coupled fermions in an optical lattice clock

NASA Astrophysics Data System (ADS)

Kolkowitz, S.; Bromley, S. L.; Bothwell, T.; Wall, M. L.; Marti, G. E.; Koller, A. P.; Zhang, X.; Rey, A. M.; Ye, J.

2017-02-01

Engineered spin-orbit coupling (SOC) in cold-atom systems can enable the study of new synthetic materials and complex condensed matter phenomena. However, spontaneous emission in alkali-atom spin-orbit-coupled systems is hindered by heating, limiting the observation of many-body effects and motivating research into potential alternatives. Here we demonstrate that spin-orbit-coupled fermions can be engineered to occur naturally in a one-dimensional optical lattice clock. In contrast to previous SOC experiments, here the SOC is both generated and probed using a direct ultra-narrow optical clock transition between two electronic orbital states in 87Sr atoms. We use clock spectroscopy to prepare lattice band populations, internal electronic states and quasi-momenta, and to produce spin-orbit-coupled dynamics. The exceptionally long lifetime of the excited clock state (160 seconds) eliminates decoherence and atom loss from spontaneous emission at all relevant experimental timescales, allowing subsequent momentum- and spin-resolved in situ probing of the SOC band structure and eigenstates. We use these capabilities to study Bloch oscillations, spin-momentum locking and Van Hove singularities in the transition density of states. Our results lay the groundwork for using fermionic optical lattice clocks to probe new phases of matter.

Spin and charge controlled by antisymmetric spin-orbit coupling in a triangular-triple-quantum-dot Kondo system

NASA Astrophysics Data System (ADS)

Koga, M.; Matsumoto, M.; Kusunose, H.

2018-05-01

We study a local antisymmetric spin-orbit (ASO) coupling effect on a triangular-triple-quantum-dot (TTQD) system as a theoretical proposal for a new application of the Kondo physics to nanoscale devices. The electric polarization induced by the Kondo effect is strongly correlated with the spin configurations and molecular orbital degrees of freedom in the TTQD. In particular, an abrupt sign reversal of the emergent electric polarization is associated with a quantum critical point in a magnetic field, which can also be controlled by the ASO coupling that changes the mixing weight of different orbital components in the TTQD ground state.

The Consequences of Spin-Orbit Coupling on the 5d3 Electronic Configuration

NASA Astrophysics Data System (ADS)

Christianson, A. D.

The impact of spin-orbit coupling on collective properties of matter is of considerable interest. The most intensively investigated materials in this regard are Iridium-based transition metal oxides which exhibit a host of interesting ground states that originate from a 5d5 Jeff = 1/2 electronic configuration. Moving beyond the Jeff = 1/2 paradigm to other electronic configurations where spin-orbit coupling plays a prominent role is a key objective of ongoing research. Here we focus on several Osmium-based transition metal oxides such as NaOsO3, Cd2Os2O7, Ca3LiOsO6, Sr2ScOsO6, Ba2YOsO6, and Sr2FeOsO6, which are nominally in the 5d3 electronic configuration. Within the LS coupling picture and a strong octahedral crystal field, the 5d3 configuration is expected to be an orbital singlet and spin-orbit effects should be minimal. Nevertheless, our neutron and x-ray scattering investigations of these materials as well as investigations by other groups show dramatic effects of spin-orbit coupling including reduced moment magnetic order, enhanced spin-phonon coupling, and large spin gaps. In particular, the anisotropy induced by spin-orbit coupling tips the balance of the frustrated interactions and drives the selection of particular magnetic ground states. To understand the mechanism driving the spin-orbit effects, we have explored the ground state t2g manifold with resonant inelastic x-ray scattering and observe a spectrum inexplicable by an LS coupling picture. On the other hand, an intermediate coupling approach reveals that the ground state wave function is a J =3/2 configuration which answers the question of how strong spin-orbit coupling effects arise in 5d3 systems.

Exciton Polaritons in a Two-Dimensional Lieb Lattice with Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Whittaker, C. E.; Cancellieri, E.; Walker, P. M.; Gulevich, D. R.; Schomerus, H.; Vaitiekus, D.; Royall, B.; Whittaker, D. M.; Clarke, E.; Iorsh, I. V.; Shelykh, I. A.; Skolnick, M. S.; Krizhanovskii, D. N.

2018-03-01

We study exciton polaritons in a two-dimensional Lieb lattice of micropillars. The energy spectrum of the system features two flat bands formed from S and Px ,y photonic orbitals, into which we trigger bosonic condensation under high power excitation. The symmetry of the orbital wave functions combined with photonic spin-orbit coupling gives rise to emission patterns with pseudospin texture in the flat band condensates. Our Letter shows the potential of polariton lattices for emulating flat band Hamiltonians with spin-orbit coupling, orbital degrees of freedom, and interactions.

Exciton Polaritons in a Two-Dimensional Lieb Lattice with Spin-Orbit Coupling.

PubMed

Whittaker, C E; Cancellieri, E; Walker, P M; Gulevich, D R; Schomerus, H; Vaitiekus, D; Royall, B; Whittaker, D M; Clarke, E; Iorsh, I V; Shelykh, I A; Skolnick, M S; Krizhanovskii, D N

2018-03-02

We study exciton polaritons in a two-dimensional Lieb lattice of micropillars. The energy spectrum of the system features two flat bands formed from S and P_{x,y} photonic orbitals, into which we trigger bosonic condensation under high power excitation. The symmetry of the orbital wave functions combined with photonic spin-orbit coupling gives rise to emission patterns with pseudospin texture in the flat band condensates. Our Letter shows the potential of polariton lattices for emulating flat band Hamiltonians with spin-orbit coupling, orbital degrees of freedom, and interactions.

Electric field controlled spin interference in a system with Rashba spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciftja, Orion, E-mail: ogciftja@pvamu.edu

There have been intense research efforts over the last years focused on understanding the Rashba spin-orbit coupling effect from the perspective of possible spintronics applications. An important component of this line of research is aimed at control and manipulation of electron’s spin degrees of freedom in semiconductor quantum dot devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system embedded in a host semiconducting material that lacks inversion-symmetry. This way, the Rashba spin-orbit coupling effect may potentially lead to fabrication of amore » new generation of spintronic devices where control of spin, thus magnetic properties, is achieved via an electric field and not a magnetic field. In this work we investigate theoretically the electron’s spin interference and accumulation process in a Rashba spin-orbit coupled system consisting of a pair of two-dimensional semiconductor quantum dots connected to each other via two conducting semi-circular channels. The strength of the confinement energy on the quantum dots is tuned by gate potentials that allow “leakage” of electrons from one dot to another. While going through the conducting channels, the electrons are spin-orbit coupled to a microscopically generated electric field applied perpendicular to the two-dimensional system. We show that interference of spin wave functions of electrons travelling through the two channels gives rise to interference/conductance patterns that lead to the observation of the geometric Berry’s phase. Achieving a predictable and measurable observation of Berry’s phase allows one to control the spin dynamics of the electrons. It is demonstrated that this system allows use of a microscopically generated electric field to control Berry’s phase, thus, enables one to tune the spin-dependent interference pattern and spintronic properties with no need for injection of spin-polarized electrons.« less

The influence of spin orbit coupling and a current dependent potential on the residual resistivity of disordered magnetic alloys

NASA Astrophysics Data System (ADS)

Ebert, H.; Vernes, A.; Banhart, J.

1999-11-01

It has been shown recently, for a number of various magnetic disordered alloy systems, that the spin-orbit coupling (SOC) may have an important influence on the isotropic residual resistivity and that it is the primary source of the galvano-magnetic properties spontaneous magnetoresistance anisotropy (SMA) and anomalous Hall resistivity (AHR). Here it is demonstrated that—in contrast to many other spin-orbit induced phenomena—all these findings stem from the part of the spin-orbit coupling that gives rise to a mixing of the two spin sub-systems. In line with this result it is shown that inclusion of a current dependent potential within a calculation of the underlying electronic structure hardly affects the transport properties if the corresponding magnetic vector potential does not lead to a mixing of the spin sub-systems.

Towards a global model of spin-orbit coupling in the halocarbenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nyambo, Silver; Karshenas, Cyrus; Reid, Scott A., E-mail: scott.reid@marquette.edu, E-mail: dawesr@mst.edu

We report a global analysis of spin-orbit coupling in the mono-halocarbenes, CH(D)X, where X = Cl, Br, and I. These are model systems for examining carbene singlet-triplet energy gaps and spin-orbit coupling. Over the past decade, rich data sets collected using single vibronic level emission spectroscopy and stimulated emission pumping spectroscopy have yielded much information on the ground vibrational level structure and clearly demonstrated the presence of perturbations involving the low-lying triplet state. To model these interactions globally, we compare two approaches. First, we employ a diabatic treatment of the spin-orbit coupling, where the coupling matrix elements are written inmore » terms of a purely electronic spin-orbit matrix element which is independent of nuclear coordinates, and an integral representing the overlap of the singlet and triplet vibrational wavefunctions. In this way, the structures, harmonic frequencies, and normal mode displacements from ab initio calculations were used to calculate the vibrational overlaps of the singlet and triplet state levels, including the full effects of Duschinsky mixing. These calculations have allowed many new assignments to be made, particularly for CHI, and provided spin-orbit coupling parameters and values for the singlet-triplet gaps. In a second approach, we have computed and fit full geometry dependent spin-orbit coupling surfaces and used them to compute matrix elements without the product form approximation. Those matrix elements were used in similar fits varying the anharmonic constants and singlet-triplet gap to reproduce the experimental levels. The derived spin-orbit parameters for carbenes CHX (X = Cl, Br, and I) show an excellent linear correlation with the atomic spin-orbit constant of the corresponding halogen, indicating that the spin-orbit coupling in the carbenes is consistently around 14% of the atomic value.« less

Unconventional Bose—Einstein Condensations from Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Wu, Cong-Jun; Ian, Mondragon-Shem; Zhou, Xiang-Fa

2011-09-01

According to the “no-node" theorem, the many-body ground state wavefunctions of conventional Bose—Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on a subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree—Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the “order-from-disorder" mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.

Generalized Stoner criterion and versatile spin ordering in two-dimensional spin-orbit coupled electron systems

NASA Astrophysics Data System (ADS)

Liu, Weizhe Edward; Chesi, Stefano; Webb, David; Zülicke, U.; Winkler, R.; Joynt, Robert; Culcer, Dimitrie

2017-12-01

Spin-orbit coupling is a single-particle phenomenon known to generate topological order, and electron-electron interactions cause ordered many-body phases to exist. The rich interplay of these two mechanisms is present in a broad range of materials and has been the subject of considerable ongoing research and controversy. Here we demonstrate that interacting two-dimensional electron systems with strong spin-orbit coupling exhibit a variety of time reversal symmetry breaking phases with unconventional spin alignment. We first prove that a Stoner-type criterion can be formulated for the spin polarization response to an electric field, which predicts that the spin polarization susceptibility diverges at a certain value of the electron-electron interaction strength. The divergence indicates the possibility of unconventional ferromagnetic phases even in the absence of any applied electric or magnetic field. This leads us, in the second part of this work, to study interacting Rashba spin-orbit coupled semiconductors in equilibrium in the Hartree-Fock approximation as a generic minimal model. Using classical Monte Carlo simulations, we construct the complete phase diagram of the system as a function of density and spin-orbit coupling strength. It includes both an out-of-plane spin-polarized phase and in-plane spin-polarized phases with shifted Fermi surfaces and rich spin textures, reminiscent of the Pomeranchuk instability, as well as two different Fermi-liquid phases having one and two Fermi surfaces, respectively, which are separated by a Lifshitz transition. We discuss possibilities for experimental observation and useful application of these novel phases, especially in the context of electric-field-controlled macroscopic spin polarizations.

Analysis of Bose system in spin-orbit coupled Bose-Fermi mixture to induce a spin current of fermions

NASA Astrophysics Data System (ADS)

Sakamoto, R.; Ono, Y.; Hatsuda, R.; Shiina, K.; Arahata, E.; Mori, H.

2018-03-01

We found that a spin current of fermions could be induced in spin-orbit coupled Bose-Fermi mixture at zero temperature. Since spatial change of the spin structure of the bosons is necessary to induce the spin current of the fermions, we analyzed the ground state of the bosons in the mixture system, using a variational method. The obtained phase diagram indicated the presence of a bosonic phase that allowed the fermions to have a spin current.

The Influence of the Optical Phonons on the Non-equilibrium Spin Current in the Presence of Spin-Orbit Couplings

NASA Astrophysics Data System (ADS)

Hasanirokh, K.; Phirouznia, A.; Majidi, R.

2016-02-01

The influence of the electron coupling with non-polarized optical phonons on magnetoelectric effects of a two-dimensional electron gas system has been investigated in the presence of the Rashba and Dresselhaus spin-orbit couplings. Numerical calculations have been performed in the non-equilibrium regime. In the previous studies in this field, it has been shown that the Rashba and Dresselhaus couplings cannot generate non-equilibrium spin current and the spin current vanishes identically in the absence of other relaxation mechanisms such as lattice vibrations. However, in the current study, based on a semiclassical approach, it was demonstrated that in the presence of electron-phonon coupling, the spin current and other magnetoelectric quantities have been modulated by the strength of the spin-orbit interactions.

Measure synchronization in a spin-orbit-coupled bosonic Josephson junction

NASA Astrophysics Data System (ADS)

Wang, Wen-Yuan; Liu, Jie; Fu, Li-Bin

2015-11-01

We present measure synchronization (MS) in a bosonic Josephson junction with spin-orbit coupling. The two atomic hyperfine states are coupled by a Raman dressing scheme, and they are regarded as two orientations of a pseudo-spin-1 /2 system. A feature specific to a spin-orbit-coupled (SOC) bosonic Josephson junction is that the transition from non-MS to MS dynamics can be modulated by Raman laser intensity, even in the absence of interspin atomic interaction. A phase diagram of non-MS and MS dynamics as functions of Raman laser intensity and Josephson tunneling amplitude is presented. Taking into account interspin atomic interactions, the system exhibits MS breaking dynamics resulting from the competition between intraspin and interspin atomic interactions. When interspin atomic interactions dominate in the competition, the system always exhibits MS dynamics. For interspin interaction weaker than intraspin interaction, a window for non-MS dynamics is present. Since SOC Bose-Einstein condensates provide a powerful platform for studies on physical problems in various fields, the study of MS dynamics is valuable in researching the collective coherent dynamical behavior in a spin-orbit-coupled bosonic Josephson junction.

Exact results relating spin-orbit interactions in two-dimensional strongly correlated systems

NASA Astrophysics Data System (ADS)

Kucska, Nóra; Gulácsi, Zsolt

2018-06-01

A 2D square, two-bands, strongly correlated and non-integrable system is analysed exactly in the presence of many-body spin-orbit interactions via the method of Positive Semidefinite Operators. The deduced exact ground states in the high concentration limit are strongly entangled, and given by the spin-orbit coupling are ferromagnetic and present an enhanced carrier mobility, which substantially differs for different spin projections. The described state emerges in a restricted parameter space region, which however is clearly accessible experimentally. The exact solutions are provided via the solution of a matching system of equations containing 74 coupled, non-linear and complex algebraic equations. In our knowledge, other exact results for 2D interacting systems with spin-orbit interactions are not present in the literature.

Energetic and dynamical instability of spin-orbit coupled Bose-Einstein condensate in a deep optical lattice

NASA Astrophysics Data System (ADS)

Yu, Zi-Fa; Chai, Xu-Dan; Xue, Ju-Kui

2018-05-01

We investigate the energetic and dynamical instability of spin-orbit coupled Bose-Einstein condensate in a deep optical lattice via a tight-binding model. The stability phase diagram is completely revealed in full parameter space, while the dependence of superfluidity on the dispersion relation is illustrated explicitly. In the absence of spin-orbit coupling, the superfluidity only exists in the center of the Brillouin zone. However, the combination of spin-orbit coupling, Zeeman field, nonlinearity and optical lattice potential can modify the dispersion relation of the system, and change the position of Brillouin zone for generating the superfluidity. Thus, the superfluidity can appear in either the center or the other position of the Brillouin zone. Namely, in the center of the Brillouin zone, the system is either superfluid or Landau unstable, which depends on the momentum of the lowest energy. Therefore, the superfluidity can occur at optional position of the Brillouin zone by elaborating spin-orbit coupling, Zeeman splitting, nonlinearity and optical lattice potential. For the linear case, the system is always dynamically stable, however, the nonlinearity can induce the dynamical instability, and also expand the superfluid region. These predicted results can provide a theoretical evidence for exploring the superfluidity of the system experimentally.

Spin-Orbit Coupling Controlled J = 3 / 2 Electronic Ground State in 5 d 3 Oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, A. E.; Calder, S.; Morrow, R.

Entanglement of spin and orbital degrees of freedom drives the formation of novel quantum and topological physical states. Here we report resonant inelastic x-ray scattering measurements of the transition metal oxides Ca3LiOsO6 and Ba2YOsO6, which reveals a dramatic spitting of the t2g manifold. We invoke an intermediate coupling approach that incorporates both spin-orbit coupling and electron-electron interactions on an even footing and reveal that the ground state of 5d3-based compounds, which has remained elusive in previously applied models, is a novel spin-orbit entangled J=3/2 electronic ground state. This work reveals the hidden diversity of spin-orbit controlled ground states in 5dmore » systems and introduces a new arena in the search for spin-orbit controlled phases of matter.« less

Perspective: Interface generation of spin-orbit torques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Perspective: Interface generation of spin-orbit torques

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2016-11-14

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Spin-orbit torques and anisotropic magnetization damping in skyrmion crystals

NASA Astrophysics Data System (ADS)

Hals, Kjetil M. D.; Brataas, Arne

2014-02-01

The length scale of the magnetization gradients in chiral magnets is determined by the relativistic Dzyaloshinskii-Moriya interaction. Thus, even conventional spin-transfer torques are controlled by the relativistic spin-orbit coupling in these systems, and additional relativistic corrections to the current-induced torques and magnetization damping become important for a complete understanding of the current-driven magnetization dynamics. We theoretically study the effects of reactive and dissipative homogeneous spin-orbit torques and anisotropic damping on the current-driven skyrmion dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit torques play a significant role in the current-induced skyrmion velocity. The dissipative spin-orbit torque generates a relativistic Magnus force on the skyrmions, whereas the reactive spin-orbit torque yields a correction to both the drift velocity along the current direction and the transverse velocity associated with the Magnus force. The spin-orbit torque corrections to the velocity scale linearly with the skyrmion size, which is inversely proportional to the spin-orbit coupling. Consequently, the reactive spin-orbit torque correction can be the same order of magnitude as the nonrelativistic contribution. More importantly, the dissipative spin-orbit torque can be the dominant force that causes a deflected motion of the skyrmions if the torque exhibits a linear or quadratic relationship with the spin-orbit coupling. In addition, we demonstrate that the skyrmion velocity is determined by anisotropic magnetization damping parameters governed by the skyrmion size.

Stationary states and rotational properties of spin-orbit-coupled Bose-Einstein condensates held under a toroidal trap

NASA Astrophysics Data System (ADS)

He, Zhang-Ming; Zhang, Xiao-Fei; Kato, Masaya; Han, Wei; Saito, Hiroki

2018-06-01

We consider a pseudospin-1/2 Bose-Einstein condensate with Rashba spin-orbit coupling in a two-dimensional toroidal trap. By solving the damped Gross-Pitaevskii equations for this system, we show that the system exhibits a rich variety of stationary states, such as vehicle wheel and flower-petal stripe patterns. These stationary states are stable against perturbation with thermal energy and can survive for a long time. In the presence of rotation, our results show that the rotating systems have exotic vortex configurations. These phenomenon originates from the interplay among spin-orbit coupling, trap geometry, and rotation.

Synthetic Spin-Orbit and Light Field Coupling in Ultra-cold Quantum Gases

NASA Astrophysics Data System (ADS)

Dong, Lin

Ultra-cold quantum gases subjected to light-induced synthetic gauge potentials have become an emergent field of theoretical and experimental studies. Because of the novel application of two-photon Raman transitions, ultra-cold neutral atoms behave like charged particles in magnetic field. The Raman coupling naturally gives rise to an effective spin-orbit interaction which couples the atoms center-of-mass motion to its selected pseudo-spin degrees of freedom. Combined with unprecedented controllability of interactions, geometry, disorder strength, spectroscopy, and high resolution measurement of momentum distribution, etc., we are truly in an exciting era of fulfilling and going beyond Richard Feynman's vision. of realizing quantum simulators to better understand the quantum mechanical nature of the universe, manifested immensely in the ultra-cold regimes. In this dissertation, we present a collection of theoretical progresses made by the doctoral candidate and his colleagues and collaborators. From the past few years of work, we mainly address three aspects of the synthetic spin-orbit and light field induced coupling in ultracold quantum gases: a) The ground-state physics of singleparticle system, two-body bound states, and many-body systems, all of which are subjected to spin-orbit coupling originated from synthetic gauge potentials; b) The symmetry breaking, topological phase transition and quench dynamics, which are conveniently offered by the realized experimental setup; c) The proposal and implications of light field induced dynamical spin-orbit coupling for atoms inside optical cavity. Our work represents an important advancement of theoretical understanding to the active research frontier of ultra-cold atom physics with spin-orbit coupling.

Ab initio theory of spin-orbit coupling for quantum bits in diamond exhibiting dynamic Jahn-Teller effect

NASA Astrophysics Data System (ADS)

Gali, Adam; Thiering, Gergő

Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. In particular, the high-spin negatively charged nitrogen-vacancy defect (NV) in diamond has become a leading contender in solid-state quantum information processing. The initialization and readout of the spin is based on the spin-selective decay of the photo-excited electron to the ground state which is mediated by spin-orbit coupling between excited states states and phonons. Generally, the spin-orbit coupling plays a crucial role in the optical spinpolarization and readout of NV quantum bit (qubit) and alike. Strong electron-phonon coupling in dynamic Jahn-Teller (DJT) systems can substantially influence the effective strength of spin-orbit coupling. Here we show by ab initio supercell density functional theory (DFT) calculations that the intrinsic spin-orbit coupling is strongly damped by DJT effect in the triplet excited state that has a consequence on the rate of non-radiative decay. This theory is applied to the ground state of silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in their negatively charged state that can also act like qubits. We show that the intrinsic spin-orbit coupling in SiV and GeV centers is in the 100 GHz region, in contrast to the NV center of 10 GHz region. Our results provide deep insight in the nature of SiV and GeV qubits in diamond. EU FP7 DIADEMS project (Contract No. 611143).

Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene

NASA Astrophysics Data System (ADS)

Ferreira, Aires; Milletari, Mirco

Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect. A.F. gratefully acknowledges the financial support of the Royal Society (U.K.).

Energy-level repulsion by spin-orbit coupling in two-dimensional Rydberg excitons

NASA Astrophysics Data System (ADS)

Stephanovich, V. A.; Sherman, E. Ya.; Zinner, N. T.; Marchukov, O. V.

2018-05-01

We study the effects of Rashba spin-orbit coupling on two-dimensional Rydberg exciton systems. Using analytical and numerical arguments we demonstrate that this coupling considerably modifies the wave functions and leads to a level repulsion that results in a deviation from the Poissonian statistics of the adjacent level distance distribution. This signifies the crossover to nonintegrability of the system and hints at the possibility of quantum chaos emerging. Such behavior strongly differs from the classical realization, where spin-orbit coupling produces highly entangled, chaotic electron trajectories in an exciton. We also calculate the oscillator strengths and show that randomization appears in the transitions between states with different total momenta.

Ultracold Atoms in a Square Lattice with Spin-Orbit Coupling: Charge Order, Superfluidity, and Topological Signatures

NASA Astrophysics Data System (ADS)

Rosenberg, Peter; Shi, Hao; Zhang, Shiwei

2017-12-01

We present an ab initio, numerically exact study of attractive fermions in square lattices with Rashba spin-orbit coupling. The ground state of this system is a supersolid, with coexisting charge and superfluid order. The superfluid is composed of both singlet and triplet pairs induced by spin-orbit coupling. We perform large-scale calculations using the auxiliary-field quantum Monte Carlo method to provide the first full, quantitative description of the charge, spin, and pairing properties of the system. In addition to characterizing the exotic physics, our results will serve as essential high-accuracy benchmarks for the intense theoretical and especially experimental efforts in ultracold atoms to realize and understand an expanding variety of quantum Hall and topological superconductor systems.

Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling

PubMed Central

Levy, Miguel; Karki, Dolendra

2017-01-01

We present a formulation of electromagnetic spin-orbit coupling in magneto-optic media, and propose an alternative source of spin-orbit coupling to non-paraxial optics vortices. Our treatment puts forth a formulation of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media. It shows that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity- and magnetization-dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation. This unidirectional effect produces different orbital angular momenta in opposite directions upon excitation-spin-helicity reversals. PMID:28059120

Mid-IR Lasers: Challenges Imposed by the Population Dynamics of the Gain System

DTIC Science & Technology

2010-09-01

MicroSystems (IOMS) Central-Field Approximation: Perturbations 1. a) Non-centrosymmetric splitting (Coulomb interaction) ⇒ total orbital angular momentum b...Accordingly: ⇒ total electron-spin momentum 2. Spin-orbit coupling (“LS” coupling) ⇒ total angular momentum lanthanides: intermediate coupling (LS / jj) 3...MicroSystems (IOMS) Luminescence Decay Curves Rate-equation for decay: Solution ( Bernoulli -Eq.): Linearized solution: T. Jensen, Ph.D. Thesis, Univ. Hamburg

Finite-Momentum Dimer Bound State in Spin-Orbit Coupled Fermi Gas

NASA Astrophysics Data System (ADS)

Dong, Lin; Jiang, Lei; Hu, Hui; Pu, Han

2013-03-01

We investigate the two-body properties of a spin-1/2 Fermi gas subject to a spin-orbit coupling induced by laser fields. When attractive s-wave interaction between unlike spins is present, the system may form a dimer bound state. Surprisingly, under proper conditions, the bound state obtains finite center-of-mass momentum, whereas under the same condition but in the absence of the two-body interaction, the system has zero total momentum. This unusual result can be regarded as a consequence of the broken Galilean invariance by the spin-orbit coupling. Such a finite-momentum bound state will have profound effects on the many-body properties of the system. HP is supported by the NSF, the Welch Foundation (Grant No. C-1669), and DARPA. HH is supported by the ARC Discovery Projects (Grant No. DP0984522) and the National Basic Research Program of China (NFRP-China, Grant No. 2011CB921502).

Reinventing atomic magnetic simulations with spin-orbit coupling

DOE PAGES

Perera, Meewanage Dilina N.; Eisenbach, Markus; Nicholson, Don M.; ...

2016-02-10

We propose a powerful extension to the combined molecular and spin dynamics method that fully captures the coupling between the atomic and spin subsystems via spin-orbit interactions. Moreover, the foundation of this method lies in the inclusion of the local magnetic anisotropies that arise as a consequence of the lattice symmetry breaking due to phonons or crystallographic defects. By using canonical simulations of bcc iron with the system coupled to a phonon heat bath, we show that our extension enables the previously unachievable angular momentum exchange between the atomic and spin degrees of freedom.

Effects of structural spin-orbit coupling in two dimensional electron and hole liquids

NASA Astrophysics Data System (ADS)

Chesi, Stefano

The recent interest in spin-dependent phenomena in semiconductor heterostructures motivates our detailed study of the structural spin-orbit coupling present in clean two-dimensional electron and hole liquids. Interesting polarization effects are produced in a system out of equilibrium, as when a finite current flows in the sample. In particular, the consequences of a lateral confinement creating a quasi one-dimensional wire are studied in detail, partially motivated by a recent experimental investigation of the point-contact transmission for two-dimensional holes. We also address the role of the electron-electron interaction in the presence of spin-orbit coupling, which has received little attention in the literature. We discuss the formulation of the Hartree-Fock approximation in the particular case of linear Rashba spin-orbit. We establish the form of the mean-field phase diagram in the homogeneous case, which shows a complex interplay between paramagnetic and ferromagnetic states. The latter can be polarized in the plane or in a transverse direction, and are characterized by a complex spin structure and nontrivial occupation. The generality of the Hartree-Fock method allows a simple treatment of the Pauli spin susceptibility, and the application to different forms of spin-orbit coupling. Correlation corrections can be obtained in an analytic form for particular asymptotic regimes. For linear Rashba spin-orbit we identified the relevance of the large spin-orbit limit, dominated by many-body effects, and explicitly treated the high density limit, in which the system is asymptotically noninteracting. As a special case, we derive a new exact formula for the polarization dependence of the ring-diagram correlation energy.

Highly Anisotropic Magnon Dispersion in Ca_{2}RuO_{4}: Evidence for Strong Spin Orbit Coupling.

PubMed

Kunkemöller, S; Khomskii, D; Steffens, P; Piovano, A; Nugroho, A A; Braden, M

2015-12-11

The magnon dispersion in Ca_{2}RuO_{4} has been determined by inelastic neutron scattering on single crytals containing 1% of Ti. The dispersion is well described by a conventional Heisenberg model suggesting a local moment model with nearest neighbor interaction of J=8  meV. Nearest and next-nearest neighbor interaction as well as interlayer coupling parameters are required to properly describe the entire dispersion. Spin-orbit coupling induces a very large anisotropy gap in the magnetic excitations in apparent contrast with a simple planar magnetic model. Orbital ordering breaking tetragonal symmetry, and strong spin-orbit coupling can thus be identified as important factors in this system.

Theoretical study of spin Hall effect in conjugated Organic semiconductors

NASA Astrophysics Data System (ADS)

Mahani, M. R.; Delin, A.

The spin Hall effect (SHE), a direct conversion between electronic and spin currents, is a rapidly growing branch of spintronics. The study of SHE in conjugated polymers has gained momentum recently due to the weak spin-orbit couplings and hyperfine interactions in these materials. Our calculations of SHE based on the recent work, are the result of the misalignment of pi-orbitals in triads consisting of three molecules. In disordered organics, where the electronic conduction is through hopping of the electrons among randomly oriented molecules, instead of identifying a hopping triad to represent the entire system, we numerically solve the master equations for electrical and spin hall conductivities by summing the contributions from all triads in a sufficiently large system. The interference between the direct and indirect hoppings in these triads leads to SHE proportional to the orientation vector of molecule at the first order of spin-orbit coupling. Hence, our results show, the degree of molecular alignment as well as the strength of the spin-orbit coupling can be used to control the SHE in organics.

Spin-orbit coupling and the static polarizability of single-wall carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, Ginetom S., E-mail: ginetom@gmail.com; Ulloa, Sergio E.

2014-07-14

We calculate the static longitudinal polarizability of single-wall carbon tubes in the long wavelength limit taking into account spin-orbit effects. We use a four-orbital orthogonal tight-binding formalism to describe the electronic states and the random phase approximation to calculate the dielectric function. We study the role of both the Rashba as well as the intrinsic spin-orbit interactions on the longitudinal dielectric response, i.e., when the probing electric field is parallel to the nanotube axis. The spin-orbit interaction modifies the nanotube electronic band dispersions, which may especially result in a small gap opening in otherwise metallic tubes. The bandgap size andmore » state features, the result of competition between Rashba and intrinsic spin-orbit interactions, result in drastic changes in the longitudinal static polarizability of the system. We discuss results for different nanotube types and the dependence on nanotube radius and spin-orbit couplings.« less

Development of New Open-Shell Perturbation and Coupled-Cluster Theories Based on Symmetric Spin Orbitals

NASA Technical Reports Server (NTRS)

Lee, Timothy J.; Arnold, James O. (Technical Monitor)

1994-01-01

A new spin orbital basis is employed in the development of efficient open-shell coupled-cluster and perturbation theories that are based on a restricted Hartree-Fock (RHF) reference function. The spin orbital basis differs from the standard one in the spin functions that are associated with the singly occupied spatial orbital. The occupied orbital (in the spin orbital basis) is assigned the delta(+) = 1/square root of 2(alpha+Beta) spin function while the unoccupied orbital is assigned the delta(-) = 1/square root of 2(alpha-Beta) spin function. The doubly occupied and unoccupied orbitals (in the reference function) are assigned the standard alpha and Beta spin functions. The coupled-cluster and perturbation theory wave functions based on this set of "symmetric spin orbitals" exhibit much more symmetry than those based on the standard spin orbital basis. This, together with interacting space arguments, leads to a dramatic reduction in the computational cost for both coupled-cluster and perturbation theory. Additionally, perturbation theory based on "symmetric spin orbitals" obeys Brillouin's theorem provided that spin and spatial excitations are both considered. Other properties of the coupled-cluster and perturbation theory wave functions and models will be discussed.

Resonant spin Hall effect in two dimensional electron gas

NASA Astrophysics Data System (ADS)

Shen, Shun-Qing

2005-03-01

Remarkable phenomena have been observed in 2DEG over last two decades, most notably, the discovery of integer and fractional quantum Hall effect. The study of spin transport provides a good opportunity to explore spin physics in two-dimensional electron gas (2DEG) with spin-orbit coupling and other interaction. It is already known that the spin-orbit coupling leads to a zero-field spin splitting, and competes with the Zeeman spin splitting if the system is subjected to a magnetic field perpendicular to the plane of 2DEG. The result can be detected as beating of the Shubnikov-de Haas oscillation. Very recently the speaker and his collaborators studied transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin-orbit coupling competes with the Zeeman splitting to generate additional degeneracies between different Landau levels at certain magnetic fields. It is predicted theoretically that this degeneracy, if occurring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as -lnT at low temperatures. The charge Hall conductance changes by 2e^2/h instead of e^2/h as the magnetic field changes through the resonant point. The speaker will address the resonance condition, symmetries in the spin-orbit coupling, the singularity of magnetic susceptibility, nonlinear electric field effect, the edge effect and the disorder effect due to impurities. This work was supported by the Research Grants Council of Hong Kong under Grant No.: HKU 7088/01P. *S. Q. Shen, M. Ma, X. C. Xie, and F. C. Zhang, Phys. Rev. Lett. 92, 256603 (2004) *S. Q. Shen, Y. J. Bao, M. Ma, X. C. Xie, and F. C. Zhang, cond-mat/0410169

Observation of orbital order in the half-filled 4 f Gd compound

DOE PAGES

Jang, H.; Kang, B. Y.; Cho, B. K.; ...

2016-11-18

Half-filled electron systems, even with the maximized spin angular moment, have been given little attention because of their zero-orbital angular moment according to Hund’s rule. Nevertheless, there are several measurements that show evidence of a nonzero orbital moment as well as spin-orbit coupling. Here we report for the first time the orbital order in a half-filled 4f-electron system GdB 4, using the resonant soft x-ray scattering at Gd M 4,5-edges. Furthermore, we discovered that the development of this orbital order is strongly coupled with the antiferromagnetic spin order. Lastly, these results clearly demonstrate that even in half-filled electron systems themore » orbital angular moment can be an important parameter to describe material properties, and may provide significant opportunities for tailoring new correlated electron systems.« less

Observation of orbital order in the half-filled 4 f Gd compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, H.; Kang, B. Y.; Cho, B. K.

Half-filled electron systems, even with the maximized spin angular moment, have been given little attention because of their zero-orbital angular moment according to Hund’s rule. Nevertheless, there are several measurements that show evidence of a nonzero orbital moment as well as spin-orbit coupling. Here we report for the first time the orbital order in a half-filled 4f-electron system GdB 4, using the resonant soft x-ray scattering at Gd M 4,5-edges. Furthermore, we discovered that the development of this orbital order is strongly coupled with the antiferromagnetic spin order. Lastly, these results clearly demonstrate that even in half-filled electron systems themore » orbital angular moment can be an important parameter to describe material properties, and may provide significant opportunities for tailoring new correlated electron systems.« less

Perturbative treatment of spin-orbit-coupling within spin-free exact two-component theory using equation-of-motion coupled-cluster methods

NASA Astrophysics Data System (ADS)

Cheng, Lan; Wang, Fan; Stanton, John F.; Gauss, Jürgen

2018-01-01

A scheme is reported for the perturbative calculation of spin-orbit coupling (SOC) within the spin-free exact two-component theory in its one-electron variant (SFX2C-1e) in combination with the equation-of-motion coupled-cluster singles and doubles method. Benchmark calculations of the spin-orbit splittings in 2Π and 2P radicals show that the accurate inclusion of scalar-relativistic effects using the SFX2C-1e scheme extends the applicability of the perturbative treatment of SOC to molecules that contain heavy elements. The contributions from relaxation of the coupled-cluster amplitudes are shown to be relatively small; significant contributions from correlating the inner-core orbitals are observed in calculations involving third-row and heavier elements. The calculation of term energies for the low-lying electronic states of the PtH radical, which serves to exemplify heavy transition-metal containing systems, further demonstrates the quality that can be achieved with the pragmatic approach presented here.

The effects of Rashba spin-orbit coupling on spin-polarized transport in hexagonal graphene nano-rings and flakes

NASA Astrophysics Data System (ADS)

Laghaei, M.; Heidari Semiromi, E.

2018-03-01

Quantum transport properties and spin polarization in hexagonal graphene nanostructures with zigzag edges and different sizes were investigated in the presence of Rashba spin-orbit interaction (RSOI). The nanostructure was considered as a channel to which two semi-infinite armchair graphene nanoribbons were coupled as input and output leads. Spin transmission and spin polarization in x, y, and z directions were calculated through applying Landauer-Buttiker formalism with tight binding model and the Green's function to the system. In these quantum structures it is shown that changing the size of system, induce and control the spin polarized currents. In short, these graphene systems are typical candidates for electrical spintronic devices as spin filtering.

Quantum ring with the Rashba spin-orbit interaction in the regime of strong light-matter coupling

NASA Astrophysics Data System (ADS)

Kozin, V. K.; Iorsh, I. V.; Kibis, O. V.; Shelykh, I. A.

2018-04-01

We developed the theory of electronic properties of semiconductor quantum rings with the Rashba spin-orbit interaction irradiated by an off-resonant high-frequency electromagnetic field (dressing field). Within the Floquet theory of periodically driven quantum systems, it is demonstrated that the dressing field drastically modifies all electronic characteristics of the rings, including spin-orbit coupling, effective electron mass, and optical response. In particular, the present effect paves the way to controlling the spin polarization of electrons with light in prospective ring-shaped spintronic devices.

Interface roughness mediated phonon relaxation rates in Si quantum dots.

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Hsueh, Yuling; Klimeck, Gerhard; Rahman, Rajib

2015-03-01

Si QDs are promising candidates for solid-state quantum computing due to long spin coherence times. However, the valley degeneracy in Si adds an additional degree of freedom to the electronic structure. Although the valley and orbital indices can be uniquely identified in an ideal Si QD, interface roughness mixes valley and orbital states in realistic dots. Such valley-orbit coupling can strongly influence T1 times in Si QDs. Recent experimental measurements of various relaxation rates differ from previous predictions of phonon relaxation in ideal Si QDs. To understand how roughness affects different relaxation rates, for example spin relaxation due to spin-valley coupling, which is a byproduct of spin-orbit and valley-orbit coupling, we need to understand the effect of valley-orbit coupling on valley relaxation first. Using a full-band atomistic tight-binding description for both the system's electron and electron-phonon hamiltonian, we analyze the effect of atomic-scale interface disorder on phonon induced valley relaxation and spin relaxation in a Si QD. We find that, the valley splitting dependence of valley relaxation rate governs the magnetic field dependence of spin relaxation rate. Our results help understand experimentally measured relaxation times.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

NASA Astrophysics Data System (ADS)

Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

2015-10-01

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

Phonon-drag magnetothermopower in Rashba spin-split two-dimensional electron systems.

PubMed

Biswas, Tutul; Ghosh, Tarun Kanti

2013-10-16

We study the phonon-drag contribution to the thermoelectric power in a quasi-two-dimensional electron system confined in GaAs/AlGaAs heterostructure in the presence of both Rashba spin-orbit interaction and perpendicular magnetic field at very low temperature. It is observed that the peaks in the phonon-drag thermopower split into two when the Rashba spin-orbit coupling constant is strong. This splitting is a direct consequence of the Rashba spin-orbit interaction. We show the dependence of phonon-drag thermopower on both magnetic field and temperature numerically. A power-law dependence of phonon-drag magnetothermopower on the temperature in the Bloch-Gruneisen regime is found. We also extract the exponent of the temperature dependence of phonon-drag thermopower for different parameters like electron density, magnetic field, and the spin-orbit coupling constant.

Bose-Einstein condensate in an optical lattice with Raman-assisted two-dimensional spin-orbit coupling

NASA Astrophysics Data System (ADS)

Pan, Jian-Song; Zhang, Wei; Yi, Wei; Guo, Guang-Can

2016-10-01

In a recent experiment (Z. Wu, L. Zhang, W. Sun, X.-T. Xu, B.-Z. Wang, S.-C. Ji, Y. Deng, S. Chen, X.-J. Liu, and J.-W. Pan, arXiv:1511.08170 [cond-mat.quant-gas]), a Raman-assisted two-dimensional spin-orbit coupling has been realized for a Bose-Einstein condensate in an optical lattice potential. In light of this exciting progress, we study in detail key properties of the system. As the Raman lasers inevitably couple atoms to high-lying bands, the behaviors of the system in both the single- and many-particle sectors are significantly affected. In particular, the high-band effects enhance the plane-wave phase and lead to the emergence of "roton" gaps at low Zeeman fields. Furthermore, we identify high-band-induced topological phase boundaries in both the single-particle and the quasiparticle spectra. We then derive an effective two-band model, which captures the high-band physics in the experimentally relevant regime. Our results not only offer valuable insights into the two-dimensional lattice spin-orbit coupling, but also provide a systematic formalism to model high-band effects in lattice systems with Raman-assisted spin-orbit couplings.

Dynamics of bright-bright solitons in Bose-Einstein condensate with Raman-induced one-dimensional spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wen, Lin; Zhang, Xiao-Fei; Hu, Ai-Yuan; Zhou, Jing; Yu, Peng; Xia, Lei; Sun, Qing; Ji, An-Chun

2018-03-01

We investigate the dynamics of bright-bright solitons in one-dimensional two-component Bose-Einstein condensates with Raman-induced spin-orbit coupling, via the variational approximation and the numerical simulation of Gross-Pitaevskii equations. For the uniform system without trapping potential, we obtain two population balanced stationary solitons. By performing the linear stability analysis, we find a Goldstone eigenmode and an oscillation eigenmode around these stationary solitons. Moreover, we derive a general dynamical solution to describe the center-of-mass motion and spin evolution of the solitons under the action of spin-orbit coupling. The effects of a harmonic trap have also been discussed.

Spin-exchange-induced spin-orbit coupling in a superfluid mixture

NASA Astrophysics Data System (ADS)

Chen, Li; Zhu, Chuanzhou; Zhang, Yunbo; Pu, Han

2018-03-01

We investigate the ground-state properties of a dual-species spin-1/2 Bose-Einstein condensate. One of the species is subjected to a pair of Raman laser beams that induces spin-orbit (SO) coupling, whereas the other species is not coupled to the Raman laser. In certain limits, analytical results can be obtained. It is clearly shown that, through the interspecies spin-exchange interaction, the second species also exhibits SO coupling. This mixture system displays a very rich phase diagram, with many of the phases not present in an SO-coupled single-species condensate. Our work provides a way of creating SO coupling in atomic quantum gases, and opens up an avenue of research in SO-coupled superfluid mixtures. From a practical point of view, the spin-exchange-induced SO coupling may overcome the heating issue for certain atomic species when subjected to Raman beams.

Angular dependence of spin-orbit spin-transfer torques

NASA Astrophysics Data System (ADS)

Lee, Ki-Seung; Go, Dongwook; Manchon, Aurélien; Haney, Paul M.; Stiles, M. D.; Lee, Hyun-Woo; Lee, Kyung-Jin

2015-04-01

In ferromagnet/heavy-metal bilayers, an in-plane current gives rise to spin-orbit spin-transfer torque, which is usually decomposed into fieldlike and dampinglike torques. For two-dimensional free-electron and tight-binding models with Rashba spin-orbit coupling, the fieldlike torque acquires nontrivial dependence on the magnetization direction when the Rashba spin-orbit coupling becomes comparable to the exchange interaction. This nontrivial angular dependence of the fieldlike torque is related to the Fermi surface distortion, determined by the ratio of the Rashba spin-orbit coupling to the exchange interaction. On the other hand, the dampinglike torque acquires nontrivial angular dependence when the Rashba spin-orbit coupling is comparable to or stronger than the exchange interaction. It is related to the combined effects of the Fermi surface distortion and the Fermi sea contribution. The angular dependence is consistent with experimental observations and can be important to understand magnetization dynamics induced by spin-orbit spin-transfer torques.

Spin orbital singlet system FeSc2S4 under pressure

NASA Astrophysics Data System (ADS)

Biffin, Alun; Chernyshov, Dmitry; Canevet, Emmanuel; Fennell, Tom; White, Jonathan S.; Khasanov, Rustem; Luetkens, Hubertus; Loidl, Alois; Tsurkan, Vladimir; Rüegg, Christian

The role of orbital degrees of freedom in quantum magnets is receiving intense focus recently, with the understanding that spin-orbit coupled systems can display physics qualitatively different from their spin only counter parts. An example is the spin-orbital singlet (SOS) state, which can provide an alternative to the conventional spin and orbitally ordered groundstates of quantum magnets. In such a scenario, the relative strengths of the exchange interaction and spin orbit coupling parameters determine the low temperature structure, with the former preferring ordered moments and the latter a non-magnetic singlet. Moreover the quantum critical point separating these two phases is rather unique in that it marks the onset of criticality in both the spin and orbital sectors. This SOS picture has recently been applied to FeSc2S4, where despite strong antiferromagnetic exchange between Jahn-Teller active Fe2+ ions no experimental signature of spin or orbital order has been detected. Building on our previous neutron scattering measurements, we have used hydrostatic pressure in neutron scattering, muon spin rotation and x-ray diffraction measurements to probe the unique phase diagram of FeSc2S4. My talk will focus on the results and interpretation of these experiments SNF SCOPES project IZ73Z0_152734/1, the Marie Curie FP7 COFUND PSI Fellowship program, Swiss National Science Foundation.

Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes.

PubMed

Seo, Dong-Kyun

2007-11-14

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.

Circular-Polarization-Selective Transmission Induced by Spin-Orbit Coupling in a Helical Tape Waveguide

NASA Astrophysics Data System (ADS)

Liu, Yahong; Guo, Qinghua; Liu, Hongchao; Liu, Congcong; Song, Kun; Yang, Biao; Hou, Quanwen; Zhao, Xiaopeng; Zhang, Shuang; Navarro-Cía, Miguel

2018-05-01

Spin-orbit coupling of light, describing the interaction between the polarization (spin) and spatial degrees of freedom (orbit) of light, plays an important role in subwavelength scale systems and leads to many interesting phenomena, such as the spin Hall effect of light. Here, based on the spin-orbit coupling, we design and fabricate a helical tape waveguide (HTW), which can realize a circular-polarization-selective process. When the incident circularly polarized wave is of the same handedness as the helix of the HTW, a nearly complete transmission is observed; in contrast, a counterrotating circular polarization of incident wave results in a much lower transmission or is even totally blocked by the HTW. Indeed, both simulations and experiments reveal that the blocked component of power leaks through the helical aperture of the HTW and forms a conical beam analogous to helical Cherenkov radiation due to the conversion from the spin angular momentum to the orbital angular momentum. Our HTW structure demonstrates its potential as a polarization selector in a broadband frequency range.

Spin-orbit coupling effects in zinc-blende InSb and wurtzite InAs nanowires: Realistic calculations with multiband k .p method

NASA Astrophysics Data System (ADS)

Campos, Tiago; Faria Junior, Paulo E.; Gmitra, Martin; Sipahi, Guilherme M.; Fabian, Jaroslav

2018-06-01

A systematic numerical investigation of spin-orbit fields in the conduction bands of III-V semiconductor nanowires is performed. Zinc-blende (ZB) InSb nanowires are considered along [001], [011], and [111] directions, while wurtzite (WZ) InAs nanowires are studied along [0001] and [10 1 ¯0 ] or [11 2 ¯0 ] directions. Robust multiband k .p Hamiltonians are solved by using plane-wave expansions of real-space parameters. In all cases, the linear and cubic spin-orbit coupling parameters are extracted for nanowire widths from 30 to 100 nm. Typical spin-orbit energies are on the μ eV scale, except for WZ InAs nanowires grown along [10 1 ¯0 ] or [11 2 ¯0 ] , in which the spin-orbit energy is about meV, largely independent of the wire diameter. Significant spin-orbit coupling is obtained by applying a transverse electric field, causing the Rashba effect. For an electric field of about 4 mV/nm, the obtained spin-orbit energies are about 1 meV for both materials in all investigated growth directions. The most favorable system, in which the spin-orbit effects are maximal, are WZ InAs nanowires grown along [1010] or [11 2 ¯0 ] since here spin-orbit energies are giant (meV) already in the absence of electric field. The least favorable are InAs WZ nanowires grown along [0001] since here even the electric field does not increase the spin-orbit energies beyond 0.1 meV. The presented results should be useful for investigations of optical orientation, spin transport, weak localization, and superconducting proximity effects in semiconductor nanowires.

One-electron versus electron-electron interaction contributions to the spin-spin coupling mechanism in nuclear magnetic resonance spectroscopy: Analysis of basic electronic effects

NASA Astrophysics Data System (ADS)

Gräfenstein, Jürgen; Cremer, Dieter

2004-12-01

For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. 1J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas 2J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of 1J(C,H) and 2J(H,H), respectively, for hydrocarbons.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

DOE PAGES

Ma, X.; Fang, F.; Li, Q.; ...

2015-10-28

In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

Inverse engineering for fast transport and spin control of spin-orbit-coupled Bose-Einstein condensates in moving harmonic traps

NASA Astrophysics Data System (ADS)

Chen, Xi; Jiang, Ruan-Lei; Li, Jing; Ban, Yue; Sherman, E. Ya.

2018-01-01

We investigate fast transport and spin manipulation of tunable spin-orbit-coupled Bose-Einstein condensates in a moving harmonic trap. Motivated by the concept of shortcuts to adiabaticity, we design inversely the time-dependent trap position and spin-orbit-coupling strength. By choosing appropriate boundary conditions we obtain fast transport and spin flip simultaneously. The nonadiabatic transport and relevant spin dynamics are illustrated with numerical examples and compared with the adiabatic transport with constant spin-orbit-coupling strength and velocity. Moreover, the influence of nonlinearity induced by interatomic interaction is discussed in terms of the Gross-Pitaevskii approach, showing the robustness of the proposed protocols. With the state-of-the-art experiments, such an inverse engineering technique paves the way for coherent control of spin-orbit-coupled Bose-Einstein condensates in harmonic traps.

Drude weight and optical conductivity of a two-dimensional heavy-hole gas with k-cubic spin-orbit interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mawrie, Alestin; Ghosh, Tarun Kanti

We present a detailed theoretical study on zero-frequency Drude weight and optical conductivity of a two-dimensional heavy-hole gas (2DHG) with k-cubic Rashba and Dresselhaus spin-orbit interactions. The presence of k-cubic spin-orbit couplings strongly modifies the Drude weight in comparison to the electron gas with k-linear spin-orbit couplings. For large hole density and strong k-cubic spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. We establish a relation between optical conductivity and the Berry connection. Unlike two-dimensional electron gas with k-linear spin-orbit couplings, we explicitly show that the optical conductivity does not vanish even for equal strengthmore » of the two spin-orbit couplings. We attribute this fact to the non-zero Berry phase for equal strength of k-cubic spin-orbit couplings. The least photon energy needed to set in the optical transition in hole gas is one order of magnitude smaller than that of electron gas. Types of two van Hove singularities appear in the optical spectrum are also discussed.« less

Majorana surface modes of nodal topological pairings in spin-3/2 semimetals

NASA Astrophysics Data System (ADS)

Yang, Wang; Xiang, Tao; Wu, Congjun

2017-10-01

When solid state systems possess active orbital-band structures subject to spin-orbit coupling, their multicomponent electronic structures are often described in terms of effective large-spin fermion models. Their topological structures of superconductivity are beyond the framework of spin singlet and triplet Cooper pairings for spin-1/2 systems. Examples include the half-Heusler compound series of RPtBi, where R stands for a rare-earth element. Their spin-orbit coupled electronic structures are described by the Luttinger-Kohn model with effective spin-3/2 fermions and are characterized by band inversion. Recent experiments provide evidence to unconventional superconductivity in the YPtBi material with nodal spin-septet pairing. We systematically study topological pairing structures in spin-3/2 systems with the cubic group symmetries and calculate the surface Majorana spectra, which exhibit zero energy flat bands, or, cubic dispersion depending on the specific symmetry of the superconducting gap functions. The signatures of these surface states in the quasiparticle interference patterns of tunneling spectroscopy are studied, which can be tested in future experiments.

Effect of cubic Dresselhaus interaction on the longitudinal optical conductivity of a spin-orbit coupled system

NASA Astrophysics Data System (ADS)

Cruz, Elmer; López-Bastidas, Catalina; Maytorena, Jesús A.

2018-03-01

We investigate the effect of the oft-neglected cubic terms of the Dresselhaus spin-orbit coupling on the longitudinal current response of a two-dimensional electron gas with both Rashba and linear Dresselhaus interactions. For a quantum well grown in the [001] direction, the changes caused by these nonlinear-in-momentum terms on the absorption spectrum become more notable under SU(2) symmetry conditions, when the Rashba and linear Dresselhaus coupling strengths are tuned to be equal. The longitudinal optical response no longer vanishes then and shows a strong dependence on the direction of the externally applied electric field, giving a signature of the relative size of several spin-orbit contributions. This anisotropic response arises from the nonisotropic splitting of the spin states induced by the interplay of Rashba and Dresselhaus couplings. However, the presence of cubic terms introduces characteristic spectral features and can modify the overall shape of the spectra for some values of the relative sizes of the spin-orbit parameters. We compare this behavior to the case of a sample with [110] crystal orientation which, under conditions of spin-preserving symmetry, has a collinear spin-orbit vector field that leads to vanishing conductivity, even in the presence of cubic terms. In addition to the control through the driven frequency or electrical gating, such a directional aspect of the current response suggests new ways of manipulation and supports the use of interband optics as a sensitive probe of spin-orbit mechanisms in semiconductor spintronics.

Antisymmetric Spin-Orbit Coupling in a d-p Model on a Zigzag Chain

DOE PAGES

Sugita, Yusuke; Hayami, Satoru; Motome, Yukitoshi

2015-12-29

In this paper, we theoretically investigate how an antisymmetric spin-orbit coupling emerges in electrons moving on lattice structures which are centrosymmetric but break the spatial inversion symme- try at atomic positions. We construct an effective d-p model on the simplest lattice structure, a zigzag chain of edge-sharing octahedra, with taking into account the crystalline electric field, the spin-orbit coupling, and on-site and inter-site d-p hybridizations. We show that an effective antisymmetric spin-orbit coupling arises in the sublattice-dependent form, which results in a hidden spin polarization in the band structure. Finally, we explicitly derive the effective antisymmetric spin-orbit coupling for dmore » electrons, which not only explains the hidden spin polarization but also indicates how to enhance it.« less

Antisymmetric Spin-Orbit Coupling in a d-p Model on a Zigzag Chain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugita, Yusuke; Hayami, Satoru; Motome, Yukitoshi

In this paper, we theoretically investigate how an antisymmetric spin-orbit coupling emerges in electrons moving on lattice structures which are centrosymmetric but break the spatial inversion symme- try at atomic positions. We construct an effective d-p model on the simplest lattice structure, a zigzag chain of edge-sharing octahedra, with taking into account the crystalline electric field, the spin-orbit coupling, and on-site and inter-site d-p hybridizations. We show that an effective antisymmetric spin-orbit coupling arises in the sublattice-dependent form, which results in a hidden spin polarization in the band structure. Finally, we explicitly derive the effective antisymmetric spin-orbit coupling for dmore » electrons, which not only explains the hidden spin polarization but also indicates how to enhance it.« less

Relativistic effects on the NMR parameters of Si, Ge, Sn, and Pb alkynyl compounds: Scalar versus spin-orbit effects

NASA Astrophysics Data System (ADS)

Demissie, Taye B.

2017-11-01

The NMR chemical shifts and indirect spin-spin coupling constants of 12 molecules containing 29Si, 73Ge, 119Sn, and 207Pb [X(CCMe)4, Me2X(CCMe)2, and Me3XCCH] are presented. The results are obtained from non-relativistic as well as two- and four-component relativistic density functional theory (DFT) calculations. The scalar and spin-orbit relativistic contributions as well as the total relativistic corrections are determined. The main relativistic effect in these molecules is not due to spin-orbit coupling but rather to the scalar relativistic contraction of the s-shells. The correlation between the calculated and experimental indirect spin-spin coupling constants showed that the four-component relativistic density functional theory (DFT) approach using the Perdew's hybrid scheme exchange-correlation functional (PBE0; using the Perdew-Burke-Ernzerhof exchange and correlation functionals) gives results in good agreement with experimental values. The indirect spin-spin coupling constants calculated using the spin-orbit zeroth order regular approximation together with the hybrid PBE0 functional and the specially designed J-coupling (JCPL) basis sets are in good agreement with the results obtained from the four-component relativistic calculations. For the coupling constants involving the heavy atoms, the relativistic corrections are of the same order of magnitude compared to the non-relativistically calculated results. Based on the comparisons of the calculated results with available experimental values, the best results for all the chemical shifts and non-existing indirect spin-spin coupling constants for all the molecules are reported, hoping that these accurate results will be used to benchmark future DFT calculations. The present study also demonstrates that the four-component relativistic DFT method has reached a level of maturity that makes it a convenient and accurate tool to calculate indirect spin-spin coupling constants of "large" molecular systems involving heavy atoms.

Symmetry-enriched Bose-Einstein condensates in a spin-orbit-coupled bilayer system

NASA Astrophysics Data System (ADS)

Cheng, Jia-Ming; Zhou, Xiang-Fa; Zhou, Zheng-Wei; Guo, Guang-Can; Gong, Ming

2018-01-01

We consider the fate of Bose-Einstein condensation with time-reversal symmetry and inversion symmetry in a spin-orbit-coupled bilayer system. When these two symmetry operators commute, all the single-particle bands are exactly twofold degenerate in the momentum space. The scattering in the twofold-degenerate rings can relax the spin-momentum locking effect from spin-orbit-coupling interaction and thus can realize the spin-polarized plane-wave phase even when the interparticle interaction dominates. When these two operators anticommute, the lowest two bands may have the same minimal energy, but with totally different spin structures. As a result, the competition between different condensates in these two energetically degenerate rings can give rise to different stripe phases with atoms condensed at two or four collinear momenta. We find that the crossover between these two cases is accompanied by the excited band condensation when the interference energy can overcome the increased single-particle energy in the excited band. This effect is not based on strong interaction and thus can be realized even with moderate interaction strength.

Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-04-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary disks, and inclined binary companions may tilt the stellar spin axis with respect to the disk's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disk evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disk photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disk-binary systems. We take into account planet-disk interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disk via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with "cold" Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Planet formation in discs with inclined binary companions: can primordial spin-orbit misalignment be produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-07-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary discs, and inclined binary companions may tilt the stellar spin axis with respect to the disc's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disc evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disc photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disc-binary systems. We take into account planet-disc interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disc via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with `cold' Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Local nature of impurity induced spin-orbit torques

NASA Astrophysics Data System (ADS)

Nikolaev, Sergey; Kalitsov, Alan; Chshiev, Mairbec; Mryasov, Oleg

Spin-orbit torques are of a great interest due to their potential applications for spin electronics. Generally, it originates from strong spin orbit coupling of heavy 4d/5d elements and its mechanism is usually attributed either to the Spin Hall effect or Rashba spin-orbit coupling. We have developed a quantum-mechanical approach based on the non-equilibrium Green's function formalism and tight binding Hamiltonian model to study spin-orbit torques and extended our theory for the case of extrinsic spin-orbit coupling induced by impurities. For the sake of simplicity, we consider a magnetic material on a two dimensional lattice with a single non-magnetic impurity. However, our model can be easily extended for three dimensional layered heterostructures. Based on our calculations, we present the detailed analysis of the origin of local spin-orbit torques and persistent charge currents around the impurity, that give rise to spin-orbit torques even in equilibrium and explain the existence of anisotropy.

Strong spin-orbit coupling and Zeeman spin splitting in angle dependent magnetoresistance of Bi{sub 2}Te{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Rik, E-mail: rikdey@utexas.edu; Pramanik, Tanmoy; Roy, Anupam

We have studied angle dependent magnetoresistance of Bi{sub 2}Te{sub 3} thin film with field up to 9 T over 2–20 K temperatures. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the spin-orbit relaxation time. We have obtained the out-of-plane spin-orbit relaxation time to be small and the in-plane spin-orbit relaxation time to be comparable to the momentum relaxation time. The estimation of these charge and spin transport parameters are useful for spintronics applications. For parallel field magnetoresistance,more » we have confirmed the presence of Zeeman effect which is otherwise suppressed in perpendicular field magnetoresistance due to strong spin-orbit coupling. The parallel field data have been explained using both the contributions from the Maekawa-Fukuyama localization theory for non-interacting electrons and Lee-Ramakrishnan theory of electron-electron interactions. The estimated Zeeman g-factor and the strength of Coulomb screening parameter agree well with the theory. Finally, the anisotropy in magnetoresistance with respect to angle has been described by the Hikami-Larkin-Nagaoka theory. This anisotropy can be used in anisotropic magnetic sensor applications.« less

Spin-orbit coupling and tidal dissipation in hot Jupiter systems

NASA Astrophysics Data System (ADS)

Shabaltas, Natalia Igorevna

Hot Jupiters are giant planets located extremely close to their host stars, with orbital periods less than 5 days. Many aspects of hot Jupiter (HJ) formation remain unclear, but several clues, such as the observed misalignment between their orbital axes and their hosts' spin axes, point to a dynamical origin. In the first portion of this work we explore the stellar spin-orbit dynamics of one such dynamical formation channel, the Lidov-Kozai mechanism. We show that the coupling between the stellar spin and the planet orbit can lead to complex, and sometimes chaotic, behavior of the stellar spin vector. Many features of this behavior arise due to a set of resonances between the stellar spin axis precession timescale and the Lidov-Kozai timescale. Under the assumption that the stellar quadrupole does not induce precession in the planet's orbit, given a system with a set of initial parameters, we show that it is possible to predict whether the system can attain high spin-orbit misalignments. In the second portion of this work, we discuss tidal dissipation in giant planets, another aspect that is crucial to dynamical HJ formation theories. We show that tidal dissipation in the cores of giant planets can be significant, and can help reconcile inconsistencies in the tidal dissipation efficiencies inferred from observations of Jupiter's moons and from high-eccentricity HJ migration theories. Finally, we improve upon existing core tidal dissipation theories by presenting semi-analytical formulae for dissipation in a core surrounded by a polytropic n = 1 envelope.

Quantum phases of two-component bosons with spin-orbit coupling in optical lattices

NASA Astrophysics Data System (ADS)

Yamamoto, Daisuke; Spielman, I. B.; Sá de Melo, C. A. R.

2017-12-01

Ultracold bosons in optical lattices are one of the few systems where bosonic matter is known to exhibit strong correlations. Here we push the frontier of our understanding of interacting bosons in optical lattices by adding synthetic spin-orbit coupling, and show that new kinds of density and chiral orders develop. The competition between the optical lattice period and the spin-orbit coupling length—which can be made comparable in experiments—along with the spin hybridization induced by a transverse field (i.e., Rabi coupling) and interparticle interactions create a rich variety of quantum phases including uniform, nonuniform, and phase-separated superfluids, as well as Mott insulators. The spontaneous symmetry-breaking phenomena at the transitions between them are explained by a two-order-parameter Ginzburg-Landau model with multiparticle umklapp processes. Finally, in order to characterize each phase, we calculated their experimentally measurable crystal momentum distributions.

Topologically nontrivial electronic bands and tunable Dirac cones in graphynes with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Juricic, Vladimir; van Miert, Guido; Morais Smith, Cristiane

2015-03-01

Graphynes represent an emerging family of carbon allotropes that differ from graphene by the presence of the triple bonds (-C ≡C-) in their band structure. They have recently attracted much interest due to the tunability of the Dirac cones in the band structure. I will show that the spin-orbit coupling in β-graphyne could produce various effects related to the topological properties of its electronic bands. Intrinsic spin-orbit coupling yields high- and tunable Chern-number bands, which may host both topological and Chern insulators, in the presence and absence of time-reversal symmetry, respectively. Furthermore, Rashba spin-orbit coupling can be used to control the position and the number of Dirac cones in the Brillouin zone. Finally, I will also discuss the electronic properties of α - and γ - graphyne in the presence of the spin-orbit coupling within recently developed general theory of spin-orbit couplings in graphynes. Work supported by the Netherlands Organization for Scientific Research (NWO).

Spin-Orbit Coupling and the Conservation of Angular Momentum

ERIC Educational Resources Information Center

Hnizdo, V.

2012-01-01

In nonrelativistic quantum mechanics, the total (i.e. orbital plus spin) angular momentum of a charged particle with spin that moves in a Coulomb plus spin-orbit-coupling potential is conserved. In a classical nonrelativistic treatment of this problem, in which the Lagrange equations determine the orbital motion and the Thomas equation yields the…

Spin-orbit torque in a thin film of the topological insulator Bi2Se3: Crossover from the ballistic to diffusive regime

NASA Astrophysics Data System (ADS)

Ren, Y. J.; Deng, W. Y.; Geng, H.; Shen, R.; Shao, L. B.; Sheng, L.; Xing, D. Y.

2017-12-01

The spin-orbit torque provides an efficient method for switching the direction of a magnetization by using an electric field. Owing to the spin-orbit coupling, when an electric field is applied, a nonequilibrium spin density is generated, which exerts a torque on the local magnetization. Here, we investigate the spin-orbit torque in a thin film of topological insulator \\text{Bi}2\\text{Se}3 based upon a Boltzmann equation, with proper boundary conditions, which is applicable from the ballistic regime to the diffusive regime. It is shown that due to the spin-momentum interlocking of the electron surface states, the magnitude of the field-like torque is simply in linear proportion to the longitudinal electrical current. For a fixed electric field, the spin-orbit torque is proportional to the sample length in the ballistic limit, and saturates to a constant in the diffusive limit. The dependence of the torque on the magnetization direction and exchange coupling strength is also studied. Our theory may offer useful guidance for experimental investigations of the spin-orbit torque in finite-size systems.

Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces

NASA Astrophysics Data System (ADS)

Lesne, E.; Fu, Yu; Oyarzun, S.; Rojas-Sánchez, J. C.; Vaz, D. C.; Naganuma, H.; Sicoli, G.; Attané, J.-P.; Jamet, M.; Jacquet, E.; George, J.-M.; Barthélémy, A.; Jaffrès, H.; Fert, A.; Bibes, M.; Vila, L.

2016-12-01

The spin-orbit interaction couples the electrons’ motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism--the Rashba effect--in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.

Rashba spin-orbit coupling and orbital chirality in magnetic bilayers

NASA Astrophysics Data System (ADS)

Lee, Hyun-Woo

2013-03-01

The phenomenon of the Rashba spin-orbit coupling is examined theoretically for an ultrathin magnetic layer in contact with a non-magnetic heavy metal layer. From first-principles calculation, large Rashba parameter of order 1 eV .Å is obtained, which is strong enough to generate large spin transfer torque of spin-orbit coupling origin. Large Rashba parameter is attributed to the orbital mixing of 3 d magnetic atoms and non-magnetic heavy elements with significant atomic spin-orbit coupling. Interestingly the magnitude and sign of the parameter vary from energy bands to bands, which we attribute to band-specific chiral ordering of orbital angular momentum. Through a simple tight-binding model analysis, we demonstrate that d-orbital hybridization allowed by the breaking of structural inversion symmetry generates band-specific chiral ordering of orbital angular momentum, which combines with atomic spin-orbit coupling to give rise to band-specific Rashba parameter. The band-dependence of the Rashba parameter is discussed in connection with recent experiments and we argue that the dependence may be utilized to enhance device application potentials. This work is supported by NRF grant (2010-0008529, 2011-0015631, 2010-0014109, 2011-0030789).

Spin-orbit torques in magnetic bilayers

NASA Astrophysics Data System (ADS)

Haney, Paul

2015-03-01

Spintronics aims to utilize the coupling between charge transport and magnetic dynamics to develop improved and novel memory and logic devices. Future progress in spintronics may be enabled by exploiting the spin-orbit coupling present at the interface between thin film ferromagnets and heavy metals. In these systems, applying an in-plane electrical current can induce magnetic dynamics in single domain ferromagnets, or can induce rapid motion of domain wall magnetic textures. There are multiple effects responsible for these dynamics. They include spin-orbit torques and a chiral exchange interaction (the Dzyaloshinskii-Moriya interaction) in the ferromagnet. Both effects arise from the combination of ferromagnetism and spin-orbit coupling present at the interface. There is additionally a torque from the spin current flux impinging on the ferromagnet, arising from the spin hall effect in the heavy metal. Using a combination of approaches, from drift-diffusion to Boltzmann transport to first principles methods, we explore the relative contributions to the dynamics from these different effects. We additionally propose that the transverse spin current is locally enhanced over its bulk value in the vicinity of an interface which is oriented normal to the charge current direction.

Role of spin-orbit coupling in the Kugel-Khomskii model on the honeycomb lattice

NASA Astrophysics Data System (ADS)

Koga, Akihisa; Nakauchi, Shiryu; Nasu, Joji

2018-03-01

We study the effective spin-orbital model for honeycomb-layered transition metal compounds, applying the second-order perturbation theory to the three-orbital Hubbard model with the anisotropic hoppings. This model is reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining the cluster mean-field approximations with the exact diagonalization, we treat the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an equal footing to discuss ground-state properties. We find that a zigzag ordered state is realized in the model within nearest-neighbor interactions. We clarify how the ordered state competes with the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit. Thermodynamic properties are also addressed. The present paper should provide another route to account for the Kitaev-based magnetic properties in candidate materials.

Teetering Stars: Resonant Excitation of Stellar Obliquities by Hot and Warm Jupiters with External Companions

NASA Astrophysics Data System (ADS)

Anderson, Kassandra; Lai, Dong

2018-04-01

Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have been extensively probed in recent years thanks to Rossiter-McLaughlin observations. Such obliquities may reveal clues about hot Jupiter dynamical and migration histories. Common explanations for generating stellar obliquities include high-eccentricity migration, or primordial disk misalignment. This talk investigates another mechanism for producing stellar spin-orbit misalignments in systems hosting a close-in giant planet with an external, inclined planetary companion. Spin-orbit misalignment may be excited due to a secular resonance, occurring when the precession rate of the stellar spin axis (due to the inner orbit) becomes comparable to the precession rate of the inner orbital axis (due to the outer companion). Due to the spin-down of the host star via magnetic braking, this resonance may be achieved at some point during the star's main sequence lifetime for a wide range of giant planet masses and orbital architectures. We focus on both hot Jupiters (with orbital periods less than ten days) and warm Jupiters (with orbital periods around tens of days), and identify the outer perburber properties needed to generate substantial obliquities via resonant excitation, in terms of mass, separation, and inclination. For hot Jupiters, the stellar spin axis is strongly coupled to the orbital axis, and resonant excitation of obliquity requires a close perturber, located within 1-2 AU. For warm Jupiters, the spin and orbital axes are more weakly coupled, and the resonance may be achieved for more distant perturbers (at several to tens of AU). Resonant excitation of the stellar obliquity is accompanied by a decrease in the planets' mutual orbital inclination, and can thus erase high mutual inclinations in two-planet systems. Since many warm Jupiters are known to have outer planetary companions at several AU or beyond, stellar obliquities in warm Jupiter systems may be common, regardless of the formation/migration mechanism. Future observations probing warm Jupiter obliquities may indicate the presence of a hitherto undetected outer companion.

Rashba and Dresselhaus spin-orbit interactions effects on electronic features of a two dimensional elliptic quantum dot

NASA Astrophysics Data System (ADS)

Mokhtari, P.; Rezaei, G.; Zamani, A.

2017-06-01

In this paper, electronic structure of a two dimensional elliptic quantum dot under the influence of external electric and magnetic fields are studied in the presence of Rashba and Dresselhaus spin-orbit interactions. This investigation is done computationally and to do this, at first, the effective Hamiltonian of the system by considering the spin-orbit coupling is demonstrated in the presence of applied electric and magnetic fields and afterwards the Schrödinger equation is solved using the finite difference approach. Utilizing finite element method, eigenvalues and eigenstates of the system are calculated and the effect of the external fields, the size of the dot as well as the strength of Rashba spin-orbit interaction are studied. Our results indicate that, Spin-orbit interactions, external fields and the dot size have a great influence on the electronic structure of the system.

Full Stark control of polariton states on a spin-orbit hypersphere

NASA Astrophysics Data System (ADS)

Li, Feng; Cancellieri, E.; Buonaiuto, G.; Skolnick, M. S.; Krizhanovskii, D. N.; Whittaker, D. M.

2016-11-01

The orbital angular momentum and the polarization of light are physical quantities widely investigated for classical and quantum information processing. In this work we propose to take advantage of strong light-matter coupling, circular-symmetric confinement, and transverse-electric transverse-magnetic splitting to exploit states where these two degrees of freedom are combined. To this end we develop a model based on a spin-orbit Poincaré hypersphere. Then we consider the example of semiconductor polariton systems and demonstrate full ultrafast Stark control of spin-orbit states. Moreover, by controlling states on three different spin-orbit spheres and switching from one sphere to another we demonstrate the control of different logic bits within one single physical system.

A new spin on electron liquids: Phenomena in systems with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Bernevig, B. Andrei

Conventional microelectronic devices are based on the ability to store and control the flow of electronic charge. Spin-based electronics promises a radical alternative, offering the possibility of logic operations with much lower power consumption than equivalent charge-based logic operations. Our research suggests that spin transport is fundamentally different from the transport of charge. The generalized Ohm's law that governs the flow of spins indicates that the generation of spin current by an electric field can be reversible and non-dissipative. Spin-orbit coupling and spin currents appear in many other seemingly unrelated areas of physics. Spin currents are as fundamental in theoretical physics as charge currents. In strongly correlated systems such as spin-chains, one can write down the Hamiltonian as a spin-current - spin-current interaction. The research presented here shows that the fractionalized excitations of one-dimensional spin chains are gapless and carry spin current. We present the most interesting example of such a chain, the Haldane-Shastry spin chain, which is exactly solvable in terms of real-space wavefunctions. Spin-orbit coupling can be found in high-energy physics, hidden under a different name: non-trivial fibrations. Particles moving in a space which is non-trivially related to an (iso)spin space acquire a gauge connection (the condensed-matter equivalent of a Berry phase) which can be either abelian or non-abelian. In most cases, the consequences of such gauge connection are far-reaching. We present a problem where particles move on an 8-dimensional manifold and posses an isospin space with is a 7-sphere S 7. The non-trivial isospin space gives the Hamiltonian SO (8) landau-level structure, and the system exhibits a higher-dimensional Quantum Hall Effect.

Spin orbit coupling in graphene through gold intercalation

NASA Astrophysics Data System (ADS)

Mukherjee, Paromita; O'Farrell, Eoin; Tan, Jun You; Yeo, Yuting; Koon, G. K. W.; Özyilmaz, Barbaros; Watanabe, K.; Taniguchi, T.

Graphene has a very low value of spin orbit coupling. There have been several efforts to enhance the spin orbit interaction in graphene. Our previous work has provided clear evidence that spin orbit coupling can be induced in graphene through Rashba interaction with intercalated gold. By applying an additional electric field, this splitting can be increased or decreased depending on its relative direction with the internal electric field induced by gold in graphene. A large negative magnetoresistance due to an in-plane magnetic field has been observed which can be attributed to the fact that a magnetic moment is induced in gold due to spin-orbit coupling. Anomalous Hall Effect which decreases with an in-plane magnetic field further suggests the formation of a collective magnetic phase. We would like to further elaborate on the spin-orbit coupling in graphene using non local measurements. Hence, by intercalating graphene with gold, we can have a direct electric manipulation of the spin degrees of freedom and lead to its much awaited applications in spintronics, quantum computing. National University of Singapore, Singapore.

Numerical analysis of spin-orbit-coupled one-dimensional Fermi gas in a magnetic field

NASA Astrophysics Data System (ADS)

Chan, Y. H.

2015-06-01

Based on the density-matrix renormalization group and the infinite time-evolving block decimation methods we study the interacting spin-orbit-coupled 1D Fermi gas in a transverse magnetic field. We find that the system with an attractive interaction can have a polarized insulator phase, a superconducting (SC) phase, a Luther-Emery (LE) phase, and a band insulator phase as we vary the chemical potential and the strength of the magnetic field. Spin-orbit coupling (SOC) enhances the triplet pairing order at zero momentum in both the SC and the LE phase, which leads to an algebraically decaying correlation with the same exponent as that of the singlet pairing one. In contrast to the Fulde-Ferrell-Larkin-Ovchinnikov phase found in the spin imbalanced system without SOC, pairings at finite momentum in these two phases have larger exponents hence do not dictate the long-range behavior. We also test for the presence of Majorana fermions in this system. Unlike results from the mean-field study, we do not find positive evidence of Majorana fermions.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocharian, Armen N.; Fernando, Gayanath W.; Fang, Kun

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges andmore » opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.« less

Spin-Orbit Coupled Quantum Magnetism in the 3D-Honeycomb Iridates

NASA Astrophysics Data System (ADS)

Kimchi, Itamar

In this doctoral dissertation, we consider the significance of spin-orbit coupling for the phases of matter which arise for strongly correlated electrons. We explore emergent behavior in quantum many-body systems, including symmetry-breaking orders, quantum spin liquids, and unconventional superconductivity. Our study is cemented by a particular class of Mott-insulating materials, centered around a family of two- and three-dimensional iridium oxides, whose honeycomb-like lattice structure admits peculiar magnetic interactions, the so-called Kitaev exchange. By analyzing recent experiments on these compounds, we show that this unconventional exchange is the key ingredient in describing their magnetism, and then use a combination of numerical and analytical techniques to investigate the implications for the phase diagram as well as the physics of the proximate three-dimensional quantum spin liquid phases. These long-ranged-entangled fractionalized phases should exhibit special features, including finite-temperature stability as well as unconventional high-Tc superconductivity upon charge-doping, which should aid future experimental searches for spin liquid physics. Our study explores the nature of frustration and fractionalization which can arise in quantum systems in the presence of strong spin-orbit coupling.

Momentum-resolved radio-frequency spectroscopy of a spin-orbit-coupled atomic Fermi gas near a Feshbach resonance in harmonic traps

NASA Astrophysics Data System (ADS)

Peng, Shi-Guo; Liu, Xia-Ji; Hu, Hui; Jiang, Kaijun

2012-12-01

We theoretically investigate the momentum-resolved radio-frequency spectroscopy of a harmonically trapped atomic Fermi gas near a Feshbach resonance in the presence of equal Rashba and Dresselhaus spin-orbit coupling. The system is qualitatively modeled as an ideal gas mixture of atoms and molecules, in which the properties of molecules, such as the wave function, binding energy, and effective mass, are determined from the two-particle solution of two interacting atoms. We calculate separately the radio-frequency response from atoms and molecules at finite temperatures by using the standard Fermi golden rule and take into account the effect of harmonic traps within local density approximation. The total radio-frequency spectroscopy is discussed as functions of temperature and spin-orbit coupling strength. Our results give a qualitative picture of radio-frequency spectroscopy of a resonantly interacting spin-orbit-coupled Fermi gas and can be directly tested in atomic Fermi gases of 40K atoms at Shanxi University and 6Li atoms at the Massachusetts Institute of Technology.

Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

PubMed Central

Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

2016-01-01

Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors. PMID:27991541

Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

NASA Astrophysics Data System (ADS)

Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

2016-12-01

Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors.

Degenerate quantum gases with spin-orbit coupling: a review.

PubMed

Zhai, Hui

2015-02-01

This review focuses on recent developments in synthetic spin-orbit (SO) coupling in ultracold atomic gases. Two types of SO coupling are discussed. One is Raman process induced coupling between spin and motion along one of the spatial directions and the other is Rashba SO coupling. We emphasize their common features in both single-particle and two-body physics and the consequences of both in many-body physics. For instance, single particle ground state degeneracy leads to novel features of superfluidity and a richer phase diagram; increased low-energy density-of-state enhances interaction effects; the absence of Galilean invariance and spin-momentum locking gives rise to intriguing behaviours of superfluid critical velocity and novel quantum dynamics; and the mixing of two-body singlet and triplet states yields a novel fermion pairing structure and topological superfluids. With these examples, we show that investigating SO coupling in cold atom systems can, enrich our understanding of basic phenomena such as superfluidity, provide a good platform for simulating condensed matter states such as topological superfluids and more importantly, result in novel quantum systems such as SO coupled unitary Fermi gas and high spin quantum gases. Finally we also point out major challenges and some possible future directions.

Gravitational waveforms from unequal-mass binaries with arbitrary spins under leading order spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tessmer, Manuel

This paper generalizes the structure of gravitational waves from orbiting spinning binaries under leading order spin-orbit coupling, as given in the work by Koenigsdoerffer and Gopakumar [Phys. Rev. D 71, 024039 (2005)] for single-spin and equal-mass binaries, to unequal-mass binaries and arbitrary spin configurations. The orbital motion is taken to be quasicircular and the fractional mass difference is assumed to be small against one. The emitted gravitational waveforms are given in analytic form.

Spin-orbit coupled systems in the atomic limit: rhenates, osmates, iridates

NASA Astrophysics Data System (ADS)

Paramekanti, Arun; Singh, David J.; Yuan, Bo; Casa, Diego; Said, Ayman; Kim, Young-June; Christianson, A. D.

2018-06-01

Motivated by RIXS experiments on a wide range of complex heavy oxides, including rhenates, osmates, and iridates, we discuss the theory of RIXS for site-localized t2 g orbital systems with strong spin-orbit coupling. For such systems, we present exact diagonalization results for the spectrum at different electron fillings, showing that it accesses "single-particle" and "multiparticle" excitations. This leads to a simple picture for the energies and intensities of the RIXS spectra in Mott insulators such as double perovskites which feature highly localized electrons, and yields estimates of the spin-orbit coupling and Hund's coupling in correlated 5 d oxides. We present new higher resolution RIXS data at the Re L3 edge in Ba2YReO6 which finds a previously unresolved peak splitting, providing further confirmation of our theoretical predictions. Using ab initio electronic structure calculations on Ba2M ReO6 (with M =Re , Os, Ir) we show that while the atomic limit yields a reasonable effective Hamiltonian description of the experimental observations, effects such as t2 g-eg interactions and hybridization with oxygen are important. Our ab initio estimate for the strength of the intersite exchange coupling shows that, compared to the d3 systems, the exchange is one or two orders of magnitude weaker in the d2 and d4 materials, which may partly explain the suppression of long-range magnetic order in the latter compounds. As a way to interpolate between the site-localized picture and our electronic structure band calculations, we discuss the spin-orbital levels of the M O6 cluster. This suggests a possible role for intracluster excitons in Ba2YIrO6 which may lead to a weak breakdown of the atomic Jeff=0 picture and to small magnetic moments.

Threshold Ionization and Spin-Orbit Coupling of Cerium Monoxide

NASA Astrophysics Data System (ADS)

Cao, Wenjin; Zhang, Yuchen; Wu, Lu; Yang, Dong-Sheng

2017-06-01

Cerium oxides are widely used in heterogeneous catalysis due to their ability to switch between different oxidation states. We report here the mass-analyzed threshold ionization (MATI) spectroscopy of cerium monoxide (CeO) produced by laser ablating a Ce rod in a molecular beam source. The MATI spectrum in the range of 40000-45000 \\wn exhibits several band systems with similar vibrational progressions. The strongest band is at 43015 (5) \\wn, which can be assigned as the adiabatic ionization energy of the neutral species. The spectrum also shows Ce-O stretching frequencies of 817 and 890 \\wn in the neutral and ion states, respectively. By comparing with spin-orbit coupled multireference quasi-degenerate perturbation theory (SO-MCQDPT) calculations, the observed band systems are assigned to transitions from various low-energy spin-orbit levels of the neutral oxide to the two lowest spin-orbit levels of the corresponding ion. The current work will also be compared with previous experimental and computational studies on the neutral species.

Experimental investigation of spin-orbit coupling in n-type PbTe quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peres, M. L.; Monteiro, H. S.; Castro, S. de

2014-03-07

The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δ{sub so}. The values of Δ{sub so} are linearly dependent on the Fermi wave vector (k{sub F}) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.

Universal relations for spin-orbit-coupled Fermi gas near an s -wave resonance

NASA Astrophysics Data System (ADS)

Zhang, Pengfei; Sun, Ning

2018-04-01

Synthetic spin-orbit-coupled quantum gases have been widely studied both experimentally and theoretically in the past decade. As shown in previous studies, this modification of single-body dispersion will in general couple different partial waves of the two-body scattering and thus distort the wave function of few-body bound states which determines the short-distance behavior of many-body wave function. In this work, we focus on the two-component Fermi gas with one-dimensional or three-dimensional spin-orbit coupling (SOC) near an s -wave resonance. Using the method of effective field theory and the operator product expansion, we derive universal relations for both systems, including the adiabatic theorem, viral theorem, and pressure relation, and obtain the momentum distribution matrix 〈ψa†(q ) ψb(q ) 〉 at large q (a ,b are spin indices). The momentum distribution matrix shows both spin-dependent and spatial anisotropic features. And the large momentum tail is modified at the subleading order thanks to the SOC. We also discuss the experimental implication of these results depending on the realization of the SOC.

Spin-orbit-coupled Fermi gases of two-electron ytterbium atoms

NASA Astrophysics Data System (ADS)

He, Chengdong; Song, Bo; Haciyev, Elnur; Ren, Zejian; Seo, Bojeong; Zhang, Shanchao; Liu, Xiong-Jun; Jo, Gyu-Boong

2017-04-01

Spin-orbit coupling (SOC) has been realized in bosonic and fermionic atomic gases opening an avenue to novel physics associated with spin-momentum locking. In this talk, we will demonstrate all-optical method coupling two hyperfine ground states of 173Yb fermions through a narrow optical transition 1S0 -> 3P1. An optical AC Stark shift is applied to split the ground hyperfine levels and separate out an effective spin-1/2 subspace from other spin states for the realization of SOC. The spin dephasing dynamics and the asymmetric momentum distribution of the spin-orbit coupled Fermi gas are observed as a hallmark of SOC. The implementation of all-optical SOC for ytterbium fermions should offer a new route to a long-lived spin-orbit coupled Fermi gas and greatly expand our capability in studying novel spin-orbit physics with alkaline-earth-like atoms. Other ongoing experimental works related to SOC will be also discussed. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants); MOST (Grant No. 2016YFA0301604) and NSFC (No. 11574008).

Magnitude of finite-nucleus-size effects in relativistic density functional computations of indirect NMR nuclear spin-spin coupling constants.

PubMed

Autschbach, Jochen

2009-09-14

A spherical Gaussian nuclear charge distribution model has been implemented for spin-free (scalar) and two-component (spin-orbit) relativistic density functional calculations of indirect NMR nuclear spin-spin coupling (J-coupling) constants. The finite nuclear volume effects on the hyperfine integrals are quite pronounced and as a consequence they noticeably alter coupling constants involving heavy NMR nuclei such as W, Pt, Hg, Tl, and Pb. Typically, the isotropic J-couplings are reduced in magnitude by about 10 to 15 % for couplings between one of the heaviest NMR nuclei and a light atomic ligand, and even more so for couplings between two heavy atoms. For a subset of the systems studied, viz. the Hg atom, Hg(2) (2+), and Tl--X where X=Br, I, the basis set convergence of the hyperfine integrals and the coupling constants was monitored. For the Hg atom, numerical and basis set calculations of the electron density and the 1s and 6s orbital hyperfine integrals are directly compared. The coupling anisotropies of TlBr and TlI increase by about 2 % due to finite-nucleus effects.

Electric-field-induced interferometric resonance of a one-dimensional spin-orbit-coupled electron

PubMed Central

Fan, Jingtao; Chen, Yuansen; Chen, Gang; Xiao, Liantuan; Jia, Suotang; Nori, Franco

2016-01-01

The efficient control of electron spins is of crucial importance for spintronics, quantum metrology, and quantum information processing. We theoretically formulate an electric mechanism to probe the electron spin dynamics, by focusing on a one-dimensional spin-orbit-coupled nanowire quantum dot. Owing to the existence of spin-orbit coupling and a pulsed electric field, different spin-orbit states are shown to interfere with each other, generating intriguing interference-resonant patterns. We also reveal that an in-plane magnetic field does not affect the interval of any neighboring resonant peaks, but contributes a weak shift of each peak, which is sensitive to the direction of the magnetic field. We find that this proposed external-field-controlled scheme should be regarded as a new type of quantum-dot-based interferometry. This interferometry has potential applications in precise measurements of relevant experimental parameters, such as the Rashba and Dresselhaus spin-orbit-coupling strengths, as well as the Landé factor. PMID:27966598

Assessment of bilayer silicene to probe as quantum spin and valley Hall effect

NASA Astrophysics Data System (ADS)

Rehman, Majeed Ur; Qiao, Zhenhua

2018-02-01

Silicene takes precedence over graphene due to its buckling type structure and strong spin orbit coupling. Motivated by these properties, we study the silicene bilayer in the presence of applied perpendicular electric field and intrinsic spin orbit coupling to probe as quantum spin/valley Hall effect. Using analytical approach, we calculate the spin Chern-number of bilayer silicene and then compare it with monolayer silicene. We reveal that bilayer silicene hosts double spin Chern-number as compared to single layer silicene and therefore accordingly has twice as many edge states in contrast to single layer silicene. In addition, we investigate the combined effect of intrinsic spin orbit coupling and the external electric field, we find that bilayer silicene, likewise single layer silicene, goes through a phase transitions from a quantum spin Hall state to a quantum valley Hall state when the strength of the applied electric field exceeds the intrinsic spin orbit coupling strength. We believe that the results and outcomes obtained for bilayer silicene are experimentally more accessible as compared to bilayer graphene, because of strong SO coupling in bilayer silicene.

Dark solitons with Majorana fermions in spin-orbit-coupled Fermi gases.

PubMed

Xu, Yong; Mao, Li; Wu, Biao; Zhang, Chuanwei

2014-09-26

We show that a single dark soliton can exist in a spin-orbit-coupled Fermi gas with a high spin imbalance, where spin-orbit coupling favors uniform superfluids over nonuniform Fulde-Ferrell-Larkin-Ovchinnikov states, leading to dark soliton excitations in highly imbalanced gases. Above a critical spin imbalance, two topological Majorana fermions without interactions can coexist inside a dark soliton, paving a way for manipulating Majorana fermions through controlling solitons. At the topological transition point, the atom density contrast across the soliton suddenly vanishes, suggesting a signature for identifying topological solitons.

First-Principles Evaluation of the Dzyaloshinskii-Moriya Interaction

NASA Astrophysics Data System (ADS)

Koretsune, Takashi; Kikuchi, Toru; Arita, Ryotaro

2018-04-01

We review recent developments of formulations to calculate the Dzyaloshinskii-Moriya (DM) interaction from first principles. In particular, we focus on three approaches. The first one evaluates the energy change due to the spin twisting by directly calculating the helical spin structure. The second one employs the spin gauge field technique to perform the derivative expansion with respect to the magnetic moment. This gives a clear picture that the DM interaction can be represented as the spin current in the equilibrium within the first order of the spin-orbit couplings. The third one is the perturbation expansion with respect to the exchange couplings and can be understood as the extension of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction to the noncentrosymmetric spin-orbit systems. By calculating the DM interaction for the typical chiral ferromagnets Mn1-xFexGe and Fe1-xCoxGe, we discuss how these approaches work in actual systems.

Spin-Orbit Coupled Bose-Einstein Condensates

DTIC Science & Technology

2016-11-03

generalized the new concepts to interacting spin-1/2 bosons in optical lattices and described a superfluid-to-Mott insulator transition in spin-orbit...and quantum phase transitions in topological insulators , Physical Review B, (09 2010): 0. doi: 10.1103/PhysRevB.82.115125 Christopher Varney, Kai...109.235308 J. Radi?, A. Di Ciolo, K. Sun, V. Galitski. Exotic Quantum Spin Models in Spin-Orbit-Coupled Mott Insulators , Physical Review Letters

New opportunities at the frontiers of spintronics

DOE PAGES

Hoffmann, Axel; Bader, Sam D.

2015-10-05

The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields. These new directions involve the study of collective spin excitations and couplings of the spin system to additional degrees of freedom of a material, as well as metastable phenomena due to perturbations that drive the system far from equilibrium. The interactions lead to possibilities for future applications within the realm of energy-efficient information technologies. Examples discussed herein include research opportunities associated with (i) various spin-orbit couplings, such as spin Hall effects, (ii) couplings to the thermal bath of a system, such as in spin Seebeckmore » effects, (iii) spin-spin couplings, such as via induced and interacting magnon excitations, and (iv) spin-photon couplings, such as in ultra-fast magnetization switching due to coherent photon pulses. These four basic frontier areas of research are giving rise to new applied disciplines known as spin-orbitronics, spin-caloritronics, magnonics, and spin-photonics, respectively. These topics are highlighted in order to stimulate interest in the new directions that spintronics research is taking, and to identify open issues to pursue.« less

Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Seibold, G.; Bucheli, D.; Caprara, S.; Grilli, M.

2015-01-01

We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant g=g(n) depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum kF. At higher density the instability criterion becomes independent of kF and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces.

Bosons with Synthetic Rashba Spin-Orbit Coupling at Finite Power

NASA Astrophysics Data System (ADS)

Anderson, Brandon; Clark, Charles

2013-05-01

Isotropic spin-orbit couplings, such as Rashba in two dimensions, have a continuous symmetry that produces a large degeneracy in the momentum-space dispersion. This degeneracy leads to an enhanced density-of-states, producing novel phases in systems of bosonic atoms. This model is idealistic, however, in that the symmetry of the lasers will weakly break the continuous symmetry to a discrete one in experimental manifestations. This perturbation typically scales inversely with the optical power, and only at infinite power will ideal symmetry be restored. In this talk, we consider the effects of this weak symmetry breaking in a system of bosons at finite power with synthetic Rashba coupling. We solve the mean-field equations and find new phases, such as a stripe phase with a larger symmetry group. We then consider the experimentally relevant scheme where the spin-orbit fields are turned on adiabatically from an initial spin-polarized state. At intermediate power, stripe phases are found, while at sufficiently high power it appears that the system quenches to phases similar to that of the ideal limit. Techniques for optimizing the adiabatic ramping sequence are discussed. NSF PFC Grant PHY-0822671 and by the ARO under the DARPA OLE program.

Creating Spin-One Fermions in the Presence of Artificial Spin-Orbit Fields: Emergent Spinor Physics and Spectroscopic Properties

NASA Astrophysics Data System (ADS)

Kurkcuoglu, Doga Murat; de Melo, C. A. R. Sá

2018-05-01

We propose the creation and investigation of a system of spin-one fermions in the presence of artificial spin-orbit coupling, via the interaction of three hyperfine states of fermionic atoms to Raman laser fields. We explore the emergence of spinor physics in the Hamiltonian described by the interaction between light and atoms, and analyze spectroscopic properties such as dispersion relation, Fermi surfaces, spectral functions, spin-dependent momentum distributions and density of states. Connections to spin-one bosons and SU(3) systems is made, as well relations to the Lifshitz transition and Pomeranchuk instability are presented.

Spin-orbit splitted excited states using explicitly-correlated equation-of-motion coupled-cluster singles and doubles eigenvectors

NASA Astrophysics Data System (ADS)

Bokhan, Denis; Trubnikov, Dmitrii N.; Perera, Ajith; Bartlett, Rodney J.

2018-04-01

An explicitly-correlated method of calculation of excited states with spin-orbit couplings, has been formulated and implemented. Developed approach utilizes left and right eigenvectors of equation-of-motion coupled-cluster model, which is based on the linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] method. The spin-orbit interactions are introduced by using the spin-orbit mean field (SOMF) approximation of the Breit-Pauli Hamiltonian. Numerical tests for several atoms and molecules show good agreement between explicitly-correlated results and the corresponding values, calculated in complete basis set limit (CBS); the highly-accurate excitation energies can be obtained already at triple- ζ level.

Spin-orbit proximity effect in graphene

NASA Astrophysics Data System (ADS)

Avsar, A.; Tan, J. Y.; Taychatanapat, T.; Balakrishnan, J.; Koon, G. K. W.; Yeo, Y.; Lahiri, J.; Carvalho, A.; Rodin, A. S.; O'Farrell, E. C. T.; Eda, G.; Castro Neto, A. H.; Özyilmaz, B.

2014-09-01

The development of spintronics devices relies on efficient generation of spin-polarized currents and their electric-field-controlled manipulation. While observation of exceptionally long spin relaxation lengths makes graphene an intriguing material for spintronics studies, electric field modulation of spin currents is almost impossible due to negligible intrinsic spin-orbit coupling of graphene. In this work, we create an artificial interface between monolayer graphene and few-layer semiconducting tungsten disulphide. In these devices, we observe that graphene acquires spin-orbit coupling up to 17 meV, three orders of magnitude higher than its intrinsic value, without modifying the structure of the graphene. The proximity spin-orbit coupling leads to the spin Hall effect even at room temperature, and opens the door to spin field effect transistors. We show that intrinsic defects in tungsten disulphide play an important role in this proximity effect and that graphene can act as a probe to detect defects in semiconducting surfaces.

Spin-Orbit Torques and Anisotropic Magnetization Damping in Skyrmion Crystals

NASA Astrophysics Data System (ADS)

Hals, Kjetil; Brataas, Arne

2014-03-01

We theoretically study the effects of reactive and dissipative homogeneous spin-orbit torques and anisotropic damping on the current-driven skyrmion dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit torques play a significant role in the current-induced skyrmion velocity. The dissipative spin-orbit torque generates a relativistic Magnus force on the skyrmions, whereas the reactive spin-orbit torque yields a correction to both the drift velocity along the current direction and the transverse velocity associated with the Magnus force. The spin-orbit torque corrections to the velocity scale linearly with the skyrmion size, which is inversely proportional to the spin-orbit coupling. Consequently, the reactive spin-orbit torque correction can be the same order of magnitude as the non-relativistic contribution. More importantly, the dissipative spin-orbit torque can be the dominant force that causes a deflected motion of the skyrmions if the torque exhibits a linear or quadratic relationship with the spin-orbit coupling. In addition, we demonstrate that the skyrmion velocity is determined by anisotropic magnetization damping parameters governed by the skyrmion size.

Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

NASA Astrophysics Data System (ADS)

Tazai, Rina; Yamakawa, Youichi; Tsuchiizu, Masahisa; Kontani, Hiroshi

2016-09-01

In various multiorbital systems, the emergence of the orbital fluctuations and their role on the pairing mechanism attract increasing attention. To achieve deep understanding on these issues, we perform a functional renormalization group (fRG) study for the two-orbital Hubbard model. The vertex corrections for the electron-boson coupling (U -VC), which are dropped in the Migdal-Eliashberg gap equation, are obtained by solving the RG equation. We reveal that the dressed electron-boson coupling for the charge channel Ûeffc becomes much larger than the bare Coulomb interaction Û 0 due to the U -VC in the presence of moderate spin fluctuations. For this reason, the attractive pairing interaction due to the charge or orbital fluctuations is enlarged by the factor (Ûeffc/Û0) 2≫1 . In contrast, the spin fluctuation pairing interaction is suppressed by the spin-channel U -VC, because of the relation Ûeffs≪Û 0 . The present study demonstrates that the orbital or charge fluctuation pairing mechanism can be realized in various multiorbital systems thanks to the U -VC, such as in Fe-based superconductors.

Conductance dips and spin precession in a nonuniform waveguide with spin–orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malyshev, A. I., E-mail: malyshev@phys.unn.ru; Kozulin, A. S.

An infinite waveguide with a nonuniformity, a segment of finite length with spin–orbit coupling, is considered in the case when the Rashba and Dresselhaus parameters are identical. Analytical expressions have been derived in the single-mode approximation for the conductance of the system for an arbitrary initial spin state. Based on numerical calculations with several size quantization modes, we have detected and described the conductance dips arising when the waves are localized in the nonuniformity due to the formation of an effective potential well in it. We show that allowance for the evanescent modes under carrier spin precession in an effectivemore » magnetic field does not lead to a change in the direction of the average spin vector at the output of the system.« less

Full counting statistics in a serially coupled double quantum dot system with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wang, Qiang; Xue, Hai-Bin; Xie, Hai-Qing

2018-04-01

We study the full counting statistics of electron transport through a serially coupled double quantum dot (QD) system with spin-orbit coupling (SOC) weakly coupled to two electrodes. We demonstrate that the spin polarizations of the source and drain electrodes determine whether the shot noise maintains super-Poissonian distribution, and whether the sign transitions of the skewness from positive to negative values and of the kurtosis from negative to positive values take place. In particular, the interplay between the spin polarizations of the source and drain electrodes and the magnitude of the external magnetic field, can give rise to a gate-voltage-tunable strong negative differential conductance (NDC) and the shot noise in this NDC region is significantly enhanced. Importantly, for a given SOC parameter, the obvious variation of the high-order current cumulants as a function of the energy-level detuning in a certain range, especially the dip position of the Fano factor of the skewness can be used to qualitatively extract the information about the magnitude of the SOC.

Topological states of matter in two-dimensional fermionic systems

NASA Astrophysics Data System (ADS)

Beugeling, W.

2012-09-01

Topological states of matter in two-dimensional systems are characterised by the different properties of the edges and the bulk of the system: The edges conduct electrical current while the bulk is insulating. The first well-known example is the quantum Hall effect, which is induced by a perpendicular magnetic field that generates chiral edge channels along which the current propagates. Each channel contributes one quantum to the Hall conductivity. Due to the chirality, i.e., all currents propagate in the same direction, backscattering due to impurities is absent, and the Hall conductivity carried by the edge states is therefore protected from perturbations. Another example is the quantum spin Hall effect, induced by intrinsic spin-orbit coupling in absence of a magnetic field. There the edge states are helical, i.e., spin up and down currents propagate oppositely. In this case, the spin Hall conductivity is quantized, and it is protected by time-reversal symmetry from backscattering due to impurities. In Chapter 2 of the thesis, I discuss the combined effect of the magnetic field and intrinsic spin-orbit coupling. In addition, I discuss the influence of the Rashba spin-orbit coupling and of the Zeeman effect. In particular, I show that in absence of magnetic impurities, a weaker form of the quantum spin Hall state persists in the presence of a magnetic field. In addition, I show that the intrinsic spin-orbit coupling and the Zeeman effect act similarly in the low-flux limit. I furthermore analyse the phase transitions induced by intrinsic spin-orbit coupling at a fixed magnetic field, thereby explaining the change of the Hall and spin Hall conductivities at the transition. I also study the subtle interplay between the effects of the different terms in the Hamiltonian. In Chapter 3, I investigate an effective model for HgTe quantum wells doped with Mn ions. Without doping, HgTe quantum wells may exhibit the quantum spin Hall effect, depending on the thickness of the well. The doping with Mn ions modifies the behaviour of the system in two ways: First, the quantum spin Hall gap is reduced in size, and secondly, the system becomes paramagnetic. The latter effect causes a bending of the Landau levels, which is responsible for reentrant behaviour of the (spin) Hall conductivity. I investigate the different types of reentrant behaviour, and I estimate the experimental resolvability of this effect. In Chapter 4, I present a framework to describe the fractional quantum Hall effect in systems with multiple internal degrees of freedom, e.g., spin or pseudospin. This framework describes the so-called flux attachment in terms of a Chern-Simons theory in Hamiltonian form, proposed earlier for systems without internal degrees of freedom. Here, I show a generalization of these results, by replacing the number of attached flux quanta by a matrix. In particular, the plasma analogy proposed by Laughlin still applies, and Kohn’s theorem remains valid. I also show that the results remain valid when the flux-attachment matrix is singular.

Tunable spin-orbit coupling for ultracold atoms in two-dimensional optical lattices

NASA Astrophysics Data System (ADS)

Grusdt, Fabian; Li, Tracy; Bloch, Immanuel; Demler, Eugene

2017-06-01

Spin-orbit coupling (SOC) is at the heart of many exotic band structures and can give rise to many-body states with topological order. Here we present a general scheme based on a combination of microwave driving and lattice shaking for the realization of two-dimensional SOC with ultracold atoms in systems with inversion symmetry. We show that the strengths of Rashba and Dresselhaus SOC can be independently tuned in a spin-dependent square lattice. More generally, our method can be used to open gaps between different spin states without breaking time-reversal symmetry. We demonstrate that this allows for the realization of topological insulators with nontrivial spin textures closely related to the Kane-Mele model.

Spin-polarized currents in a two-terminal double quantum ring driven by magnetic fields and Rashba spin-orbit interaction

NASA Astrophysics Data System (ADS)

Dehghan, E.; Khoshnoud, D. Sanavi; Naeimi, A. S.

2018-06-01

Aim of this study is to investigate spin transportation in double quantum ring (DQR). We developed an array of DQR to measure the transmission coefficient and analyze the spin transportation through this system in the presence of Rashba spin-orbit interaction (RSOI) and magnetic flux estimated using S-matrix method. In this article, we compute the spin transport and spin-current characteristics numerically as functions of electron energy, angles between the leads, coupling constant of the leads, RSOI, and magnetic flux. Our results suggest that, for typical values of the magnetic flux (ϕ /ϕ0) and Rashba constant (αR), such system can demonstrates many spintronic properties. It is possible to design a new geometry of DQR by incoming electrons polarization in a way to optimize the system to work as a spin-filtering and spin-inverting nano-device with very high efficiency. The results prove that the spin current will strongly modulate with an increase in the magnetic flux and Rashba constant. Moreover it is shown that, when the lead coupling is weak, the perfect spin-inverter does not occur.

Electrical and thermoelectric transport properties of two-dimensional fermionic systems with k-cubic spin-orbit coupling.

PubMed

Mawrie, Alestin; Verma, Sonu; Ghosh, Tarun Kanti

2017-10-25

We investigate the effect of k-cubic spin-orbit interaction on the electrical and thermoelectric transport properties of two-dimensional fermionic systems. We obtain exact analytical expressions of the inverse relaxation time (IRT) and the Drude conductivity for long-range Coulomb and short-range delta scattering potentials. The IRT reveals that the scattering is completely suppressed along the three directions [Formula: see text] with [Formula: see text]. We also obtain analytical results of the thermopower and thermal conductivity at low temperature. The thermoelectric transport coefficients obey the Wiedemann-Franz law, even in the presence of k-cubic Rashba spin-orbit interaction (RSOI) at low temperature. In the presence of a quantizing magnetic field, the signature of the RSOI is revealed through the appearance of the beating pattern in the Shubnikov-de Haas (SdH) oscillations of thermopower and thermal conductivity in the low magnetic field regime. The empirical formulae for the SdH oscillation frequencies accurately describe the locations of the beating nodes. The beating pattern in magnetothermoelectric measurement can be used to extract the spin-orbit coupling constant.

Controlling the superconducting transition by spin-orbit coupling

NASA Astrophysics Data System (ADS)

Banerjee, N.; Ouassou, J. A.; Zhu, Y.; Stelmashenko, N. A.; Linder, J.; Blamire, M. G.

2018-05-01

Whereas considerable evidence exists for the conversion of singlet Cooper pairs into triplet Cooper pairs in the presence of inhomogeneous magnetic fields, recent theoretical proposals have suggested an alternative way to exert control over triplet generation: intrinsic spin-orbit coupling in a homogeneous ferromagnet coupled to a superconductor. Here, we proximity couple Nb to an asymmetric Pt/Co/Pt trilayer, which acts as an effective spin-orbit-coupled ferromagnet owing to structural inversion asymmetry. Unconventional modulation of the superconducting critical temperature as a function of in-plane and out-of-plane applied magnetic fields suggests the presence of triplets that can be controlled by the magnetic orientation of a single homogeneous ferromagnet. Our studies demonstrate an active role of spin-orbit coupling in controlling the triplets, an important step towards the realization of novel superconducting spintronic devices.

Dynamic localization in optical and Zeeman lattices in the presence of spin-orbit coupling

NASA Astrophysics Data System (ADS)

Kartashov, Yaroslav V.; Konotop, Vladimir V.; Zezyulin, Dmitry A.; Torner, Lluis

2016-12-01

The dynamic localization of a two-level atom in a periodic potential under the action of spin-orbit coupling and a weak harmonically varying linear force is studied. We consider optical and Zeeman potentials that are either in phase or out of phase in two spinor components, respectively. The expectation value for the position of the atom after one oscillation period of the linear force is recovered in authentic resonances or in pseudoresonances. The frequencies of the linear force corresponding to authentic resonances are determined by the band structure of the periodic potential and are affected by the spin-orbit coupling. The width or dispersion of the wave packet in authentic resonances is usually minimal. The frequencies corresponding to pseudoresonances do not depend on the type of potential and on the strength of the spin-orbit coupling, while the evolution of excitations at the corresponding frequencies is usually accompanied by significant dispersion. Pseudoresonances are determined by the initial phase of the linear force and by the quasimomentum of the wave packet. Due to the spinor nature of the system, the motion of the atom is accompanied by periodic, but not harmonic, spin oscillations. Under the action of spin-orbit coupling the oscillations of the wave packet can be nearly completely suppressed in optical lattices. Dynamic localization in Zeeman lattices is characterized by doubling of the resonant oscillation periods due to band crossing at the boundary of the Brillouin zone. We also show that higher harmonics in the Fourier expansion of the energy band lead to effective dispersion, which can be strong enough to prevent dynamic localization of the Bloch wave packet.

Strong Electron Correlation in Photoionization of Spin-Orbit Doublets

NASA Astrophysics Data System (ADS)

Amusia, M. Ya.; Chernsheva, L. V.; Mnason, S. T.; Msezane, A. Z.; Radojevic, V.

2002-05-01

A new and explicitly many-body aspect of the "leveraging" of the spin-orbit interaction is demonstrated, spin-orbit activated interchannel coupling, which can significantly alter the photoionization cross section of a spin-orbit doublet. As an example, using a modified version of the Spin-Polarized Random-Phase-Approximation with Exchange methodology, a recently observed structure in the photoionization of Xe 3d(A. Kivimaki et al, Phys. Rev. A 63), 012716 (2000) has been explained both qualitatively and quantitatively. The structure is entirely due to this new spin-orbit activated interchannel coupling effect, which should be a general feature of inner-shell photoionization. This work was supported by NSF, NASA, DOE and ISTC.

Control of the spin geometric phase in semiconductor quantum rings.

PubMed

Nagasawa, Fumiya; Frustaglia, Diego; Saarikoski, Henri; Richter, Klaus; Nitta, Junsaku

2013-01-01

Since the formulation of the geometric phase by Berry, its relevance has been demonstrated in a large variety of physical systems. However, a geometric phase of the most fundamental spin-1/2 system, the electron spin, has not been observed directly and controlled independently from dynamical phases. Here we report experimental evidence on the manipulation of an electron spin through a purely geometric effect in an InGaAs-based quantum ring with Rashba spin-orbit coupling. By applying an in-plane magnetic field, a phase shift of the Aharonov-Casher interference pattern towards the small spin-orbit-coupling regions is observed. A perturbation theory for a one-dimensional Rashba ring under small in-plane fields reveals that the phase shift originates exclusively from the modulation of a pure geometric-phase component of the electron spin beyond the adiabatic limit, independently from dynamical phases. The phase shift is well reproduced by implementing two independent approaches, that is, perturbation theory and non-perturbative transport simulations.

Magnetotransport in Layered Dirac Fermion System Coupled with Magnetic Moments

NASA Astrophysics Data System (ADS)

Iwasaki, Yoshiki; Morinari, Takao

2018-03-01

We theoretically investigate the magnetotransport of Dirac fermions coupled with localized moments to understand the physical properties of the Dirac material EuMnBi2. Using an interlayer hopping form, which simplifies the complicated interaction between the layers of Dirac fermions and the layers of magnetic moments in EuMnBi2, the theory reproduces most of the features observed in this system. The hysteresis observed in EuMnBi2 can be caused by the valley splitting that is induced by the spin-orbit coupling and the external magnetic field with the molecular field created by localized moments. Our theory suggests that the magnetotransport in EuMnBi2 is due to the interplay among Dirac fermions, localized moments, and spin-orbit coupling.

SU (N ) spin-wave theory: Application to spin-orbital Mott insulators

NASA Astrophysics Data System (ADS)

Dong, Zhao-Yang; Wang, Wei; Li, Jian-Xin

2018-05-01

We present the application of the SU (N ) spin-wave theory to spin-orbital Mott insulators whose ground states exhibit magnetic orders. When taking both spin and orbital degrees of freedom into account rather than projecting Hilbert space onto the Kramers doublet, which is the lowest spin-orbital locked energy levels, the SU (N ) spin-wave theory should take the place of the SU (2 ) one due to the inevitable spin-orbital multipole exchange interactions. To implement the application, we introduce an efficient general local mean-field method, which involves all local fluctuations, and develop the SU (N ) linear spin-wave theory. Our approach is tested firstly by calculating the multipolar spin-wave spectra of the SU (4 ) antiferromagnetic model. Then, we apply it to spin-orbital Mott insulators. It is revealed that the Hund's coupling would influence the effectiveness of the isospin-1 /2 picture when the spin-orbital coupling is not large enough. We further carry out the SU (N ) spin-wave calculations of two materials, α -RuCl3 and Sr2IrO4 , and find that the magnonic and spin-orbital excitations are consistent with experiments.

Quantitative analysis on electric dipole energy in Rashba band splitting.

PubMed

Hong, Jisook; Rhim, Jun-Won; Kim, Changyoung; Ryong Park, Seung; Hoon Shim, Ji

2015-09-01

We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime.

Quantitative analysis on electric dipole energy in Rashba band splitting

PubMed Central

Hong, Jisook; Rhim, Jun-Won; Kim, Changyoung; Ryong Park, Seung; Hoon Shim, Ji

2015-01-01

We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime. PMID:26323493

Spin-orbit coupling in ultracold Fermi gases of 173Yb atoms

NASA Astrophysics Data System (ADS)

Song, Bo; He, Chengdong; Hajiyev, Elnur; Ren, Zejian; Seo, Bojeong; Cai, Geyue; Amanov, Dovran; Zhang, Shanchao; Jo, Gyu-Boong

2017-04-01

Synthetic spin-orbit coupling (SOC) in cold atoms opens an intriguing new way to probe nontrivial topological orders beyond natural conditions. Here, we report the realization of the SOC physics both in a bulk system and in an optical lattice. First, we demonstrate two hallmarks induced from SOC in a bulk system, spin dephasing in the Rabi oscillation and asymmetric atomic distribution in the momentum space respectively. Then we describe the observation of non-trivial spin textures and the determination of the topological phase transition in a spin-dependent optical lattice dressed by the periodic Raman field. Furthermore, we discuss the quench dynamics between topological and trivial states by suddenly changing the band topology. Our work paves a new way to study non-equilibrium topological states in a controlled manner. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants).

Accurate spin-orbit and spin-other-orbit contributions to the g-tensor for transition metal containing systems.

PubMed

Van Yperen-De Deyne, A; Pauwels, E; Van Speybroeck, V; Waroquier, M

2012-08-14

In this paper an overview is presented of several approximations within Density Functional Theory (DFT) to calculate g-tensors in transition metal containing systems and a new accurate description of the spin-other-orbit contribution for high spin systems is suggested. Various implementations in a broad variety of software packages (ORCA, ADF, Gaussian, CP2K, GIPAW and BAND) are critically assessed on various aspects including (i) non-relativistic versus relativistic Hamiltonians, (ii) spin-orbit coupling contributions and (iii) the gauge. Particular attention is given to the level of accuracy that can be achieved for codes that allow g-tensor calculations under periodic boundary conditions, as these are ideally suited to efficiently describe extended condensed-phase systems containing transition metals. In periodic codes like CP2K and GIPAW, the g-tensor calculation schemes currently suffer from an incorrect treatment of the exchange spin-orbit interaction and a deficient description of the spin-other-orbit term. In this paper a protocol is proposed, making the predictions of the exchange part to the g-tensor shift more plausible. Focus is also put on the influence of the spin-other-orbit interaction which becomes of higher importance for high-spin systems. In a revisited derivation of the various terms arising from the two-electron spin-orbit and spin-other-orbit interaction (SOO), new insight has been obtained revealing amongst other issues new terms for the SOO contribution. The periodic CP2K code has been adapted in view of this new development. One of the objectives of this study is indeed a serious enhancement of the performance of periodic codes in predicting g-tensors in transition metal containing systems at the same level of accuracy as the most advanced but time consuming spin-orbit mean-field approach. The methods are first applied on rhodium carbide but afterwards extended to a broad test set of molecules containing transition metals from the fourth, fifth and sixth row of the periodic table. The set contains doublets as well as high-spin molecules.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal-metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces.

PubMed

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M D

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

PubMed Central

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-01-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism. PMID:29333523

Spin-orbit coupled systems in the atomic limit: rhenates, osmates, iridates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paramekanti, Arun; Singh, David J.; Yuan, Bo

Motivated by RIXS experiments on a wide range of complex heavy oxides, including rhenates, osmates, and iridates, we discuss the theory of RIXS for site-localized t 2g orbital systems with strong spin-orbit coupling. For such systems, we present exact diagonalization results for the spectrum at different electron fillings, showing that it accesses “single-particle” and “multiparticle” excitations. This leads to a simple picture for the energies and intensities of the RIXS spectra in Mott insulators such as double perovskites which feature highly localized electrons, and yields estimates of the spin-orbit coupling and Hund's coupling in correlated 5d oxides. We present newmore » higher resolution RIXS data at the Re L 3 edge in Ba 2YReO 6 which finds a previously unresolved peak splitting, providing further confirmation of our theoretical predictions. Using ab initio electronic structure calculations on Ba 2MReO 6 (with M=Re, Os, Ir) we show that while the atomic limit yields a reasonable effective Hamiltonian description of the experimental observations, effects such as t 2g–e g interactions and hybridization with oxygen are important. Our ab initio estimate for the strength of the intersite exchange coupling shows that, compared to the d 3 systems, the exchange is one or two orders of magnitude weaker in the d 2 and d 4 materials, which may partly explain the suppression of long-range magnetic order in the latter compounds. As a way to interpolate between the site-localized picture and our electronic structure band calculations, we discuss the spin-orbital levels of the MO 6 cluster. In conclusion, this suggests a possible role for intracluster excitons in Ba 2YIrO 6 which may lead to a weak breakdown of the atomic J eff = 0 picture and to small magnetic moments.« less

Spin-orbit coupled systems in the atomic limit: rhenates, osmates, iridates

DOE PAGES

Paramekanti, Arun; Singh, David J.; Yuan, Bo; ...

2018-06-11

Motivated by RIXS experiments on a wide range of complex heavy oxides, including rhenates, osmates, and iridates, we discuss the theory of RIXS for site-localized t 2g orbital systems with strong spin-orbit coupling. For such systems, we present exact diagonalization results for the spectrum at different electron fillings, showing that it accesses “single-particle” and “multiparticle” excitations. This leads to a simple picture for the energies and intensities of the RIXS spectra in Mott insulators such as double perovskites which feature highly localized electrons, and yields estimates of the spin-orbit coupling and Hund's coupling in correlated 5d oxides. We present newmore » higher resolution RIXS data at the Re L 3 edge in Ba 2YReO 6 which finds a previously unresolved peak splitting, providing further confirmation of our theoretical predictions. Using ab initio electronic structure calculations on Ba 2MReO 6 (with M=Re, Os, Ir) we show that while the atomic limit yields a reasonable effective Hamiltonian description of the experimental observations, effects such as t 2g–e g interactions and hybridization with oxygen are important. Our ab initio estimate for the strength of the intersite exchange coupling shows that, compared to the d 3 systems, the exchange is one or two orders of magnitude weaker in the d 2 and d 4 materials, which may partly explain the suppression of long-range magnetic order in the latter compounds. As a way to interpolate between the site-localized picture and our electronic structure band calculations, we discuss the spin-orbital levels of the MO 6 cluster. In conclusion, this suggests a possible role for intracluster excitons in Ba 2YIrO 6 which may lead to a weak breakdown of the atomic J eff = 0 picture and to small magnetic moments.« less

Spin transport study in a Rashba spin-orbit coupling system

PubMed Central

Mei, Fuhong; Zhang, Shan; Tang, Ning; Duan, Junxi; Xu, Fujun; Chen, Yonghai; Ge, Weikun; Shen, Bo

2014-01-01

One of the most important topics in spintronics is spin transport. In this work, spin transport properties of two-dimensional electron gas in AlxGa1-xN/GaN heterostructure were studied by helicity-dependent photocurrent measurements at room temperature. Spin-related photocurrent was detected under normal incidence of a circularly polarized laser with a Gaussian distribution. On one hand, spin polarized electrons excited by the laser generate a diffusive spin polarization current, which leads to a vortex charge current as a result of anomalous circular photogalvanic effect. On the other hand, photo-induced spin polarized electrons driven by a longitudinal electric field give rise to a transverse current via anomalous Hall Effect. Both of these effects originated from the Rashba spin-orbit coupling. By analyzing spin-related photocurrent varied with laser position, the contributions of the two effects were differentiated and the ratio of the spin diffusion coefficient to photo-induced anomalous spin Hall mobility Ds/μs = 0.08 V was extracted at room temperature. PMID:24504193

Combining the spin-separated exact two-component relativistic Hamiltonian with the equation-of-motion coupled-cluster method for the treatment of spin-orbit splittings of light and heavy elements.

PubMed

Cao, Zhanli; Li, Zhendong; Wang, Fan; Liu, Wenjian

2017-02-01

The spin-separated exact two-component (X2C) relativistic Hamiltonian [sf-X2C+so-DKHn, J. Chem. Phys., 2012, 137, 154114] is combined with the equation-of-motion coupled-cluster method with singles and doubles (EOM-CCSD) for the treatment of spin-orbit splittings of open-shell molecular systems. Scalar relativistic effects are treated to infinite order from the outset via the spin-free part of the X2C Hamiltonian (sf-X2C), whereas the spin-orbit couplings (SOC) are handled at the CC level via the first-order Douglas-Kroll-Hess (DKH) type of spin-orbit operator (so-DKH1). Since the exponential of single excitations, i.e., exp(T 1 ), introduces sufficient spin orbital relaxations, the inclusion of SOC at the CC level is essentially the same in accuracy as the inclusion of SOC from the outset in terms of the two-component spinors determined variationally by the sf-X2C+so-DKH1 Hamiltonian, but is computationally more efficient. Therefore, such an approach (denoted as sf-X2C-EOM-CCSD(SOC)) can achieve uniform accuracy for the spin-orbit splittings of both light and heavy elements. For light elements, the treatment of SOC can even be postponed until the EOM step (denoted as sf-X2C-EOM(SOC)-CCSD), so as to further reduce the computational cost. To reveal the efficacy of sf-X2C-EOM-CCSD(SOC) and sf-X2C-EOM(SOC)-CCSD, the spin-orbit splittings of the 2 Π states of monohydrides up to the sixth row of the periodic table are investigated. The results show that sf-X2C-EOM-CCSD(SOC) predicts very accurate results (within 5%) for elements up to the fifth row, whereas sf-X2C-EOM(SOC)-CCSD is useful only for light elements (up to the third row but with some exceptions). For comparison, the sf-X2C-S-TD-DFT-SOC approach [spin-adapted open-shell time-dependent density functional theory, Mol. Phys., 2013, 111, 3741] is applied to the same systems. The overall accuracy (1-10%) is satisfactory.

Quantum oscillation signatures of spin-orbit interactions controlling the residual nodal bilayer-splitting in underdoped high-Tc cuprates

NASA Astrophysics Data System (ADS)

Harrison, Neil; Shekhter, Arkady

2015-03-01

We investigate the origin of the small residual nodal bilayer-splitting in the underdoped high-Tc superconductor YBa2Cu3O6+x using the results of recently published angle-resolved quantum oscillation data [Sebastian et al., Nature 511, 61 (2014)]. A crucial clue to the origin of the residual bilayer-splitting is found to be provided by the anomalously small Zeeman-splitting of some of the observed cyclotron orbits. We show that such an anomalously Zeeman-splitting (or small effective g-factor) for a subset of orbits can be explained by spin-orbit interactions, which become significant in the nodal regions as a result of the vanishing bilayer coupling. The primary effect of spin-orbit interactions is to cause quasiparticles traversing the nodal region of the Brillouin zone to undergo a spin flip. We suggest that the Rashba-like spin-orbit interactions, naturally present in bilayer systems, have the right symmetry and magnitude to give rise to a network of coupled orbits consistent with experimental observations in underdoped YBa2Cu3O6+x. This work is supported by the DOEm BES proposal LANLF100, while the magnet lab is supported by the NSF and Florida State.

Spin Seebeck effect and thermal spin galvanic effect in Ni80Fe20/p-Si bilayers

NASA Astrophysics Data System (ADS)

Bhardwaj, Ravindra G.; Lou, Paul C.; Kumar, Sandeep

2018-01-01

The development of spintronics and spin-caloritronics devices needs efficient generation, detection, and manipulation of spin current. The thermal spin current from the spin-Seebeck effect has been reported to be more energy efficient than the electrical spin injection methods. However, spin detection has been the one of the bottlenecks since metals with large spin-orbit coupling is an essential requirement. In this work, we report an efficient thermal generation and interfacial detection of spin current. We measured a spin-Seebeck effect in Ni80Fe20 (25 nm)/p-Si (50 nm) (polycrystalline) bilayers without a heavy metal spin detector. p-Si, having a centrosymmetric crystal structure, has insignificant intrinsic spin-orbit coupling, leading to negligible spin-charge conversion. We report a giant inverse spin-Hall effect, essential for the detection of spin-Seebeck effects, in the Ni80Fe20/p-Si bilayer structure, which originates from Rashba spin orbit coupling due to structure inversion asymmetry at the interface. In addition, the thermal spin pumping in p-Si leads to spin current from p-Si to the Ni80Fe20 layer due to the thermal spin galvanic effect and the spin-Hall effect, causing spin-orbit torques. The thermal spin-orbit torques lead to collapse of magnetic hysteresis of the 25 nm thick Ni80Fe20 layer. The thermal spin-orbit torques can be used for efficient magnetic switching for memory applications. These scientific breakthroughs may give impetus to the silicon spintronics and spin-caloritronics devices.

A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd 2Re 2O 7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harter, J. W.; Zhao, Z. Y.; Yan, J. -Q.

Strong electron interactions can drive metallic systems toward a variety of well-known symmetry-broken phases, but the instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncovered a multipolar nematic phase of matter in the metallic pyrochlore Cd 2Re 2O 7 using spatially resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic nematic phases, this multipolar phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of themore » multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 kelvin in Cd 2Re 2O 7 and induces a parity-breaking lattice distortion as a secondary order.« less

A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd2Re2O7

NASA Astrophysics Data System (ADS)

Harter, J. W.; Zhao, Z. Y.; Yan, J.-Q.; Mandrus, D. G.; Hsieh, D.

2017-04-01

Strong electron interactions can drive metallic systems toward a variety of well-known symmetry-broken phases, but the instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncovered a multipolar nematic phase of matter in the metallic pyrochlore Cd2Re2O7 using spatially resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic nematic phases, this multipolar phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 kelvin in Cd2Re2O7 and induces a parity-breaking lattice distortion as a secondary order.

A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd 2Re 2O 7

DOE PAGES

Harter, J. W.; Zhao, Z. Y.; Yan, J. -Q.; ...

2017-04-21

Strong electron interactions can drive metallic systems toward a variety of well-known symmetry-broken phases, but the instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncovered a multipolar nematic phase of matter in the metallic pyrochlore Cd 2Re 2O 7 using spatially resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic nematic phases, this multipolar phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of themore » multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 kelvin in Cd 2Re 2O 7 and induces a parity-breaking lattice distortion as a secondary order.« less

A spin-orbit coupling for a neutral particle from Lorentz symmetry breaking effects in the CPT-odd sector of the Standard Model Extension

NASA Astrophysics Data System (ADS)

Belich, H.; Bakke, K.

2015-07-01

We start by investigating the arising of a spin-orbit coupling and a Darwin-type term that stem from Lorentz symmetry breaking effects in the CPT-odd sector of the Standard Model Extension. Then, we establish a possible scenario of the violation of the Lorentz symmetry that gives rise to a linear confining potential and an effective electric field in which determines the spin-orbit coupling for a neutral particle analogous to the Rashba coupling [E. I. Rashba, Sov. Phys. Solid State 2, 1109 (1960)]. Finally, we confine the neutral particle to a quantum dot [W.-C. Tan and J. C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)] and analyze the influence of the linear confining potential and the spin-orbit coupling on the spectrum of energy.

Damping of spin-dipole mode and generation of quadrupole mode excitations in a spin-orbit coupled Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Li, Chuan-Hsun; Blasing, David; Chen, Yong

2017-04-01

In cold atom systems, spin excitations have been shown to be a sensitive probe of interactions and quantum statistical effects, and can be used to study spin transport in both Fermi and Bose gases. In particular, spin-dipole mode (SDM) is a type of excitation that can generate a spin current without a net mass current. We present recent measurements and analysis of SDM in a disorder-free, interacting three-dimensional (3D) 87Rb Bose-Einstein condensate (BEC) by applying spin-dependent synthetic electric fields to actuate head-on collisions between two BECs of different spin states. We experimentally study and compare the behaviors of the system following SDM excitations in the presence as well as absence of synthetic 1D spin-orbit coupling (SOC). We find that in the absence of SOC, SDM is relatively weakly damped, accompanied with collision-induced thermalization which heats up the atomic cloud. However, in the presence of SOC, we find that SDM is more strongly damped with reduced thermalization, and observe excitation of a quadrupole mode that exhibits BEC shape oscillation even after SDM is damped out. Such a mode conversion bears analogies with the Beliaev coupling process or the parametric frequency down conversion of light in nonlinear optics.

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

NASA Astrophysics Data System (ADS)

Avilés-Félix, L.; Butera, A.; González-Chávez, D. E.; Sommer, R. L.; Gómez, J. E.

2018-03-01

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

Ground-state phase diagram in the Kugel-Khomskii model with finite spin-orbit interactions

NASA Astrophysics Data System (ADS)

Koga, Akihisa; Nakauchi, Shiryu; Nasu, Joji

2018-05-01

We study ground-state properties in the Kugel-Khomskii model on the two-dimensional honeycomb lattice. Using the cluster mean-field approximations, we deal with the exchange and spin-orbit couplings on an equal footing. We then discuss the stability of the ferromagnetically ordered states against the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit.

Strong-coupling phases of the spin-orbit-coupled spin-1 Bose-Hubbard chain: Odd-integer Mott lobes and helical magnetic phases

NASA Astrophysics Data System (ADS)

Pixley, J. H.; Cole, William S.; Spielman, I. B.; Rizzi, Matteo; Das Sarma, S.

2017-10-01

We study the odd-integer filled Mott phases of a spin-1 Bose-Hubbard chain and determine their fate in the presence of a Raman induced spin-orbit coupling which has been achieved in ultracold atomic gases; this system is described by a quantum spin-1 chain with a spiral magnetic field. The spiral magnetic field initially induces helical order with either ferromagnetic or dimer order parameters, giving rise to a spiral paramagnet at large field. The spiral ferromagnet-to-paramagnet phase transition is in a universality class with critical exponents associated with the divergence of the correlation length ν ≈2 /3 and the order-parameter susceptibility γ ≈1 /2 . We solve the effective spin model exactly using the density-matrix renormalization group, and compare with both a large-S classical solution and a phenomenological Landau theory. We discuss how these exotic bosonic magnetic phases can be produced and probed in ultracold atomic experiments in optical lattices.

Spin-orbit coupling, strong correlation, and insulator-metal transitions: The J eff = 3 2 ferromagnetic Dirac-Mott insulator Ba 2 NaOsO 6

DOE PAGES

Gangopadhyay, Shruba; Pickett, Warren E.

2015-01-15

The double perovskite Ba 2NaOsO 6 (BNOO), an exotic example of a very high oxidation state (heptavalent) osmium d1 compound and also uncommon by being a ferromagnetic open d-shell (Mott) insulator without Jahn-Teller (JT) distortion, is modeled using a density functional theory based hybrid functional incorporating exact exchange for correlated electronic orbitals and including the large spin-orbit coupling (SOC). The experimentally observed narrow-gap ferromagnetic insulating ground state is obtained, but only when including spin-orbit coupling, making this a Dirac-Mott insulator. The calculated easy axis along [110] is in accord with experiment, providing additional support that this approach provides a realisticmore » method for studying this system. The predicted spin density for [110] spin orientation is nearly cubic (unlike for other directions), providing an explanation for the absence of JT distortion. An orbital moment of –0.4μ B strongly compensates the +0.5μ B spin moment on Os, leaving a strongly compensated moment more in line with experiment. Remarkably, the net moment lies primarily on the oxygen ions. An insulator-metal transition, by rotating the magnetization direction with an external field under moderate pressure, is predicted as one consequence of strong SOC, and metallization under moderate pressure is predicted. In conclusion, a comparison is made with the isostructural, isovalent insulator Ba 2LiOsO 6, which, however, orders antiferromagnetically.« less

Spin Hall and Spin Swapping Torques in Diffusive Ferromagnets

NASA Astrophysics Data System (ADS)

Pauyac, Christian Ortiz; Chshiev, Mairbek; Manchon, Aurelien; Nikolaev, Sergey A.

2018-04-01

A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession, and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precession effects displays a complex spatial dependence that can be exploited to generate torques and nucleate or propagate domain walls in centrosymmetric geometries without the use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

SPIN–SPIN COUPLING IN THE SOLAR SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Batygin, Konstantin; Morbidelli, Alessandro, E-mail: kbatygin@gps.caltech.edu

The richness of dynamical behavior exhibited by the rotational states of various solar system objects has driven significant advances in the theoretical understanding of their evolutionary histories. An important factor that determines whether a given object is prone to exhibiting non-trivial rotational evolution is the extent to which such an object can maintain a permanent aspheroidal shape, meaning that exotic behavior is far more common among the small body populations of the solar system. Gravitationally bound binary objects constitute a substantial fraction of asteroidal and TNO populations, comprising systems of triaxial satellites that orbit permanently deformed central bodies. In thismore » work, we explore the rotational evolution of such systems with specific emphasis on quadrupole–quadrupole interactions, and show that for closely orbiting, highly deformed objects, both prograde and retrograde spin–spin resonances naturally arise. Subsequently, we derive capture probabilities for leading order commensurabilities and apply our results to the illustrative examples of (87) Sylvia and (216) Kleopatra asteroid systems. Cumulatively, our results suggest that spin–spin coupling may be consequential for highly elongated, tightly orbiting binary objects.« less

Topological quantum phase transitions and edge states in spin-orbital coupled Fermi gases.

PubMed

Zhou, Tao; Gao, Yi; Wang, Z D

2014-06-11

We study superconducting states in the presence of spin-orbital coupling and Zeeman field. It is found that a phase transition from a Fulde-Ferrell-Larkin-Ovchinnikov state to the topological superconducting state occurs upon increasing the spin-orbital coupling. The nature of this topological phase transition and its critical property are investigated numerically. Physical properties of the topological superconducting phase are also explored. Moreover, the local density of states is calculated, through which the topological feature may be tested experimentally.

Electric control of superconducting transition through a spin-orbit coupled interface

PubMed Central

Ouassou, Jabir Ali; Di Bernardo, Angelo; Robinson, Jason W. A.; Linder, Jacob

2016-01-01

We demonstrate theoretically all-electric control of the superconducting transition temperature using a device comprised of a conventional superconductor, a ferromagnetic insulator, and semiconducting layers with intrinsic spin-orbit coupling. By using analytical calculations and numerical simulations, we show that the transition temperature of such a device can be controlled by electric gating which alters the ratio of Rashba to Dresselhaus spin-orbit coupling. The results offer a new pathway to control superconductivity in spintronic devices. PMID:27426887

A state interaction spin-orbit coupling density matrix renormalization group method

NASA Astrophysics Data System (ADS)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

2016-06-01

We describe a state interaction spin-orbit (SISO) coupling method using density matrix renormalization group (DMRG) wavefunctions and the spin-orbit mean-field (SOMF) operator. We implement our DMRG-SISO scheme using a spin-adapted algorithm that computes transition density matrices between arbitrary matrix product states. To demonstrate the potential of the DMRG-SISO scheme we present accurate benchmark calculations for the zero-field splitting of the copper and gold atoms, comparing to earlier complete active space self-consistent-field and second-order complete active space perturbation theory results in the same basis. We also compute the effects of spin-orbit coupling on the spin-ladder of the iron-sulfur dimer complex [Fe2S2(SCH3)4]3-, determining the splitting of the lowest quartet and sextet states. We find that the magnitude of the zero-field splitting for the higher quartet and sextet states approaches a significant fraction of the Heisenberg exchange parameter.

Electrical and thermoelectric transport properties of two-dimensional fermionic systems with k-cubic spin-orbit coupling.

PubMed

Mawrie, Alestin; Verma, Sonu; Ghosh, Tarun Kanti

2017-09-01

We investigate effect of <i>k</i>-cubic spin-orbit interaction on electrical and thermoelectric transport properties of two-dimensional fermionic systems. We obtain exact analytical expressions of the inverse relaxation time (IRT) and the Drude conductivity for long-range Coulomb and short-range delta scattering potentials. The IRT reveals that the scattering is completely suppressed along the three directions θ = (2n+1)π/3 with n=1,2,3. We also obtain analytical results of the thermopower and thermal conductivity at low temperature. The thermoelectric transport coefficients obey the Wiedemann-Franz law, even in the presence of <i>k</i>-cubic Rashba spin-orbit interaction (RSOI) at low temperature. In the presence of quantizing magnetic field, the signature of the RSOI is revealed through the appearance of the beating pattern in the Shubnikov-de Haas (SdH) oscillations of thermopower and thermal conductivity in low magnetic field regime. The empirical formulae for the SdH oscillation frequencies accurately describe the locations of the beating nodes. The beating pattern in magnetothermoelectric measurement can be used to extract the spin-orbit coupling constant. © 2017 IOP Publishing Ltd.

Electrical and thermoelectric transport properties of two-dimensional fermionic systems with k-cubic spin-orbit coupling

NASA Astrophysics Data System (ADS)

Mawrie, Alestin; Verma, Sonu; Kanti Ghosh, Tarun

2017-11-01

We investigate the effect of k-cubic spin-orbit interaction on the electrical and thermoelectric transport properties of two-dimensional fermionic systems. We obtain exact analytical expressions of the inverse relaxation time (IRT) and the Drude conductivity for long-range Coulomb and short-range delta scattering potentials. The IRT reveals that the scattering is completely suppressed along the three directions θ^\\prime = (2n+1)π/3 with n=1, 2, 3 . We also obtain analytical results of the thermopower and thermal conductivity at low temperature. The thermoelectric transport coefficients obey the Wiedemann-Franz law, even in the presence of k-cubic Rashba spin-orbit interaction (RSOI) at low temperature. In the presence of a quantizing magnetic field, the signature of the RSOI is revealed through the appearance of the beating pattern in the Shubnikov-de Haas (SdH) oscillations of thermopower and thermal conductivity in the low magnetic field regime. The empirical formulae for the SdH oscillation frequencies accurately describe the locations of the beating nodes. The beating pattern in magnetothermoelectric measurement can be used to extract the spin-orbit coupling constant.

Flipping-shuttle oscillations of bright one- and two-dimensional solitons in spin-orbit-coupled Bose-Einstein condensates with Rabi mixing

NASA Astrophysics Data System (ADS)

Sakaguchi, Hidetsugu; Malomed, Boris A.

2017-10-01

We analyze the possibility of macroscopic quantum effects in the form of coupled structural oscillations and shuttle motion of bright two-component spin-orbit-coupled striped (one-dimensional, 1D) and semivortex (two-dimensional, 2D) matter-wave solitons, under the action of linear mixing (Rabi coupling) between the components. In 1D, the intrinsic oscillations manifest themselves as flippings between spatially even and odd components of striped solitons, while in 2D the system features periodic transitions between zero-vorticity and vortical components of semivortex solitons. The consideration is performed by means of a combination of analytical and numerical methods.

Protected Pseudohelical Edge States in Z2-Trivial Proximitized Graphene

NASA Astrophysics Data System (ADS)

Frank, Tobias; Högl, Petra; Gmitra, Martin; Kochan, Denis; Fabian, Jaroslav

2018-04-01

We investigate topological properties of models that describe graphene on realistic substrates which induce proximity spin-orbit coupling in graphene. A Z2 phase diagram is calculated for the parameter space of (generally different) intrinsic spin-orbit coupling on the two graphene sublattices, in the presence of Rashba coupling. The most fascinating case is that of staggered intrinsic spin-orbit coupling which, despite being topologically trivial, Z2=0 , does exhibit edge states protected by time-reversal symmetry for zigzag ribbons as wide as micrometers. We call these states pseudohelical as their helicity is locked to the sublattice. The spin character and robustness of the pseudohelical modes is best exhibited on a finite flake, which shows that the edge states have zero g factor, carry a pure spin current in the cross section of the flake, and exhibit spin-flip reflectionless tunneling at the armchair edges.

Magnetism in S = 1 / 2 Double Perovskites with Strong Spin-Orbit Interactions

NASA Astrophysics Data System (ADS)

Ishizuka, Hiroaki; Balents, Leon

2015-03-01

Motivated by recent studies on heavy-element double-perovskite (DP) compounds, we theoretically studied spin models on a FCC lattice with anisotropic interactions. In these systems, competition/cooperation of spin, orbital, and the lattice degrees of freedoms in the presence of the strong-spin orbit coupling is of particular interest. In a previous theoretical study, the magnetic phase diagrams of DP compounds with 5d1 electron configuration was studied using a model with four-fold degenerated single-ion state. On the other hand, a recent experiment on a DP material, Ba2Na2OsO6, reported that the compound is likely to be an effective S = 1 / 2 magnet. Inspired by the experimental observation, we considered spin models with symmetry-allowed anisotropic nearest-neighbor interactions. By a combination of various analytical and numerical techniques, we present the magnetic phase diagram of the model and the effect of thermal and quantum fluctuations. In particular, we show that fluctuations induce < 110 > anisotropy of magnetic moments. We also discuss a possible ``nematic'' phase driven by spin-phonon couplings.

Drag balance Cubesat attitude motion effects on in-situ thermosphere density measurements

NASA Astrophysics Data System (ADS)

Felicetti, Leonard; Santoni, Fabio

2014-08-01

The dynamics of Cubesats carrying a drag balance instrument (DBI) for in situ atmosphere density measurements is analyzed. Atmospheric drag force is measured by the displacement of two light plates exposed to the incoming particle flow. This system is well suited for a distributed sensor network in orbit, to get simultaneous in situ local (non orbit averaged) measurements in multiple positions and orbit heights, contributing to the development and validation of global atmosphere models. The implementation of the DBI leads to orbit normal pointing spinning two body system. The use of a spin-magnetic attitude control system is suggested, based only on magnetometer readings, contributing to making the system simple, inexpensive, and reliable. It is shown, by an averaging technique, that this system provides for orbit normal spin axis pointing. The effect of the coupling between the attitude dynamics and the DBI is evaluated, analyzing its frequency content and showing that no frequency components arise, affecting the DBI performance. The analysis is confirmed by Monte Carlo numerical simulation results.

Spin-Orbital Excitations in Ca2 RuO4 Revealed by Resonant Inelastic X-Ray Scattering

NASA Astrophysics Data System (ADS)

Das, L.; Forte, F.; Fittipaldi, R.; Fatuzzo, C. G.; Granata, V.; Ivashko, O.; Horio, M.; Schindler, F.; Dantz, M.; Tseng, Yi; McNally, D. E.; Rønnow, H. M.; Wan, W.; Christensen, N. B.; Pelliciari, J.; Olalde-Velasco, P.; Kikugawa, N.; Neupert, T.; Vecchione, A.; Schmitt, T.; Cuoco, M.; Chang, J.

2018-01-01

The strongly correlated insulator Ca2 RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K -edge resonant inelastic x-ray scattering study of the antiferromagnetic Mott insulating state of Ca2 RuO4 . A set of low-energy (about 80 and 400 meV) and high-energy (about 1.3 and 2.2 eV) excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modeling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveils the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2 RuO4 .

Generalized valence bond description of the ground states (X(1)Σg(+)) of homonuclear pnictogen diatomic molecules: N2, P2, and As2.

PubMed

Xu, Lu T; Dunning, Thom H

2015-06-09

The ground state, X1Σg+, of N2 is a textbook example of a molecule with a triple bond consisting of one σ and two π bonds. This assignment, which is usually rationalized using molecular orbital (MO) theory, implicitly assumes that the spins of the three pairs of electrons involved in the bonds are singlet-coupled (perfect pairing). However, for a six-electron singlet state, there are five distinct ways to couple the electron spins. The generalized valence bond (GVB) wave function lifts this restriction, including all of the five spin functions for the six electrons involved in the bond. For N2, we find that the perfect pairing spin function is indeed dominant at Re but that it becomes progressively less so from N2 to P2 and As2. Although the perfect pairing spin function is still the most important spin function in P2, the importance of a quasi-atomic spin function, which singlet couples the spins of the electrons in the σ orbitals while high spin coupling those of the electrons in the π orbitals on each center, has significantly increased relative to N2 and, in As2, the perfect pairing and quasi-atomic spin couplings are on essentially the same footing. This change in the spin coupling of the electrons in the bonding orbitals down the periodic table may contribute to the rather dramatic decrease in the strengths of the Pn2 bonds from N2 to As2 as well as in the increase in their chemical reactivity and should be taken into account in more detailed analyses of the bond energies in these species. We also compare the spin coupling in N2 with that in C2, where the quasi-atomic spin coupling dominants around Re.

Three-dimensional vortex-bright solitons in a spin-orbit-coupled spin-1 condensate

NASA Astrophysics Data System (ADS)

Gautam, Sandeep; Adhikari, S. K.

2018-01-01

We demonstrate stable and metastable vortex-bright solitons in a three-dimensional spin-orbit-coupled three-component hyperfine spin-1 Bose-Einstein condensate (BEC) using numerical solution and variational approximation of a mean-field model. The spin-orbit coupling provides attraction to form vortex-bright solitons in both attractive and repulsive spinor BECs. The ground state of these vortex-bright solitons is axially symmetric for weak polar interaction. For a sufficiently strong ferromagnetic interaction, we observe the emergence of a fully asymmetric vortex-bright soliton as the ground state. We also numerically investigate moving solitons. The present mean-field model is not Galilean invariant, and we use a Galilean-transformed mean-field model for generating the moving solitons.

Model of quantum kinetics of spin-orbit coupled two-dimensional electron gas in the presence of strong electromagnetic field

NASA Astrophysics Data System (ADS)

Turkin, Yaroslav V.; Kuptsov, Pavel V.

2018-04-01

A quantum model of spin dynamics of spin-orbit coupled two-dimensional electron gas in the presence of strong high- frequency electromagnetic field is suggested. Interaction of electrons with optical phonons is taken into account in the second order of perturbation theory.

Photoinduced dynamics to photoluminescence in Ln3+ (Ln = Ce, Pr) doped β-NaYF4 nanocrystals computed in basis of non-collinear spin DFT with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Han, Yulun; Vogel, Dayton J.; Inerbaev, Talgat M.; May, P. Stanley; Berry, Mary T.; Kilin, Dmitri S.

2018-03-01

In this work, non-collinear spin DFT + U approaches with spin-orbit coupling (SOC) are applied to Ln3+ doped β-NaYF4 (Ln = Ce, Pr) nanocrystals in Vienna ab initio Simulation Package taking into account unpaired spin configurations using the Perdew-Burke-Ernzerhof functional in a plane wave basis set. The calculated absorption spectra from non-collinear spin DFT + U approaches are compared with that from spin-polarised DFT + U approaches. The spectral difference indicates the importance of spin-flip transitions of Ln3+ ions. Suite of codes for nonadiabatic dynamics has been developed for 2-component spinor orbitals. On-the-fly nonadiabatic coupling calculations provide transition probabilities facilitated by nuclear motion. Relaxation rates of electrons and holes are calculated using Redfield theory in the reduced density matrix formalism cast in the basis of non-collinear spin DFT + U with SOC. The emission spectra are calculated using the time-integrated method along the excited state trajectories based on nonadiabatic couplings.

Force on an electric/magnetic dipole and classical approach to spin-orbit coupling in hydrogen-like atoms

NASA Astrophysics Data System (ADS)

Kholmetskii, A. L.; Missevitch, O. V.; Yarman, T.

2017-09-01

We carry out the classical analysis of spin-orbit coupling in hydrogen-like atoms, using the modern expressions for the force and energy of an electric/magnetic dipole in an electromagnetic field. We disclose a novel physical meaning of this effect and show that for a laboratory observer the energy of spin-orbit interaction is represented solely by the mechanical energy of the spinning electron (considered as a gyroscope) due to the Thomas precession of its spin. Concurrently we disclose some errors in the old and new publications on this subject.

Spin-Driven Emergent Antiferromagnetism and Metal-Insulator Transition in Nanoscale p-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through Rashba spin-orbit coupling mediated spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. The phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage, which is related to the thermal conductivity and heat capacity.

Extrinsic spin Hall effect in graphene

NASA Astrophysics Data System (ADS)

Rappoport, Tatiana

The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

Nonlinear spin current generation in noncentrosymmetric spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Hamamoto, Keita; Ezawa, Motohiko; Kim, Kun Woo; Morimoto, Takahiro; Nagaosa, Naoto

2017-06-01

Spin current plays a central role in spintronics. In particular, finding more efficient ways to generate spin current has been an important issue and has been studied actively. For example, representative methods of spin-current generation include spin-polarized current injections from ferromagnetic metals, the spin Hall effect, and the spin battery. Here, we theoretically propose a mechanism of spin-current generation based on nonlinear phenomena. By using Boltzmann transport theory, we show that a simple application of the electric field E induces spin current proportional to E2 in noncentrosymmetric spin-orbit coupled systems. We demonstrate that the nonlinear spin current of the proposed mechanism is supported in the surface state of three-dimensional topological insulators and two-dimensional semiconductors with the Rashba and/or Dresselhaus interaction. In the latter case, the angular dependence of the nonlinear spin current can be manipulated by the direction of the electric field and by the ratio of the Rashba and Dresselhaus interactions. We find that the magnitude of the spin current largely exceeds those in the previous methods for a reasonable magnitude of the electric field. Furthermore, we show that application of ac electric fields (e.g., terahertz light) leads to the rectifying effect of the spin current, where dc spin current is generated. These findings will pave a route to manipulate the spin current in noncentrosymmetric crystals.

Quantum entanglement and quantum information in biological systems (DNA)

NASA Astrophysics Data System (ADS)

Hubač, Ivan; Švec, Miloslav; Wilson, Stephen

2017-12-01

Recent studies of DNA show that the hydrogen bonds between given base pairs can be treated as diabatic systems with spin-orbit coupling. For solid state systems strong diabaticity and spin-orbit coupling the possibility of forming Majorana fermions has been discussed. We analyze the hydrogen bonds in the base pairs in DNA from this perspective. Our analysis is based on a quasiparticle supersymmetric transformation which couples electronic and vibrational motion and includes normal coordinates and the corresponding momenta. We define qubits formed by Majorana fermions in the hydrogen bonds and also discuss the entangled states in base pairs. Quantum information and quantum entropy are introduced. In addition to the well-known classical information connected with the DNA base pairs, we also consider quantum information and show that the classical and quantum information are closely connected.

Strongly anisotropic spin relaxation in graphene-transition metal dichalcogenide heterostructures at room temperature

NASA Astrophysics Data System (ADS)

Benítez, L. Antonio; Sierra, Juan F.; Savero Torres, Williams; Arrighi, Aloïs; Bonell, Frédéric; Costache, Marius V.; Valenzuela, Sergio O.

2018-03-01

A large enhancement in the spin-orbit coupling of graphene has been predicted when interfacing it with semiconducting transition metal dichalcogenides. Signatures of such an enhancement have been reported, but the nature of the spin relaxation in these systems remains unknown. Here, we unambiguously demonstrate anisotropic spin dynamics in bilayer heterostructures comprising graphene and tungsten or molybdenum disulphide (WS2, MoS2). We observe that the spin lifetime varies over one order of magnitude depending on the spin orientation, being largest when the spins point out of the graphene plane. This indicates that the strong spin-valley coupling in the transition metal dichalcogenide is imprinted in the bilayer and felt by the propagating spins. These findings provide a rich platform to explore coupled spin-valley phenomena and offer novel spin manipulation strategies based on spin relaxation anisotropy in two-dimensional materials.

UNO DMRG CASCI calculations of effective exchange integrals for m-phenylene-bis-methylene spin clusters

NASA Astrophysics Data System (ADS)

Kawakami, Takashi; Sano, Shinsuke; Saito, Toru; Sharma, Sandeep; Shoji, Mitsuo; Yamada, Satoru; Takano, Yu; Yamanaka, Shusuke; Okumura, Mitsutaka; Nakajima, Takahito; Yamaguchi, Kizashi

2017-09-01

Theoretical examinations of the ferromagnetic coupling in the m-phenylene-bis-methylene molecule and its oligomer were carried out. These systems are good candidates for exchange-coupled systems to investigate strong electronic correlations. We studied effective exchange integrals (J), which indicated magnetic coupling between interacting spins in these species. First, theoretical calculations based on a broken-symmetry single-reference procedure, i.e. the UHF, UMP2, UMP4, UCCSD(T) and UB3LYP methods, were carried out with a GAUSSIAN program code under an SR wave function. From these results, the J value by the UHF method was largely positive because of the strong ferromagnetic spin polarisation effect. The J value by the UCCSD(T) and UB3LYP methods improved an overestimation problem by correcting the dynamical electronic correlation. Next, magnetic coupling among these spins was studied using the CAS-based method of the symmetry-adapted multireference methods procedure. Thus, the UNO DMRG CASCI (UNO, unrestricted natural orbital; DMRG, density matrix renormalised group; CASCI, complete active space configuration interaction) method was mainly employed with a combination of ORCA and BLOCK program codes. DMRG CASCI calculations in valence electron counting, which included all orbitals to full valence CI, provided the most reliable result, and support the UB3LYP method for extended systems.

Role of spin-orbit coupling in the electronic structure of Ir O2

NASA Astrophysics Data System (ADS)

Das, Pranab Kumar; Sławińska, Jagoda; Vobornik, Ivana; Fujii, Jun; Regoutz, Anna; Kahk, Juhan M.; Scanlon, David O.; Morgan, Benjamin J.; McGuinness, Cormac; Plekhanov, Evgeny; Di Sante, Domenico; Huang, Ying-Sheng; Chen, Ruei-San; Rossi, Giorgio; Picozzi, Silvia; Branford, William R.; Panaccione, Giancarlo; Payne, David J.

2018-06-01

The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rutile binary iridate, Ir O2 , is investigated. The detailed study of electronic bands measured on a high-quality single crystalline sample and use of a wide range of photon energy provide a huge improvement over the previous studies. The excellent agreement between theory and experimental results shows that the single-particle DFT description of Ir O2 band structure is adequate, without the need of invoking any treatment of correlation effects. Although many observed features point to a 3D nature of the electronic structure, clear surface effects are revealed. The discussion of the orbital character of the relevant bands crossing the Fermi level sheds light on spin-orbit-coupling-driven phenomena in this material, unveiling a spin-orbit-induced avoided crossing, a property likely to play a key role in its large spin Hall effect.

Near-Earth asteroid satellite spins under spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naidu, Shantanu P.; Margot, Jean-Luc

We develop a fourth-order numerical integrator to simulate the coupled spin and orbital motions of two rigid bodies having arbitrary mass distributions under the influence of their mutual gravitational potential. We simulate the dynamics of components in well-characterized binary and triple near-Earth asteroid systems and use surface of section plots to map the possible spin configurations of the satellites. For asynchronous satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. For synchronous satellites, we show that libration amplitudes can reach detectable values even for moderately elongated shapes. The presence of chaoticmore » regions in the phase space has important consequences for the evolution of binary asteroids. It may substantially increase spin synchronization timescales, explain the observed fraction of asychronous binaries, delay BYORP-type evolution, and extend the lifetime of binaries. The variations in spin rate due to large librations also affect the analysis and interpretation of light curve and radar observations.« less

A state interaction spin-orbit coupling density matrix renormalization group method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

We describe a state interaction spin-orbit (SISO) coupling method using density matrix renormalization group (DMRG) wavefunctions and the spin-orbit mean-field (SOMF) operator. We implement our DMRG-SISO scheme using a spin-adapted algorithm that computes transition density matrices between arbitrary matrix product states. To demonstrate the potential of the DMRG-SISO scheme we present accurate benchmark calculations for the zero-field splitting of the copper and gold atoms, comparing to earlier complete active space self-consistent-field and second-order complete active space perturbation theory results in the same basis. We also compute the effects of spin-orbit coupling on the spin-ladder of the iron-sulfur dimer complex [Fe{submore » 2}S{sub 2}(SCH{sub 3}){sub 4}]{sup 3−}, determining the splitting of the lowest quartet and sextet states. We find that the magnitude of the zero-field splitting for the higher quartet and sextet states approaches a significant fraction of the Heisenberg exchange parameter.« less

Theory of electrically controlled resonant tunneling spin devices

NASA Technical Reports Server (NTRS)

Ting, David Z. -Y.; Cartoixa, Xavier

2004-01-01

We report device concepts that exploit spin-orbit coupling for creating spin polarized current sources using nonmagnetic semiconductor resonant tunneling heterostructures, without external magnetic fields. The resonant interband tunneling psin filter exploits large valence band spin-orbit interaction to provide strong spin selectivity.

Magnetoelectric Andreev Effect due to Proximity-Induced Nonunitary Triplet Superconductivity in Helical Metals

NASA Astrophysics Data System (ADS)

Tkachov, G.

2017-01-01

Noncentrosymmetric superconductors exhibit the magnetoelectric effect, which manifests itself in the appearance of the magnetic spin polarization in response to a dissipationless electric current (supercurrent). While much attention has been dedicated to the thermodynamic version of this phenomenon (Edelstein effect), nonequilibrium transport magnetoelectric effects have not been explored yet. We propose the magnetoelectric Andreev effect (MAE), which consists in the generation of spin-polarized triplet Andreev conductance by an electric supercurrent. The MAE stems from the spin polarization of the Cooper-pair condensate due to a supercurrent-induced nonunitary triplet pairing. We propose the realization of such a nonunitary pairing and MAE in superconducting proximity structures based on two-dimensional helical metals—strongly spin-orbit-coupled electronic systems with the Dirac spectrum such as the topological surface states. Our results uncover an unexplored route towards electrically controlled superconducting spintronics and are a smoking gun for induced unconventional superconductivity in spin-orbit-coupled materials.

Analytical spectrum for a Hamiltonian of quantum dots with Rashba spin-orbit coupling

NASA Astrophysics Data System (ADS)

Dossa, Anselme F.; Avossevou, Gabriel Y. H.

2014-12-01

We determine the analytical solution for a Hamiltonian describing a confined charged particle in a quantum dot, including Rashba spin-orbit coupling and Zeeman splitting terms. The approach followed in this paper is straightforward and uses the symmetrization of the wave function's components. The eigenvalue problem for the Hamiltonian in Bargmann's Hilbert space reduces to a system of coupled first-order differential equations. Then we exploit the symmetry in the system to obtain uncoupled second-order differential equations, which are found to be the Whittaker-Ince limit of the confluent Heun equations. Analytical expressions as well as numerical results are obtained for the spectrum. One of the main features of such models, namely, the level splitting, is present through the spectrum obtained in this paper.

Density matrix-based time-dependent configuration interaction approach to ultrafast spin-flip dynamics

NASA Astrophysics Data System (ADS)

Wang, Huihui; Bokarev, Sergey I.; Aziz, Saadullah G.; Kühn, Oliver

2017-08-01

Recent developments in attosecond spectroscopy yield access to the correlated motion of electrons on their intrinsic timescales. Spin-flip dynamics is usually considered in the context of valence electronic states, where spin-orbit coupling is weak and processes related to the electron spin are usually driven by nuclear motion. However, for core-excited states, where the core-hole has a nonzero angular momentum, spin-orbit coupling is strong enough to drive spin-flips on a much shorter timescale. Using density matrix-based time-dependent restricted active space configuration interaction including spin-orbit coupling, we address an unprecedentedly short spin-crossover for the example of L-edge (2p→3d) excited states of a prototypical Fe(II) complex. This process occurs on a timescale, which is faster than that of Auger decay (∼4 fs) treated here explicitly. Modest variations of carrier frequency and pulse duration can lead to substantial changes in the spin-state yield, suggesting its control by soft X-ray light.

Theoretical Study of the Jahn-Teller effect in CH3CN+ (X2E) and CD3CN+ (X2E): multimode spin-vibronic energy level calculations.

PubMed

Zhang, Shiyang; Mo, Yuxiang

2009-10-15

The spin-vibronic energy levels for CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) have been calculated using a diabatic model including multimode vibronic couplings and spin-orbit interaction without adjusting any parameter. The diabatic potential energy surfaces are represented by the Taylor expansions including linear, quadratic and bilinear vibronic coupling terms. The normal coordinates used in the Taylor expansion were expressed by the mass-weighted Cartesian coordinates. The adiabatic potential energy surfaces for CH(3)CN(+) and CD(3)CN(+) were calculated at the level of CASPT2/cc-pvtz, and the spin-orbit coupling constant was calculated at the level of MRCI/CAS/cc-pvtz. The spin-orbit energy splittings for the ground vibrational states of CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) are 20 and 16 cm(-1), respectively, which are resulted from the quenching of the spin-orbit coupling strength of 51 cm(-1). The calculated spin-vibronic levels are in good agreement with the experimental data. The calculation results show that the Jahn-Teller effects in CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) are essential to understand their spin-vibronic energy structure.

New observations and new models of spin-orbit coupling in binary asteroids

NASA Astrophysics Data System (ADS)

Margot, Jean-Luc; Naidu, Shantanu

2015-08-01

The YORP-induced rotational fission hypothesis is the leading candidate for explaining the formation of binaries, triples, and pairs among small (<20 km) asteroids (e.g., Margot et al, Asteroids IV, subm., 2015). Various evolutionary paths following rotational fission have been suggested, but many important questions remain about the evolutionary mechanisms and timescales. We test hypotheses about the evolution of binary asteroids by obtaining precise descriptions of the orbits and components of binary systems with radar and by examining the system dynamics with detailed numerical simulations. Predictions for component spin states and orbital precession rates can then be compared to observables in our data sets or in other data sets to elucidate the states of various systems and their likely evolutionary paths.Accurate simulations require knowledge of the masses, shapes, and spin states of individual binary components. Because radar observations can provide exquisite data sets spanning days with spatial resolutions at the decameter level, we can invert for the component shapes and measure spin states. We can also solve for the mutual orbit by fitting the observed separations between components. In addition, the superb (10e-7--10e-8) fractional uncertainties in range allow us to measure the reflex motions directly, allowing masses of individual components to be determined.We use recently published observations of the binary 2000 DP107 (Naidu et al. AJ, subm., 2015) and that of other systems to simulate the dynamics of components in well-characterized binary systems (Naidu and Margot, AJ 149, 80, 2015). We model the coupled spin and orbital motions of two rigid, ellipsoidal bodies under the influence of their mutual gravitational potential. We use surface of section plots to map the possible spin configurations of the satellites. For asynchronous satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. The presence of chaotic regions may substantially increase spin synchronization timescales, delay BYORP-type evolution, extend the lifetime of binaries, and explain the observed fraction of asynchronous binaries.

Theory of electronic and spin-orbit proximity effects in graphene on Cu(111)

NASA Astrophysics Data System (ADS)

Frank, Tobias; Gmitra, Martin; Fabian, Jaroslav

2016-04-01

We study orbital and spin-orbit proximity effects in graphene adsorbed to the Cu(111) surface by means of density functional theory (DFT). The proximity effects are caused mainly by the hybridization of graphene π and copper d orbitals. Our electronic structure calculations agree well with the experimentally observed features. We carry out a graphene-Cu(111) distance dependent study to obtain proximity orbital and spin-orbit coupling parameters, by fitting the DFT results to a robust low energy model Hamiltonian. We find a strong distance dependence of the Rashba and intrinsic proximity induced spin-orbit coupling parameters, which are in the meV and hundreds of μ eV range, respectively, for experimentally relevant distances. The Dirac spectrum of graphene also exhibits a proximity orbital gap, of about 20 meV. Furthermore, we find a band inversion within the graphene states accompanied by a reordering of spin and pseudospin states, when graphene is pressed towards copper.

Probability Current in Hydrogen with Spin-Orbit Interaction

NASA Astrophysics Data System (ADS)

Hodge, William; Migirditch, Sam; Kerr, William

2013-03-01

The spin-orbit interaction is a coupling between a particle's spin and its motion. The Hamiltonian for a spin- 1 / 2 particle which includes this coupling is H =p2/2 m + V (x) +∇/V (x) × p 2m2c2 . S . To describe the flow of probability in this system, we derive the continuity equation, which takes the usual form. In this case, however, we find the probability current density j (x , t) to be the sum of two terms. The first term is the one obtained by most quantum mechanics textbooks during their derivation of the continuity equation. The second term, js (x , t) =1/2m2c2 ∑ σ , σ ' = ↑ , ↓ [ ψ* (x , σ , t) < σ | S | σ ' > ψ (x , σ ' , t) ] × ∇ V (x) , arises due to the inclusion of the spin-orbit term in the Hamiltonian and is small compared to the first. Using a perturbative treatment, we calculate j (x , t) for hydrogenlike atoms; for states with l = 0 , we find that j (x , t) =js (x , t) .

Spontaneous Currents in Superconducting Systems with Strong Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Mironov, S.; Buzdin, A.

2017-02-01

We show that Rashba spin-orbit coupling at the interface between a superconductor and a ferromagnet should produce a spontaneous current in the atomic thickness region near the interface. This current is counterbalanced by the superconducting screening current flowing in the region of the width of the London penetration depth near the interface. Such a current-carrying state creates a magnetic field near the superconductor surface, generates a stray magnetic field outside the sample edges, changes the slope of the temperature dependence of the critical field Hc 3 , and may generate the spontaneous Abrikosov vortices near the interface.

The energy-level crossing behavior and quantum Fisher information in a quantum well with spin-orbit coupling

PubMed Central

Wang, Z. H.; Zheng, Q.; Wang, Xiaoguang; Li, Yong

2016-01-01

We study the energy-level crossing behavior in a two-dimensional quantum well with the Rashba and Dresselhaus spin-orbit couplings (SOCs). By mapping the SOC Hamiltonian onto an anisotropic Rabi model, we obtain the approximate ground state and its quantum Fisher information (QFI) via performing a unitary transformation. We find that the energy-level crossing can occur in the quantum well system within the available parameters rather than in cavity and circuit quantum eletrodynamics systems. Furthermore, the influence of two kinds of SOCs on the QFI is investigated and an intuitive explanation from the viewpoint of the stationary perturbation theory is given. PMID:26931762

The energy-level crossing behavior and quantum Fisher information in a quantum well with spin-orbit coupling.

PubMed

Wang, Z H; Zheng, Q; Wang, Xiaoguang; Li, Yong

2016-03-02

We study the energy-level crossing behavior in a two-dimensional quantum well with the Rashba and Dresselhaus spin-orbit couplings (SOCs). By mapping the SOC Hamiltonian onto an anisotropic Rabi model, we obtain the approximate ground state and its quantum Fisher information (QFI) via performing a unitary transformation. We find that the energy-level crossing can occur in the quantum well system within the available parameters rather than in cavity and circuit quantum eletrodynamics systems. Furthermore, the influence of two kinds of SOCs on the QFI is investigated and an intuitive explanation from the viewpoint of the stationary perturbation theory is given.

The energy-level crossing behavior and quantum Fisher information in a quantum well with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wang, Z. H.; Zheng, Q.; Wang, Xiaoguang; Li, Yong

2016-03-01

We study the energy-level crossing behavior in a two-dimensional quantum well with the Rashba and Dresselhaus spin-orbit couplings (SOCs). By mapping the SOC Hamiltonian onto an anisotropic Rabi model, we obtain the approximate ground state and its quantum Fisher information (QFI) via performing a unitary transformation. We find that the energy-level crossing can occur in the quantum well system within the available parameters rather than in cavity and circuit quantum eletrodynamics systems. Furthermore, the influence of two kinds of SOCs on the QFI is investigated and an intuitive explanation from the viewpoint of the stationary perturbation theory is given.

Sr 2 IrO 4 : Gateway to cuprate superconductivity?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchell, J. F.

2015-06-01

To understand the varied magnetic and electronic properties of 3d transition metal oxides (TMO), we routinely invoke a separability among charge-, spin- and orbital degrees of freedom, tightly coupled yet distinct sectors that can be identified, measured, and understood individually. But something interesting happens on the way down the Periodic Table—relativistic spin-orbit coupling (SOC) grows progressively stronger, blurring the lines among these spin, charge, and orbital sectors. SOC forces us to consider a different conceptual framework for 4d, and particularly 5d TMO systems, than has been sufficient for our present day understanding of 3d analogs. Ironically, this rethinking needed formore » 5d oxides may turn out to be critical to our understanding of one of 3d TMO’s greatest treasures – cuprate superconductivity — and in the process may lead us on a pathway to discovery of a new class of high-Tc materials.« less

Coupled potential energy surface for the F(2P)+CH4→HF+CH3 entrance channel and quantum dynamics of the CH4·F- photodetachment.

PubMed

Westermann, Till; Eisfeld, Wolfgang; Manthe, Uwe

2013-07-07

An approach to construct vibronically and spin-orbit coupled diabatic potential energy surfaces (PESs) which describe all three relevant electronic states in the entrance channels of the X(P) + CH4 →HX + CH3 reactions (with X=F((2)P), Cl((2)P), or O((3)P)) is introduced. The diabatization relies on the permutational symmetry present in the methane molecule and results in diabatic states which transform as the three p orbitals of the X atom. Spin-orbit coupling is easily and accurately included using the atomic spin-orbit coupling matrix of the isolated X atom. The method is applied to the F + CH4 system obtaining an accurate PES for the entrance channel based on ab initio multi-reference configuration interaction (MRCI) calculations. Comparing the resulting PESs with spin-orbit MRCI calculations, excellent agreement is found for the excited electronic states at all relevant geometries. The photodetachment spectrum of CH4·F(-) is investigated via full-dimensional (12D) quantum dynamics calculations on the coupled PESs using the multi-layer multi-configurational time-dependent Hartree approach. Extending previous work [J. Palma and U. Manthe, J. Chem. Phys. 137, 044306 (2012)], which was restricted to the dynamics on a single adiabatic PES, the contributions of the electronically excited states to the photodetachment spectrum are calculated and compared to experiment. Considering different experimental setups, good agreement between experiment and theory is found. Addressing questions raised in the previous work, the present dynamical calculations show that the main contribution to the second peak in the photodetachment spectrum results from electron detachment into the electronically excited states of the CH4F complex.

Interplay between resonant tunneling and spin precession oscillations in all-electric all-semiconductor spin transistors

NASA Astrophysics Data System (ADS)

Alomar, M. I.; Serra, Llorenç; Sánchez, David

2016-08-01

We investigate the transmission properties of a spin transistor coupled to two quantum point contacts acting as a spin injector and detector. In the Fabry-Pérot regime, transport is mediated by quasibound states formed between tunnel barriers. Interestingly, the spin-orbit interaction of the Rashba type can be tuned in such a way that nonuniform spin-orbit fields can point along distinct directions at different points of the sample. We discuss both spin-conserving and spin-flipping transitions as the spin-orbit angle of orientation increases from parallel to antiparallel configurations. Spin precession oscillations are clearly seen as a function of the length of the central channel. Remarkably, we find that these oscillations combine with the Fabry-Pérot motion, giving rise to quasiperiodic transmissions in the purely one-dimensional case. Furthermore, we consider the more realistic case of a finite width in the transverse direction and find that the coherent oscillations become deteriorated for moderate values of the spin-orbit strength. Our results then determine the precise role of the spin-orbit intersubband coupling potential in the Fabry-Pérot-Datta-Das intermixed oscillations.

A primordial origin for misalignments between stellar spin axes and planetary orbits.

PubMed

Batygin, Konstantin

2012-11-15

The existence of gaseous giant planets whose orbits lie close to their host stars ('hot Jupiters') can largely be accounted for by planetary migration associated with viscous evolution of proto-planetary nebulae. Recently, observations of the Rossiter-McLaughlin effect during planetary transits have revealed that a considerable fraction of hot Jupiters are on orbits that are misaligned with respect to the spin axes of their host stars. This observation has cast doubt on the importance of disk-driven migration as a mechanism for producing hot Jupiters. Here I show that misaligned orbits can be a natural consequence of disk migration in binary systems whose orbital plane is uncorrelated with the spin axes of the individual stars. The gravitational torques arising from the dynamical evolution of idealized proto-planetary disks under perturbations from massive distant bodies act to misalign the orbital planes of the disks relative to the spin poles of their host stars. As a result, I suggest that in the absence of strong coupling between the angular momentum of the disk and that of the host star, or of sufficient dissipation that acts to realign the stellar spin axis and the planetary orbits, the fraction of planetary systems (including systems of 'hot Neptunes' and 'super-Earths') whose angular momentum vectors are misaligned with respect to their host stars will be commensurate with the rate of primordial stellar multiplicity.

Spin-orbit scattering visualized in quasiparticle interference

NASA Astrophysics Data System (ADS)

Kohsaka, Y.; Machida, T.; Iwaya, K.; Kanou, M.; Hanaguri, T.; Sasagawa, T.

2017-03-01

In the presence of spin-orbit coupling, electron scattering off impurities depends on both spin and orbital angular momentum of electrons—spin-orbit scattering. Although some transport properties are subject to spin-orbit scattering, experimental techniques directly accessible to this effect are limited. Here we show that a signature of spin-orbit scattering manifests itself in quasiparticle interference (QPI) imaged by spectroscopic-imaging scanning tunneling microscopy. The experimental data of a polar semiconductor BiTeI are well reproduced by numerical simulations with the T -matrix formalism that include not only scalar scattering normally adopted but also spin-orbit scattering stronger than scalar scattering. To accelerate the simulations, we extend the standard efficient method of QPI calculation for momentum-independent scattering to be applicable even for spin-orbit scattering. We further identify a selection rule that makes spin-orbit scattering visible in the QPI pattern. These results demonstrate that spin-orbit scattering can exert predominant influence on QPI patterns and thus suggest that QPI measurement is available to detect spin-orbit scattering.

Theory of the inverse spin galvanic effect in quantum wells

NASA Astrophysics Data System (ADS)

Maleki Sheikhabadi, Amin; Miatka, Iryna; Sherman, E. Ya.; Raimondi, Roberto

2018-06-01

The understanding of the fundamentals of spin and charge densities and currents interconversion by spin-orbit coupling can enable efficient applications beyond the possibilities offered by conventional electronics. For this purpose we consider various forms of the frequency-dependent inverse spin galvanic effect in semiconductor quantum wells and epilayers taking into account the cubic in the electron momentum spin-orbit coupling in the Rashba and Dresselhaus forms, concentrating on the current-induced spin polarization (CISP). We find that including the cubic terms qualitatively explains recent findings of the CISP in InGaAs epilayers being the strongest if the internal spin-orbit coupling field is the smallest and vice versa [Norman et al., Phys. Rev. Lett. 112, 056601 (2014), 10.1103/PhysRevLett.112.056601; Luengo-Kovac et al., Phys. Rev. B 96, 195206 (2017), 10.1103/PhysRevB.96.195206], in contrast to the common understanding. Our results provide a promising framework for the control of spin transport in future spintronics devices.

Empirical Monod-Beuneu relation of spin relaxation revisited for elemental metals

NASA Astrophysics Data System (ADS)

Szolnoki, L.; Kiss, A.; Forró, L.; Simon, F.

2014-03-01

Monod and Beuneu [P. Monod and F. Beuneu, Phys. Rev. B 19, 911 (1979), 10.1103/PhysRevB.19.911] established the validity of the Elliott-Yafet theory for elemental metals through correlating the experimental electron spin resonance linewidth with the so-called spin-orbit admixture coefficients and the momentum-relaxation theory. The spin-orbit admixture coefficients data were based on atomic spin-orbit splitting. We highlight two shortcomings of the previous description: (i) the momentum-relaxation involves the Debye temperature and the electron-phonon coupling whose variation among the elemental metals was neglected, (ii) the Elliott-Yafet theory involves matrix elements of the spin-orbit coupling (SOC), which are however not identical to the SOC induced energy splitting of the atomic levels, even though the two have similar magnitudes. We obtain the empirical spin-orbit admixture parameters for the alkali metals by considering the proper description of the momentum relaxation theory. In addition we present a model calculation, which highlights the difference between the SOC matrix element and energy splitting.

Spin-charge coupled dynamics driven by a time-dependent magnetization

NASA Astrophysics Data System (ADS)

Tölle, Sebastian; Eckern, Ulrich; Gorini, Cosimo

2017-03-01

The spin-charge coupled dynamics in a thin, magnetized metallic system are investigated. The effective driving force acting on the charge carriers is generated by a dynamical magnetic texture, which can be induced, e.g., by a magnetic material in contact with a normal-metal system. We consider a general inversion-asymmetric substrate/normal-metal/magnet structure, which, by specifying the precise nature of each layer, can mimic various experimentally employed setups. Inversion symmetry breaking gives rise to an effective Rashba spin-orbit interaction. We derive general spin-charge kinetic equations which show that such spin-orbit interaction, together with anisotropic Elliott-Yafet spin relaxation, yields significant corrections to the magnetization-induced dynamics. In particular, we present a consistent treatment of the spin density and spin current contributions to the equations of motion, inter alia, identifying a term in the effective force which appears due to a spin current polarized parallel to the magnetization. This "inverse-spin-filter" contribution depends markedly on the parameter which describes the anisotropy in spin relaxation. To further highlight the physical meaning of the different contributions, the spin-pumping configuration of typical experimental setups is analyzed in detail. In the two-dimensional limit the buildup of dc voltage is dominated by the spin-galvanic (inverse Edelstein) effect. A measuring scheme that could isolate this contribution is discussed.

Fractional and hidden magnetic excitations in f-electron metal Yb2Pt2Pb

NASA Astrophysics Data System (ADS)

Zaliznyak, Igor

Quantum states with fractionalized excitations such as spinons in one-dimensional chains are commonly viewed as belonging to the domain of S=1/2 spin systems. However, recent experiments on the quantum antiferromagnet Yb2Pt2Pb, part of a large family of R2T2X (R=rare earth, T=transition metal, X=main group) materials spectacularly disqualify this opinion. The results show that spinons can also emerge in an f-electron system with strong spin-orbit coupling, where magnetism is mainly associated with large and anisotropic orbital moment. Here, the competition of several high-energy interactions Coulomb repulsion, spin-orbit coupling, crystal field, and the peculiar crystal structure, which combines low dimensionality and geometrical frustration, lead to the emergence, at low energy, of an effective spin-1/2, purely quantum Hamiltonian. Consequently, it produces unusual spin-liquid states and fractional excitations enabled by the inherently quantum mechanical nature of the moments. The emergent quantum spins bear the unique birthmark of their unusual origin in that they only lead to measurable longitudinal magnetic fluctuations, while the transverse excitations such as spin waves remain invisible to scattering experiments. Similarlyhidden would be transverse magnetic ordering, although it would have visible excitations. The rich magnetic phase diagram of Yb2Pt2Pb is suggestive of the existence of hidden-order phases, while the recent experiments indeed reveal the dark magnon, a hidden excitation in the saturated ferromagnetic (FM) phase of Yb2Pt2Pb. Unlike copper-based spin-1/2 chains, where the magnon in the FM state accounts for the full spectral weight of the zero-field spinon continuum, in the spin-orbital chains in Yb2Pt2Pb it is 100 times, or more weaker. It thus presents an example of dark magnon matter\\x9D, whose Hamiltonian is that of the effective spin-1/2 chain, but whose coupling to magnetic field, the physical probe at our disposal, is vanishingly small. The work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-SC00112704, and by by NSF-DMR-1310008.

Controlling nonlinear optical response in an open four-level molecular system using quantum control of spin-orbit interaction

NASA Astrophysics Data System (ADS)

Jamshidi-Ghaleh, Kazem; Ebrahimi-hamed, Zahra; Sahrai, Mostafa

2017-10-01

This paper investigates the behavior of linear and nonlinear optical susceptibility of an open four-level molecular system, under two-step excitation based on electromagnetically induced transparency (EIT). The system was irradiated with a weak probe field and strong coupling field. It is shown that the use of a strong coupling field in the triplet states of an alkali-metal dimer can change the spin-orbit interaction (SOI). The optical response of the system can then be modified in a controllable way. The electromagnetically induced transparency transforms into electromagnetically induced absorption (EIA) in the presence of a coupling field. Changing the sign of the dispersion, this region is associated with switching subluminal and superluminal propagation. Furthermore, for the proper value of the coupling field, the controllable parameters, enhanced Kerr nonlinearity with reduced linear absorption, can be obtained under a weak probe field. With this approach, SOI can be controlled by changing only one of the controllable parameters, using triplet-triplet strong coupling with different spin state. Therefore, the desired region of the spectra can be obtained, in contrast to the other four-level system, in which at least two strong fields are used to change optical properties. This mechanism can be suitable in molecular systems or semiconductors to be used in optical bistability and fast all-optical switching devices.

Electrical control of a confined electron spin in a silicene quantum dot

NASA Astrophysics Data System (ADS)

Szafran, Bartłomiej; Mreńca-Kolasińska, Alina; Rzeszotarski, Bartłomiej; Żebrowski, Dariusz

2018-04-01

We study spin control for an electron confined in a flake of silicene. We find that the lowest-energy conduction-band levels are split by the diagonal intrinsic spin-orbit coupling into Kramers doublets with a definite projection of the spin on the orbital magnetic moment. We study the spin control by AC electric fields using the nondiagonal Rashba component of the spin-orbit interactions with the time-dependent atomistic tight-binding approach. The Rashba interactions in AC electric fields produce Rabi spin-flip times of the order of a nanosecond. These times can be reduced to tens of picoseconds provided that the vertical electric field is tuned to an avoided crossing opened by the Rashba spin-orbit interaction. We demonstrate that the speedup of the spin transitions is possible due to the intervalley coupling induced by the armchair edge of the flake. The study is confronted with the results for circular quantum dots decoupled from the edge with well defined angular momentum and valley index.

Hund's Rule-Driven Dzyaloshinskii-Moriya Interaction at 3d-5d Interfaces.

PubMed

Belabbes, A; Bihlmayer, G; Bechstedt, F; Blügel, S; Manchon, A

2016-12-09

Using relativistic first-principles calculations, we show that the chemical trend of the Dzyaloshinskii-Moriya interaction (DMI) in 3d-5d ultrathin films follows Hund's first rule with a tendency similar to their magnetic moments in either the unsupported 3d monolayers or 3d-5d interfaces. We demonstrate that, besides the spin-orbit coupling (SOC) effect in inversion asymmetric noncollinear magnetic systems, the driving force is the 3d orbital occupations and their spin-flip mixing processes with the spin-orbit active 5d states control directly the sign and magnitude of the DMI. The magnetic chirality changes are discussed in the light of the interplay between SOC, Hund's first rule, and the crystal-field splitting of d orbitals.

Driving magnetization dynamics with interfacial spin-orbit torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Hoffmann, Axel F.; Zhang, Wei; Sklenar, Joseph; Jungfleisch, Matthias Benjamin; Jiang, Wanjun; Hsu, Bo; Xiao, Jiao; Pearson, John E.; Fradin, Frank Y.; Liu, Yaohua; Ketterson, John B.; Yang, Zheng

2016-10-01

Bulk spin Hall effects are well know to provide spin orbit torques, which can be used to drive magnetization dynamics [1]. But one of the reoccurring questions is to what extend spin orbit torques may also originate at the interface between materials with strong spin orbit coupling and the ferromagnets. Using spin torque driven ferromagnetic resonance we show for two systems, where interfacial torques dominate, that they can be large enough to be practically useful. First, we show spin transfer torque driven magnetization dynamics based on Rashba-Edelstein effects at the Bi/Ag interface [2]. Second, we will show that combining permalloy with monolayer MoS2 gives rise to sizable spin-orbit torques. Given the monolayer nature of MoS2 it is clear that bilk spin Hall effects are negligible and therefore the spin transfer torques are completely interfacial in nature. Interestingly the spin orbit torques with MoS2 show a distinct dependence on the orientation of the magnetization in the permalloy, and become strongly enhanced, when the magnetization is pointing perpendicular to the interfacial plane. This work was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division. [1] A. Hoffmann, IEEE Trans. Mag. 49, 5172 (2013). [2] W. Zhang et al., J. Appl. Phys. 117, 17C727 (2015). [3] M. B. Jungfleisch et al., arXiv:1508.01410.

Flocking from a quantum analogy: spin-orbit coupling in an active fluid

NASA Astrophysics Data System (ADS)

Loewe, Benjamin; Souslov, Anton; Goldbart, Paul M.

2018-01-01

Systems composed of strongly interacting self-propelled particles can form a spontaneously flowing polar active fluid. The study of the connection between the microscopic dynamics of a single such particle and the macroscopic dynamics of the fluid can yield insights into experimentally realizable active flows, but this connection is well understood in only a few select cases. We introduce a model of self-propelled particles based on an analogy with the motion of electrons that have strong spin-orbit coupling. We find that, within our model, self-propelled particles are subject to an analog of the Heisenberg uncertainty principle that relates translational and rotational noise. Furthermore, by coarse-graining this microscopic model, we establish expressions for the coefficients of the Toner-Tu equations—the hydrodynamic equations that describe an active fluid composed of these ‘active spins.’ The connection between stochastic self-propelled particles and quantum particles with spin may help realize exotic phases of matter using active fluids via analogies with systems composed of strongly correlated electrons.

Characteristics of persistent spin current components in a quasi-periodic Fibonacci ring with spin–orbit interactions: Prediction of spin–orbit coupling and on-site energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Moumita; Maiti, Santanu K., E-mail: santanu.maiti@isical.ac.in

In the present work we investigate the behavior of all three components of persistent spin current in a quasi-periodic Fibonacci ring subjected to Rashba and Dresselhaus spin–orbit interactions. Analogous to persistent charge current in a conducting ring where electrons gain a Berry phase in presence of magnetic flux, spin Berry phase is associated during the motion of electrons in presence of a spin–orbit field which is responsible for the generation of spin current. The interplay between two spin–orbit fields along with quasi-periodic Fibonacci sequence on persistent spin current is described elaborately, and from our analysis, we can estimate the strengthmore » of any one of two spin–orbit couplings together with on-site energy, provided the other is known. - Highlights: • Determination of Rashba and Dresselhaus spin–orbit fields is discussed. • Characteristics of all three components of spin current are explored. • Possibility of estimating on-site energy is given. • Results can be generalized to any lattice models.« less

From nodal-ring topological superfluids to spiral Majorana modes in cold atomic systems

NASA Astrophysics Data System (ADS)

He, Wen-Yu; Xu, Dong-Hui; Zhou, Benjamin T.; Zhou, Qi; Law, K. T.

2018-04-01

In this work, we consider a three-dimensional (3D) cubic optical lattice composed of coupled 1D wires with 1D spin-orbit coupling. When the s -wave pairing is induced through Feshbach resonance, the system becomes a topological superfluid with ring nodes, which are the ring nodal degeneracies in the bulk, and supports a large number of surface Majorana zero-energy modes. The large number of surface Majorana modes remain at zero energy even in the presence of disorder due to the protection from a chiral symmetry. When the chiral symmetry is broken, the system becomes a Weyl topological superfluid with Majorana arcs. With 3D spin-orbit coupling, the Weyl superfluid becomes a gapless phase with spiral Majorana modes on the surface. A spatial-resolved radio-frequency spectroscopy is suggested to detect this nodal-ring topological superfluid phase.

Spin filtering effect generated by the inter-subband spin-orbit coupling in the bilayer nanowire with the quantum point contact

PubMed Central

Wójcik, Paweł; Adamowski, Janusz

2017-01-01

The spin filtering effect in the bilayer nanowire with quantum point contact is investigated theoretically. We demonstrate the new mechanism of the spin filtering based on the lateral inter-subband spin-orbit coupling, which for the bilayer nanowires has been reported to be strong. The proposed spin filtering effect is explained as the joint effect of the Landau-Zener intersubband transitions caused by the hybridization of states with opposite spin (due to the lateral Rashba SO interaction) and the confinement of carriers in the quantum point contact region. PMID:28358141

Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules

NASA Astrophysics Data System (ADS)

Deng, Y.; You, L.; Yi, S.

2018-05-01

An experimental proposal for realizing spin-orbit (SO) coupling of pseudospin 1 in the ground manifold 1Σ (υ =0 ) of (bosonic) bialkali polar molecules is presented. The three spin components are composed of the ground rotational state and two substates from the first excited rotational level. Using hyperfine resolved Raman processes through two select excited states resonantly coupled by a microwave, an effective coupling between the spin tensor and linear momentum is realized. The properties of Bose-Einstein condensates for such SO-coupled molecules exhibiting dipolar interactions are further explored. In addition to the SO-coupling-induced stripe structures, the singly and doubly quantized vortex phases are found to appear, implicating exciting opportunities for exploring novel quantum physics using SO-coupled rotating polar molecules with dipolar interactions.

Electron-phonon coupling and superconductivity in the (4/3)-monolayer of Pb on Si(111): Role of spin-orbit interaction

NASA Astrophysics Data System (ADS)

Sklyadneva, I. Yu.; Heid, R.; Bohnen, K.-P.; Echenique, P. M.; Chulkov, E. V.

2018-05-01

The effect of spin-orbit coupling on the electron-phonon interaction in a (4/3)-monolayer of Pb on Si(111) is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. We show that the spin-orbit interaction produces a large weakening of the electron-phonon coupling strength, which appears to be strongly overestimated in the scalar relativistic calculations. The effect of spin-orbit interaction is largely determined by the induced modification of Pb electronic bands and a stiffening of the low-energy part of phonon spectrum, which favor a weakening of the electron-phonon coupling strength. The state-dependent strength of the electron-phonon interaction in occupied Pb electronic bands varies depending on binding energy rather than electronic momentum. It is markedly larger than the value averaged over electron momentum because substrate electronic bands make a small contribution to the phonon-mediated scattering and agrees well with the experimental data.

Charge instability in double quantum dots in Ge/Si core/shell nanowires

NASA Astrophysics Data System (ADS)

Zarassi, Azarin; Su, Zhaoen; Schwenderling, Jens; Frolov, Sergey M.; Hocevar, Moïra; Nguyen, Binh-Minh; Yoo, Jinkyoung; Dayeh, Shadi A.

Controlling dephasing times are of great challenge in the studies of spin qubit. Reported long spin coherence time and predicted strong spin-orbit interaction of holes in Ge/Si core/shell nanowires, as well as their weak coupling to very few nuclear spins of these group IV semiconductors, persuade electrical spin control. We have established Pauli spin blockade in gate-tunable quantum dots formed in these nanowires. The g-factor has been measured and evidence of spin-orbit interaction has been observed in the presence of magnetic field. However, electrical control of spins requires considerable stability in the double dot configuration, and imperfectly these dots suffer from poor stability. We report on fabrication modifications on Ge/Si core/shell nanowires, as well as measurement techniques to suppress the charge instabilities and ease the way to study spin-orbit coupling and resolve electric dipole spin resonance.

Density matrix renormalization group study of a three-orbital Hubbard model with spin-orbit coupling in one dimension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaushal, Nitin; Herbrych, Jacek W.; Nocera, Alberto

Using the density matrix renormalization group technique we study the effect of spin-orbit coupling on a three-orbital Hubbard model in the (t 2g) 4 sector and in one dimension. Fixing the Hund coupling to a robust value compatible with some multiorbital materials, we present the phase diagram varying the Hubbard U and spin-orbit coupling λ, at zero temperature. Our results are shown to be qualitatively similar to those recently reported using the dynamical mean-field theory in higher dimensions, providing a robust basis to approximate many-body techniques. Among many results, we observe an interesting transition from an orbital-selective Mott phase tomore » an excitonic insulator with increasing λ at intermediate U. In the strong U coupling limit, we find a nonmagnetic insulator with an effective angular momentum <(J eff) 2>≠0 near the excitonic phase, smoothly connected to the <(J eff) 2>=0 regime. In conclusion, we also provide a list of quasi-one-dimensional materials where the physics discussed in this paper could be realized.« less

Density matrix renormalization group study of a three-orbital Hubbard model with spin-orbit coupling in one dimension

NASA Astrophysics Data System (ADS)

Kaushal, Nitin; Herbrych, Jacek; Nocera, Alberto; Alvarez, Gonzalo; Moreo, Adriana; Reboredo, F. A.; Dagotto, Elbio

2017-10-01

Using the density matrix renormalization group technique we study the effect of spin-orbit coupling on a three-orbital Hubbard model in the (t2g) 4 sector and in one dimension. Fixing the Hund coupling to a robust value compatible with some multiorbital materials, we present the phase diagram varying the Hubbard U and spin-orbit coupling λ , at zero temperature. Our results are shown to be qualitatively similar to those recently reported using the dynamical mean-field theory in higher dimensions, providing a robust basis to approximate many-body techniques. Among many results, we observe an interesting transition from an orbital-selective Mott phase to an excitonic insulator with increasing λ at intermediate U . In the strong U coupling limit, we find a nonmagnetic insulator with an effective angular momentum 〈(Jeff)2〉≠0 near the excitonic phase, smoothly connected to the 〈(Jeff)2〉=0 regime. We also provide a list of quasi-one-dimensional materials where the physics discussed in this paper could be realized.

Density matrix renormalization group study of a three-orbital Hubbard model with spin-orbit coupling in one dimension

DOE PAGES

Kaushal, Nitin; Herbrych, Jacek W.; Nocera, Alberto; ...

2017-10-09

Using the density matrix renormalization group technique we study the effect of spin-orbit coupling on a three-orbital Hubbard model in the (t 2g) 4 sector and in one dimension. Fixing the Hund coupling to a robust value compatible with some multiorbital materials, we present the phase diagram varying the Hubbard U and spin-orbit coupling λ, at zero temperature. Our results are shown to be qualitatively similar to those recently reported using the dynamical mean-field theory in higher dimensions, providing a robust basis to approximate many-body techniques. Among many results, we observe an interesting transition from an orbital-selective Mott phase tomore » an excitonic insulator with increasing λ at intermediate U. In the strong U coupling limit, we find a nonmagnetic insulator with an effective angular momentum <(J eff) 2>≠0 near the excitonic phase, smoothly connected to the <(J eff) 2>=0 regime. In conclusion, we also provide a list of quasi-one-dimensional materials where the physics discussed in this paper could be realized.« less

Filling constraints for spin-orbit coupled insulators in symmorphic and nonsymmorphic crystals

PubMed Central

Watanabe, Haruki; Po, Hoi Chun; Vishwanath, Ashvin; Zaletel, Michael

2015-01-01

We determine conditions on the filling of electrons in a crystalline lattice to obtain the equivalent of a band insulator—a gapped insulator with neither symmetry breaking nor fractionalized excitations. We allow for strong interactions, which precludes a free particle description. Previous approaches that extend the Lieb–Schultz–Mattis argument invoked spin conservation in an essential way and cannot be applied to the physically interesting case of spin-orbit coupled systems. Here we introduce two approaches: The first one is an entanglement-based scheme, and the second one studies the system on an appropriate flat “Bieberbach” manifold to obtain the filling conditions for all 230 space groups. These approaches assume only time reversal rather than spin rotation invariance. The results depend crucially on whether the crystal symmetry is symmorphic. Our results clarify when one may infer the existence of an exotic ground state based on the absence of order, and we point out applications to experimentally realized materials. Extensions to new situations involving purely spin models are also mentioned. PMID:26604304

Correlation Effects and Hidden Spin-Orbit Entangled Electronic Order in Parent and Electron-Doped Iridates Sr2 IrO4

NASA Astrophysics Data System (ADS)

Zhou, Sen; Jiang, Kun; Chen, Hua; Wang, Ziqiang

2017-10-01

Analogs of the high-Tc cuprates have been long sought after in transition metal oxides. Because of the strong spin-orbit coupling, the 5 d perovskite iridates Sr2 IrO4 exhibit a low-energy electronic structure remarkably similar to the cuprates. Whether a superconducting state exists as in the cuprates requires understanding the correlated spin-orbit entangled electronic states. Recent experiments discovered hidden order in the parent and electron-doped iridates, some with striking analogies to the cuprates, including Fermi surface pockets, Fermi arcs, and pseudogap. Here, we study the correlation and disorder effects in a five-orbital model derived from the band theory. We find that the experimental observations are consistent with a d -wave spin-orbit density wave order that breaks the symmetry of a joint twofold spin-orbital rotation followed by a lattice translation. There is a Berry phase and a plaquette spin flux due to spin procession as electrons hop between Ir atoms, akin to the intersite spin-orbit coupling in quantum spin Hall insulators. The associated staggered circulating Jeff=1 /2 spin current can be probed by advanced techniques of spin-current detection in spintronics. This electronic order can emerge spontaneously from the intersite Coulomb interactions between the spatially extended iridium 5 d orbitals, turning the metallic state into an electron-doped quasi-2D Dirac semimetal with important implications on the possible superconducting state suggested by recent experiments.

Rashba effect and enriched spin-valley coupling in Ga X /M X2 (M = Mo, W; X = S, Se, Te) heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Qingyun; Schwingenschlögl, Udo

2018-04-01

Using first-principles calculations, we investigate the electronic properties of the two-dimensional Ga X /MX 2 (M = Mo, W; X = S, Se, Te) heterostructures. Orbital hybridization between Ga X and MX 2 is found to result in Rashba splitting at the valence-band edge around the Γ point, which grows for increasing strength of the spin-orbit coupling in the p orbitals of the chalcogenide atoms. The location of the valence-band maximum in the Brillouin zone can be tuned by strain and application of an out-of-plane electric field. The coexistence of Rashba splitting (in-plane spin direction) and band splitting at the K and K' valleys (out-of-plane spin direction) makes Ga X /MX 2 heterostructures interesting for spintronics and valleytronics. They are promising candidates for two-dimensional spin-field-effect transistors and spin-valley Hall effect devices. Our findings shed light on the spin-valley coupling in van der Waals heterostructures.

Mixing of t2 g-eg orbitals in 4 d and 5 d transition metal oxides

NASA Astrophysics Data System (ADS)

Stamokostas, Georgios L.; Fiete, Gregory A.

2018-02-01

Using exact diagonalization, we study the spin-orbit coupling and interaction-induced mixing between t2 g and egd -orbital states in a cubic crystalline environment, as commonly occurs in transition metal oxides. We make a direct comparison with the widely used t2 g-only or eg-only models, depending on electronic filling. We consider all electron fillings of the d shell and compute the total magnetic moment, the spin, the occupancy of each orbital, and the effective spin-orbit coupling strength (renormalized through interaction effects) in terms of the bare interaction parameters, spin-orbit coupling, and crystal-field splitting, focusing on the parameter ranges relevant to 4 d and 5 d transition metal oxides. In various limits, we provide perturbative results consistent with our numerical calculations. We find that the t2 g-eg mixing can be large, with up to 20% occupation of orbitals that are nominally "empty," which has experimental implications for the interpretation of the branching ratio in experiments, and can impact the effective local moment Hamiltonian used to study magnetic phases and magnetic excitations in transition metal oxides. Our results can aid the theoretical interpretation of experiments on these materials, which often fall in a regime of intermediate coupling with respect to electron-electron interactions.

Isotropic and anisotropic regimes of the field-dependent spin dynamics in Sr 2 IrO 4 : Raman scattering studies

DOE PAGES

Gim, Y.; Sethi, A.; Zhao, Q.; ...

2016-01-11

A major focus of experimental interest in Sr 2IrO 4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of an isotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low energy magnetic excitation spectrum of Sr 2IrO 4 and doped Eu-doped Sr 2IrO 4 as functions of both temperature and applied magnetic field. We show that the high-field (H > 1.5 T) in-plane spin dynamics ofmore » Sr 2IrO 4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr 2IrO 4 at lower fields (H < 1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr 2IrO 4 that occurs either discontinuously or via a continuous rotation of the spins, depending upon the in-plane orientation of the applied field. Furthermore, these results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr 2IrO 4.« less

Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

DOE PAGES

Zhou, Miao; Ming, Wenmei; Liu, Zheng; ...

2014-11-19

For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of ≥0.5more » eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states.« less

Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling.

PubMed

Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Yao, Yugui; Liu, Feng

2014-11-19

For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of ≥ 0.5 eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states.

Double perovskites with strong spin-orbit coupling

NASA Astrophysics Data System (ADS)

Cook, Ashley M.

We first present theoretical analysis of powder inelastic neutron scattering experiments in Ba2FeReO6 performed by our experimental collaborators. Ba2FeReO6, a member of the double perovskite family of materials, exhibits half-metallic behavior and high Curie temperatures Tc, making it of interest for spintronics applications. To interpret the experimental data, we develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures the experimental observations. We then develop a tight-binding model of the double perovskite Ba 2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. The uncovered interplay of strong correlations and spin-orbit coupling lends partial support to our previous work, which used a local moment description to capture the spin wave dispersion found in neutron scattering measurements. We then adapt this tight-binding model to study {111}-grown bilayers of half-metallic double perovskites such as Sr2FeMoO6. The combination of spin-orbit coupling, inter-orbital hybridization and symmetry-allowed trigonal distortion leads to a rich phase diagram with tunable ferromagnetic order, topological C= +/-1, +/-2 Chern bands, and a C = +/-2 quantum anomalous Hall insulator regime. We have also performed theoretical analysis of inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO 6 and La2MgIrO6. Models with dominant Kitaev exchange seem to most naturally account for the neutron data as well as the measured frustration parameters of these materials, while the uniaxial Ising anisotropy does not. Our findings highlight how even seemingly conventional magnetic orders in oxide materials containing heavy transition metal ions may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling. Motivated by experiments on the double perovskites La2ZnIrO 6 and La2MgIrO6, we lastly study the magnetism of spin-orbit coupled jeff =1/2 iridium moments on the three-dimensional, geometrically frustrated, facecentered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear AII type antiferromagnetism, stripe order with moments along the {111}-direction, and incommensurate non-coplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures.

Interplay of spin-dependent delocalization and magnetic anisotropy in the ground and excited states of [Gd2@C78]- and [Gd2@C80]-

NASA Astrophysics Data System (ADS)

Mansikkamäki, Akseli; Popov, Alexey A.; Deng, Qingming; Iwahara, Naoya; Chibotaru, Liviu F.

2017-09-01

The magnetic properties and electronic structure of the ground and excited states of two recently characterized endohedral metallo-fullerenes, [Gd2@C78]- (1) and [Gd2@C80]- (2), have been studied by theoretical methods. The systems can be considered as [Gd2]5+ dimers encapsulated in a fullerene cage with the fifteen unpaired electrons ferromagnetically coupled into an S = 15/2 high-spin configuration in the ground state. The microscopic mechanisms governing the Gd-Gd interactions leading to the ferromagnetic ground state are examined by a combination of density functional and ab initio calculations and the full energy spectrum of the ground and lowest excited states is constructed by means of ab initio model Hamiltonians. The ground state is characterized by strong electron delocalization bordering on a σ type one-electron covalent bond and minor zero-field splitting (ZFS) that is successfully described as a second order spin-orbit coupling effect. We have shown that the observed ferromagnetic interaction originates from Hund's rule coupling and not from the conventional double exchange mechanism. The calculated ZFS parameters of 1 and 2 in their optimized geometries are in qualitative agreement with experimental EPR results. The higher excited states display less electron delocalization, but at the same time they possess unquenched first-order angular momentum. This leads to strong spin-orbit coupling and highly anisotropic energy spectrum. The analysis of the excited states presented here constitutes the first detailed study of the effects of spin-dependent delocalization in the presence of first order orbital angular momentum and the obtained results can be applied to other mixed valence lanthanide systems.

Coupled spin and electron-phonon interaction at the Tl/Si(111) surface from relativistic first-principles calculations

NASA Astrophysics Data System (ADS)

Garcia-Goiricelaya, Peio; Gurtubay, Idoia G.; Eiguren, Asier

2018-05-01

We investigate the role played by the electron spin and the spin-orbit interaction in the exceptional electron-phonon coupling at the Tl/Si(111) surface. Our first-principles calculations demonstrate that the particular spin pattern of this system dominates the whole low-energy electron-phonon physics, which is remarkably explained by forbidden spin-spin scattering channels. In particular, we show that the strength of the electron-phonon coupling appears drastically weakened for surface states close to the K ¯ and K'¯ valleys, which is unambiguously attributed to the spin polarization through the associated modulation due to the spinor overlaps. However, close to the Γ ¯ point, the particular spin pattern in this area is less effective in damping the electron-phonon matrix elements, and the result is an exceptional strength of the electron-phonon coupling parameter λ ˜1.4 . These results are rationalized by a simple model for the electron-phonon matrix elements including the spinor terms.

A Crystal Field Approach to Orbitally Degenerate SMMs: Beyond the Spin-Only Hamiltonian

NASA Astrophysics Data System (ADS)

Bhaskaran, Lakshmi; Marriott, Katie; Murrie, Mark; Hill, Stephen

Single-Molecule Magnets (SMMs) with large magnetization reversal barriers are promising candidates for high-density information storage. Recently, a large uniaxial magnetic anisotropy was observed for a mononuclear trigonal bipyramidal (TBP) [NiIICl3(Me-abco)2] SMM. High-field EPR studies analyzed on the basis of a spin-only Hamiltonian give ¦D¦>400 cm-1, which is close to the spin-orbit coupling parameter λ = 668 cm-1 for NiII, suggesting an orbitally degenerate ground state. The spin-only description is ineffective in this limit, necessitating the development of a model that includes the orbital moment. Here we describe a phenomenological approach that takes into account a full description of crystal field, electron-electron repulsion and spin-orbit coupling effects on the ground state of a NiII ion in a TBP coordination geometry. The model is in good agreement with the high-field EPR experiments, validating its use for spectroscopic studies of orbitally degenerate molecular nanomagnets. This work was supported by the NSF (DMR-1309463).

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings

NASA Astrophysics Data System (ADS)

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-01

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure—a magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings.

PubMed

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-11

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure-a magnetically confined GaAs/Al x Ga 1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor Sb2Se3

NASA Astrophysics Data System (ADS)

Das, Shekhar; Sirohi, Anshu; Kumar Gupta, Gaurav; Kamboj, Suman; Vasdev, Aastha; Gayen, Sirshendu; Guptasarma, Prasenjit; Das, Tanmoy; Sheet, Goutam

2018-06-01

Majority of the A2B3 -type chalcogenide systems with strong spin-orbit coupling (SOC), such as Bi2Se3,Bi2Te3 , and Sb2Te3 , etc., are topological insulators. One important exception is Sb2Se3 where a topological nontrivial phase was argued to be possible under ambient conditions, but such a phase could be detected to exist only under pressure. In this paper, we show that Sb2Se3 like Bi2Se3 displays a generation of highly spin-polarized current under mesoscopic superconducting point contacts as measured by point-contact Andreev reflection spectroscopy. In addition, we observe a large negative and anisotropic magnetoresistance of the mesoscopic metallic point contacts formed on Sb2Se3 . Our band-structure calculations confirm the trivial nature of Sb2Se3 crystals and reveal two trivial surface states one of which shows large spin splitting due to Rashba-type SOC. The observed high spin polarization and related phenomena in Sb2Se3 can be attributed to this spin splitting.

Revealing weak spin-orbit coupling effects on charge carriers in a π -conjugated polymer

NASA Astrophysics Data System (ADS)

Malissa, H.; Miller, R.; Baird, D. L.; Jamali, S.; Joshi, G.; Bursch, M.; Grimme, S.; van Tol, J.; Lupton, J. M.; Boehme, C.

2018-04-01

We measure electrically detected magnetic resonance on organic light-emitting diodes made of the polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] at room temperature and high magnetic fields where spectral broadening of the resonance due to spin-orbit coupling (SOC) exceeds that due to the local hyperfine fields. Density-functional-theory calculations on an open-shell model of the material reveal g -tensors of charge-carrier spins in the lowest unoccupied (electron) and highest occupied (hole) molecular orbitals. These tensors are used for simulations of magnetic resonance line shapes. Besides providing the first quantification and direct observation of SOC effects on charge-carrier states in these weakly SO-coupled hydrocarbons, this procedure demonstrates that spin-related phenomena in these materials are fundamentally monomolecular in nature.

Spin fine structure of optically excited quantum dot molecules

NASA Astrophysics Data System (ADS)

Scheibner, M.; Doty, M. F.; Ponomarev, I. V.; Bracker, A. S.; Stinaff, E. A.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

2007-06-01

The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of InAs/GaAs double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.

Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions

PubMed Central

Hankiewicz, Ewelina M.; Culcer, Dimitrie

2017-01-01

Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless Dirac fermions in topological insulators and massive Dirac fermions in Weyl semimetal thin films, taking into account both intrinsic and extrinsic spin-orbit interactions. The physics is governed by the complex interplay of the chiral spin texture, quasiparticle mass, and scalar and spin-orbit scattering. We demonstrate that terms linear in the extrinsic spin-orbit scattering are generally present in the Bloch and momentum relaxation times in all topological materials, and the correction to the diffusion constant is linear in the strength of the extrinsic spin-orbit. In topological insulators, which have zero quasiparticle mass, the terms linear in the impurity spin-orbit coupling lead to an observable density dependence in the weak antilocalization correction. They produce substantial qualitative modifications to the magnetoconductivity, differing greatly from the conventional Hikami-Larkin-Nagaoka formula traditionally used in experimental fits, which predicts a crossover from weak localization to antilocalization as a function of the extrinsic spin-orbit strength. In contrast, our analysis reveals that topological insulators always exhibit weak antilocalization. In Weyl semimetal thin films having intermediate to large values of the quasiparticle mass, we show that extrinsic spin-orbit scattering strongly affects the boundary of the weak localization to antilocalization transition. We produce a complete phase diagram for this transition as a function of the mass and spin-orbit scattering strength. Throughout the paper, we discuss implications for experimental work, and, at the end, we provide a brief comparison with transition metal dichalcogenides. PMID:28773167

Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

2015-02-14

We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

Effect of asymmetric interface on charge and spin transport across two dimensional electron gas with Dresselhaus spin-orbit coupling/ferromagnet junction

NASA Astrophysics Data System (ADS)

Srisongmuang, B.; Pasanai, K.

2018-04-01

We theoretically studied the effect of interfacial scattering on the transport of charge and spin across the junction of a two-dimensional electron gas with Dresselhaus spin-orbit coupling and ferromagnetic material junction, via the conductance (G) and the spin-polarization of the conductance spectra (P) using the scattering method. At the interface, not only were the effects of spin-conserving (Z0) and spin-flip scattering (Zf) considered, but also the interfacial Rashba spin-orbit coupling scattering (ZRSOC) , which was caused by the asymmetry of the interface, was taken into account, and all of them were modeled by the delta potential. It was found that G was suppressed with increasing Z0 , as expected. Interestingly, a particular value of Zf can cause G and P to reach a maximum value. In particular, ZRSOC plays a crucial role to reduce G and P in the metallic limit, but its influence on the tunneling limit was quite weak. On the other hand, the effect of ZRSOC was diminished in the tunneling limit of the magnetic junction.

Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

NASA Astrophysics Data System (ADS)

Parker, Edward; Balents, Leon

2018-05-01

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spin-orbit-coupled nearest-neighbor triangular-lattice model for the candidate U (1 ) quantum spin liquid YbMgGaO4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains—possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry.

Rashba and Dresselhaus spin-orbit couplings effects on electromagnetically induced transparency of a lens-shaped quantum dot: External electric and magnetic fields

NASA Astrophysics Data System (ADS)

Zamani, A.; Setareh, F.; Azargoshasb, T.; Niknam, E.; Mohammadhosseini, E.

2017-06-01

In this article the spin of electron as well as simultaneous effects of Rashba and Dresselhaus spin-orbit interactions are considered for a lens-shaped GaAs quantum dot and the influences of applied electric field and Zeeman effect on the electromagnetically induced transparency (EIT) of this system are investigated. To do so, the absorption, refractive index as well as the group velocity of the probe light pulse are presented and discussed. Study of the absorption and refractive index reveals that, at a particular frequency of probe field, absorption diminishes, refractive index becomes unity and so the EIT occurs. Furthermore, the investigation of group velocity show that, around such frequency the probe propagation is sub-luminal, which shifts to super-luminal for higher and lower frequencies. Our results illustrate that the EIT frequency, transparency window and sub(super)-luminal frequency intervals are strongly sensitive to applied fields in the presence of spin-orbit couplings. It is found that, in comparison with the investigations with negligence of spin, the EIT behavior under the effects of applied fields are quite different.

Interfacial Dzyaloshinskii-Moriya interaction, surface anisotropy energy, and spin pumping at spin orbit coupled Ir/Co interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun

2016-04-04

The interfacial Dzyaloshinskii-Moriya interaction (iDMI), surface anisotropy energy, and spin pumping at the Ir/Co interface are experimentally investigated by performing Brillouin light scattering. Contrary to previous reports, we suggest that the sign of the iDMI at the Ir/Co interface is the same as in the case of the Pt/Co interface. We also find that the magnitude of the iDMI energy density is relatively smaller than in the case of the Pt/Co interface, despite the large strong spin-orbit coupling (SOC) of Ir. The saturation magnetization and the perpendicular magnetic anisotropy (PMA) energy are significantly improved due to a strong SOC. Ourmore » findings suggest that an SOC in an Ir/Co system behaves in different ways for iDMI and PMA. Finally, we determine the spin pumping effect at the Ir/Co interface, and it increases the Gilbert damping constant from 0.012 to 0.024 for 1.5 nm-thick Co.« less

Spin orbit coupling for molecular ab initio density matrix renormalization group calculations: Application to g-tensors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roemelt, Michael, E-mail: michael.roemelt@theochem.rub.de

Spin Orbit Coupling (SOC) is introduced to molecular ab initio density matrix renormalization group (DMRG) calculations. In the presented scheme, one first approximates the electronic ground state and a number of excited states of the Born-Oppenheimer (BO) Hamiltonian with the aid of the DMRG algorithm. Owing to the spin-adaptation of the algorithm, the total spin S is a good quantum number for these states. After the non-relativistic DMRG calculation is finished, all magnetic sublevels of the calculated states are constructed explicitly, and the SOC operator is expanded in the resulting basis. To this end, spin orbit coupled energies and wavefunctionsmore » are obtained as eigenvalues and eigenfunctions of the full Hamiltonian matrix which is composed of the SOC operator matrix and the BO Hamiltonian matrix. This treatment corresponds to a quasi-degenerate perturbation theory approach and can be regarded as the molecular equivalent to atomic Russell-Saunders coupling. For the evaluation of SOC matrix elements, the full Breit-Pauli SOC Hamiltonian is approximated by the widely used spin-orbit mean field operator. This operator allows for an efficient use of the second quantized triplet replacement operators that are readily generated during the non-relativistic DMRG algorithm, together with the Wigner-Eckart theorem. With a set of spin-orbit coupled wavefunctions at hand, the molecular g-tensors are calculated following the scheme proposed by Gerloch and McMeeking. It interprets the effective molecular g-values as the slope of the energy difference between the lowest Kramers pair with respect to the strength of the applied magnetic field. Test calculations on a chemically relevant Mo complex demonstrate the capabilities of the presented method.« less

Uniaxial strain control of spin-polarization in multicomponent nematic order of BaFe 2As 2

DOE PAGES

Kissikov, T.; Sarkar, R.; Lawson, M.; ...

2018-03-13

The iron-based high temperature superconductors exhibit a rich phase diagram reflecting a complex interplay between spin, lattice, and orbital degrees of freedom. The nematic state observed in these compounds epitomizes this complexity, by entangling a real-space anisotropy in the spin fluctuation spectrum with ferro-orbital order and an orthorhombic lattice distortion. A subtle and less-explored facet of the interplay between these degrees of freedom arises from the sizable spin-orbit coupling present in these systems, which translates anisotropies in real space into anisotropies in spin space. We present nuclear magnetic resonance studies, which reveal that the magnetic fluctuation spectrum in the paramagneticmore » phase of BaFe 2As 2 acquires an anisotropic response in spin-space upon application of a tetragonal symmetry-breaking strain field. Lastly, our results unveil an internal spin structure of the nematic order parameter, indicating that electronic nematic materials may offer a route to magneto-mechanical control.« less

Tunable Spin-orbit Coupling and Quantum Phase Transition in a Trapped Bose-Einstein Condensate

PubMed Central

Zhang, Yongping; Chen, Gang; Zhang, Chuanwei

2013-01-01

Spin-orbit coupling (SOC), the intrinsic interaction between a particle spin and its motion, is responsible for various important phenomena, ranging from atomic fine structure to topological condensed matter physics. The recent experimental breakthrough on the realization of SOC for ultra-cold atoms provides a completely new platform for exploring spin-orbit coupled superfluid physics. However, the SOC strength in the experiment is not tunable. In this report, we propose a scheme for tuning the SOC strength through a fast and coherent modulation of the laser intensities. We show that the many-body interaction between atoms, together with the tunable SOC, can drive a quantum phase transition (QPT) from spin-balanced to spin-polarized ground states in a harmonic trapped Bose-Einstein condensate (BEC), which resembles the long-sought Dicke QPT. We characterize the QPT using the periods of collective oscillations of the BEC, which show pronounced peaks and damping around the quantum critical point. PMID:23727689

Simulating Chiral Magnetic and Separation Effects with Spin-Orbit Coupled Atomic Gases

PubMed Central

Huang, Xu-Guang

2016-01-01

The chiral magnetic and chiral separation effects—quantum-anomaly-induced electric current and chiral current along an external magnetic field in parity-odd quark-gluon plasma—have received intense studies in the community of heavy-ion collision physics. We show that analogous effects occur in rotating trapped Fermi gases with Weyl-Zeeman spin-orbit coupling where the rotation plays the role of an external magnetic field. These effects can induce a mass quadrupole in the atomic cloud along the rotation axis which may be tested in future experiments. Our results suggest that the spin-orbit coupled atomic gases are potential simulators of the chiral magnetic and separation effects. PMID:26868084

Calculation of nuclear spin-spin coupling constants using frozen density embedding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Götz, Andreas W., E-mail: agoetz@sdsc.edu; Autschbach, Jochen; Visscher, Lucas, E-mail: visscher@chem.vu.nl

2014-03-14

We present a method for a subsystem-based calculation of indirect nuclear spin-spin coupling tensors within the framework of current-spin-density-functional theory. Our approach is based on the frozen-density embedding scheme within density-functional theory and extends a previously reported subsystem-based approach for the calculation of nuclear magnetic resonance shielding tensors to magnetic fields which couple not only to orbital but also spin degrees of freedom. This leads to a formulation in which the electron density, the induced paramagnetic current, and the induced spin-magnetization density are calculated separately for the individual subsystems. This is particularly useful for the inclusion of environmental effects inmore » the calculation of nuclear spin-spin coupling constants. Neglecting the induced paramagnetic current and spin-magnetization density in the environment due to the magnetic moments of the coupled nuclei leads to a very efficient method in which the computationally expensive response calculation has to be performed only for the subsystem of interest. We show that this approach leads to very good results for the calculation of solvent-induced shifts of nuclear spin-spin coupling constants in hydrogen-bonded systems. Also for systems with stronger interactions, frozen-density embedding performs remarkably well, given the approximate nature of currently available functionals for the non-additive kinetic energy. As an example we show results for methylmercury halides which exhibit an exceptionally large shift of the one-bond coupling constants between {sup 199}Hg and {sup 13}C upon coordination of dimethylsulfoxide solvent molecules.« less

Spin-orbit coupling in GaN/AlGaN wurtzite quantum wells

NASA Astrophysics Data System (ADS)

Penteado, Poliana H.; Fu, J. Y.; Bernardes, Esmerindo; Egues, J. Carlos

2012-02-01

We investigate the spin-orbit coupling for electrons in wurtzite quantum wells with two subbands [1]. By folding down the 8x8 Kane model, accounting for the s-pz orbital mixing [2, 3] absent in zincblende structures, we derive an effective 2x2 Hamiltonian for the conduction electrons. In this derivation we consider the renormalization of the spinor component of the conduction band wave function, which is crucial to properly obtain the corresponding spin-orbit couplings. In addition to the Rashba-type term arising from the bulk inversion asymmetry of the wurtzite lattice, we obtain the usual linear in momentum Rashba term induced by the structural inversion asymmetry of the well and; interestingly, we also find a new Rashba-like contribution. The spin-orbit coupling parameters are obtained via a self-consistent calculation. For completeness, the Dresselhaus term is also included in our calculation. [4pt] [1] Rafael S. Calsaverini, Esmerindo Bernardes, J. Carlos Egues, and Daniel Loss, Phys. Rev. B 78, 155313 (2008). [0pt] [2] L. C. Lew Yan Voon, M. Willatzen, and M. Cardona, Phys. Rev. B 53, 10703 (1996). [0pt] [3] J. Y. Fu and M. W. Wu, J. Appl. Phys 104, 093712 (2008).

Spin-Orbit Coupling Controlled J = 3 / 2 Electronic Ground State in 5 d 3 Oxides

DOE PAGES

Taylor, A. E.; Calder, S.; Morrow, R.; ...

2017-05-16

Spin-orbit entanglement in 5d-based transition metal oxides (TMOs) has been identified as a route to a host of unconventional physical states including quantum spin liquids, Weyl semimetals, and axion insulators. Yet despite intense interest, no clear rules have emerged for the treatment of spin-orbit coupling (SOC) in 5d TMOs outside of idealised LS or jj coupling paradigms. This is exemplified in 5d 3 oxides in which an orbitally-quenched singlet ground state is anticipated, yet SOC is manifest in the observed magnetic properties. Here we solve this long-outstanding puzzle by revealing that the electronic ground state of Os5+ 5d 3 ionsmore » is an unquenched J = 3/2 state. Resonant inelastic x-ray scattering (RIXS) in Ca3LiOsO6 and Ba 2YOsO 6 exposes a SOC-controlled splitting of the t 2g manifold. The results are successfully described using an intermediate-coupling framework in which oxygen hybridisation promotes the breakdown of the orbital singlet. This framework opens the door to realistic treatment of SOC across a range of 5d TMOs beyond the 5d 3 case.« less

Spin-Orbit Coupling Controlled J = 3 / 2 Electronic Ground State in 5 d 3 Oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, A. E.; Calder, S.; Morrow, R.

Spin-orbit entanglement in 5d-based transition metal oxides (TMOs) has been identified as a route to a host of unconventional physical states including quantum spin liquids, Weyl semimetals, and axion insulators. Yet despite intense interest, no clear rules have emerged for the treatment of spin-orbit coupling (SOC) in 5d TMOs outside of idealised LS or jj coupling paradigms. This is exemplified in 5d 3 oxides in which an orbitally-quenched singlet ground state is anticipated, yet SOC is manifest in the observed magnetic properties. Here we solve this long-outstanding puzzle by revealing that the electronic ground state of Os5+ 5d 3 ionsmore » is an unquenched J = 3/2 state. Resonant inelastic x-ray scattering (RIXS) in Ca3LiOsO6 and Ba 2YOsO 6 exposes a SOC-controlled splitting of the t 2g manifold. The results are successfully described using an intermediate-coupling framework in which oxygen hybridisation promotes the breakdown of the orbital singlet. This framework opens the door to realistic treatment of SOC across a range of 5d TMOs beyond the 5d 3 case.« less

Fermi Surface of Sr_{2}RuO_{4}: Spin-Orbit and Anisotropic Coulomb Interaction Effects.

PubMed

Zhang, Guoren; Gorelov, Evgeny; Sarvestani, Esmaeel; Pavarini, Eva

2016-03-11

The topology of the Fermi surface of Sr_{2}RuO_{4} is well described by local-density approximation calculations with spin-orbit interaction, but the relative size of its different sheets is not. By accounting for many-body effects via dynamical mean-field theory, we show that the standard isotropic Coulomb interaction alone worsens or does not correct this discrepancy. In order to reproduce experiments, it is essential to account for the Coulomb anisotropy. The latter is small but has strong effects; it competes with the Coulomb-enhanced spin-orbit coupling and the isotropic Coulomb term in determining the Fermi surface shape. Its effects are likely sizable in other correlated multiorbital systems. In addition, we find that the low-energy self-energy matrix-responsible for the reshaping of the Fermi surface-sizably differs from the static Hartree-Fock limit. Finally, we find a strong spin-orbital entanglement; this supports the view that the conventional description of Cooper pairs via factorized spin and orbital part might not apply to Sr_{2}RuO_{4}.

Excitonic magnet in external field: Complex order parameter and spin currents

NASA Astrophysics Data System (ADS)

Geffroy, D.; Hariki, A.; Kuneš, J.

2018-04-01

We investigate spin-triplet exciton condensation in the two-orbital Hubbard model close to half-filling by means of dynamical mean-field theory. Employing an impurity solver that handles complex off-diagonal hybridization functions, we study the behavior of excitonic condensate in stoichiometric and doped systems subject to external magnetic field. We find a general tendency of the triplet order parameter to lie perpendicular with the applied field and identify exceptions from this rule. For solutions exhibiting k -odd spin textures, we discuss the Bloch theorem, which, in the absence of spin-orbit coupling, forbids the appearance of spontaneous net spin current. We demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field theory.

Application of the multireference equation of motion coupled cluster method, including spin-orbit coupling, to the atomic spectra of Cr, Mn, Fe and Co

NASA Astrophysics Data System (ADS)

Liu, Zhebing; Huntington, Lee M. J.; Nooijen, Marcel

2015-10-01

The recently introduced multireference equation of motion (MR-EOM) approach is combined with a simple treatment of spin-orbit coupling, as implemented in the ORCA program. The resulting multireference equation of motion spin-orbit coupling (MR-EOM-SOC) approach is applied to the first-row transition metal atoms Cr, Mn, Fe and Co, for which experimental data are readily available. Using the MR-EOM-SOC approach, the splittings in each L-S multiplet can be accurately assessed (root mean square (RMS) errors of about 70 cm-1). The RMS errors for J-specific excitation energies range from 414 to 783 cm-1 and are comparable to previously reported J-averaged MR-EOM results using the ACESII program. The MR-EOM approach is highly efficient. A typical MR-EOM calculation of a full spin-orbit spectrum takes about 2 CPU hours on a single processor of a 12-core node, consisting of Intel XEON 2.93 GHz CPUs with 12.3 MB of shared cache memory.

Quantum Hall effect in graphene with interface-induced spin-orbit coupling

NASA Astrophysics Data System (ADS)

Cysne, Tarik P.; Garcia, Jose H.; Rocha, Alexandre R.; Rappoport, Tatiana G.

2018-02-01

We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analyzing the spin splitting of the quantum Hall states as a function of magnetic field and gate voltage, we obtain different scaling laws that can be used to characterize the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity.

Equation-of-motion coupled-cluster method for ionised states with spin-orbit coupling using open-shell reference wavefunction

NASA Astrophysics Data System (ADS)

Wang, Zhifan; Wang, Fan

2018-04-01

The equation-of-motion coupled-cluster method for ionised states at the singles and doubles level (EOM-IP-CCSD) with spin-orbit coupling (SOC) included in post-Hartree-Fock (HF) steps is extended to spatially non-degenerate open-shell systems such as high spin states of s1, p3, σ1 or π2 configuration in this work. Pseudopotentials are employed to treat relativistic effects and spin-unrestricted scalar relativistic HF determinant is adopted as reference in calculations. Symmetry is not exploited in the implementation since both time-reversal and spatial symmetry is broken due to SOC. IPs with the EOM-IP-CCSD approach are those from the 3Σ1- states for high spin state of π2 configuration, while the ground state is the 3Σ0- state. When removing an electron from the high spin state of p3 configuration, only the 3P2 state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s1 configuration, diatomic molecules with π2 configuration and SOC splitting of the ionised π1 state, as well as IPs of VA atoms with p3 configuration. Our results demonstrate that this approach can be applied to ionised states of spatially non-degenerate open-shell states containing heavy elements with reasonable accuracy.

Highly anisotropic exchange interactions in a trigonal bipyramidal cyanide-bridged Ni(II)3Os(III)2 cluster.

PubMed

Palii, Andrei V; Reu, Oleg S; Ostrovsky, Sergei M; Klokishner, Sophia I; Tsukerblat, Boris S; Hilfiger, Matthew; Shatruk, Michael; Prosvirin, Andrey; Dunbar, Kim R

2009-06-25

This article is a part of our efforts to control the magnetic anisotropy in cyanide-based exchange-coupled systems with the eventual goal to obtain single-molecule magnets with higher blocking temperatures. We give the theoretical interpretation of the magnetic properties of the new pentanuclear complex {[Ni(II)(tmphen)(2)](3)[Os(III)(CN)(6)](2)} x 6 CH(3)CN (Ni(II)(3)Os(III)(2) cluster). Because the system contains the heavy Os(III) ions, spin-orbit coupling considerably exceeds the contributions from the low-symmetry crystal field and exchange coupling. The magnetic properties of the Ni(II)(3)Os(III)(2) cluster are described in the framework of a highly anisotropic pseudo-spin Hamiltonian that corresponds to the limit of strong spin-orbital coupling and takes into account the complex molecular structure. The model provides a good fit to the experimental data and allows the conclusion that the trigonal axis of the bipyramidal Ni(II)(3)Os(III)(2) cluster is a hard axis of magnetization. This explains the fact that in contrast with the isostructural trigonal bipyramidal Mn(III)(2)Mn(II)(3) cluster, the Ni(II)(3)Os(III)(2) system does not exhibit the single-molecule magnetic behavior.

Relativistic spin-orbit interactions of photons and electrons

NASA Astrophysics Data System (ADS)

Smirnova, D. A.; Travin, V. M.; Bliokh, K. Y.; Nori, F.

2018-04-01

Laboratory optics, typically dealing with monochromatic light beams in a single reference frame, exhibits numerous spin-orbit interaction phenomena due to the coupling between the spin and orbital degrees of freedom of light. Similar phenomena appear for electrons and other spinning particles. Here we examine transformations of paraxial photon and relativistic-electron states carrying the spin and orbital angular momenta (AM) under the Lorentz boosts between different reference frames. We show that transverse boosts inevitably produce a rather nontrivial conversion from spin to orbital AM. The converted part is then separated between the intrinsic (vortex) and extrinsic (transverse shift or Hall effect) contributions. Although the spin, intrinsic-orbital, and extrinsic-orbital parts all point in different directions, such complex behavior is necessary for the proper Lorentz transformation of the total AM of the particle. Relativistic spin-orbit interactions can be important in scattering processes involving photons, electrons, and other relativistic spinning particles, as well as when studying light emitted by fast-moving bodies.

The influence of Nd dopants on spin and orbital moments in Nd-doped permalloy thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Chen, E-mail: ronanluochen@gmail.com; Zhang, Wen, E-mail: xiaotur@gmail.com, E-mail: yazhai@seu.edu.cn; Zhai, Ya, E-mail: xiaotur@gmail.com, E-mail: yazhai@seu.edu.cn

2014-08-25

Magnetic properties of Nd{sub X}-Ni{sub 80}Fe{sub 20(1−X)} thin films have been investigated using x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at room temperature. With the Nd concentration increasing, the ratio of orbital-to-spin moment of Ni and Fe increases significantly, indicating that the spin-orbit coupling in permalloy thin films is enhanced due to the Nd impurities. The spin and orbital moments have been obtained by the sum rules analysis, which shows that the Nd impurities lead to a strong dispersion of spin moments of Fe and Ni while have no effect on orbital moments in Nd-doped permalloy thin films.more » Element-specific XMCD hysteresis loops suggest an antiferromagnetic coupling between the magnetic moments of Nd and permalloy at room temperature. The static magnetic properties have been studied by vibrating sample magnetometer for comparison, which shows a nice agreement with the XMCD results.« less

Strain engineering of the silicon-vacancy center in diamond

NASA Astrophysics Data System (ADS)

Meesala, Srujan; Sohn, Young-Ik; Pingault, Benjamin; Shao, Linbo; Atikian, Haig A.; Holzgrafe, Jeffrey; Gündoǧan, Mustafa; Stavrakas, Camille; Sipahigil, Alp; Chia, Cleaven; Evans, Ruffin; Burek, Michael J.; Zhang, Mian; Wu, Lue; Pacheco, Jose L.; Abraham, John; Bielejec, Edward; Lukin, Mikhail D.; Atatüre, Mete; Lončar, Marko

2018-05-01

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multiqubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain susceptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.

Helical Majorana fermions in d+id'-wave topological superconductivity of doped correlated quantum spin Hall insulators

NASA Astrophysics Data System (ADS)

Chung, Chung-Hou; Sun, Shih-Jye; Chang, Yung-Yeh; Tsai, Wei-Feng; Zhang, Fuchun

Large Hubbard U limit of the Kane-Mele model on a zigzag ribbon of honeycomb lattice near half-filling is studied via a renormalized mean-field theory. The ground state exhibits time-reversal symmetry (TRS) breaking dx2 -y2 + idxy -wave superconductivity. At large spin-orbit coupling, the Z2 topological phase with non-trivial spin Chern number in the pure Kane-Mele model is persistent into the TRS broken state (called ``spin-Chern phase''), and has two pairs of counter-propagating helical Majorana modes at the edges. As the spin-orbit coupling is reduced, the system undergoes a topological quantum phase transition from the spin-Chern to chiral superconducting states. Possible relevance of our results to adatom-doped graphene and irridate compounds is discussed.Ref.:Shih-Jye Sun, Chung-Hou Chung, Yung-Yeh Chang, Wei-Feng Tsai, and Fu-Chun Zhang, arXiv:1506.02584. CHC acknowledges support from NSC Grant No. 98-2918-I-009-06, No. 98-2112-M-009-010-MY3, the NCTU-CTS, the MOE-ATU program, the NCTS of Taiwan, R.O.C.

Giant Optical Polarization Rotation Induced by Spin-Orbit Coupling in Polarons

NASA Astrophysics Data System (ADS)

Casals, Blai; Cichelero, Rafael; García Fernández, Pablo; Junquera, Javier; Pesquera, David; Campoy-Quiles, Mariano; Infante, Ingrid C.; Sánchez, Florencio; Fontcuberta, Josep; Herranz, Gervasi

2016-07-01

We have uncovered a giant gyrotropic magneto-optical response for doped ferromagnetic manganite La2 /3Ca1 /3MnO3 around the near room-temperature paramagnetic-to-ferromagnetic transition. At odds with current wisdom, where this response is usually assumed to be fundamentally fixed by the electronic band structure, we point to the presence of small polarons as the driving force for this unexpected phenomenon. We explain the observed properties by the intricate interplay of mobility, Jahn-Teller effect, and spin-orbit coupling of small polarons. As magnetic polarons are ubiquitously inherent to many strongly correlated systems, our results provide an original, general pathway towards the generation of magnetic-responsive gigantic gyrotropic responses that may open novel avenues for magnetoelectric coupling beyond the conventional modulation of magnetization.

Classification of "multipole" superconductivity in multiorbital systems and its implications

NASA Astrophysics Data System (ADS)

Nomoto, T.; Hattori, K.; Ikeda, H.

2016-11-01

Motivated by a growing interest in multiorbital superconductors with spin-orbit interactions, we perform the group-theoretical classification of various unconventional superconductivity emerging in symmorphic O , D4, and D6 space groups. The generalized Cooper pairs, which we here call "multipole" superconductivity, possess spin-orbital coupled (multipole) degrees of freedom, instead of the conventional spin singlet/triplet in single-orbital systems. From the classification, we obtain the following key consequences, which have never been focused in the long history of research in this field: (1) A superconducting gap function with Γ9⊗Γ9 in D6 possesses nontrivial momentum dependence different from the usual spin-1/2 classification. (2) Unconventional gap structure can be realized in the BCS approximation of purely local (onsite) interactions irrespective of attraction/repulsion. It implies the emergence of an electron-phonon (e-ph) driven unconventional superconductivity. (3) Reflecting symmetry of orbital basis functions there appear not symmetry protected but inevitable line nodes/gap minima, and thus, anisotropic s -wave superconductivity can be naturally explained even in the absence of competing fluctuations.

Spin-orbit coupling for tidally evolving super-Earths

NASA Astrophysics Data System (ADS)

Rodríguez, A.; Callegari, N.; Michtchenko, T. A.; Hussmann, H.

2012-12-01

We investigate the spin behaviour of close-in rocky planets and the implications for their orbital evolution. Considering that the planet rotation evolves under simultaneous actions of the torque due to the equatorial deformation and the tidal torque, both raised by the central star, we analyse the possibility of temporary captures in spin-orbit resonances. The results of the numerical simulations of the exact equations of motions indicate that, whenever the planet rotation is trapped in a resonant motion, the orbital decay and the eccentricity damping are faster than the ones in which the rotation follows the so-called pseudo-synchronization. Analytical results obtained through the averaged equations of the spin-orbit problem show a good agreement with the numerical simulations. We apply the analysis to the cases of the recently discovered hot super-Earths Kepler-10 b, GJ 3634 b and 55 Cnc e. The simulated dynamical history of these systems indicates the possibility of capture in several spin-orbit resonances; particularly, GJ 3634 b and 55 Cnc e can currently evolve under a non-synchronous resonant motion for suitable values of the parameters. Moreover, 55 Cnc e may avoid a chaotic rotation behaviour by evolving towards synchronization through successive temporary resonant trappings.

Control of electron spin and orbital resonances in quantum dots through spin-orbit interactions

NASA Astrophysics Data System (ADS)

Stano, Peter; Fabian, Jaroslav

2008-01-01

The influence of a resonant oscillating electromagnetic field on a single electron in coupled lateral quantum dots in the presence of phonon-induced relaxation and decoherence is investigated. Using symmetry arguments, it is shown that the spin and orbital resonances can be efficiently controlled by spin-orbit interactions. The control is possible due to the strong sensitivity of the Rabi frequency to the dot configuration (the orientation of the dot and the applied static magnetic field); the sensitivity is a result of the anisotropy of the spin-orbit interactions. The so-called easy passage configuration is shown to be particularly suitable for a magnetic manipulation of spin qubits, ensuring long spin relaxation times and protecting the spin qubits from electric field disturbances accompanying on-chip manipulations.

Bulk electron spin polarization generated by the spin Hall current

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2006-07-01

It is shown that the spin Hall current generates a nonequilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known “equilibrium” polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

Quantum anomalous Hall phase in a one-dimensional optical lattice

NASA Astrophysics Data System (ADS)

Liu, Sheng; Shao, L. B.; Hou, Qi-Zhe; Xue, Zheng-Yuan

2018-03-01

We propose to simulate and detect quantum anomalous Hall phase with ultracold atoms in a one-dimensional optical lattice, with the other synthetic dimension being realized by modulating spin-orbit coupling. We show that the system manifests a topologically nontrivial phase with two chiral edge states which can be readily detected in this synthetic two-dimensional system. Moreover, it is interesting that at the phase transition point there is a flat energy band and this system can also be in a topologically nontrivial phase with two Fermi zero modes existing at the boundaries by considering the synthetic dimension as a modulated parameter. We also show how to measure these topological phases experimentally in ultracold atoms. Another model with a random Rashba and Dresselhaus spin-orbit coupling strength is also found to exhibit topological nontrivial phase, and the impact of the disorder to the system is revealed.

Topological Fulde-Ferrell and Larkin-Ovchinnikov states in spin-orbit-coupled lattice system

NASA Astrophysics Data System (ADS)

Guo, Yao-Wu; Chen, Yan

2018-04-01

The spin-orbit coupled lattice system under Zeeman fields provides an ideal platform to realize exotic pairing states. Notable examples range from the topological superfluid/superconducting (tSC) state, which is gapped in the bulk but metallic at the edge, to the Fulde-Ferrell (FF) state (having a phase-modulated order parameter with a uniform amplitude) and the Larkin-Ovchinnikov (LO) state (having a spatially varying order parameter amplitude). Here, we show that the topological FF state with Chern number ( C = -1) (tFF1) and topological LO state with C= 2 (tLO2) can be stabilized in Rashba spin-orbit coupled lattice systems in the presence of both in-plane and out-of-plane Zeeman fields. Besides the inhomogeneous tSC states, in the presence of a weak in-plane Zeeman field, two topological BCS phases may emerge with C = -1 (tBCS1) far from half filling and C = 2 (tBCS2) near half filling. We show intriguing effects such as different spatial profiles of order parameters for FF and LO states, the topological evolution among inhomogeneous tSC states, and different non-trivial Chern numbers for the tFF1 and tLO1,2 states, which are peculiar to the lattice system. Global phase diagrams for various topological phases are presented for both half-filling and doped cases. The edge states as well as local density of states spectra are calculated for tSC states in a 2D strip.

Ultracoherent operation of spin qubits with superexchange coupling

NASA Astrophysics Data System (ADS)

Rančić, Marko J.; Burkard, Guido

2017-11-01

With the use of nuclear-spin-free materials such as silicon and germanium, spin-based quantum bits (qubits) have evolved to become among the most coherent systems for quantum information processing. The new frontier for spin qubits has therefore shifted to the ubiquitous charge noise and spin-orbit interaction, which are limiting the coherence times and gate fidelities of solid-state qubits. In this paper we investigate superexchange, as a means of indirect exchange interaction between two single electron spin qubits, each embedded in a single semiconductor quantum dot (QD), mediated by an intermediate, empty QD. Our results suggest the existence of "supersweet spots", in which the qubit operations implemented by superexchange interaction are simultaneously first-order-insensitive to charge noise and to errors due to spin-orbit interaction. The proposed spin-qubit architecture is scalable and within the manufacturing capabilities of semiconductor industry.

Cooling a Mechanical Resonator with Nitrogen-Vacancy Centres Using a Room Temperature Excited State Spin-Strain Interaction

DOE PAGES

MacQuarrie, E. R.; Otten, M.; Gray, S. K.; ...

2017-02-06

Cooling a mechanical resonator mode to a sub-thermal state has been a long-standing challenge in physics. This pursuit has recently found traction in the field of optomechanics in which a mechanical mode is coupled to an optical cavity. An alternate method is to couple the resonator to a well-controlled two-level system. Here we propose a protocol to dissipatively cool a room temperature mechanical resonator using a nitrogen-vacancy centre ensemble. The spin ensemble is coupled to the resonator through its orbitally-averaged excited state, which has a spin-strain interaction that has not been previously studied. We experimentally demonstrate that the spin-strain couplingmore » in the excited state is 13.5 ± 0.5 times stronger than the ground state spin-strain coupling. Lastly, we then theoretically show that this interaction, combined with a high-density spin ensemble, enables the cooling of a mechanical resonator from room temperature to a fraction of its thermal phonon occupancy.« less

Cooling a Mechanical Resonator with Nitrogen-Vacancy Centres Using a Room Temperature Excited State Spin-Strain Interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacQuarrie, E. R.; Otten, M.; Gray, S. K.

Cooling a mechanical resonator mode to a sub-thermal state has been a long-standing challenge in physics. This pursuit has recently found traction in the field of optomechanics in which a mechanical mode is coupled to an optical cavity. An alternate method is to couple the resonator to a well-controlled two-level system. Here we propose a protocol to dissipatively cool a room temperature mechanical resonator using a nitrogen-vacancy centre ensemble. The spin ensemble is coupled to the resonator through its orbitally-averaged excited state, which has a spin-strain interaction that has not been previously studied. We experimentally demonstrate that the spin-strain couplingmore » in the excited state is 13.5 ± 0.5 times stronger than the ground state spin-strain coupling. Lastly, we then theoretically show that this interaction, combined with a high-density spin ensemble, enables the cooling of a mechanical resonator from room temperature to a fraction of its thermal phonon occupancy.« less

CERES: An ab initio code dedicated to the calculation of the electronic structure and magnetic properties of lanthanide complexes.

PubMed

Calvello, Simone; Piccardo, Matteo; Rao, Shashank Vittal; Soncini, Alessandro

2018-03-05

We have developed and implemented a new ab initio code, Ceres (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimized implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of 4f quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state-of-the-art ab initio strategy to determine crystal field levels and properties, and show that our methodology, as implemented in Ceres, represents a more time-efficient computational strategy for the evaluation of the magnetic properties of lanthanide complexes, also allowing a full representation of non-perturbative spin-orbit coupling effects. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Spin-orbit beams for optical chirality measurement

NASA Astrophysics Data System (ADS)

Samlan, C. T.; Suna, Rashmi Ranjan; Naik, Dinesh N.; Viswanathan, Nirmal K.

2018-01-01

Accurate measurement of chirality is essential for the advancement of natural and pharmaceutical sciences. We report here a method to measure chirality using non-separable states of light with geometric phase-gradient in the circular polarization basis, which we refer to as spin-orbit beams. A modified polarization Sagnac interferometer is used to generate spin-orbit beams wherein the spin and orbital angular momentum of the input Gaussian beam are coupled. The out-of-phase interference between counter-propagating Gaussian beams with orthogonal spin states and lateral-shear or/and linear-phase difference between them results in spin-orbit beams with linear and azimuthal phase gradient. The spin-orbit beams interact efficiently with the chiral medium, inducing a measurable change in the center-of-mass of the beam, using the polarization rotation angle and hence the chirality of the medium are accurately calculated. Tunable dynamic range of measurement and flexibility to introduce large values of orbital angular momentum for the spin-orbit beam, to improve the measurement sensitivity, highlight the techniques' versatility.

Spin-orbit-coupled superconductivity

PubMed Central

Lo, Shun-Tsung; Lin, Shih-Wei; Wang, Yi-Ting; Lin, Sheng-Di; Liang, C.-T.

2014-01-01

Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature Tc, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < Tc, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity. PMID:24961726

Anisotropic optical absorption induced by Rashba spin-orbit coupling in monolayer phosphorene

NASA Astrophysics Data System (ADS)

Li, Yuan; Li, Xin; Wan, Qi; Bai, R.; Wen, Z. C.

2018-04-01

We obtain the effective Hamiltonian of the phosphorene including the effect of Rashba spin-orbit coupling in the frame work of the low-energy theory. The spin-splitting energy bands show an anisotropy feature for the wave vectors along kx and ky directions, where kx orients to ΓX direction in the k space. We numerically study the optical absorption of the electrons for different wave vectors with Rashba spin-orbit coupling. We find that the spin-flip transition from the valence band to the conduction band induced by the circular polarized light closes to zero with increasing the x-component wave vector when ky equals to zero, while it can be significantly increased to a large value when ky gets a small value. When the wave vector varies along the ky direction, the spin-flip transition can also increase to a large value, however, which shows an anisotropy feature for the optical absorption. Especially, the spin-conserved transitions keep unchanged and have similar varying trends for different wave vectors. This phenomenon provides a novel route for the manipulation of the spin-dependent property of the fermions in the monolayer phosphorene.

Dynamics of interacting fermions under spin-orbit coupling in an optical lattice clock

NASA Astrophysics Data System (ADS)

Bromley, S. L.; Kolkowitz, S.; Bothwell, T.; Kedar, D.; Safavi-Naini, A.; Wall, M. L.; Salomon, C.; Rey, A. M.; Ye, J.

2018-04-01

Quantum statistics and symmetrization dictate that identical fermions do not interact via s-wave collisions. However, in the presence of spin-orbit coupling (SOC), fermions prepared in identical internal states with distinct momenta become distinguishable. The resulting strongly interacting system can exhibit exotic topological and pairing behaviours, many of which are yet to be observed in condensed matter systems. Ultracold atomic gases offer a promising pathway for simulating these rich phenomena, but until recently have been hindered by heating and losses. Here we enter a new regime of many-body interacting SOC in a fermionic optical lattice clock (OLC), where the long-lived electronic clock states mitigate unwanted dissipation. Using clock spectroscopy, we observe the precession of the collective magnetization and the emergence of spin-locking effects arising from an interplay between p-wave and SOC-induced exchange interactions. The many-body dynamics are well captured by a collective XXZ spin model, which describes a broad class of condensed matter systems ranging from superconductors to quantum magnets. Furthermore, our work will aid in the design of next-generation OLCs by offering a route for avoiding the observed large density shifts caused by SOC-induced exchange interactions.

Orbit-spin coupling and the interannual variability of global-scale dust storm occurrence on Mars

NASA Astrophysics Data System (ADS)

Shirley, James H.; Mischna, Michael A.

2017-05-01

A new physical hypothesis predicts that a weak coupling of the orbital and rotational motions of extended bodies may give rise to a modulation of circulatory flows within their atmospheres. Driven cycles of intensification and relaxation of large-scale circulatory flows are predicted, with the phasing of these changes linked directly to the rate of change of the orbital angular momentum, dL/dt, with respect to inertial frames. We test the hypothesis that global-scale dust storms (GDS) on Mars may occur when periods of circulatory intensification (associated with positive and negative extrema of the dL/dt waveform) coincide with the southern summer dust storm season on Mars. The orbit-spin coupling hypothesis additionally predicts that the intervening 'transitional' periods, which are characterized by the disappearance and subsequent sign change of dL/dt, may be unfavorable for the occurrence of GDS, when they occur during the southern summer dust storm season. These hypotheses are strongly supported by comparisons between calculated dynamical time series of dL/dt and historic observations. All of the nine known global-scale dust storms on Mars took place during Mars years when circulatory intensification during the dust storm season is 'retrodicted' under the orbit-spin coupling hypothesis. None of the historic global-scale dust storms of our catalog occurred during transitional intervals. Orbit-spin coupling appears to play an important role in the excitation of the interannual variability of the atmospheric circulation of Mars.

Aspects of Dzyaloshinskii-Moriya Interaction in Two Dimensional Magnetic Structures

NASA Astrophysics Data System (ADS)

Kundu, Anirban

Research on topologically protected chiral magnetic structures such as magnetic domain walls (DWs) and skyrmions, have gained extensive interest because of their possible applications in magnetic data storage industries. The recently observed chiral DW structures in ultrathin ferromagnetic lms with perpendicular magnetic anisotropy has been attributed to the presence of a strong Dzyaloshinskii-Moriya interaction (DMI). In this thesis, the DMI mediated by the conduction electrons in two dimensional magnetic systems such as magnetic thin lms or at the interfaces between two magnetic materials has been studied. I calculate the Ruderman-Kittel- Kasuya-Yosida (RKKY) type indirect exchange coupling between two magnetic moments at nite temperature using the free electron band. At high temperature, the coupling strength decays with distance faster than the coupling at zero temperature but the period of oscillation remains same. However, the free electron band alone could not produce DMI. In the next step, I show addition of Rashba spin-orbit coupling (RSOC) with the spin-polarized conduction electron band produces the DMI between two magnetic ions. The essential feature of this DMI is: the coupling strength increases with the strength of RSOC, but decreases signi cantly with the Heisenberg exchange coupling. The DMI calculated with this model well explains the possibility of preferred Neel or Bloch DW structures with specifc chirality. In addition: I study switching of magnetization with ultrafast laser pulse by inverse Faraday e ect (IFE) where an optically induced non-equilibrium orbital momentum generates an e ective magnetic eld via spin-orbit coupling for magnetization switching. I calculate the magnitude of induced orbital moment for the generic itinerant band and show that magnitude is not large enough to make the switching by a single pulse, however, switching could be possible if multiple pulses are applied to the material.

Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

NASA Astrophysics Data System (ADS)

Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye A.; Sun, Yi-Yang; Zhang, Shengbai; Zhang, Peihong

2016-02-01

The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organic-inorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle self-energy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

Electronic structure and Landé g-factor of a quantum ring in the presence of spin-orbit coupling: Temperature and Zeeman effect

NASA Astrophysics Data System (ADS)

Zamani, A.; Setareh, F.; Azargoshasb, T.; Niknam, E.

2017-10-01

A wide variety of semiconductor nanostructures have been fabricated experimentally and both theoretical and experimental investigations of their features imply the great role they have in new generation technological devices. However, mathematical modeling provide a powerful means due to definitive goal of predicting the features and understanding of such structures behavior under different circumstances. Therefore, effective Hamiltonian for an electron in a quantum ring with axial symmetry in the presence of both Rashba and Dresselhaus spin-orbit interactions (SOI) is derived. Here we report our study of the electronic structure and electron g-factor in the presence of spin-orbit (SO) couplings under the influence of external magnetic field at finite temperature. This investigation shows that, when Rashba and Dresselhaus couplings are simultaneously present, the degeneracy is removed and energy levels split into two branches. Furthermore, with enhancing the applied magnetic field, separation of former degenerate levels increases and also avoided crossings (anti-crossing) in the energy spectra is detected. It is also discussed how the energy levels of the system can be adjusted with variation of temperature as well as the magnetic field and geometrical sizes.

Fully relativistic pseudopotential formalism under an atomic orbital basis: spin-orbit splittings and magnetic anisotropies.

PubMed

Cuadrado, R; Cerdá, J I

2012-02-29

We present an efficient implementation of the spin-orbit coupling within the density functional theory based SIESTA code (2002 J. Phys.: Condens. Matter 14 2745) using the fully relativistic and totally separable pseudopotential formalism of Hemstreet et al (1993 Phys. Rev. B 47 4238). First, we obtain the spin-orbit splittings for several systems ranging from isolated atoms to bulk metals and semiconductors as well as the Au(111) surface state. Next, and after extensive tests on the accuracy of the formalism, we also demonstrate its capability to yield reliable values for the magnetic anisotropy energy in magnetic systems. In particular, we focus on the L1(0) binary alloys and on two large molecules: Mn(6)O(2)(H -sao)(6)(O(2)CH)(2)(CH(3)OH)(4) and Co(4)(hmp)(4)(CH(3)OH)(4)Cl(4). In all cases our calculated anisotropies are in good agreement with those obtained with full-potential methods, despite the latter being, in general, computationally more demanding.

Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, Subrata; Vijay, Amrendra, E-mail: avijay@iitm.ac.in

Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, whichmore » is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.« less

Communication: GAIMS—Generalized Ab Initio Multiple Spawning for both internal conversion and intersystem crossing processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Curchod, Basile F. E.; Martínez, Todd J., E-mail: toddjmartinez@gmail.com; SLAC National Accelerator Laboratory, Menlo Park, California 94025

2016-03-14

Full multiple spawning is a formally exact method to describe the excited-state dynamics of molecular systems beyond the Born-Oppenheimer approximation. However, it has been limited until now to the description of radiationless transitions taking place between electronic states with the same spin multiplicity. This Communication presents a generalization of the full and ab initio multiple spawning methods to both internal conversion (mediated by nonadiabatic coupling terms) and intersystem crossing events (triggered by spin-orbit coupling matrix elements) based on a spin-diabatic representation. The results of two numerical applications, a model system and the deactivation of thioformaldehyde, validate the presented formalism andmore » its implementation.« less

Communication: GAIMS—generalized ab initio multiple spawning for both internal conversion and intersystem crossing processes

DOE PAGES

Curchod, Basile F. E.; Rauer, Clemens; Marquetand, Philipp; ...

2016-03-11

Full Multiple Spawning is a formally exact method to describe the excited-state dynamics of molecular systems beyond the Born-Oppenheimer approximation. However, it has been limited until now to the description of radiationless transitions taking place between electronic states with the same spin multiplicity. This Communication presents a generalization of the full and ab initio Multiple Spawning methods to both internal conversion (mediated by nonadiabatic coupling terms) and intersystem crossing events (triggered by spin-orbit coupling matrix elements) based on a spin-diabatic representation. Lastly, the results of two numerical applications, a model system and the deactivation of thioformaldehyde, validate the presented formalismmore » and its implementation.« less

Elastic and inelastic scattering for the 10B+58Ni system at near-barrier energies

NASA Astrophysics Data System (ADS)

Scarduelli, V.; Crema, E.; Guimarães, V.; Abriola, D.; Arazi, A.; de Barbará, E.; Capurro, O. A.; Cardona, M. A.; Gallardo, J.; Hojman, D.; Martí, G. V.; Pacheco, A. J.; Rodrígues, D.; Yang, Y. Y.; Deshmukh, N. N.; Paes, B.; Lubian, J.; Mendes Junior, D. R.; Morcelle, V.; Monteiro, D. S.

2017-11-01

Full angular distributions of the 10B elastically and inelastically scattered by 58Ni have been measured at different energies around the Coulomb barrier. The elastic and inelastic scattering of 10B on a medium mass target has been measured for the first time. The obtained angular distributions have been analyzed in terms of large-scale coupled reaction channel calculations, where several inelastic transitions of the projectile and the target, as well as the most relevant one- and two-step transfer reactions have been included in the coupling matrix. The roles of the spin reorientation, the spin-orbit interaction, and the large ground-state deformation of the 10B, in the reaction mechanism, were also investigated. The real part of the interaction potential between projectile and target was represented by a parameter-free double-folding potential, whereas no imaginary potential at the surface was considered. In this sense, the theoretical calculations were parameter free and their results were compared to experimental data to investigate the relative importance of the different reaction channels. A striking influence of the ground-state spin reorientation of the 10B nucleus was found, while all transfer reactions investigated had a minimum contribution to the dynamics of the system. Finally, the large static deformation of the 10B and the spin-orbit coupling can also play an important role in the system studied.

Two-Magnon Scattering in Spin-Orbital Mott Insulator Ba2IrO4

NASA Astrophysics Data System (ADS)

Tsuda, Shunsuke; Okabe, Hirotaka; Isobe, Masaaki; Uji, Shinya

2016-02-01

A spin-orbit induced Mott insulator Ba2IrO4 with the pseudo-spin Jeff = 1/2, showing an antiferromagnetic order (TN = 240 K), has been investigated by Raman spectroscopy. A broad peak with the B1g symmetry is found in a wide temperature region up to 400 K, which is ascribed to the two-magnon scattering. From the peak position and width, the exchange coupling and the antiferromagnetic correlation length are estimated to be 590 cm-1 and 45 Å at 90 K, respectively. The results are compared with the antiferromagnet La2CuO4 with the spin S = 1/2. We conclude that there is no significant difference in the short wavelength spin-excitation between the S = 1/2 and Jeff = 1/2 systems.

Magnetoelectric Effect in a Spin-State Transition System

NASA Astrophysics Data System (ADS)

Naka, Makoto; Mizoguchi, Eriko; Nasu, Joji; Ishihara, Sumio

2018-06-01

Magnetic, dielectric, and magnetoelectric properties in a spin-state transition system are examined, motivated by the recent discovery of multiferroic behavior in a cobalt oxide. We construct an effective model Hamiltonian on the basis of the two-orbital Hubbard model, in which the spin-state degrees of freedom in magnetic ions couple with ferroelectric-type lattice distortions. A phase transition occurs from the high-temperature low-spin phase to the low-temperature high-spin ferroelectric phase with an accompanying increase in spin entropy. The calculated results are consistent with the experimental pressure-temperature phase diagram. We predict the magnetic-field induced electric polarization in the low-spin paraelectric phase near the ferroelectric phase boundary.

A generalized spin diffusion equation with four electrochemical potentials for channels with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Sayed, Shehrin; Hong, Seokmin; Datta, Supriyo

We will present a general semiclassical theory for an arbitrary channel with spin-orbit coupling (SOC), that uses four electrochemical potential (U + , D + , U - , and D -) depending on the sign of z-component of the spin (up (U) , down (D)) and the sign of the x-component of the group velocity (+ , -) . This can be considered as an extension of the standard spin diffusion equation that uses two electrochemical potentials for up and down spin states, allowing us to take into account the unique coupling between charge and spin degrees of freedom in channels with SOC. We will describe applications of this model to answer a number of interesting questions in this field such as: (1) whether topological insulators can switch magnets, (2) how the charge to spin conversion is influenced by the channel resistivity, and (3) how device structures can be designed to enhance spin injection. This work was supported by FAME, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

Spin-orbit interaction driven dimerization in one dimensional frustrated magnets

NASA Astrophysics Data System (ADS)

Zhang, Shang-Shun; Batista, Cristian D.

Spin nematic ordering has been proposed to emerge near the saturation of field of a class of frustrated magnets. The experimental observation of this novel phase is challenging for the traditional experimental probes. Nematic spin ordering is expected to induce a local quadrupolar electric moment via the spin-orbit coupling. However, a finite spin-orbit interaction explicitly breaks the U(1) symmetry of global spin rotations down to Z2, which renders the traditional nematic order no longer well-defined. In this work we investigate the relevant effect of spin-orbit interaction on the 1D frustrated J1 -J2 model. The real and the imaginary parts of the nematic order parameter belong to different representations of the discrete symmetry group of the new Hamiltonian. We demonstrate that spin-orbit coupling stabilizes the real component and simultaneously induces bond dimerization in most of the phase diagram. Such a bond dimerization can be observed with X-rays or nuclear magnetic resonance. In addition, an incommensurate bond-density wave (ICBDW) appears for smaller values of J2 / |J1 | . The experimental fingerprint of the ICBDW is a double-horn shape of the the NMR line. These conclusions can shed light on the experimental search of this novel phase.

Colossal spin-orbit coupling in functionalized graphene

NASA Astrophysics Data System (ADS)

Balakrishnan, Jayakumar; Koon, Gavin; Oezyilmaz, Barbaros

2013-03-01

Graphene's low intrinsic spin orbit (SO) interaction strongly limits the realization of several functional spintronics devices. It is therefore quite desirable to develop methods to tune this SO coupling strength. Among the different approaches, the functionalization of graphene seems to be more promising from an application perspective. Recent theoretical and experimental results on functionalized graphene have shown interesting magnetic properties. Here, we will show our preliminary spin-transport results on such functionally modified graphene and discuss the various possibilities it holds for future graphene-based spintronics applications.

CALIBRATION OF EQUILIBRIUM TIDE THEORY FOR EXTRASOLAR PLANET SYSTEMS. II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Brad M. S., E-mail: hansen@astro.ucla.edu

2012-09-20

We present a new empirical calibration of equilibrium tidal theory for extrasolar planet systems, extending a prior study by incorporating detailed physical models for the internal structure of planets and host stars. The resulting strength of the stellar tide produces a coupling that is strong enough to reorient the spins of some host stars without causing catastrophic orbital evolution, thereby potentially explaining the observed trend in alignment between stellar spin and planetary orbital angular momentum. By isolating the sample whose spins should not have been altered in this model, we also show evidence for two different processes that contribute tomore » the population of planets with short orbital periods. We apply our results to estimate the remaining lifetimes for short-period planets, examine the survival of planets around evolving stars, and determine the limits for circularization of planets with highly eccentric orbits. Our analysis suggests that the survival of circularized planets is strongly affected by the amount of heat dissipated, which is often large enough to lead to runaway orbital inflation and Roche lobe overflow.« less

Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas.

PubMed

King, P D C; McKeown Walker, S; Tamai, A; de la Torre, A; Eknapakul, T; Buaphet, P; Mo, S-K; Meevasana, W; Bahramy, M S; Baumberger, F

2014-02-27

Two-dimensional electron gases (2DEGs) in SrTiO3 have become model systems for engineering emergent behaviour in complex transition metal oxides. Understanding the collective interactions that enable this, however, has thus far proved elusive. Here we demonstrate that angle-resolved photoemission can directly image the quasiparticle dynamics of the d-electron subband ladder of this complex-oxide 2DEG. Combined with realistic tight-binding supercell calculations, we uncover how quantum confinement and inversion symmetry breaking collectively tune the delicate interplay of charge, spin, orbital and lattice degrees of freedom in this system. We reveal how they lead to pronounced orbital ordering, mediate an orbitally enhanced Rashba splitting with complex subband-dependent spin-orbital textures and markedly change the character of electron-phonon coupling, co-operatively shaping the low-energy electronic structure of the 2DEG. Our results allow for a unified understanding of spectroscopic and transport measurements across different classes of SrTiO3-based 2DEGs, and yield new microscopic insights on their functional properties.

Tunneling Anomalous and Spin Hall Effects.

PubMed

Matos-Abiague, A; Fabian, J

2015-07-31

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems.

PubMed

Xiao, Cong; Li, Dingping

2016-06-15

Semiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy E F locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density n e and not inversely proportional to n e. While the magnetoresistance (MR) and Nernst coefficient vanish when E F locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when E F decreases below the BCP. Both of them are nonmonotonic functions of E F below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.

Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems

NASA Astrophysics Data System (ADS)

Xiao, Cong; Li, Dingping

2016-06-01

Semiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy E F locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density n e and not inversely proportional to n e. While the magnetoresistance (MR) and Nernst coefficient vanish when E F locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when E F decreases below the BCP. Both of them are nonmonotonic functions of E F below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

NASA Astrophysics Data System (ADS)

Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

2017-11-01

The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

Rashba spin-orbit coupling for neutral atoms

NASA Astrophysics Data System (ADS)

Campbell, Daniel; Juzeliūnas, Gediminas; Spielman, Ian

2011-05-01

We theoretically describe a new class of atom-laser coupling schemes which lead to effective spin-orbit coupled Hamiltonians for ultra-cold neutral atoms. By properly setting the optical phases, a pair of degenerate spin states emerge as the lowest energy states in the spectrum, and are thus immune to collisionally induced decay. These schemes use N cyclically coupled ground or metastable internal states but we will specialize to the four-level case for this talk. Time permitting, we will describe a possible implementation of this scheme for 87Rb that adds a controllable Dresselhaus component to the effective Hamiltonian in a natural way. NSF through PFC at JQI, ARO with funds from Atomtronics MURI and DARPA OLE, STREP NAMEQUAM.

New forms of spin-orbit coupling in a strontium optical lattice clock

NASA Astrophysics Data System (ADS)

Perlin, Michael; Safavi-Naini, Arghavan; Ozeri, Roee; Rey, Ana Maria

2017-04-01

Ultracold atomic systems allow for the simulation of a variety of condensed matter phenomena, including spin-orbit coupling (SOC), a key ingredient behind recently discovered topological insulators and a path for the realization of topological superfluids. While many experimental efforts have used alkali atoms to engineer SOC via Raman transitions, undesirable heating mechanisms have limited the observation of many-body phenomena manifest at long timescales. Alkaline earth atoms (AEA) have been recently shown to be a potentially better platform for the implementation of SOC due to their reduced sensitivity to spontaneous emission. While previous work has used electronic clock states as a pseudo-spin degree of freedom, we consider the effects of clock side-band transitions. We discuss the richer SOC dynamics which emerges as a result of this extension, and present methods to probe these dynamics in current AEA optical lattice clocks. AFOSR, NSF-PFC and DARPA.

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wang, Pei; Yi, Wei; Xianlong, Gao

2015-01-01

We study the quench dynamics of a one-dimensional ultracold Fermi gas with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems.

Superfluid density and Berezinskii-Kosterlitz-Thouless transition of a spin-orbit-coupled Fulde-Ferrell superfluid

DOE PAGES

Cao, Ye; Liu, Xia -Ji; He, Lianyi; ...

2015-02-09

We theoretically investigate the superfluid density and Berezinskii-Kosterlitz-Thouless (BKT) transition of a two-dimensional Rashba spin-orbit-coupled atomic Fermi gas with both in-plane and out-of-plane Zeeman fields. It was recently predicted that, by tuning the two Zeeman fields, the system may exhibit different exotic Fulde-Ferrell (FF) superfluid phases, including the gapped FF, gapless FF, gapless topological FF, and gapped topological FF states. Due to the FF paring, we show that the superfluid density (tensor) of the system becomes anisotropic. When an in-plane Zeeman field is applied along the x direction, the tensor component along the y direction n s,yy is generally largermore » than n s,xx in most parameter space. At zero temperature, there is always a discontinuity jump in n s,xx as the system evolves from a gapped FF into a gapless FF state. With increasing temperature, such a jump is gradually washed out. The critical BKT temperature has been calculated as functions of the spin-orbit-coupling strength, interatomic interaction strength, and in-plane and out-of-plane Zeeman fields. We predict that the novel FF superfluid phases have a significant critical BKT temperature, typically at the order of 0.1T F, where T F is the Fermi degenerate temperature. Furthermore, their observation is within the reach of current experimental techniques in cold-atom laboratories.« less

Wide gap Chern Mott insulating phases achieved by design

NASA Astrophysics Data System (ADS)

Guo, Hongli; Gangopadhyay, Shruba; Köksal, Okan; Pentcheva, Rossitza; Pickett, Warren E.

2017-12-01

Quantum anomalous Hall insulators, which display robust boundary charge and spin currents categorized in terms of a bulk topological invariant known as the Chern number (Thouless et al Phys. Rev. Lett. 49, 405-408 (1982)), provide the quantum Hall anomalous effect without an applied magnetic field. Chern insulators are attracting interest both as a novel electronic phase and for their novel and potentially useful boundary charge and spin currents. Honeycomb lattice systems such as we discuss here, occupied by heavy transition-metal ions, have been proposed as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the 3d series, we tune spin-orbit and interaction strength together with strain to design two Chern insulator systems with bandgaps up to 130 meV and Chern numbers C = -1 and C = 2. We find, in this class, that a trade-off between larger spin-orbit coupling and strong interactions leads to a larger gap, whereas the stronger spin-orbit coupling correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers obtaining quantum anomalous Hall character, as pointed out previously; there is only mild structural symmetry breaking of the bilayer in these robust Chern phases. Recent growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow.

Strongly Interacting Fermi Gases in Two Dimensions

DTIC Science & Technology

2012-07-17

other in k- space owing to the spin- orbit interaction. For a finite field B (Z) z , a gap opens in the spectrum. This gap, known as the spin-orbit...from the trap. Time-of-flight maps momentum to real space , allowing direct momentum resolution of the spin popula- tions. As a function of pulse...at a given quasi-momentum q, can be expanded in terms of free space eigenstates as 5 FIG. 3. Creating and probing a spin-orbit coupled lattice. (A

Perspectives from ab-initio and tight-binding: Applications to transition metal compounds and superlattices

NASA Astrophysics Data System (ADS)

Venkataraman, Vijay Shankar

The experimental and theoretical study of transition metal compounds have occupied condensed matter physicists for the best part of the last century. The rich variety of physical behaviour exhibited by these compounds owes its origin to the subtle balance of the energy scales at play for the d orbitals. In this thesis, we study three different systems comprised of transition metal atoms from the third, the fourth, and the fifth group of the periodic table using a combination of ab-initio density functional theory (DFT) computations and effective tight-binding models for the electronic properties. We first consider the electronic properties of artificially fabricated perovskite superlattices of the form [(SrIrO3)m / SrTiO3] with integer m denoting the number of layers of SrIrO3. After discussing the results of experiments undertaken by our collaborators, we present the results of our DFT calculations and build tight-binding models for the m = 1 and m = 2 superlattices. The active ingredient is found to be the 5d orbitals with significant spin-orbit coupling. We then study the energies of magnetic ground states within DFT and compare and contrast our results with those obtained for the bulk Ruddlesden-Popper iridates. Together with experimental measurements, our results suggest that these superlattices are an exciting venue to probe the magnetism and metal-insulator transitions that occur from the intricate balance of the spin-orbit coupling and electron interactions, as has been reported for their bulk counterparts. Next, we consider alpha-RuCl3, a honeycomb lattice compound. We first show using DFT calculations in conjunction with experiments performed by our collaborators, how spin-orbit coupling in the 4d orbitals of Ru is essential to understand the insulating state realized in this compound. Then, in the latter half of the chapter, we study the magnetic ground states of a two-dimensional analogue of alpha-RuCl3 in weak and strong-coupling regimes obtained from a tight-binding model for the 4d orbitals. We further compare these results with energies obtained from DFT calculations. We obtain a zig-zag magnetic ground state for this compound, in all the three approaches. Within DFT, we find that correlations enhance the spin-orbit coupling in this compound and that the anisotropic Kitaev interactions between the spins are dominant in a strong-coupling model. Then, we move on to study the electronic band structures of the higher manganese silicides, which are good thermoelectric materials. Using results from DFT calculations on Mn4Si7 and structural arguments, we construct an effective tight-binding model for the first three members of this series - Mn4Si7, Mn11Si19, and Mn15Si26.

Spin-orbit optical cross-phase-modulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brasselet, Etienne

2010-12-15

We show experimentally that optical phase singularities (PSs) can be written and erased, locally and in a controllable manner, into a light beam using the giant Kerr optical nonlinearities of liquid crystals. The method relies on the nonlinear optical spin-orbit coupling experienced by a collimated probe beam when a collinear focused pump beam imprints a radial birefringent pattern into a nematic film. In addition, experimental data are quantitatively described, accounting for the elastic anisotropy of the material and its nonlocal spatial response to the pump light field. Since we show that the optical intensity of a light beam (the 'pump')more » controls the phase of another beam (the 'probe') in a singular fashion (i.e., with the generation of a screw PS) via their interaction in a nonlinear medium that involves spin-orbit coupling, we dubbed such a nonlinear optical process as spin-orbit optical cross-phase-modulation.« less

Symmetric and asymmetric exchange stiffnesses of transition-metal thin film interfaces in external electric field

NASA Astrophysics Data System (ADS)

Nakamura, K.; Pradipto, A.-M.; Akiyama, T.; Ito, T.; Oguchi, T.; Weinert, M.

2018-07-01

The electric-field induced modifications of the symmetric and asymmetric exchange stiffness constants for the prototypical transition-metal system of a Co monolayer on Pt(111) are determined from first-principles calculated total energy differences of spin-spiral states with oppositely rotating magnetizations in the presence of both the external field and spin-orbit coupling. The trend underlying the modifications is shown to be linked to orbital magnetism. The results demonstrate that an electric field may be a promising approach to manipulate macroscopically magnetic textures.

Intervalley scattering induced by Coulomb interaction and disorder in carbon-nanotube quantum dots

NASA Astrophysics Data System (ADS)

Secchi, Andrea; Rontani, Massimo

2013-09-01

We develop a theory of intervalley Coulomb scattering in semiconducting carbon-nanotube quantum dots, taking into account the effects of curvature and chirality. Starting from the effective mass description of single-particle states, we study the two-electron system by fully including Coulomb interaction, spin-orbit coupling, and short-range disorder. We find that the energy level splittings associated with intervalley scattering are nearly independent of the chiral angle and, while smaller than those due to spin-orbit interaction, large enough to be measurable.

Magnetochromic effect in multiferroic R In 1 ₋ x Mn x O 3 ( R = Tb , Dy)

DOE PAGES

Chen, P.; Holinsworth, B. S.; O'Neal, K. R.; ...

2015-05-26

We combined high field magnetization and magneto-optical spectroscopy to investigate spin-charge coupling in Mn-substituted rare-earth indium oxides of chemical formula RIn₁₋ xMn xO₃ (R=Tb, Dy). The edge states, on-site Mn³⁺d to d excitations, and rare-earth f-manifold excitations all track the magnetization energy due to dominant Zeeman interactions. The field-induced modifications to the rare-earth excitations are quite large because spin-orbit coupling naturally mixes spin and charge, suggesting that the next logical step in the design strategy should be to bring spin-orbit coupling onto the trigonal bipyramidal chromophore site with a 4 or 5d center.

On-chip spin-controlled orbital angular momentum directional coupling

NASA Astrophysics Data System (ADS)

Xie, Zhenwei; Lei, Ting; Si, Guangyuan; Du, Luping; Lin, Jiao; Min, Changjun; Yuan, Xiaocong

2018-01-01

Optical vortex beams have many potential applications in the particle trapping, quantum encoding, optical orbital angular momentum (OAM) communications and interconnects. However, the on-chip compact OAM detection is still a big challenge. Based on a holographic configuration and a spin-dependent structure design, we propose and demonstrate an on-chip spin-controlled OAM-mode directional coupler, which can couple the OAM signal to different directions due to its topological charge. While the directional coupling function can be switched on/off by altering the spin of incident beam. Both simulation and experimental measurements verify the validity of the proposed approach. This work would benefit the on-chip OAM devices for optical communications and high dimensional quantum coding/decoding in the future.

Heavy ligand atom induced large magnetic anisotropy in Mn(ii) complexes.

PubMed

Chowdhury, Sabyasachi Roy; Mishra, Sabyashachi

2017-06-28

In the search for single molecule magnets, metal ions are considered pivotal towards achieving large magnetic anisotropy barriers. In this context, the influence of ligands with heavy elements, showing large spin-orbit coupling, on magnetic anisotropy barriers was investigated using a series of Mn(ii)-based complexes, in which the metal ion did not have any orbital contribution. The mixing of metal and ligand orbitals was achieved by explicitly correlating the metal and ligand valence electrons with CASSCF calculations. The CASSCF wave functions were further used for evaluating spin-orbit coupling and zero-field splitting parameters for these complexes. For Mn(ii) complexes with heavy ligand atoms, such as Br and I, several interesting inter-state mixings occur via the spin-orbit operator, which results in large magnetic anisotropy in these Mn(ii) complexes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schäfer, Gerhard

The current knowledge in the post-Newtonian (PN) dynamics and motion of non-spinning and spinning compact binaries will be presented based on the Arnowitt-Deser-Misner Hamiltonian approach to general relativity. The presentation will cover the binary dynamics with non-spinning components up to the 4PN order and for spinning binaries up to the next-to-next-to-leading order in the spin-orbit and spin-spin couplings. Radiation reaction will be treated for both non-spinning and spinning binaries. Explicit analytic expressions for the motion will be given, innermost stable circular orbits will be discussed.

Spin-orbit interaction of light on the surface of atomically thin crystals

NASA Astrophysics Data System (ADS)

Zhou, Junxiao; Chen, Shizhen; Zhang, Wenshuai; Luo, Hailu; Wen, Shuangchun

2017-09-01

Two-dimensional (2D) atomic crystals have extraordinary electronic and photonic properties and hold great promise in the applications of photonic and optoelectronics. Here, we review some of our works about the spin-orbit interaction of light on the surface of 2D atomic crystals. First, we propose a general model to describe the spin-orbit interaction of light of the 2D free standing atomic crystal, and find that it is not necessary to involve the effective refractive index to describe the spin-orbit interaction. By developing the quantum weak measurements, we detect the spin-orbit interaction of light in 2D atomic crystals, which can act as a simple method for defining the layer numbers of graphene. Moreover, we find the transverse spin-dependent splitting in the photonic spin Hall effect exhibits a quantized behavior. Furthermore, the spin-orbit interaction of light for the case of air-topological insulator interface can be routed by adjusting the strength of the axion coupling. These basic finding may enhance the comprehension of the spin-orbit interaction, and find the important application in optoelectronic.

Surface magnetism in a chiral d -wave superconductor with hexagonal symmetry

NASA Astrophysics Data System (ADS)

Goryo, Jun; Imai, Yoshiki; Rui, W. B.; Sigrist, Manfred; Schnyder, Andreas P.

2017-10-01

Surface properties are examined in a chiral d -wave superconductor with hexagonal symmetry, whose one-body Hamiltonian possesses intrinsic spin-orbit coupling identical to the one characterizing the topological nature of the Kane-Mele honeycomb insulator. In the normal state, spin-orbit coupling gives rise to spontaneous surface spin currents, whereas in the superconducting state, besides the spin currents, there exist also charge surface currents, due to chiral pairing symmetry. Interestingly, the combination of these two currents results in a surface spin polarization, whose spatial dependence is markedly different on the zigzag and armchair surfaces. We discuss various potential candidate materials, such as SrPtAs, which may exhibit these surface properties.

Optical control of spin-dependent thermal transport in a quantum ring

NASA Astrophysics Data System (ADS)

Abdullah, Nzar Rauf

2018-05-01

We report on calculation of spin-dependent thermal transport through a quantum ring with the Rashba spin-orbit interaction. The quantum ring is connected to two electron reservoirs with different temperatures. Tuning the Rashba coupling constant, degenerate energy states are formed leading to a suppression of the heat and thermoelectric currents. In addition, the quantum ring is coupled to a photon cavity with a single photon mode and linearly polarized photon field. In a resonance regime, when the photon energy is approximately equal to the energy spacing between two lowest degenerate states of the ring, the polarized photon field can significantly control the heat and thermoelectric currents in the system. The roles of the number of photon initially in the cavity, and electron-photon coupling strength on spin-dependent heat and thermoelectric currents are presented.

Topological phase in a two-dimensional metallic heavy-fermion system

NASA Astrophysics Data System (ADS)

Yoshida, Tsuneya; Peters, Robert; Fujimoto, Satoshi; Kawakami, Norio

2013-04-01

We report on a topological insulating state in a heavy-fermion system away from half filling, which is hidden within a ferromagnetic metallic phase. In this phase, the cooperation of the RKKY interaction and the Kondo effect, together with the spin-orbit coupling, induces a spin-selective gap, bringing about topologically nontrivial properties. This topological phase is robust against a change in the chemical potential in a much wider range than the gap size. We analyze these remarkable properties by using dynamical mean field theory and the numerical renormalization group. Its topological properties support a gapless chiral edge mode, which exhibits a non-Tomonaga-Luttinger liquid behavior due to the coupling with bulk ferromagnetic spin fluctuations. We also propose that the effects of the spin fluctuations on the edge mode can be detected via the NMR relaxation time measurement.

Ultra-strong coupling with spin-split heavyhole cyclotron resonances in sGe QWs (Conference Presentation)

NASA Astrophysics Data System (ADS)

Keller, Janine; Scalari, Giacomo; Maissen, Curdin; Paravicini-Bagliani, Gian Lorenzo; Haase, Johannes; Failla, Michele; Myronov, Maksym; Leadley, David R.; Lloyd-Hughes, James; Faist, Jérôme

2017-02-01

We study the ultra-strong coupling (USC) of Landau level transitions in strained Germanium quantum wells (sGe QW) to THz metasurfaces. The spin-splitting of the heavy-hole cyclotron resonance in sGe QWs due to the Rashba spin-orbit interaction in magnetic field offers an excellent platform to investigate ultra-strong coupling to a non-parabolic system. THz split ring resonators can be tuned to coincide with the single cyclotron transition (around 0.4 THz and a magnetic field of 1.5 T) or the spin-resolved transitions of the sGe QWs (at 1.3 THz and 4.5 T). Coupling to the single cyclotron yields a normalized USC rate of 25%, resulting from fitting with a Hopfield-like Hamiltonian model. Coupling to two or three cyclotron resonances in sGe QWs lead to the observation of multiple polaritons branches, one polariton branch for each oscillator involved in the system. An adaption of the theory allows to also describe this multiple-oscillator system and to determine the coupling strengths. The different Rabi-splittings for the multiple cyclotrons coupling to the same resonator mode relate to the underlying differences in the material. Furthermore, the visibility of an additional transition, possibly a light hole transition with very low carrier density, is strongly enhanced due to the coupling to the LC-resonance with a normalized strong coupling ratio of 4.7%. Future perspectives include controlling spin-flip transitions in USC and studying the impact of non-parabolicity on the ultra-strong coupling physics.

Negative-Mass Instability of the Spin and Motion of an Atomic Gas Driven by Optical Cavity Backaction

NASA Astrophysics Data System (ADS)

Kohler, Jonathan; Gerber, Justin A.; Dowd, Emma; Stamper-Kurn, Dan M.

2018-01-01

We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system. We observe this growth imprinted on modulations of the cavity field and estimate the full covariance of the resulting two-mode state by observing its transient decay during subsequent free evolution.

Manipulating femtosecond spin-orbit torques with laser pulse sequences to control magnetic memory states and ringing

NASA Astrophysics Data System (ADS)

Lingos, P. C.; Wang, J.; Perakis, I. E.

2015-05-01

Femtosecond (fs) coherent control of collective order parameters is important for nonequilibrium phase dynamics in correlated materials. Here, we propose such control of ferromagnetic order based on using nonadiabatic optical manipulation of electron-hole (e -h ) photoexcitations to create fs carrier-spin pulses with controllable direction and time profile. These spin pulses are generated due to the time-reversal symmetry breaking arising from nonperturbative spin-orbit and magnetic exchange couplings of coherent photocarriers. By tuning the nonthermal populations of exchange-split, spin-orbit-coupled semiconductor band states, we can excite fs spin-orbit torques that control complex magnetization pathways between multiple magnetic memory states. We calculate the laser-induced fs magnetic anisotropy in the time domain by using density matrix equations of motion rather than the quasiequilibrium free energy. By comparing to pump-probe experiments, we identify a "sudden" out-of-plane magnetization canting displaying fs magnetic hysteresis, which agrees with switchings measured by the static Hall magnetoresistivity. This fs transverse spin-canting switches direction with magnetic state and laser frequency, which distinguishes it from the longitudinal nonlinear optical and demagnetization effects. We propose that sequences of clockwise or counterclockwise fs spin-orbit torques, photoexcited by shaping two-color laser-pulse sequences analogous to multidimensional nuclear magnetic resonance (NMR) spectroscopy, can be used to timely suppress or enhance magnetic ringing and switching rotation in magnetic memories.

Absence of spontaneous magnetic order of lattice spins coupled to itinerant interacting electrons in one and two dimensions.

PubMed

Loss, Daniel; Pedrocchi, Fabio L; Leggett, Anthony J

2011-09-02

We extend the Mermin-Wagner theorem to a system of lattice spins which are spin coupled to itinerant and interacting charge carriers. We use the Bogoliubov inequality to rigorously prove that neither (anti-) ferromagnetic nor helical long-range order is possible in one and two dimensions at any finite temperature. Our proof applies to a wide class of models including any form of electron-electron and single-electron interactions that are independent of spin. In the presence of Rashba or Dresselhaus spin-orbit interactions (SOI) magnetic order is not excluded and intimately connected to equilibrium spin currents. However, in the special case when Rashba and Dresselhaus SOIs are tuned to be equal, magnetic order is excluded again. This opens up a new possibility to control magnetism electrically.

Spin-orbit coupling effects in indium antimonide quantum well structures

NASA Astrophysics Data System (ADS)

Dedigama, Aruna Ruwan

Indium antimonide (InSb) is a narrow band gap material which has the smallest electron effective mass (0.014m0) and the largest electron Lande g-facture (-51) of all the III-V semiconductors. Spin-orbit effects of III-V semiconductor heterostructures arise from two different inversion asymmetries namely bulk inversion asymmetry (BIA) and structural inversion asymmetry (SIA). BIA is due to the zinc-blende nature of this material which leads to the Dresselhaus spin splitting consisting of both linear and cubic in-plane wave vector terms. As its name implies SIA arises due to the asymmetry of the quantum well structure, this leads to the Rashba spin splitting term which is linear in wave vector. Although InSb has theoretically predicted large Dresselhaus (760 eVA3) and Rashba (523 eA 2) coefficients there has been relatively little experimental investigation of spin-orbit coefficients. Spin-orbit coefficients can be extracted from the beating patterns of Shubnikov--de Haas oscillations (SdH), for material like InSb it is hard to use this method due to the existence of large electron Lande g-facture. Therefore it is essential to use a low field magnetotransport technique such as weak antilocalization to extract spin-orbit parameters for InSb. The main focus of this thesis is to experimentally determine the spin-orbit parameters for both symmetrically and asymmetrically doped InSb/InxAl 1-xSb heterostructures. During this study attempts have been made to tune the Rashba spin-orbit coupling coefficient by using a back gate to change the carrier density of the samples. Dominant phase breaking mechanisms for InSb/InxAl1-xSb heterostructures have been identified by analyzing the temperature dependence of the phase breaking field from weak antilocalization measurements. Finally the strong spin-orbit effects on InSb/InxAl1-xSb heterostructures have been demonstrated with ballistic spin focusing devices.

Ab initio study of dynamical E × e Jahn-Teller and spin-orbit coupling effects in the transition-metal trifluorides TiF3, CrF3, and NiF3

NASA Astrophysics Data System (ADS)

Mondal, Padmabati; Opalka, Daniel; Poluyanov, Leonid V.; Domcke, Wolfgang

2012-02-01

Multiconfiguration ab initio methods have been employed to study the effects of Jahn-Teller (JT) and spin-orbit (SO) coupling in the transition-metal trifluorides TiF3, CrF3, and NiF3, which possess spatially doubly degenerate excited states (ME) of even spin multiplicities (M = 2 or 4). The ground states of TiF3, CrF3, and NiF3 are nondegenerate and exhibit minima of D3h symmetry. Potential-energy surfaces of spatially degenerate excited states have been calculated using the state-averaged complete-active-space self-consistent-field method. SO coupling is described by the matrix elements of the Breit-Pauli operator. Linear and higher order JT coupling constants for the JT-active bending and stretching modes as well as SO-coupling constants have been determined. Vibronic spectra of JT-active excited electronic states have been calculated, using JT Hamiltonians for trigonal systems with inclusion of SO coupling. The effect of higher order (up to sixth order) JT couplings on the vibronic spectra has been investigated for selected electronic states and vibrational modes with particularly strong JT couplings. While the weak SO couplings in TiF3 and CrF3 are almost completely quenched by the strong JT couplings, the stronger SO coupling in NiF3 is only partially quenched by JT coupling.

Stability of the Nagaoka-type ferromagnetic state in a t2 g orbital system on a cubic lattice

NASA Astrophysics Data System (ADS)

Bobrow, Eric; Li, Yi

2018-04-01

We generalize the previous exact results of the Nagaoka-type itinerant ferromagnetic states in a three-dimensional t2 g orbital system to allow for multiple holes. The system is a simple cubic lattice with each site possessing dx y,dy z, and dx z orbitals, which allow two-dimensional hopping within each orbital plane. In the strong-coupling limit of U →∞ , the orbital-generalized Nagaoka ferromagnetic states are proved to be degenerate with the ground state in the thermodynamic limit when the hole number per orbital layer scales slower than L1/2. This result is valid for arbitrary values of the ferromagnetic Hund's coupling J >0 and interorbital repulsion V ≥0 . The stability of the Nagaoka-type state at finite electron densities with respect to a single spin flip is investigated. These results provide helpful guidance for studying the mechanism of itinerant ferromagnetism for the t2 g orbital materials.

Ultracold collisions between spin-orbit-coupled dipoles: General formalism and universality

NASA Astrophysics Data System (ADS)

Wang, Jia; Hougaard, Christiaan R.; Mulkerin, Brendan C.; Liu, Xia-Ji

2018-04-01

A theoretical study of the low-energy scattering properties of two aligned identical bosonic and fermionic dipoles in the presence of isotropic spin-orbit coupling is presented. A general treatment of particles with arbitrary (pseudo)spin is given in the framework of multichannel scattering. At ultracold temperatures and away from shape resonances or closed-channel dominated resonances, the cross section can be well described within the Born approximation to within corrections due to the s -wave scattering. We compare our findings with numerical calculations and find excellent agreement.

Spin-current-driven thermoelectric generation based on interfacial spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagmur, A., E-mail: ahmetyagmur@imr.tohoku.ac.jp; Iguchi, R.; Karube, S.

2016-06-13

The longitudinal spin Seebeck effect (SSE) in Bi{sub 2}O{sub 3}/Cu/yttrium-iron-garnet (YIG) devices has been investigated. When an out-of-plane temperature gradient is applied to the Bi{sub 2}O{sub 3}/Cu/YIG device, a spin current is generated across the Cu/YIG interface via the SSE and then converted into electric voltage due to the spin–orbit coupling at the Bi{sub 2}O{sub 3}/Cu interface. The sign of the SSE voltage in the Bi{sub 2}O{sub 3}/Cu/YIG devices is opposite to that induced by the conventional inverse spin Hall effect in Pt/YIG devices. The SSE voltage in the Bi{sub 2}O{sub 3}/Cu/YIG devices disappears in the absence of the Bi{submore » 2}O{sub 3} layer and its thermoelectric conversion efficiency is independent of the Cu thickness, indicating the important role of the Bi{sub 2}O{sub 3}/Cu interface. This result demonstrates that not only the bulk inverse spin Hall effect but also the spin–orbit coupling near the interface can be used for SSE-based thermoelectric generation.« less

Communication: Localized molecular orbital analysis of the effect of electron correlation on the anomalous isotope effect in the NMR spin-spin coupling constant in methane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarycz, M. Natalia C., E-mail: mnzarycz@gmail.com; Provasi, Patricio F., E-mail: patricio@unne.edu.ar; Sauer, Stephan P. A., E-mail: sauer@kiku.dk

2014-10-21

We discuss the effect of electron correlation on the unexpected differential sensitivity (UDS) in the {sup 1}J(C–H) coupling constant of CH{sub 4} using a decomposition into contributions from localized molecular orbitals and compare with the {sup 1}J(N–H) coupling constant in NH{sub 3}. In particular, we discuss the well known fact that uncorrelated coupled Hartree-Fock (CHF) calculations are not able to reproduce the UDS in methane. For this purpose we have implemented for the first time a localized molecular orbital analysis for the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes—SOPPA(CCSD) in the DALTON program. Comparing themore » changes in the localized orbital contributions at the correlated SOPPA and SOPPA(CCSD) levels and at the uncorrelated CHF level, we find that the latter overestimates the effect of stretching the bond between the coupled atoms on the contribution to the coupling from the localized bonding orbital between these atoms. This disturbs the subtle balance between the molecular orbital contributions, which lead to the UDS in methane.« less

Spin polarization properties of benzene/graphene with transition metals as dopants: First principles calculations

NASA Astrophysics Data System (ADS)

Yuan, X. B.; Tian, Y. L.; Zhao, X. W.; Yue, W. W.; Hu, G. C.; Ren, J. F.

2018-05-01

First principles calculations are used to study the spin polarization properties of benzene molecule adsorbed on the graphene surface which doped with transition metals including Mn, Cr, Fe, Co, and Ni. The densities of states (DOS) of the benzene molecule can be induced to be spin split at the Fermi level only when it is adsorbed on Mn-, and Cr-doped graphene. The p-orbital of the benzene molecule will interact with the d orbital of the doped atoms, which will generate new spin coupling states and lead to obvious spin polarization of the benzene molecule. The spin-polarized density distributions as well as the differential charge density distributions of the systems also suggest that Mn-doped graphene will induce bigger spin polarization than that of Cr-doped graphene. Benzene molecule could be spin-polarized when it is adsorbed on the graphene surface with transition metal dopants, which could be a new method for researching graphene-based organic spintronic devices.

Persistent Spin Current in a Hard-Wall Confining Quantum Wire with Weak Dresselhaus Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Fu, Xi; Zhou, Guang-Hui

2009-02-01

We investigate theoretically the spin current in a quantum wire with weak Dresselhaus spin-orbit coupling connected to two normal conductors. Both the quantum wire and conductors are described by a hard-wall confining potential. Using the electron wave-functions in the quantum wire and a new definition of spin current, we have calculated the elements of linear spin current density js,xiT and js,yiT (i = x, y, z). We find that the elements jTs,xx and jTs,yy have a antisymmetrical relation and the element jTs,yz has the same amount level as js,xxT and js,yyT. We also find a net linear spin current density, which has peaks at the center of quantum wire. The net linear spin current can induce a linear electric field, which may imply a way of spin current detection.

Analytical slave-spin mean-field approach to orbital selective Mott insulators

NASA Astrophysics Data System (ADS)

Komijani, Yashar; Kotliar, Gabriel

2017-09-01

We use the slave-spin mean-field approach to study particle-hole symmetric one- and two-band Hubbard models in the presence of Hund's coupling interaction. By analytical analysis of the Hamiltonian, we show that the locking of the two orbitals vs orbital selective Mott transition can be formulated within a Landau-Ginzburg framework. By applying the slave-spin mean field to impurity problems, we are able to make a correspondence between impurity and lattice. We also consider the stability of the orbital selective Mott phase to the hybridization between the orbitals and study the limitations of the slave-spin method for treating interorbital tunnelings in the case of multiorbital Bethe lattices with particle-hole symmetry.

Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard

2008-07-15

Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the 'effective' Hamiltonian and the 'real' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pade-resummed coefficients) which depends on the choice of some basic 'effective spin vector' S{sub eff}, and which is deformed by comparable-mass effects; and (iv)more » an additional effective spin-orbit interaction term involving another spin vector {sigma}. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter a{sub LSO}{identical_to}cJ{sub LSO}/(G(H{sub LSO}/c{sup 2}){sup 2}). We find that the inclusion of NLO spin-orbit terms has a significant 'moderating' effect on the dynamical characteristics of the circular orbits for large and parallel spins.« less

Emergent odd-parity multipoles and magnetoelectric effects on a diamond structure: Implication for the 5 d transition metal oxides A OsO4 (A =K ,Rb, and Cs)

NASA Astrophysics Data System (ADS)

Hayami, Satoru; Kusunose, Hiroaki; Motome, Yukitoshi

2018-01-01

We report our theoretical predictions on the linear magnetoelectric (ME) effects originating from odd-parity multipoles associated with spontaneous spin and orbital ordering on a diamond structure. We derive a two-orbital model for d electrons in eg orbitals by including the effective spin-orbit coupling which arises from the mixing between eg and t2 g orbitals. We show that the model acquires a net antisymmetric spin-orbit coupling once staggered spin and orbital orders occur spontaneously. The staggered orders are accompanied by odd-parity multipoles: magnetic monopole, quadrupoles, and toroidal dipoles. We classify the types of the odd-parity multipoles according to the symmetry of the spin and orbital orders. Furthermore, by computing the ME tensor using the linear response theory, we show that the staggered orders induce a variety of the linear ME responses. We elaborate all possible ME responses for each staggered order, which are useful to identify the order parameter and to detect the odd-parity multipoles by measuring the ME effects. We also elucidate the effect of lowering symmetry by a tetragonal distortion, which leads to richer ME responses. The implications of our results are discussed for the 5 d transition metal oxides, A OsO4 (A =K,Rb, and Cs) , in which the order parameters are not fully identified.

DUO: Spectra of diatomic molecules

NASA Astrophysics Data System (ADS)

Yurchenko, Sergei N.; Lodi, Lorenzo; Tennyson, Jonathan; Stolyarov, Andrey V.

2016-05-01

Duo computes rotational, rovibrational and rovibronic spectra of diatomic molecules. The software, written in Fortran 2003, solves the Schrödinger equation for the motion of the nuclei for the simple case of uncoupled, isolated electronic states and also for the general case of an arbitrary number and type of couplings between electronic states. Possible couplings include spin-orbit, angular momenta, spin-rotational and spin-spin. Introducing the relevant couplings using so-called Born-Oppenheimer breakdown curves can correct non-adiabatic effects.

Coherent strong field interactions between a nanomagnet and a photonic cavity

NASA Astrophysics Data System (ADS)

Soykal, Oney Orhunc

Strong coupling of light and matter is an essential element of cavity quantum electrodynamics (cavity-QED) and quantum optics, which may lead to novel mixed states of light and matter and to applications such as quantum computation. In the strong-coupling regime, where the coupling strength exceeds the dissipation, the light-matter interaction produces a characteristic vacuum Rabi splitting. Therefore, strong coupling can be utilized as an effective coherent interface between light and matter (in the form of electron charge, spin or superconducting Cooper pairs) to achieve components of quantum information technology including quantum memory, teleportation, and quantum repeaters. Semiconductor quantum dots, nuclear spins and paramagnetic spin systems are only some of the material systems under investigation for strong coupling in solid-state physics. Mixed states of light and matter coupled via electric dipole transitions often suffer from short coherence times (nanoseconds). Even though magnetic transitions appear to be intrinsically more quantum coherent than orbital transitions, their typical coupling strengths have been estimated to be much smaller. Hence, they have been neglected for the purposes of quantum information technology. However, we predict that strong coupling is feasible between photons and a ferromagnetic nanomagnet, due to exchange interactions that cause very large numbers of spins to coherently lock together with a significant increase in oscillator strength while still maintaining very long coherence times. In order to examine this new exciting possibility, the interaction of a ferromagnetic nanomagnet with a single photonic mode of a cavity is analyzed in a fully quantum-mechanical treatment. Exceptionally large quantum-coherent magnet-photon coupling with coupling terms in excess of several THz are predicted to be achievable in a spherical cavity of ˜ 1 mm radius with a nanomagnet of ˜ 100 nm radius and ferromagnet resonance frequency of ˜ 200 GHz. This should substantially exceed the coupling observed in solids between orbital transitions and light. Eigenstates of the nanomagnet-photon system correspond to entangled states of spin orientation and photon number over 105 values of each quantum number. Initial coherent state of definite spin and photon number evolve dynamically to produce large coherent oscillations in the microwave power with exceptionally long dephasing times of few seconds. In addition to dephasing, several decoherence mechanisms including elementary excitation of magnons and crystalline magnetic anisotropy are investigated and shown to not substantially affect coherence upto room temperature. For small nanomagnets the crystalline magnetic anisotropy of the magnet strongly localize the eigenstates in photon and spin number, quenching the potential for coherent states and for a sufficiently large nanomagnet the macrospin approximation breaks down and different domains of the nanomagnet may couple separately to the photonic mode. Thus the optimal nanomagnet size is predicted to be just below the threshold for failure of the macrospin approximation. Moreover, it is shown that initially unentangled coherent states of light (cavity field) and spin (nanomagnet spin orientation) can be phase-locked to evolve into a coherent entangled states of the system under the influence of strong coupling.

Controlled enhancement of spin-current emission by three-magnon splitting.

PubMed

Kurebayashi, Hidekazu; Dzyapko, Oleksandr; Demidov, Vladislav E; Fang, Dong; Ferguson, A J; Demokritov, Sergej O

2011-07-03

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.

Electromagnetic wave propagating along a space curve

NASA Astrophysics Data System (ADS)

Lai, Meng-Yun; Wang, Yong-Long; Liang, Guo-Hua; Wang, Fan; Zong, Hong-Shi

2018-03-01

By using the thin-layer approach, we derive the effective equation for the electromagnetic wave propagating along a space curve. We find intrinsic spin-orbit, extrinsic spin-orbit, and extrinsic orbital angular-momentum and intrinsic orbital angular-momentum couplings induced by torsion, which can lead to geometric phase, spin, and orbital Hall effects. And we show the helicity inversion induced by curvature that can convert a right-handed circularly polarized electromagnetic wave into a left-handed polarized one, vice versa. Finally, we demonstrate that the gauge invariance of the effective dynamics is protected by the geometrically induced gauge potential.

Spin-resolved photoemission study of epitaxially grown MoSe 2 and WSe 2 thin films

DOE PAGES

Mo, Sung-Kwan; Hwang, Choongyu; Zhang, Yi; ...

2016-09-12

Few-layer thick MoSe 2 and WSe 2 possess non-trivial spin textures with sizable spin splitting due to the inversion symmetry breaking embedded in the crystal structure and strong spin–orbit coupling. Here, we report a spin-resolved photoemission study of MoSe 2 and WSe 2 thin film samples epitaxially grown on a bilayer graphene substrate. Furthermore, we only found spin polarization in the single- and trilayer samples—not in the bilayer sample—mostly along the out-of-plane direction of the sample surface. The measured spin polarization is found to be strongly dependent on the light polarization as well as the measurement geometry, which reveals intricatemore » coupling between the spin and orbital degrees of freedom in this class of material.« less

Spin-Orbital entangled 2DEG in the δ-doped interface LaδSr2IrO4: Density-Functional Studies and Transport Results from Boltzmann Equations

NASA Astrophysics Data System (ADS)

Bhandari, Churna; Popovic, Zoran; Satpathy, Sashi

The strong spin-orbit coupled iridates are of considerable interest because of the Mottminsulating state,which is produced by the combined effect of a strong spin-orbit coupling (SOC) and Coulomb repulsion. In this work, using density-functional methods, we predict the existence of a spin-orbital entangled two dimensional electron gas (2DEG) in the delta-doped structure, where a single SrO layer is replaced by an LaO layer. In the bulk Sr2IrO4, a strong SOC splits the t2 g states into Jeff = 1 / 2 and 3 / 2 states. The Coulomb repulsion further splits the half-filled Jeff = 1 / 2 bands into a lower and an upper Hubbard band (UHB) producing a Mott insulator. In the δ-doped structure, La dopes electrons into the UHB, and our results show that the doped electrons are strongly localized in one or two Ir layers at the interface, reminiscent of the 2DEG in the well-studied LaAlO3/SrTiO3 interface. The UHB, consisting of spin-orbit entangled states, is partially filled, resulting in a spin-orbital entangled 2DEG. Transport properties of the 2DEG shows many interesting features, which we study by solving the semi-classical Boltzmann transport equation in the presence of the magnetic and electric fields.

Ab Initio Calculations of Spin-Orbit Coupling for Heavy-Metal Containing Radicals

NASA Astrophysics Data System (ADS)

Cheng, Lan

2016-06-01

The perturbative treatment of spin-orbit coupling (SOC) on top of scalar-relativistic calculations is a cost-effective alternative to rigorous fully relativistic calculations. In this work the applicability of the perturbative scheme in the framework of spin-free exact two-component theory is demonstrated with calculations of SO splittings and SOC contributions to molecular properties in small heavy-metal containing radicals, including AuO, AuS, and ThO^+. The equation of motion coupled cluster techniques have been used to accurately account for the electron-correlation effects in these radicals, and basis-set effects are carefully analyzed. The computed results are compared with experimental measurements for SO splittings and dipole moments when available.

Coriolis effect in optics: unified geometric phase and spin-Hall effect.

PubMed

Bliokh, Konstantin Y; Gorodetski, Yuri; Kleiner, Vladimir; Hasman, Erez

2008-07-18

We examine the spin-orbit coupling effects that appear when a wave carrying intrinsic angular momentum interacts with a medium. The Berry phase is shown to be a manifestation of the Coriolis effect in a noninertial reference frame attached to the wave. In the most general case, when both the direction of propagation and the state of the wave are varied, the phase is given by a simple expression that unifies the spin redirection Berry phase and the Pancharatnam-Berry phase. The theory is supported by the experiment demonstrating the spin-orbit coupling of electromagnetic waves via a surface plasmon nanostructure. The measurements verify the unified geometric phase, demonstrated by the observed polarization-dependent shift (spin-Hall effect) of the waves.

Boosting spin-caloritronic effects by attractive correlations in molecular junctions.

PubMed

Weymann, Ireneusz

2016-01-25

In nanoscopic systems quantum confinement and interference can lead to an enhancement of thermoelectric properties as compared to conventional bulk materials. For nanostructures, such as molecules or quantum dots coupled to external leads, the thermoelectric figure of merit can reach or even exceed unity. Moreover, in the presence of external magnetic field or when the leads are ferromagnetic, an applied temperature gradient can generate a spin voltage and an associated spin current flow in the system, which makes such nanostructures particularly interesting for future thermoelectric applications. In this study, by using the numerical renormalization group method, we examine the spin-dependent thermoelectric transport properties of a molecular junction involving an orbital level with attractive Coulomb correlations coupled to ferromagnetic leads. We analyze how attractive correlations affect the spin-resolved transport properties of the system and find a nontrivial dependence of the conductance and tunnel magnetoresistance on the strength and sign of those correlations. We also demonstrate that attractive correlations can lead to an enhancement of the spin thermopower and the figure of merit, which can be controlled by a gate voltage.

Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

NASA Astrophysics Data System (ADS)

Milletarı, Mirco; Offidani, Manuel; Ferreira, Aires; Raimondi, Roberto

2017-12-01

We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin-valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies.

Spin-orbit coupling effect on structural and magnetic properties of ConRh13-n (n = 0-13) clusters

NASA Astrophysics Data System (ADS)

Bai, Xi; Lv, Jin; Zhang, Fu-Qiang; Jia, Jian-Feng; Wu, Hai-Shun

2018-04-01

The effect of spin-orbit interaction on the structures and magnetism of ConRh13-n (n = 0-13) clusters have been systematically investigated by using the spin-orbit coupling (SOC) implementation of the density functional theory (DFT). The results calculated without SOC (NSOC) show that Rh13 prefers the double simple-cubic configuration, and icosahedron is the favorable structure for n = 1-9, while n ≥ 10, clusters favor the hexagonal bilayer structure. The inclusion of SOC in calculation does not change the geometries of clusters. Compared with that in NSOC calculation, although the binding energy per atom in clusters with same composition decreases in SOC calculation, the relative stability of clusters with different compositions does not change. An interesting result is that the spin moments of clusters for n = 1-9 are almost constant (21 μB). Spin-orbit interaction recovers orbital moment and its anisotropy by removing crystal-field effect in calculation. The destruction of bonding symmetry and relaxation of bonding account for high anisotropies of orbital moments in Co11Rh2 and CoRh12 clusters. With atomic composition (Co/Rh) around 4/9-5/8 and 9/4, the Co-Rh clusters exhibit high magnetic anisotropy energies.

Magnetic-field-induced mixed-level Kondo effect in two-level systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wong, Arturo; Ngo, Anh T.; Ulloa, Sergio E.

2016-10-17

We consider a two-orbital impurity system with intra-and interlevel Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local-singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite-spin states. We use the numerical renormalization group approach to fully characterize this mixed-level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature, and system parameters. Under suitable conditions,more » the total spectral function is shown to develop a Fermi-level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as a function of temperature. These features, as well as the local moment and entropy contribution of the impurity system, are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.« less

Direct observation of the orbital spin Kondo effect in gallium arsenide quantum dots

NASA Astrophysics Data System (ADS)

Shang, Ru-Nan; Zhang, Ting; Cao, Gang; Li, Hai-Ou; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping

2018-02-01

Besides the spin Kondo effect, other degrees of freedom can give rise to the pseudospin Kondo effect. We report a direct observation of the orbital spin Kondo effect in a series-coupled gallium arsenide (GaAs) double quantum dot device where orbital degrees act as pseudospin. Electron occupation in both dots induces a pseudospin Kondo effect. In a region of one net spin impurity, complete spectra with three resonance peaks are observed. Furthermore, we observe a pseudo-Zeeman effect and demonstrate its electrical controllability for the artificial pseudospin in this orbital spin Kondo process via gate voltage control. The fourfold degeneracy point is realized at a specific value supplemented by spin degeneracy, indicating a transition from the SU(2) to the SU(4) Kondo effect.

X-ray microprobe of orbital alignment in strong-field ionized atoms.

PubMed

Young, L; Arms, D A; Dufresne, E M; Dunford, R W; Ederer, D L; Höhr, C; Kanter, E P; Krässig, B; Landahl, E C; Peterson, E R; Rudati, J; Santra, R; Southworth, S H

2006-08-25

We have developed a synchrotron-based, time-resolved x-ray microprobe to investigate optical strong-field processes at intermediate intensities (10(14) - 10(15) W/cm2). This quantum-state specific probe has enabled the direct observation of orbital alignment in the residual ion produced by strong-field ionization of krypton atoms via resonant, polarized x-ray absorption. We found strong alignment to persist for a period long compared to the spin-orbit coupling time scale (6.2 fs). The observed degree of alignment can be explained by models that incorporate spin-orbit coupling. The methodology is applicable to a wide range of problems.

Inverse spin Hall and spin rectification effects in NiFe/FeMn exchange-biased thin films

NASA Astrophysics Data System (ADS)

Garcia, W. J. S.; Seeger, R. L.; da Silva, R. B.; Harres, A.

2017-11-01

Materials presenting high spin-orbit coupling are able to convert spin currents in charge currents. The phenomenon, known as inverse spin Hall effect, promises to revolutionize spintronic technology enabling the electrical detection of spin currents. It has been observed in a variety of systems, usually non-magnetic metals. We study the voltage emerging in exchange biased Ta/NiFe/FeMn/Ta thin films near the ferromagnetic resonance. Measured signals are related to both inverse spin Hall and spin rectification effects, and two distinct protocols were employed to separate their contributions.The curve shift due to the exchange bias effect may enable high frequency applications without an external applied magnetic field.

Electronic, structural, and thermodynamic properties of mixed actinide dioxides (U, Pu, Am) O2 from hybrid density functional theory

NASA Astrophysics Data System (ADS)

Ma, Li; Ray, Asok K.

2010-03-01

As a continuation of our studies of pure actinide metals using hybrid density functional theory,footnotetextR. Atta-Fynn and A. K. Ray, Europhysics Letters, 85, 27008-p1- p6 (2009); Chemical Physics Letters, 482, 223-227 (2009). we present here a systematic study of the electronic and geometric structure properties of mixed actinide dioxides, U0.5Pu0.5O2, U0.5Am0.5O2, Pu0.5Am0.5 O2 and U0.8Pu0.2O2. The fraction of exact Hartree-Fock exchange used was 40%. To investigate the effect of spin-orbit coupling on the ground state electronic and geometric structure properties, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling and one at the fully relativistic level with spin-orbit coupling. Thermodynamic properties have been calculated by a coupling of first-principles calculation and lattice dynamics.

Spin properties of black phosphorus and phosphorene, and their prospects for spincalorics

NASA Astrophysics Data System (ADS)

Kurpas, Marcin; Gmitra, Martin; Fabian, Jaroslav

2018-05-01

Semiconducting black phosphorus attracts a lot of attention due to its extraordinary electronic properties. Its application to spincalorics requires the knowledge about the spin and thermal properties. Here, we describe first principles calculations of the spin–orbit coupling and spin scattering in phosphorene and bulk black phosphorus. We find that the intrinsic spin–orbit coupling is of the order of 20 meV for the valence and conduction band, both for phosphorene and bulk black phosphorus, and induces spin mixing with the probability b2 ≈ 10-5 –10‑4. A strong anisotropy of b 2 is observed. The calculated Elliott–Yafet spin relaxation times reach nanoseconds for realistic values of the momentum relaxation times. The extrinsic spin–orbit coupling, enabling the D’yakonov–Perel’ spin relaxation mechanism, is studied for phosphorene by application of a transverse electric field. We observe a strong anisotropy of the extrinsic effects for the valence band and much weaker for the conduction band. It is shown, that for small enough electric fields the spin relaxation is dominated by the Elliott–Yafet mechanism, while the D’yakonov–Perel’ matters for higher electric fields. Our theoretical results stay in a good agreement with the experimental findings, and indicates that long spin lifetimes in black phosphorus and phosphorene makes them prospective materials for spincalorics and spintronics.

Transport spin dependent in nanostructures: Current and geometry effect of quantum dots in presence of spin-orbit interaction

NASA Astrophysics Data System (ADS)

Paredes-Gutiérrez, H.; Pérez-Merchancano, S. T.; Beltran-Rios, C. L.

2017-12-01

In this work, we study the quantum electron transport through a Quantum Dots Structure (QDs), with different geometries, embedded in a Quantum Well (QW). The behaviour of the current through the nanostructure (dot and well) is studied considering the orbital spin coupling of the electrons and the Rashba effect, by means of the second quantization theory and the standard model of Green’s functions. Our results show the behaviour of the current in the quantum system as a function of the electric field, presenting resonant states for specific values of both the external field and the spin polarization. Similarly, the behaviour of the current on the nanostructure changes when the geometry of the QD and the size of the same are modified as a function of the polarization of the electron spin and the potential of quantum confinement.

Realization of two-dimensional spin-orbit coupling for Bose-Einstein condensates.

PubMed

Wu, Zhan; Zhang, Long; Sun, Wei; Xu, Xiao-Tian; Wang, Bao-Zong; Ji, Si-Cong; Deng, Youjin; Chen, Shuai; Liu, Xiong-Jun; Pan, Jian-Wei

2016-10-07

Cold atoms with laser-induced spin-orbit (SO) interactions provide a platform to explore quantum physics beyond natural conditions of solids. Here we propose and experimentally realize two-dimensional (2D) SO coupling and topological bands for a rubidium-87 degenerate gas through an optical Raman lattice, without phase-locking or fine-tuning of optical potentials. A controllable crossover between 2D and 1D SO couplings is studied, and the SO effects and nontrivial band topology are observed by measuring the atomic cloud distribution and spin texture in momentum space. Our realization of 2D SO coupling with advantages of small heating and topological stability opens a broad avenue in cold atoms to study exotic quantum phases, including topological superfluids. Copyright © 2016, American Association for the Advancement of Science.

Implanting Strong Spin-Orbit Coupling at Magnetoelectric Interfaces

DTIC Science & Technology

2017-12-19

one is polar. Because the broken inversion symmetry in the polar structure is driven by a combination of the Sr-Ca cation mismatch and the octahedral...ME coefficient without breaking the inversion symmetry manifest a large boost of the ME effect with strong spin-orbit coupling. Results on the polar... inversion center. These peaks are absent in the nonpolar structure and appear here due to the A-site ordering and the resulting inversion symmetry

μ SR Investigation of Superconducting PbTaSe2

NASA Astrophysics Data System (ADS)

Wilson, Murray; Hallas, Alannah; Cai, Yipeng; Guo, Shengli; Gong, Zizhou; Ali, Mazhar; Cava, Robert; Uemura, Yasutomo; Luke, Graeme

Noncentrosymmetric superconductors are a topic of considerable interest in the condensed matter physics community. These materials have the potential to exhibit exotic superconducting states, particularly in the presence of strong spin orbit coupling. PbTaSe2 is a noncentrosymmetric material which has very strong spin orbit coupling, and is superconducting with a TC of 3.6 K. Previous studies of this material have identified exotic properties such as Dirac cones gapped by spin-orbit coupling, a topological semi-metal state, and possible multi-band superconductivity. To further explore this material, it is of considerable interest to investigate the pairing symmetry of the superconducting state, and determine whether odd-parity superconductivity may exist. In this talk we will present a μSR investigation of the penetration depth temperature dependece to infer the pairing symmetry. We will also present zero field μSR measurements which suggest that this material has an even-parity superconducting state.

Searching for Supersolidity in Ultracold Atomic Bose Condensates with Rashba Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Liao, Renyuan

2018-04-01

We developed a functional integral formulation for the stripe phase of spinor Bose-Einstein condensates with Rashba spin-orbit coupling. The excitation spectrum is found to exhibit double gapless band structures, identified to be two Goldstone modes resulting from spontaneously broken internal gauge symmetry and translational invariance symmetry. The sound velocities display anisotropic behavior with the lower branch vanishing in the direction perpendicular to the stripe in the x -y plane. At the transition point between the plane-wave phase and the stripe phase, physical quantities such as fluctuation correction to the ground-state energy and quantum depletion of the condensates exhibit discontinuity, characteristic of the first-order phase transition. Despite strong quantum fluctuations induced by Rashba spin-orbit coupling, we show that the supersolid phase is stable against quantum depletion. Finally, we extend our formulation to finite temperatures to account for interactions between excitations.

Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model.

PubMed

Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Chen, Chun-Nan; Wang, Wan-Tsang; Hsu, Yu-Chi; Ren, Chung-Yuan; Lee, Meng-En; Wu, Chieh-Lung; Gau, Ming-Hong

2012-10-17

We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion k at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.

High-order moments of spin-orbit energy in a multielectron configuration

NASA Astrophysics Data System (ADS)

Na, Xieyu; Poirier, M.

2016-07-01

In order to analyze the energy-level distribution in complex ions such as those found in warm dense plasmas, this paper provides values for high-order moments of the spin-orbit energy in a multielectron configuration. Using second-quantization results and standard angular algebra or fully analytical expressions, explicit values are given for moments up to 10th order for the spin-orbit energy. Two analytical methods are proposed, using the uncoupled or coupled orbital and spin angular momenta. The case of multiple open subshells is considered with the help of cumulants. The proposed expressions for spin-orbit energy moments are compared to numerical computations from Cowan's code and agree with them. The convergence of the Gram-Charlier expansion involving these spin-orbit moments is analyzed. While a spectrum with infinitely thin components cannot be adequately represented by such an expansion, a suitable convolution procedure ensures the convergence of the Gram-Charlier series provided high-order terms are accounted for. A corrected analytical formula for the third-order moment involving both spin-orbit and electron-electron interactions turns out to be in fair agreement with Cowan's numerical computations.

Mean-field study of correlation-induced antisymmetric spin-orbit coupling in a two-orbital honeycomb model

NASA Astrophysics Data System (ADS)

Hayami, Satoru; Kusunose, Hiroaki; Motome, Yukitoshi

2018-05-01

We investigate a two-orbital Hubbard model on a honeycomb structure, with a special focus on the antisymmetric spin-orbit coupling (ASOC) induced by symmetry breaking in the electronic degrees of freedom. By investigating the ground-state phase diagram by the mean-field approximation in addition to the analysis in the strong correlation limit, we obtain a variety of symmetry-broken phases that induce different types of effective ASOCs by breaking of spatial inversion symmetry. We find several unusual properties emergent from the ASOCs, such as a linear magnetoelectric effect in a spin-orbital ordered phase at 1/4 filling and a spin splitting in the band structure in charge ordered phases at 1/4 and 1/2 fillings. We also show that a staggered potential on the honeycomb structure leads to another type of ASOC, which gives rise to a valley splitting in the band structure at 1/2 filling. We discuss the experimental relevance of our results to candidate materials including transition metal dichalcogenides and trichalcogenides.

Weak-coupling superconductivity in a strongly correlated iron pnictide

PubMed Central

Charnukha, A.; Post, K. W.; Thirupathaiah, S.; Pröpper, D.; Wurmehl, S.; Roslova, M.; Morozov, I.; Büchner, B.; Yaresko, A. N.; Boris, A. V.; Borisenko, S. V.; Basov, D. N.

2016-01-01

Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations. PMID:26729630

Electronic structure, local magnetism, and spin-orbit effects of Ir(IV)-, Ir(V)-, and Ir(VI)-based compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laguna-Marco, M. A.; Kayser, P.; Alonso, J. A.

2015-06-01

Element- and orbital-selective x-ray absorption and magnetic circular dichroism measurements are carried out to probe the electronic structure and magnetism of Ir 5d electronic states in double perovskite Sr2MIrO6 (M = Mg, Ca, Sc, Ti, Ni, Fe, Zn, In) and La2NiIrO6 compounds. All the studied systems present a significant influence of spin-orbit interactions in the electronic ground state. In addition, we find that the Ir 5d local magnetic moment shows different character depending on the oxidation state despite the net magnetization being similar for all the compounds. Ir carries an orbital contribution comparable to the spin contribution for Ir4+ (5d(5))more » and Ir5+ (5d(4)) oxides, whereas the orbital contribution is quenched for Ir6+ (5d(3)) samples. Incorporation of a magnetic 3d atom allows getting insight into the magnetic coupling between 5d and 3d transition metals. Together with previous susceptibility and neutron diffractionmeasurements, the results indicate that Ir carries a significant local magnetic moment even in samples without a 3d metal. The size of the (small) net magnetization of these compounds is a result of predominant antiferromagnetic interactions between local moments coupled with structural details of each perovskite structure« less

The role of spin-orbit coupling in topologically protected interface states in Dirac materials

NASA Astrophysics Data System (ADS)

Abergel, D. S. L.; Edge, Jonathan M.; Balatsky, Alexander V.

2014-06-01

We highlight the fact that two-dimensional (2D) materials with Dirac-like low energy band structures and spin-orbit coupling (SOC) will produce linearly dispersing topologically protected Jackiw-Rebbi modes at interfaces where the Dirac mass changes sign. These modes may support persistent spin or valley currents parallel to the interface, and the exact arrangement of such topologically protected currents depends crucially on the details of the SOC in the material. As examples, we discuss buckled 2D hexagonal lattices such as silicene or germanene, and transition metal dichalcogenides such as Mo{{S}_{2}}.

Tunneling anisotropic magnetoresistance driven by resonant surface states: first-principles calculations on an Fe(001) surface.

PubMed

Chantis, Athanasios N; Belashchenko, Kirill D; Tsymbal, Evgeny Y; van Schilfgaarde, Mark

2007-01-26

Fully relativistic first-principles calculations of the Fe(001) surface demonstrate that resonant surface (interface) states may produce sizable tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a single magnetic electrode. The effect is driven by the spin-orbit coupling. It shifts the resonant surface band via the Rashba effect when the magnetization direction changes. We find that spin-flip scattering at the interface is controlled not only by the strength of the spin-orbit coupling, but depends strongly on the intrinsic width of the resonant surface states.

Emergent spin electromagnetism induced by magnetization textures in the presence of spin-orbit interaction (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tatara, Gen, E-mail: gen.tatara@riken.jp; Nakabayashi, Noriyuki; Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 Japan

2014-05-07

Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.

Theoretical treatment of the spin-orbit coupling in the rare gas oxides NeO, ArO, KrO, and XeO

NASA Technical Reports Server (NTRS)

Langhoff, S. R.

1980-01-01

Off-diagonal spin-orbit matrix elements are calculated as a function of internuclear distance for the rare gas oxides NeO, ArO, KrO, and XeO using the full microscopic spin-orbit Hamiltonian, including all one- and two-electron integrals, and POL-CI wave functions comparable to those of Dunning and Hay (1977). A good agreement was found when comparing these results in detail with the calculations of Cohen, Wadt and Hay (1979) that utilize an effective one-electron one-center spin-orbit operator. For the rare gas oxide molecules, it is suggested that the numerical results are a more sensitive test of the wave functions (particularly to the extent of charge transfer) than the exact evaluation of all terms in the full spin-orbit operator.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamaguchi, Kizashi; Nishihara, Satomichi; Saito, Toru

First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di- and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level.more » In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure- and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di- and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.« less

Generation and detection of dissipationless spin current in a MgO/Si bilayer

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spintronics is an analogue to electronics where the spin of the electron rather than its charge is functionally controlled for devices. The generation and detection of spin current without ferromagnetic or exotic/scarce materials are two of the biggest challenges for spintronics devices. In this study, we report a solution to the two problems of spin current generation and detection in Si. Using non-local measurement, we experimentally demonstrate the generation of helical dissipationless spin current using the spin-Hall effect. Contrary to the theoretical prediction, we observe the spin-Hall effect in both n-doped and p-doped Si. The helical spin current is attributed to the site-inversion asymmetry of the diamond cubic lattice of Si and structure inversion asymmetry in a MgO/Si bilayer. The spin to charge conversion in Si is insignificant due to weak spin-orbit coupling. For the efficient detection of spin current, we report spin to charge conversion at the MgO (1 nm)/Si (2 µm) (p-doped and n-doped) thin film interface due to Rashba spin-orbit coupling. We detected the spin current at a distance of  >100 µm, which is an order of magnitude larger than the longest spin diffusion length measured using spin injection techniques. The existence of spin current in Si is verified from the coercivity reduction in a Co/Pd multilayer due to spin-orbit torque generated by spin current from Si.

Controllable spin-charge transport in strained graphene nanoribbon devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, Ginetom S., E-mail: ginetom@gmail.com; Guassi, Marcos R.; Qu, Fanyao

2014-09-21

We theoretically investigate the spin-charge transport in two-terminal device of graphene nanoribbons in the presence of a uniform uniaxial strain, spin-orbit coupling, exchange field, and smooth staggered potential. We show that the direction of applied strain can efficiently tune strain-strength induced oscillation of band-gap of armchair graphene nanoribbon (AGNR). It is also found that electronic conductance in both AGNR and zigzag graphene nanoribbon (ZGNR) oscillates with Rashba spin-orbit coupling akin to the Datta-Das field effect transistor. Two distinct strain response regimes of electronic conductance as function of spin-orbit couplings magnitude are found. In the regime of small strain, conductance ofmore » ZGNR presents stronger strain dependence along the longitudinal direction of strain. Whereas for high values of strain shows larger effect for the transversal direction. Furthermore, the local density of states shows that depending on the smoothness of the staggered potential, the edge states of AGNR can either emerge or be suppressed. These emerging states can be determined experimentally by either spatially scanning tunneling microscope or by scanning tunneling spectroscopy. Our findings open up new paradigms of manipulation and control of strained graphene based nanostructure for application on novel topological quantum devices.« less

Photon-induced tunability of the thermospin current in a Rashba ring

NASA Astrophysics Data System (ADS)

Abdullah, Nzar Rauf; Arnold, Thorsten; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

2018-04-01

The goal of this work is to show how the thermospin polarization current in a quantum ring changes in the presence of Rashba spin-orbit coupling and a quantized single photon mode of a cavity the ring is placed in. Employing the reduced density operator and a general master equation formalism, we find that both the Rashba interaction and the photon field can significantly modulate the spin polarization and the thermospin polarization current. Tuning the Rashba coupling constant, degenerate energy levels are formed corresponding to the Aharonov-Casher destructive phase interference in the quantum ring system. Our analysis indicates that the maximum spin polarization can be observed at the points of degenerate energy levels due to spin accumulation in the system without the photon field. The thermospin current is thus suppressed. In the presence of the cavity, the photon field leads to an additional kinetic momentum of the electron. As a result the spin polarization can be enhanced by the photon field.

Magnetic and transport signatures of Rashba spin-orbit coupling on the Kondo lattice model in two dimensional clusters

NASA Astrophysics Data System (ADS)

Riera, Jose

2014-03-01

Motivated by emergent phenomena at oxide surfaces and heterostructures, particularly those involving transition metal oxides with perovskite crystal structure such as LaTiO3/SrTiO3, we examine the Kondo lattice model in the presence of a Rashba spin-orbit coupling (RSOC). Using an array of numerical techniques, under the assumption that the electrons on localized orbitals may be treated as classical continuum spins, we compute various charge, spin and transport properties on square clusters and on ladders at zero and finite temperatures. The main goal is to determine magnetic and transport signatures due to the RSOC. The same model can be used to study at an effective level the combined effect on magnetic and transport properties of Rashba and ferromagnetic moments, such as the ones present at LMnO3/SrMnO3 interfaces. Support from CONICET (ARGENTINA).

Distinct nature of orbital-selective Mott phases dominated by low-energy local spin fluctuations

NASA Astrophysics Data System (ADS)

Song, Ze-Yi; Jiang, Xiu-Cai; Lin, Hai-Qing; Zhang, Yu-Zhong

2017-12-01

Quantum orbital-selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in the one-band Hubbard model when short-range antiferromagnetic order is considered.

Improper magnetic ferroelectricity of nearly pure electronic nature in helicoidal spiral CaMn7O12

NASA Astrophysics Data System (ADS)

Lim, Jin Soo; Saldana-Greco, Diomedes; Rappe, Andrew M.

2018-01-01

Helicoidal magnetic order breaks inversion symmetry in quadruple perovskite CaMn7O12 , generating one of the largest spin-induced ferroelectric polarizations measured to date. Here, the microscopic origin of the polarization, including exchange interactions, coupling to the spin helicity, and charge density redistribution, is explored via first-principles calculations. The B -site Mn4 + (Mn3) spin adopts a noncentrosymmetric configuration, stabilized not only by spin-orbit coupling (SOC), but also by the fully anisotropic Hubbard J parameter in the absence of SOC, to break inversion symmetry and generate polarization. Berry phase computed polarization (Pelec=2169 μ C /m2 ) exhibits nearly pure electronic behavior, with negligible Mn displacements (≈0.7 m Å ). Orbital-resolved density of states shows that p -d orbital mixing is microscopically driven by nonrelativistic exchange striction within the commensurate ionic structure. Persistent electronic polarization induced by helical spin order in the nearly inversion-symmetric ionic crystal lattice suggests opportunities for ultrafast magnetoelectric response.

Gigantic Dzyaloshinskii-Moriya interaction in the MnBi ultrathin films

NASA Astrophysics Data System (ADS)

Yu, Jie-Xiang; Zang, Jiadong; Zang's Team

The magnetic skyrmion, a swirling-like spin texture with nontrivial topology, is driven by strong Dzyaloshinskii-Moriya (DM) interaction originated from the spin-orbit coupling in inversion symmetry breaking systems. Here, based on first-principles calculations, we predict a new material, MnBi ultrathin film, with gigantic DM interactions. The ratio of the DM interaction to the Heisenberg exchange is about 0.3, exceeding any values reported so far. Its high Curie temperature, high coercivity, and large perpendicular magnetoanisotropy make MnBi a good candidate for future spintronics studies. Topologically nontrivial spin textures are emergent in this system. We expect further experimental efforts will be devoted into this systems.

Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves

PubMed Central

Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc

2016-01-01

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface. PMID:26786047

Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves

NASA Astrophysics Data System (ADS)

Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc

2016-01-01

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

Tunable Mode Coupling in Nanocontact Spin-Torque Oscillators

DOE PAGES

Zhang, Steven S. -L.; Iacocca, Ezio; Heinonen, Olle

2017-07-27

Recent experiments on spin-torque oscillators have revealed interactions between multiple magneto-dynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magneto-dynamic modes in a nanocontact spin-torque oscillator. Here, expressions for both linear and nonlinear coupling terms are obtained, whichmore » allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with an external magnetic field as well as with the temperature.« less

Tunable Mode Coupling in Nanocontact Spin-Torque Oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Steven S. -L.; Iacocca, Ezio; Heinonen, Olle

Recent experiments on spin-torque oscillators have revealed interactions between multiple magneto-dynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magneto-dynamic modes in a nanocontact spin-torque oscillator. Here, expressions for both linear and nonlinear coupling terms are obtained, whichmore » allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with an external magnetic field as well as with the temperature.« less

Restricted active space calculations of L-edge X-ray absorption spectra: from molecular orbitals to multiplet states.

PubMed

Pinjari, Rahul V; Delcey, Mickaël G; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

2014-09-28

The metal L-edge (2p → 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe(3+), high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)6](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

Spin-orbit coupled potential energy surfaces and properties using effective relativistic coupling by asymptotic representation.

PubMed

Ndome, Hameth; Eisfeld, Wolfgang

2012-08-14

A new method has been reported recently [H. Ndome, R. Welsch, and W. Eisfeld, J. Chem. Phys. 136, 034103 (2012)] that allows the efficient generation of fully coupled potential energy surfaces (PESs) including derivative and spin-orbit (SO) coupling. The method is based on the diabatic asymptotic representation of the molecular fine structure states and an effective relativistic coupling operator and therefore is called effective relativistic coupling by asymptotic representation (ERCAR). The resulting diabatic spin-orbit coupling matrix is constant and the geometry dependence of the coupling between the eigenstates is accounted for by the diabatization. This approach allows to generate an analytical model for the fully coupled PESs without performing any ab initio SO calculations (except perhaps for the atoms) and thus is very efficient. In the present work, we study the performance of this new method for the example of hydrogen iodide as a well-established test case. Details of the diabatization and the accuracy of the results are investigated in comparison to reference ab initio calculations. The energies of the adiabatic fine structure states are reproduced in excellent agreement with reference ab initio data. It is shown that the accuracy of the ERCAR approach mainly depends on the quality of the underlying ab initio data. This is also the case for dissociation and vibrational level energies, which are influenced by the SO coupling. A method is presented how one-electron operators and the corresponding properties can be evaluated in the framework of the ERCAR approach. This allows the computation of dipole and transition moments of the fine structure states in good agreement with ab initio data. The new method is shown to be very promising for the construction of fully coupled PESs for more complex polyatomic systems to be used in quantum dynamics studies.

Topological spinon bands and vison excitations in spin-orbit coupled quantum spin liquids

NASA Astrophysics Data System (ADS)

Sonnenschein, Jonas; Reuther, Johannes

2017-12-01

Spin liquids are exotic quantum states characterized by the existence of fractional and deconfined quasiparticle excitations, referred to as spinons and visons. Their fractional nature establishes topological properties such as a protected ground-state degeneracy. This work investigates spin-orbit coupled spin liquids where, additionally, topology enters via nontrivial band structures of the spinons. We revisit the Z2 spin-liquid phases that have recently been identified in a projective symmetry-group analysis on the square lattice when spin-rotation symmetry is maximally lifted [J. Reuther et al., Phys. Rev. B 90, 174417 (2014), 10.1103/PhysRevB.90.174417]. We find that in the case of nearest-neighbor couplings only, Z2 spin liquids on the square lattice always exhibit trivial spinon bands. Adding second-neighbor terms, the simplest projective symmetry-group solution closely resembles the Bernevig-Hughes-Zhang model for topological insulators. Assuming that the emergent gauge fields are static, we investigate vison excitations, which we confirm to be deconfined in all investigated spin phases. Particularly, if the spinon bands are topological, the spinons and visons form bound states consisting of several spinon-Majorana zero modes coupling to one vison. The existence of such zero modes follows from an exact mapping between these spin phases and topological p +i p superconductors with vortices. We propose experimental probes to detect such states in real materials.

Inclusion of orbital relaxation and correlation through the unitary group adapted open shell coupled cluster theory using non-relativistic and scalar relativistic Hamiltonians to study the core ionization potential of molecules containing light to medium-heavy elements

NASA Astrophysics Data System (ADS)

Sen, Sangita; Shee, Avijit; Mukherjee, Debashis

2018-02-01

The orbital relaxation attendant on ionization is particularly important for the core electron ionization potential (core IP) of molecules. The Unitary Group Adapted State Universal Coupled Cluster (UGA-SUMRCC) theory, recently formulated and implemented by Sen et al. [J. Chem. Phys. 137, 074104 (2012)], is very effective in capturing orbital relaxation accompanying ionization or excitation of both the core and the valence electrons [S. Sen et al., Mol. Phys. 111, 2625 (2013); A. Shee et al., J. Chem. Theory Comput. 9, 2573 (2013)] while preserving the spin-symmetry of the target states and using the neutral closed-shell spatial orbitals of the ground state. Our Ansatz invokes a normal-ordered exponential representation of spin-free cluster-operators. The orbital relaxation induced by a specific set of cluster operators in our Ansatz is good enough to eliminate the need for different sets of orbitals for the ground and the core-ionized states. We call the single configuration state function (CSF) limit of this theory the Unitary Group Adapted Open-Shell Coupled Cluster (UGA-OSCC) theory. The aim of this paper is to comprehensively explore the efficacy of our Ansatz to describe orbital relaxation, using both theoretical analysis and numerical performance. Whenever warranted, we also make appropriate comparisons with other coupled-cluster theories. A physically motivated truncation of the chains of spin-free T-operators is also made possible by the normal-ordering, and the operational resemblance to single reference coupled-cluster theory allows easy implementation. Our test case is the prediction of the 1s core IP of molecules containing a single light- to medium-heavy nucleus and thus, in addition to demonstrating the orbital relaxation, we have addressed the scalar relativistic effects on the accuracy of the IPs by using a hierarchy of spin-free Hamiltonians in conjunction with our theory. Additionally, the contribution of the spin-free component of the two-electron Gaunt term, not usually taken into consideration, has been estimated at the Self-Consistent Field (ΔSCF) level and is found to become increasingly important and eventually quite prominent for molecules with third period atoms and below. The accuracies of the IPs computed using UGA-OSCC are found to be of the same order as the Coupled Cluster Singles Doubles (ΔCCSD) values while being free from spin contamination. Since the UGA-OSCC uses a common set of orbitals for the ground state and the ion, it obviates the need of two N5 AO to MO transformation in contrast to the ΔCCSD method.

Inclusion of orbital relaxation and correlation through the unitary group adapted open shell coupled cluster theory using non-relativistic and scalar relativistic Hamiltonians to study the core ionization potential of molecules containing light to medium-heavy elements.

PubMed

Sen, Sangita; Shee, Avijit; Mukherjee, Debashis

2018-02-07

The orbital relaxation attendant on ionization is particularly important for the core electron ionization potential (core IP) of molecules. The Unitary Group Adapted State Universal Coupled Cluster (UGA-SUMRCC) theory, recently formulated and implemented by Sen et al. [J. Chem. Phys. 137, 074104 (2012)], is very effective in capturing orbital relaxation accompanying ionization or excitation of both the core and the valence electrons [S. Sen et al., Mol. Phys. 111, 2625 (2013); A. Shee et al., J. Chem. Theory Comput. 9, 2573 (2013)] while preserving the spin-symmetry of the target states and using the neutral closed-shell spatial orbitals of the ground state. Our Ansatz invokes a normal-ordered exponential representation of spin-free cluster-operators. The orbital relaxation induced by a specific set of cluster operators in our Ansatz is good enough to eliminate the need for different sets of orbitals for the ground and the core-ionized states. We call the single configuration state function (CSF) limit of this theory the Unitary Group Adapted Open-Shell Coupled Cluster (UGA-OSCC) theory. The aim of this paper is to comprehensively explore the efficacy of our Ansatz to describe orbital relaxation, using both theoretical analysis and numerical performance. Whenever warranted, we also make appropriate comparisons with other coupled-cluster theories. A physically motivated truncation of the chains of spin-free T-operators is also made possible by the normal-ordering, and the operational resemblance to single reference coupled-cluster theory allows easy implementation. Our test case is the prediction of the 1s core IP of molecules containing a single light- to medium-heavy nucleus and thus, in addition to demonstrating the orbital relaxation, we have addressed the scalar relativistic effects on the accuracy of the IPs by using a hierarchy of spin-free Hamiltonians in conjunction with our theory. Additionally, the contribution of the spin-free component of the two-electron Gaunt term, not usually taken into consideration, has been estimated at the Self-Consistent Field (ΔSCF) level and is found to become increasingly important and eventually quite prominent for molecules with third period atoms and below. The accuracies of the IPs computed using UGA-OSCC are found to be of the same order as the Coupled Cluster Singles Doubles (ΔCCSD) values while being free from spin contamination. Since the UGA-OSCC uses a common set of orbitals for the ground state and the ion, it obviates the need of two N 5 AO to MO transformation in contrast to the ΔCCSD method.

p -wave superconductivity in weakly repulsive 2D Hubbard model with Zeeman splitting and weak Rashba spin-orbit coupling

NASA Astrophysics Data System (ADS)

Hugdal, Henning G.; Sudbø, Asle

2018-01-01

We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the noninteracting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger-type interaction, while the pairing symmetry of the bands is indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction n of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning n . Moreover, n also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral px±i py type state for out-of-plane fields, to a nodal p -wave-type state for purely in-plane fields.

Fast Auroral Snapshot performance using a multi-body dynamic simulation

NASA Technical Reports Server (NTRS)

Zimbelman, Darrell; Walker, Mary

1993-01-01

This paper examines the complex dynamic interaction between two 2.6 m long stacer booms, four 30 m long flexible wire booms and the attitude control system of the Fast Auroral SnapshoT (FAST) spacecraft. The FAST vehicle will nominally operate as a negative orbit spinner, positioned in a 83 deg inclination, 350 x 4200 km orbit. For this study, a three-axis, non-linear, seven body dynamic simulation is developed using the TREETOPS software package. The significance of this approach is the ability to model each component of the FAST spacecraft as an individual member and connect them together in order to better understand the dynamic coupling between structures and the control system. Both the wire and stacer booms are modeled as separate bodies attached to a rigid central body. The wire booms are oriented perpendicular to the spin axis at right angles relative to each other, whereas the stacer booms are aligned with the spin axis. The analysis consists of a comparison between the simulated in-plane and out-of-plane boom motions with theoretically derived frequencies, and an examination of the dynamic coupling between the control system and boom oscillations. Results show that boom oscillations of up to 0.36 deg are acceptable in order to meet the performance requirements. The dynamic motion is well behaved when the precession coil is operating, however, activation of the spin coil produces an erratic trend in the spin rate which approaches the spin rate requirement.

Modeling L2,3-Edge X-ray Absorption Spectroscopy with Real-Time Exact Two-Component Relativistic Time-Dependent Density Functional Theory.

PubMed

Kasper, Joseph M; Lestrange, Patrick J; Stetina, Torin F; Li, Xiaosong

2018-04-10

X-ray absorption spectroscopy is a powerful technique to probe local electronic and nuclear structure. There has been extensive theoretical work modeling K-edge spectra from first principles. However, modeling L-edge spectra directly with density functional theory poses a unique challenge requiring further study. Spin-orbit coupling must be included in the model, and a noncollinear density functional theory is required. Using the real-time exact two-component method, we are able to variationally include one-electron spin-orbit coupling terms when calculating the absorption spectrum. The abilities of different basis sets and density functionals to model spectra for both closed- and open-shell systems are investigated using SiCl 4 and three transition metal complexes, TiCl 4 , CrO 2 Cl 2 , and [FeCl 6 ] 3- . Although we are working in the real-time framework, individual molecular orbital transitions can still be recovered by projecting the density onto the ground state molecular orbital space and separating contributions to the time evolving dipole moment.

Breit interaction contribution to parity violating potentials in chiral molecules containing light nuclei.

PubMed

Berger, Robert

2008-10-21

The importance of the Breit interaction for an accurate prediction of parity violating energy differences between enantiomers is studied within electroweak quantum chemical frameworks. Besides two-electron orbit-orbit and spin-spin coupling contributions, the Breit interaction gives rise to the spin-other-orbit coupling term of the Breit-Pauli Hamiltonian. The present numerical study demonstrates that neglect of this latter term leads in hydrogen peroxide (H(2)O(2)) to relative deviations in the parity violating potential (V(pv)) by about 10%, whereas further relativistic corrections accounted for within a four-component Dirac-Hartree-Fock-Coulomb (DHFC) framework remain smaller, below 5%. Thus, the main source of discrepancy between previous one-component based (coupled perturbed) Hartree-Fock (HF) and four-component Dirac-Hartree-Fock results for parity violating potentials in H(2)O(2) is the neglect of the Breit contribution in DHFC. In heavier homologs of hydrogen peroxide the relative contribution of the spin-other-orbit coupling term to V(pv) decreases with increasing nuclear charge, whereas other relativistic effects become increasingly important. As shown for the H(2)X(2) (X = O,S,Se,Te,Po) series of molecules and for CHBrClF, to a good approximation these other relativistic influences on V(pv) can be accounted for in one-component based HF calculations with the help of relativistic enhancement factors proposed earlier in the theory of atomic parity violation.

An AB Initio Study of SbH_2 and BiH_2: the Renner Effect, Spin-Orbit Coupling, Local Mode Vibrations and Rovibronic Energy Level Clustering in SbH_2

NASA Astrophysics Data System (ADS)

Ostojic, Bojana; Schwerdtfeger, Peter; Bunker, Phil; Jensen, Per

2016-06-01

We present the results of ab initio calculations for the lower electronic states of the Group 15 (pnictogen) dihydrides, SbH_2 and BiH_2. For each of these molecules the two lowest electronic states become degenerate at linearity and are therefore subject to the Renner effect. Spin-orbit coupling is also strong in these two heavy-element containing molecules. For the lowest two electronic states of SbH_2, we construct the three dimensional potential energy surfaces and corresponding dipole moment and transition moment surfaces by multi-reference configuration interaction techniques. Including both the Renner effect and spin-orbit coupling, we calculate term values and simulate the rovibrational and rovibronic spectra of SbH_2. Excellent agreement is obtained with the results of matrix isolation infrared spectroscopic studies and with gas phase electronic spectroscopic studies in absorption [1,2]. For the heavier dihydride BiH_2 we calculate bending potential curves and the spin-orbit coupling constant for comparison. For SbH_2 we further study the local mode vibrational behavior and the formation of rovibronic energy level clusters in high angular momentum states. [1] X. Wang, P. F. Souter and L. Andrews, J. Phys. Chem. A 107, 4244-4249 (2003) [2] N. Basco and K. K. Lee, Spectroscopy Letters 1, 13-15 (1968)

Spin-Forbidden Reactions: Adiabatic Transition States Using Spin-Orbit Coupled Density Functional Theory.

PubMed

Gaggioli, Carlo Alberto; Belpassi, Leonardo; Tarantelli, Francesco; Harvey, Jeremy N; Belanzoni, Paola

2018-04-06

A spin-forbidden chemical reaction involves a change in the total electronic spin state from reactants to products. The mechanistic study is challenging because such a reaction does not occur on a single diabatic potential energy surface (PES), but rather on two (or multiple) spin diabatic PESs. One possible approach is to calculate the so-called "minimum energy crossing point" (MECP) between the diabatic PESs, which however is not a stationary point. Inclusion of spin-orbit coupling between spin states (SOC approach) allows the reaction to occur on a single adiabatic PES, in which a transition state (TS SOC) as well as activation free energy can be calculated. This Concept article summarizes a previously published application in which, for the first time, the SOC effects, using spin-orbit ZORA Hamiltonian within density functional theory (DFT) framework, are included and account for the mechanism of a spin-forbidden reaction in gold chemistry. The merits of the MECP and TS SOC approaches and the accuracy of the results are compared, considering both our recent calculations on molecular oxygen addition to gold(I)-hydride complexes and new calculations for the prototype spin-forbidden N 2 O and N 2 Se dissociation reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic anisotropy of heteronuclear dimers in the gas phase and supported on graphene: relativistic density-functional calculations.

PubMed

Błoński, Piotr; Hafner, Jürgen

2014-04-09

The structural and magnetic properties of mixed PtCo, PtFe, and IrCo dimers in the gas phase and supported on a free-standing graphene layer have been calculated using density-functional theory, both in the scalar-relativistic limit and self-consistently including spin-orbit coupling. The influence of the strong magnetic moments of the 3d atoms on the spin and orbital moments of the 5d atoms, and the influence of the strong spin-orbit coupling contributed by the 5d atom on the orbital moments of the 3d atoms have been studied in detail. The magnetic anisotropy energy is found to depend very sensitively on the nature of the eigenstates in the vicinity of the Fermi level, as determined by band filling, exchange splitting and spin-orbit coupling. The large magnetic anisotropy energy of free PtCo and IrCo dimers relative to the easy direction parallel to the dimer axis is coupled to a strong anisotropy of the orbital magnetic moments of the Co atom for both dimers, and also on the Ir atom in IrCo. In contrast the PtFe dimer shows a weak perpendicular anisotropy and only small spin and orbital anisotropies of opposite sign on the two atoms. For dimers supported on graphene, the strong binding within the dimer and the stronger interaction of the 3d atom with the substrate stabilizes an upright geometry. Spin and orbital moments on the 3d atom are strongly quenched, but due to the weaker binding within the dimer the properties of the 5d atom are more free-atom-like with increased spin and orbital moments. The changes in the magnetic moment are reflected in the structure of the electronic eigenstates near the Fermi level, for all three dimers the easy magnetic direction is now parallel to the dimer axis and perpendicular to the graphene layer. The already very large magnetic anisotropy energy (MAE) of IrCo is further enhanced by the interaction with the support, the MAE of PtFe changes sign, and that of the PtCo dimer is reduced. These changes are discussed in relation to the relativistic electronic structure of free and supported dimers and it is demonstrated that the existence of a partially occupied quasi-degenerate state at the Fermi level favors the formation of a large magnetic anisotropy.

Probing the holographic principle using dynamical gauge effects from open spin-orbit coupling

NASA Astrophysics Data System (ADS)

Zhao, Jianshi; Price, Craig; Liu, Qi; Gemelke, Nathan

2016-05-01

Dynamical gauge fields result from locally defined symmetries and an effective over-labeling of quantum states. Coupling atoms weakly to a reservoir of laser modes can create an effective dynamical gauge field purely due to the disregard of information in the optical states. Here we report measurements revealing effects of open spin-orbit coupling in a system where an effective model can be formed from a non-abelian SU(2) × U(1) field theory following the Yang-Mills construct. Forming a close analogy to dynamical gauge effects in quantum chromodynamics, we extract a measure of atomic motion which reveals the analog of a closing mass gap for the relevant gauge boson, shedding insight on long standing open problems in gauge-fixing scale anomalies. Using arguments following the holographic principle, we measure scaling relations which can be understood by quantifying information present in the local potential. New prospects using these techniques for developing fractionalization of multi-particle and macroscopic systems using dissipative and non-abelian gauge fields will also be discussed. We acknowledge support from NSF Award No. 1068570, and the Charles E. Kaufman Foundation.

Superconductivity and spin-orbit coupling in non-centrosymmetric materials: a review

NASA Astrophysics Data System (ADS)

Smidman, M.; Salamon, M. B.; Yuan, H. Q.; Agterberg, D. F.

2017-03-01

In non-centrosymmetric superconductors, where the crystal structure lacks a centre of inversion, parity is no longer a good quantum number and an electronic antisymmetric spin-orbit coupling (ASOC) is allowed to exist by symmetry. If this ASOC is sufficiently large, it has profound consequences on the superconducting state. For example, it generally leads to a superconducting pairing state which is a mixture of spin-singlet and spin-triplet components. The possibility of such novel pairing states, as well as the potential for observing a variety of unusual behaviors, led to intensive theoretical and experimental investigations. Here we review the experimental and theoretical results for superconducting systems lacking inversion symmetry. Firstly we give a conceptual overview of the key theoretical results. We then review the experimental properties of both strongly and weakly correlated bulk materials, as well as two dimensional systems. Here the focus is on evaluating the effects of ASOC on the superconducting properties and the extent to which there is evidence for singlet-triplet mixing. This is followed by a more detailed overview of theoretical aspects of non-centrosymmetric superconductivity. This includes the effects of the ASOC on the pairing symmetry and the superconducting magnetic response, magneto-electric effects, superconducting finite momentum pairing states, and the potential for non-centrosymmetric superconductors to display topological superconductivity.

STM Studies of Spin-­Orbit Coupled Phases in Real-­ and Momentum-­Space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madhavan, Vidya

The recently discovered class of spin-orbit coupled materials with interesting topological character are fascinating both from fundamental as well as application point of view. Two striking examples are 3D topological insulators (TIs) and topological crystalline insulators (TCIs). These materials host linearly dispersing (Dirac like) surface states with an odd number of Dirac nodes and are predicted to carry a quantized half-integer value of the axion field. The non-trivial topological properties of TIs and TCIs arise from strong spin-orbit coupling leading to an inverted band structure; which also leads to the chiral spin texture in momentum space. In this project wemore » used low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) to study materials with topological phases in real- and momentum-space. We studied both single crystals and thin films of topological materials which are susceptible to being tuned by doping, strain or gating, allowing us to explore their physical properties in the most interesting regimes and set the stage for future technological applications. .« less

Engineering three-dimensional topological insulators in Rashba-type spin-orbit coupled heterostructures

PubMed Central

Das, Tanmoy; Balatsky, A. V.

2013-01-01

Topological insulators represent a new class of quantum phase defined by invariant symmetries and spin-orbit coupling that guarantees metallic Dirac excitations at its surface. The discoveries of these states have sparked the hope of realizing non-trivial excitations and novel effects such as a magnetoelectric effect and topological Majorana excitations. Here we develop a theoretical formalism to show that a three-dimensional topological insulator can be designed artificially via stacking bilayers of two-dimensional Fermi gases with opposite Rashba-type spin-orbit coupling on adjacent layers, and with interlayer quantum tunneling. We demonstrate that in the stack of bilayers grown along a (001)-direction, a non-trivial topological phase transition occurs above a critical number of Rashba bilayers. In the topological phase, we find the formation of a single spin-polarized Dirac cone at the -point. This approach offers an accessible way to design artificial topological insulators in a set up that takes full advantage of the atomic layer deposition approach. This design principle is tunable and also allows us to bypass limitations imposed by bulk crystal geometry. PMID:23739724

Split Fermi Surfaces of the Spin-Orbit-Coupled Metal Cd2Re2O7 Probed by de Haas-van Alphen Effect

NASA Astrophysics Data System (ADS)

Matsubayashi, Yasuhito; Sugii, Kaori; Hirose, Hishiro T.; Hirai, Daigorou; Sugiura, Shiori; Terashima, Taichi; Uji, Shinya; Hiroi, Zenji

2018-05-01

The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition with inversion symmetry breaking (ISB) at Ts1 = 200 K. A recent theory [L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic instability that leads to a multipolar order in the spin-orbit-coupled metal. To observe the Fermi surface of the low-temperature phase of Cd2Re2O7, we perform de Haas-van Alphen effect measurements by means of magnetic torque. In reference to a calculated band structure, the spin-split Fermi surfaces with large cyclotron masses of 5-9m0 are revealed. The splitting is suggested to be due to an antisymmetric spin-orbit coupling induced by ISB, the strength of which is estimated to be approximately 67 K, which is rather smaller than those of typical non-centrosymmetric metals.

Catalystlike effect of orbital angular momentum on the conversion of transverse to three-dimensional spin states within tightly focused radially polarized beams

NASA Astrophysics Data System (ADS)

Han, Lei; Liu, Sheng; Li, Peng; Zhang, Yi; Cheng, Huachao; Zhao, Jianlin

2018-05-01

We report on the catalystlike effect of orbital angular momentum (OAM) on local spin-state conversion within the tightly focused radially polarized beams associated with optical spin-orbit interaction. It is theoretically demonstrated that the incident OAM can lead to a conversion of purely transverse spin state to a three-dimensional spin state on the focal plane. This conversion can be conveniently manipulated by altering the sign and value of the OAM. By comparing the total OAM and spin angular momentum (SAM) on the incident plane to those on the focal plane, it is indicated that the incident OAM have no participation in the angular momentum intertransfer, and just play a role as a catalyst of local SAM conversion. Such an effect of OAM sheds new light on the optical spin-orbit interaction in tight-focusing processes. The resultant three-dimensional spin states may provide more degrees of freedom in optical manipulation and spin-dependent directive coupling.

Spin-Swapping Transport and Torques in Ultrathin Magnetic Bilayers

NASA Astrophysics Data System (ADS)

Saidaoui, Hamed Ben Mohamed; Manchon, A.

2016-07-01

Planar spin transport in disordered ultrathin magnetic bilayers comprising a ferromagnet and a normal metal (typically used for spin pumping, spin Seebeck and spin-orbit torque experiments) is investigated theoretically. Using a tight-binding model that puts the extrinsic spin Hall effect and spin swapping on equal footing, we show that the nature of spin-orbit coupled transport dramatically depends on the ratio between the layer thickness d and the mean free path λ . While the spin Hall effect dominates in the diffusive limit (d ≫λ ), spin swapping dominates in the Knudsen regime (d ≲λ ). A remarkable consequence is that spin swapping induces a substantial fieldlike torque in the Knudsen regime.

Interplay of 3 d - and 5 d -sublattice magnetism in the double perovskite substitution series La2Zn1 -xCoxIrO6

NASA Astrophysics Data System (ADS)

Vogl, M.; Corredor, L. T.; Dey, T.; Morrow, R.; Scaravaggi, F.; Wolter, A. U. B.; Aswartham, S.; Wurmehl, S.; Büchner, B.

2018-01-01

We report on the interplay of 3 d - and 5 d -sublattice magnetism in polycrystalline samples of the double perovskite substitution series La2Zn1 -xCoxIrO6 . Powder x-ray diffraction reveals no major structural changes within the series. In magnetization measurements, a gradual shift of the transition temperature from TN ≈91 K for the Co parent compound to TN ≈8.7 K for the Zn parent compound is observed. The data on the Zn-rich members of the substitution series indicate that this is accompanied by changing roles of the 3 d sublattice of Co2 + and the strongly spin-orbit coupled 5 d -sublattice of Ir4 + with its jeff=1 /2 ground state, as a function of the Co/Zn ratio. Temperature-dependent specific-heat studies revealed a reduced magnetic entropy, pointing towards a large spin-orbit coupling and orbital contribution in the system.

Photo-modulation of the spin Hall conductivity of mono-layer transition metal dichalcogenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sengupta, Parijat; Bellotti, Enrico

2016-05-23

We report on a possible optical tuning of the spin Hall conductivity in mono-layer transition metal dichalcogenides. Light beams of frequencies much higher than the energy scale of the system (the off-resonant condition) do not excite electrons but rearrange the band structure. The rearrangement is quantitatively established using the Floquet formalism. For such a system of mono-layer transition metal dichalcogenides, the spin Hall conductivity (calculated with the Kubo expression in presence of disorder) exhibits a drop at higher frequencies and lower intensities. Finally, we compare the spin Hall conductivity of the higher spin-orbit coupled WSe{sub 2} to MoS{sub 2}; themore » spin Hall conductivity of WSe{sub 2} was found to be larger.« less

Breakdown of Spin-Waves in Anisotropic Magnets: Spin Dynamics in α-RuCl3

NASA Astrophysics Data System (ADS)

Winter, Stephen; Riedl, Kira; Honecker, Andreas; Valenti, Roser

α -RuCl3 has recently emerged as a promising candidate for realizing the hexagonal Kitaev model in a real material. Similar to the related iridates (e.g. Na2IrO3), complex magnetic interactions arise from a competition between various similar energy scales, including spin-orbit coupling (SOC), Hund's coupling, and crystal-field splitting. Due to this complexity, the correct spin Hamiltonians for such systems remain hotly debated. For α-RuCl3, a combination of ab-initio calculations, microscopic considerations, and analysis of the static magnetic response have suggested off-diagonal couplings (Γ ,Γ') and long-range interactions in addition to the expected Kitaev exchange. However, the effect of such additional terms on the dynamic response remains unclear. In this contribution, we discuss the recently measured inelastic neutron scattering response in the context of realistic proposals for the microscopic spin Hamiltonian. We conclude that the observed scattering continuum, which has been taken as a signature of Kitaev spin liquid physics, likely persists over a broad range of parameters.

Magnetic-field-induced effects in the electronic structure of itinerant d- and f-metal systems

NASA Astrophysics Data System (ADS)

Grechnev, G. E.

2009-08-01

A paramagnetic response of transition metals and itinerant d- and f-metal compounds in an external magnetic field is studied by employing ab initio full-potential LMTO method in the framework of the local spin density approximation. Within this method the anisotropy of the magnetic susceptibility in hexagonal close-packed transition metals is evaluated for the first time. This anisotropy is owing to the orbital Van Vleck-like paramagnetic susceptibility, which is revealed to be substantial in transition-metal systems due to hybridization effects in the electronic structure. It is demonstrated that compounds TiCo, Ni3Al, YCo2, CeCo2, YNi5, LaNi5, and CeNi5 are strong paramagnets close to the quantum critical point. For these systems the Stoner approximation underestimates the spin susceptibility, whereas the calculated field-induced spin moments provide a good description of the large paramagnetic susceptibilities and magnetovolume effects. It is revealed that an itinerant description of hybridized f electrons produces magnetic properties of the compounds CeCo2, CeNi5, UAl3, UGa3, USi3, and UGe3 in close agreement with experiment. In the uranium compounds UX3 the strong spin-orbit coupling together with hybridization effects give rise to peculiar magnetic states in which the field-induced spin moments are antiparallel to the external field, and the magnetic response is dominated by the orbital contribution.

Cluster-Glass Phase in Pyrochlore X Y Antiferromagnets with Quenched Disorder

NASA Astrophysics Data System (ADS)

Andrade, Eric C.; Hoyos, José A.; Rachel, Stephan; Vojta, Matthias

2018-03-01

We study the impact of quenched disorder (random exchange couplings or site dilution) on easy-plane pyrochlore antiferromagnets. In the clean system, order by disorder selects a magnetically ordered state from a classically degenerate manifold. In the presence of randomness, however, different orders can be chosen locally depending on details of the disorder configuration. Using a combination of analytical considerations and classical Monte Carlo simulations, we argue that any long-range-ordered magnetic state is destroyed beyond a critical level of randomness where the system breaks into magnetic domains due to random exchange anisotropies, becoming, therefore, a glass of spin clusters, in accordance with the available experimental data. These random anisotropies originate from off-diagonal exchange couplings in the microscopic Hamiltonian, establishing their relevance to other magnets with strong spin-orbit coupling.

Magnetic coupling of Fe-porphyrin molecules adsorbed on clean and c(2×2) oxygen-reconstructed Co(100) investigated by spin-polarized photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Weber, A. P.; Caruso, A. N.; Vescovo, E.; Ali, Md. E.; Tarafder, K.; Janjua, S. Z.; Sadowski, J. T.; Oppeneer, P. M.

2013-05-01

The spin-polarized electronic structure of iron octaethylporphyrin (FeOEP) molecules adsorbed on a pristine and on a c(2×2) oxygen-reconstructed Co(100) surface has been analyzed by means of spin-polarized photoemission spectroscopy (SPPES) and first-principles density functional theory with the on-site Coulomb repulsion U term (DFT+U) calculations with and without Van der Waals corrections. The aim is to examine the magnetic exchange mechanism between the FeOEP molecules and the Co(100) substrate in the presence or absence of the oxygen mediator. The results demonstrate that the magnetic coupling from the ferromagnetic substrate to the adsorbed FeOEP molecules is ferromagnetic, whereas, the coupling is antiferromagnetic for the FeOEP on the c(2×2)O/Co(100) system. Spin-resolved partial densities of states extracted from ab initio DFT+U modeling are in fairly good comparison with the electronic spectral densities seen in angle-integrated SPPES energy dispersion curves for submonolayer coverages of FeOEP. Through combined analysis of these spectra and theoretical results, we determine that hybridization of 2p orbitals of N and O with Co 3d orbitals facilitates indirect magnetic exchange interactions between Fe and Co, whereas, a direct Fe-Co interaction involving the Fe dz2 orbital is also found for FeOEP on Co. It is observed through SPPES that the spin polarization of the photoemission-visible molecular overlayers decreases to zero as coverage is increased beyond the submonolayer regime, indicating that only interfacial magnetic coupling is at work. Microspot low-energy electron diffraction and low-energy electron microscopy were performed to characterize the physical order of the molecular coverage, revealing that FeOEP structural domains are orders of magnitude greater in size on c(2×2)O/Co(100) than on clean Co(100), which coincides with reduced scattering from the disorder and sharper features seen in SPPES.

Slave boson theory of orbital differentiation with crystal field effects: Application to UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lanatà, Nicola; Yao, Yongxin; Deng, Xiaoyu

We derive an exact operatorial reformulation of the rotational invariant slave boson method, and we apply it to describe the orbital differentiation in strongly correlated electron systems starting from first principles. The approach enables us to treat strong electron correlations, spin-orbit coupling, and crystal field splittings on the same footing by exploiting the gauge invariance of the mean-field equations. Furthermore, we apply our theory to the archetypical nuclear fuel UO 2 and show that the ground state of this system displays a pronounced orbital differentiation within the 5f manifold, with Mott-localized Γ 8 and extended Γ 7 electrons.

Slave boson theory of orbital differentiation with crystal field effects: Application to UO 2

DOE PAGES

Lanatà, Nicola; Yao, Yongxin; Deng, Xiaoyu; ...

2017-03-23

We derive an exact operatorial reformulation of the rotational invariant slave boson method, and we apply it to describe the orbital differentiation in strongly correlated electron systems starting from first principles. The approach enables us to treat strong electron correlations, spin-orbit coupling, and crystal field splittings on the same footing by exploiting the gauge invariance of the mean-field equations. Furthermore, we apply our theory to the archetypical nuclear fuel UO 2 and show that the ground state of this system displays a pronounced orbital differentiation within the 5f manifold, with Mott-localized Γ 8 and extended Γ 7 electrons.

Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application to UO_{2}.

PubMed

Lanatà, Nicola; Yao, Yongxin; Deng, Xiaoyu; Dobrosavljević, Vladimir; Kotliar, Gabriel

2017-03-24

We derive an exact operatorial reformulation of the rotational invariant slave boson method, and we apply it to describe the orbital differentiation in strongly correlated electron systems starting from first principles. The approach enables us to treat strong electron correlations, spin-orbit coupling, and crystal field splittings on the same footing by exploiting the gauge invariance of the mean-field equations. We apply our theory to the archetypical nuclear fuel UO_{2} and show that the ground state of this system displays a pronounced orbital differentiation within the 5f manifold, with Mott-localized Γ_{8} and extended Γ_{7} electrons.

Phase-space methods for the spin dynamics in condensed matter systems

PubMed Central

Hurst, Jérôme; Manfredi, Giovanni

2017-01-01

Using the phase-space formulation of quantum mechanics, we derive a four-component Wigner equation for a system composed of spin- fermions (typically, electrons) including the Zeeman effect and the spin–orbit coupling. This Wigner equation is coupled to the appropriate Maxwell equations to form a self-consistent mean-field model. A set of semiclassical Vlasov equations with spin effects is obtained by expanding the full quantum model to first order in the Planck constant. The corresponding hydrodynamic equations are derived by taking velocity moments of the phase-space distribution function. A simple closure relation is proposed to obtain a closed set of hydrodynamic equations. This article is part of the themed issue ‘Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces’. PMID:28320903

Inverse spin Hall effect from pulsed spin current in organic semiconductors with tunable spin-orbit coupling.

PubMed

Sun, Dali; van Schooten, Kipp J; Kavand, Marzieh; Malissa, Hans; Zhang, Chuang; Groesbeck, Matthew; Boehme, Christoph; Valy Vardeny, Z

2016-08-01

Exploration of spin currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates is appealing for potential spintronics applications. Owing to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals in OSECs using pulsed ferromagnetic resonance, where the ISHE is two to three orders of magnitude larger compared to cw excitation. This strong ISHE enables us to investigate a variety of OSECs ranging from π-conjugated polymers with strong SOC that contain intrachain platinum atoms, to weak SOC polymers, to C60 films, where the SOC is predominantly caused by the curvature of the molecule's surface. The pulsed-ISHE technique offers a robust route for efficient injection and detection schemes of spin currents at room temperature, and paves the way for spin orbitronics in plastic materials.

Mott-metal transition in layered perovskite iridate thin films via field-effect doping

NASA Astrophysics Data System (ADS)

Cheema, Suraj; Turcaud, Jeremy; Nelson, Chris; Salahuddin, Sayeef; Ramesh, Ramamoorthy

We report on electrostatic gating of spin-orbit coupled Mott insulator Sr2IrO4 (Sr214) via ferroelectric field effect doping. Field effect doping has been used to modulate electronic phenomena in emerging 2D systems and strongly correlated oxides, but 5 d systems with large spin-orbit coupling have yet to be explored. Upon switching the polarization field of ferroelectric Pb(Zr20Ti80)O3 (PZT) to the down-poled (electron-accumulation) state, temperature-dependent resistivity measurements indicate extremely metallic behavior in the ultrathin Sr214 channel. This work successfully closes the Mott gap in Sr214 in a ''clean'' doping environment free of chemical disorder, thereby strengthening the link to the isostrucutral high-Tc cuprates, as Sr214 has been predicted to host d-wave superconductivity upon electron doping the parent antiferromagnetic insulating phase. Furthermore, the metallic behavior in Sr214 persists for thickness beyond the expected screening length, suggestive of a collective carrier delocalization mechanism. Electrostatically doped carriers prove to be a useful method for tuning the competition between spin-orbit and Coulomb interactions in order to trigger novel phase transitions, such as the Mott-metal crossover. This work was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231.

Andreev spectrum with high spin-orbit interactions: Revealing spin splitting and topologically protected crossings

NASA Astrophysics Data System (ADS)

Murani, A.; Chepelianskii, A.; Guéron, S.; Bouchiat, H.

2017-10-01

In order to point out experimentally accessible signatures of spin-orbit interaction, we investigate numerically the Andreev spectrum of a multichannel mesoscopic quantum wire (N) with high spin-orbit interaction coupled to superconducting electrodes (S), contrasting topological and nontopological behaviors. In the nontopological case (square lattice with Rashba interactions), we find that the Kramers degeneracy of Andreev levels is lifted by a phase difference between the S reservoirs except at multiples of π , when the normal quantum wires can host several conduction channels. The level crossings at these points invariant by time-reversal symmetry are not lifted by disorder. Whereas the dc Josephson current is insensitive to these level crossings, the high-frequency admittance (susceptibility) at finite temperature reveals these level crossings and the lifting of their degeneracy at π by a small Zeeman field. We have also investigated the hexagonal lattice with intrinsic spin-orbit interaction in the range of parameters where it is a two-dimensional topological insulator with one-dimensional helical edges protected against disorder. Nontopological superconducting contacts can induce topological superconductivity in this system characterized by zero-energy level crossing of Andreev levels. Both Josephson current and finite-frequency admittance carry then very specific signatures at low temperature of this disorder-protected Andreev level crossing at π and zero energy.

Spin-orbit configuration interaction calculation of the potential energy curves of iodine oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roszak, S.; Krauss, M.; Alekseyev, A.B.

2000-04-06

An ab initio configuration interaction (CI) study including spin-orbit coupling is carried out for the ground and excited states of the IO radical by employing relativistic effective core potentials. The computed spectroscopic constants are in good agreement with available experimental data, with some tendency to underestimate the strength of bonding. The first excited state, a{sup 4}{Sigma}{sup {minus}}, which has not yet been observed experimentally, is predicted to be bound by 30.1 kJ/mol and to have a significantly larger equilibrium distance than the ground state. It is split by spin-orbit interaction into 1/2 and 3/2 components, with the 1/2 component beingmore » the lower one with a calculated spin-orbit splitting of 210 cm{sup {minus}1}. The most interesting state in the low-energy IO spectrum, A{sub 1}{sup 2}{Pi}{sub 3/2}, is shown to be predissociated due to interaction with a number of repulsive electronic states. Predissociation of the A{sup 1}, {nu}{prime} = 0, 1 vibrational levels is attributed to a fairly weak spin-orbit coupling with the {sup 2}{Delta}{sub 3/2} state, while rotationally dependent predissociation of the {nu}{prime} = 2 level is explained by the coupling with the 1/2(III) state having mainly {sup 2}{Sigma}{sup {minus}} character. Strong predissociation of the {nu}{prime} {ge} 4 levels is attributed to interaction with the higher-lying {Omega} = 3/2 states, with predominantly {sup 4}{Sigma}{sup +} and {sup 4}{Delta} origin.« less

Photodissociation of the CH3O and CH3S radical molecules: An ab initio electronic structure study

PubMed Central

Bouallagui, A.; Zanchet, A.; Yazidi, O.; Jaïdane, N.; Bañares, L.; Senent, M.L.; García-Vela, A.

2018-01-01

The electronic states and the spin-orbit couplings between them involved in the photodissociation process of the radical molecules CH3X, CH3X → CH3 + X(X = O, S), taking place after the Ā(2A1) ← X̄(2E) transition, have been investigated using highly correlated ab initio techniques. A two-dimensional representation of both the potential-energy surfaces (PESs) and the couplings is generated. This description includes the C-X dissociative mode and the CH3 umbrella mode. Spin-orbit effects are found to play a relevant role on the shape of the excited state potential-energy surfaces, particularly in the CH3S case where the spin-orbit couplings are more than twice more intense than in CH3O. The potential surfaces and couplings reported here for the present set of electronic states allow for the first complete description of the above photodissociation process. The different photodissociation mechanisms are analyzed and discussed in the light of the results obtained. PMID:29143005

Spin-Orbit Dimers and Noncollinear Phases in d1 Cubic Double Perovskites

NASA Astrophysics Data System (ADS)

Romhányi, Judit; Balents, Leon; Jackeli, George

2017-05-01

We formulate and study a spin-orbital model for a family of cubic double perovskites with d1 ions occupying a frustrated fcc sublattice. A variational approach and a complementary analytical analysis reveal a rich variety of phases emerging from the interplay of Hund's rule and spin-orbit coupling. The phase digram includes noncollinear ordered states, with or without a net moment, and, remarkably, a large window of a nonmagnetic disordered spin-orbit dimer phase. The present theory uncovers the physical origin of the unusual amorphous valence bond state experimentally suggested for Ba2B Mo O6 (B =Y , Lu) and predicts possible ordered patterns in Ba2B Os O6 (B =Na , Li) compounds.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

DOE PAGES

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide; ...

2017-11-16

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Domain wall dynamics driven by spin transfer torque and the spin-orbit field.

PubMed

Hayashi, Masamitsu; Nakatani, Yoshinobu; Fukami, Shunsuke; Yamanouchi, Michihiko; Mitani, Seiji; Ohno, Hideo

2012-01-18

We have studied current-driven dynamics of domain walls when an in-plane magnetic field is present in perpendicularly magnetized nanowires using an analytical model and micromagnetic simulations. We model an experimentally studied system, ultrathin magnetic nanowires with perpendicular anisotropy, where an effective in-plane magnetic field is developed when current is passed along the nanowire due to the Rashba-like spin-orbit coupling. Using a one-dimensional model of a domain wall together with micromagnetic simulations, we show that the existence of such in-plane magnetic fields can either lower or raise the threshold current needed to cause domain wall motion. In the presence of the in-plane field, the threshold current differs for positive and negative currents for a given wall chirality, and the wall motion becomes sensitive to out-of-plane magnetic fields. We show that large non-adiabatic spin torque can counteract the effect of the in-plane field.

Ultrafast intersystem crossings in Fe-Co Prussian blue analogues

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Veenendaal, Michel

Ultrafast spincrossover is studied in Fe-Co Prussian blue analogues using a dissipative quantum-mechanical model of a cobalt ion coupled to a breathing mode. All electronic interactions are treated on an equal footing. It is theoretically demonstrated that the divalent cobalt ion reaches 90% of the S = 3/2 value within 20 fs after photoexciting a low-spin Co 3+ ion by an iron-to-cobalt charge transfer. The doublet-to-quartet spin crossover is significantly faster than the oscillation period of the breathing mode. The system relaxes to the lowest manifold of divalent cobalt ( 4T 1) in 150-200 fs. In conclusion, strong oscillations inmore » spin-orbit coupling and the involvement of higher-lying quartets are found.« less

Ultrafast intersystem crossings in Fe-Co Prussian blue analogues

DOE PAGES

van Veenendaal, Michel

2017-07-27

Ultrafast spincrossover is studied in Fe-Co Prussian blue analogues using a dissipative quantum-mechanical model of a cobalt ion coupled to a breathing mode. All electronic interactions are treated on an equal footing. It is theoretically demonstrated that the divalent cobalt ion reaches 90% of the S = 3/2 value within 20 fs after photoexciting a low-spin Co 3+ ion by an iron-to-cobalt charge transfer. The doublet-to-quartet spin crossover is significantly faster than the oscillation period of the breathing mode. The system relaxes to the lowest manifold of divalent cobalt ( 4T 1) in 150-200 fs. In conclusion, strong oscillations inmore » spin-orbit coupling and the involvement of higher-lying quartets are found.« less

Dirac topological insulator in the dz2 manifold of a honeycomb oxide

NASA Astrophysics Data System (ADS)

Lado, J. L.; Pardo, V.

2016-09-01

We show by means of ab initio calculations and tight-binding modeling that an oxide system based on a honeycomb lattice can sustain topologically nontrivial states if a single orbital dominates the spectrum close to the Fermi level. In such a situation, the low-energy spectrum is described by two Dirac equations that become nontrivially gapped when spin-orbit coupling (SOC) is switched on. We provide one specific example but the recipe is general. We discuss a realization of this starting from a conventional spin-1/2 honeycomb antiferromagnet whose states close to the Fermi energy are dz2 orbitals. Switching off magnetism by atomic substitution and ensuring that the electronic structure becomes two-dimensional is sufficient for topologicality to arise in such a system. By deriving a tight-binding Wannier Hamiltonian, we find that the gap in such a model scales linearly with SOC, opposed to other oxide-based topological insulators, where smaller gaps tend to appear by construction of the lattice. We show that the quantum spin Hall state in this system survives in the presence of off-plane magnetism and the orbital magnetic field and we discuss its Landau level spectra, showing that our recipe provides a dz2 realization of the Kane-Mele model.

Theory of mode coupling in spin torque oscillators coupled to a thermal bath of magnons

NASA Astrophysics Data System (ADS)

Zhou, Yan; Zhang, Shulei; Li, Dong; Heinonen, Olle

Recently, numerous experimental investigations have shown that the dynamics of a single spin torque oscillator (STO) exhibits complex behavior stemming from interactions between two or more modes of the oscillator. Examples are the observed mode-hopping and mode coexistence. There has been some initial work indicating how the theory for a single-mode (macro-spin) spin torque oscillator should be generalized to include several modes and the interactions between them. In this work, we rigorously derive such a theory starting with the generalized Landau-Lifshitz-Gilbert equation in the presence of the current-driven spin transfer torques. We will first show, in general, that how a linear mode coupling would arise through the coupling of the system to a thermal bath of magnons, which implies that the manifold of orbits and fixed points may shift with temperature. We then apply our theory to two experimentally interesting systems: 1) a STO patterned into nano-pillar with circular or elliptical cross-sections and 2) a nano-contact STO. For both cases, we found that in order to get mode coupling, it would be necessary to have either a finite in-plane component of the external field or an Oersted field. We will also discuss the temperature dependence of the linear mode coupling. Y. Zhou acknowledges the support by the Seed Funding Program for Basic Research from the University of Hong Kong, and University Grants Committee of Hong Kong (Contract No. AoE/P-04/08).

Electronic transport in the quantum spin Hall state due to the presence of adatoms in graphene

NASA Astrophysics Data System (ADS)

Lima, Leandro; Lewenkopf, Caio

Heavy adatoms, even at low concentrations, are predicted to turn a graphene sheet into a topological insulator with substantial gap. The adatoms mediate the spin-orbit coupling that is fundamental to the quantum spin Hall effect. The adatoms act as local spin-orbit scatterer inducing hopping processes between distant carbon atoms giving origin to transverse spin currents. Although there are effective models that describe spectral properties of such systems with great detail, quantitative theoretical work for the transport counterpart is still lacking. We developed a multiprobe recursive Green's function technique with spin resolution to analyze the transport properties for large geometries. We use an effective tight-binding Hamiltonian to describe the problem of adatoms randomly placed at the center of the honeycomb hexagons, which is the case for most transition metals. Our choice of current and voltage probes is favorable to experiments since it filters the contribution of only one spin orientation, leading to a quantized spin Hall conductance of e2 / h . We also discuss the electronic propagation in the system by imaging the local density of states and the electronic current densities. The authors acknowledge the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlaufman, Kevin C., E-mail: kcs@ucolick.or

Of the 26 transiting exoplanet systems with measurements of the Rossiter-McLaughlin (RM) effect, eight have now been found to be significantly spin-orbit misaligned in the plane of the sky (i.e., RM misalignment angle |{lambda}| {approx}> 30{sup 0} and inconsistent with {lambda} = 0{sup 0}). Unfortunately, the RM effect does not constrain the complement misalignment angle between the orbit of the planet and the spin of its host star along the line of sight (LOS). I use a simple model of stellar rotation benchmarked with observational data to statistically identify 10 exoplanet systems from a sample of 75 for which theremore » is likely a significant degree of spin-orbit misalignment along the LOS: HAT-P-7, HAT-P-14, HAT-P-16, HD 17156, Kepler-5, Kepler-7, TrES-4, WASP-1, WASP-12, and WASP-14. All 10 systems have host stellar masses M {sub *} in the range 1.2 M {sub sun} {approx}< M {sub *} {approx}< 1.5 M {sub sun}, and the probability of this occurrence by chance is less than one in ten thousand. In addition, the planets in the candidate-misaligned systems are preferentially massive and eccentric. The coupled distribution of misalignment from the RM effect and from this analysis suggests that transiting exoplanets are more likely to be spin-orbit aligned than expected given predictions for a transiting planet population produced entirely by planet-planet scattering or Kozai cycles and tidal friction. For that reason, there are likely two populations of close-in exoplanet systems: a population of aligned systems and a population of apparently misaligned systems in which the processes that lead to misalignment or to the survival of misaligned systems operate more efficiently in systems with massive stars and planets.« less

Superconductivity in three-dimensional spin-orbit coupled semimetals

NASA Astrophysics Data System (ADS)

Savary, Lucile; Ruhman, Jonathan; Venderbos, Jörn W. F.; Fu, Liang; Lee, Patrick A.

2017-12-01

Motivated by the experimental detection of superconductivity in the low-carrier density half-Heusler compound YPtBi, we study the pairing instabilities of three-dimensional strongly spin-orbit coupled semimetals with a quadratic band touching point. In these semimetals the electronic structure at the Fermi energy is described by spin j =3/2 quasiparticles, which are fundamentally different from those in ordinary metals with spin j =1/2 . For both local and nonlocal pairing channels in j =3/2 materials we develop a general approach to analyzing pairing instabilities, thereby providing the computational tools needed to investigate the physics of these systems beyond phenomenological considerations. Furthermore, applying our method to a generic density-density interaction, we establish that: (i) The pairing strengths in the different symmetry channels uniquely encode the j =3/2 nature of the Fermi surface band structure—a manifestation of the fundamental difference with ordinary metals. (ii) The leading odd-parity pairing instabilities are different for electron doping and hole doping. Finally, we argue that polar phonons, i.e., Coulomb interactions mediated by the long-ranged electric polarization of the optical phonon modes, provide a coupling strength large enough to account for a Kelvin-range transition temperature in the s -wave channel, and are likely to play an important role in the overall attraction in non-s -wave channels. Moreover, the explicit calculation of the coupling strengths allows us to conclude that the two largest non-s -wave contributions occur in nonlocal channels, in contrast with what has been commonly assumed.

Theory of proximity-induced exchange coupling in graphene on hBN/(Co, Ni)

NASA Astrophysics Data System (ADS)

Zollner, Klaus; Gmitra, Martin; Frank, Tobias; Fabian, Jaroslav

2016-10-01

Graphene, being essentially a surface, can borrow some properties of an insulating substrate (such as exchange or spin-orbit couplings) while still preserving a great degree of autonomy of its electronic structure. Such derived properties are commonly labeled as proximity. Here we perform systematic first-principles calculations of the proximity exchange coupling, induced by cobalt (Co) and nickel (Ni) in graphene, via a few (up to three) layers of hexagonal boron nitride (hBN). We find that the induced spin splitting of the graphene bands is of the order of 10 meV for a monolayer of hBN, decreasing in magnitude but alternating in sign by adding each new insulating layer. We find that the proximity exchange can be giant if there is a resonant d level of the transition metal close to the Dirac point. Our calculations suggest that this effect could be present in Co heterostructures, in which a d level strongly hybridizes with the valence-band orbitals of graphene. Since this hybridization is spin dependent, the proximity spin splitting is unusually large, about 10 meV even for two layers of hBN. An external electric field can change the offset of the graphene and transition-metal orbitals and can lead to a reversal of the sign of the exchange parameter. This we predict to happen for the case of two monolayers of hBN, enabling electrical control of proximity spin polarization (but also spin injection) in graphene/hBN/Co structures. Nickel-based heterostructures show weaker proximity effects than cobalt heterostructures. We introduce two phenomenological models to describe the first-principles data. The minimal model comprises the graphene (effective) pz orbitals and can be used to study transport in graphene with proximity exchange, while the pz-d model also includes hybridization with d orbitals, which is important to capture the giant proximity exchange. Crucial to both models is the pseudospin-dependent exchange coupling, needed to describe the different spin splittings of the valence and conduction bands.

Engineering the quantum anomalous Hall effect in graphene with uniaxial strains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, G. S., E-mail: ginetom@gmail.com; Guassi, M. R.; Qu, F.

2013-12-28

We theoretically investigate the manipulation of the quantum anomalous Hall effect (QAHE) in graphene by means of the uniaxial strain. The values of Chern number and Hall conductance demonstrate that the strained graphene in presence of Rashba spin-orbit coupling and exchange field, for vanishing intrinsic spin-orbit coupling, possesses non-trivial topological phase, which is robust against the direction and modulus of the strain. Besides, we also find that the interplay between Rashba and intrinsic spin-orbit couplings results in a topological phase transition in the strained graphene. Remarkably, as the strain strength is increased beyond approximately 7%, the critical parameters of themore » exchange field for triggering the quantum anomalous Hall phase transition show distinct behaviors—decrease (increase) for strains along zigzag (armchair) direction. Our findings open up a new platform for manipulation of the QAHE by an experimentally accessible strain deformation of the graphene structure, with promising application on novel quantum electronic devices with high efficiency.« less

Engineering hybrid epitaxial InAsSb/Al nanowires for stronger topological protection

NASA Astrophysics Data System (ADS)

Sestoft, Joachim E.; Kanne, Thomas; Gejl, Aske Nørskov; von Soosten, Merlin; Yodh, Jeremy S.; Sherman, Daniel; Tarasinski, Brian; Wimmer, Michael; Johnson, Erik; Deng, Mingtang; Nygârd, Jesper; Jespersen, Thomas Sand; Marcus, Charles M.; Krogstrup, Peter

2018-04-01

The combination of strong spin-orbit coupling, large g factors, and the coupling to a superconductor can be used to create a topologically protected state in a semiconductor nanowire. Here we report on growth and characterization of hybrid epitaxial InAsSb/Al nanowires, with varying composition and crystal structure. We find the strongest spin-orbit interaction at intermediate compositions in zinc-blende InAs1 -xSbx nanowires, exceeding that of both InAs and InSb materials, confirming recent theoretical studies. We show that the epitaxial InAsSb/Al interface allows for a hard induced superconducting gap and 2 e transport in Coulomb charging experiments, similarly to experiments on InAs/Al and InSb/Al materials, and find measurements consistent with topological phase transitions at low magnetic fields due to large effective g factors. Finally we present a method to grow pure wurtzite InAsSb nanowires which are predicted to exhibit even stronger spin-orbit coupling than the zinc-blende structure.

Formation of a Spin Texture in a Quantum Gas Coupled to a Cavity

NASA Astrophysics Data System (ADS)

Landini, M.; Dogra, N.; Kroeger, K.; Hruby, L.; Donner, T.; Esslinger, T.

2018-06-01

We observe cavity mediated spin-dependent interactions in an off-resonantly driven multilevel atomic Bose-Einstein condensate that is strongly coupled to an optical cavity. Applying a driving field with adjustable polarization, we identify the roles of the scalar and the vectorial components of the atomic polarizability tensor for single and multicomponent condensates. Beyond a critical strength of the vectorial coupling, we infer the formation of a spin texture in a condensate of two internal states from the analysis of the cavity output field. Our work provides perspectives for global dynamical gauge fields and self-consistently spin-orbit coupled gases.

Perturbational treatment of spin-orbit coupling for generally applicable high-level multi-reference methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mai, Sebastian; Marquetand, Philipp; González, Leticia

2014-08-21

An efficient perturbational treatment of spin-orbit coupling within the framework of high-level multi-reference techniques has been implemented in the most recent version of the COLUMBUS quantum chemistry package, extending the existing fully variational two-component (2c) multi-reference configuration interaction singles and doubles (MRCISD) method. The proposed scheme follows related implementations of quasi-degenerate perturbation theory (QDPT) model space techniques. Our model space is built either from uncontracted, large-scale scalar relativistic MRCISD wavefunctions or based on the scalar-relativistic solutions of the linear-response-theory-based multi-configurational averaged quadratic coupled cluster method (LRT-MRAQCC). The latter approach allows for a consistent, approximatively size-consistent and size-extensive treatment of spin-orbitmore » coupling. The approach is described in detail and compared to a number of related techniques. The inherent accuracy of the QDPT approach is validated by comparing cuts of the potential energy surfaces of acrolein and its S, Se, and Te analoga with the corresponding data obtained from matching fully variational spin-orbit MRCISD calculations. The conceptual availability of approximate analytic gradients with respect to geometrical displacements is an attractive feature of the 2c-QDPT-MRCISD and 2c-QDPT-LRT-MRAQCC methods for structure optimization and ab inito molecular dynamics simulations.« less

Electrical Spin Driving by g -Matrix Modulation in Spin-Orbit Qubits

NASA Astrophysics Data System (ADS)

Crippa, Alessandro; Maurand, Romain; Bourdet, Léo; Kotekar-Patil, Dharmraj; Amisse, Anthony; Jehl, Xavier; Sanquer, Marc; Laviéville, Romain; Bohuslavskyi, Heorhii; Hutin, Louis; Barraud, Sylvain; Vinet, Maud; Niquet, Yann-Michel; De Franceschi, Silvano

2018-03-01

In a semiconductor spin qubit with sizable spin-orbit coupling, coherent spin rotations can be driven by a resonant gate-voltage modulation. Recently, we have exploited this opportunity in the experimental demonstration of a hole spin qubit in a silicon device. Here we investigate the underlying physical mechanisms by measuring the full angular dependence of the Rabi frequency, as well as the gate-voltage dependence and anisotropy of the hole g factor. We show that a g -matrix formalism can simultaneously capture and discriminate the contributions of two mechanisms so far independently discussed in the literature: one associated with the modulation of the g factor, and measurable by Zeeman energy spectroscopy, the other not. Our approach has a general validity and can be applied to the analysis of other types of spin-orbit qubits.

(1) Majorana fermions in pinned vortices; (2) Manipulating and probing Majorana fermions using superconducting circuits; and (3) Controlling a nanowire spin-orbit qubit via electric-dipole spin resonance

NASA Astrophysics Data System (ADS)

Nori, Franco

2014-03-01

We study a heterostructure which consists of a topological insulator and a superconductor with a hole. This system supports a robust Majorana fermion state bound to the vortex core. We study the possibility of using scanning tunneling spectroscopy (i) to detect the Majorana fermion in this setup and (ii) to study excited states bound to the vortex core. The Majorana fermion manifests itself as an H-dependent zero-bias anomaly of the tunneling conductance. The excited states spectrum differs from the spectrum of a typical Abrikosov vortex, providing additional indirect confirmation of the Majorana state observation. We also study how to manipulate and probe Majorana fermions using super-conducting circuits. In we consider a semiconductor nanowire quantum dot with strong spin-orbit coupling (SOC), which can be used to achieve a spin-orbit qubit. In contrast to a spin qubit, the spin-orbit qubit can respond to an external ac electric field, i.e., electric-dipole spin resonance. We develop a theory that can apply in the strong SOC regime. We find that there is an optimal SOC strength ηopt = √ 2/2, where the Rabi frequency induced by the ac electric field becomes maximal. Also, we show that both the level spacing and the Rabi frequency of the spin-orbit qubit have periodic responses to the direction of the external static magnetic field. These responses can be used to determine the SOC in the nanowire. FN is partly supported by the RIKEN CEMS, iTHES Project, MURI Center for Dynamic Magneto-Optics, JSPS-RFBR Contract No. 12-02-92100, Grant-in-Aid for Scientific Research (S), MEXT Kakenhi on Quantum Cybernetics, and the JSPS via its FIRST program.

Electron spin relaxation in a transition-metal dichalcogenide quantum dot

NASA Astrophysics Data System (ADS)

Pearce, Alexander J.; Burkard, Guido

2017-06-01

We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin-orbit admixture mechanisms allow for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as \\propto B 6 for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but depends strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.

Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; Demann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carvalho, R. S.; Ávila, H. C.; Cremona, M., E-mail: cremona@fis.puc-rio.br

The recently discovered organic magnetoresistance effect (OMAR) reveals the spin-dependent behavior of the charge transport in organic semiconductors. So far, it is known that hyperfine interactions play an important role in this phenomenon and also that spin-orbit coupling is negligible for light-atom based compounds. However, in the presence of heavy atoms, spin-orbit interactions should play an important role in OMAR. It is known that these interactions are responsible for singlet and triplet states mixing via intersystem crossing and the change of spin-charge relaxation time in the charge mobility process. In this work, we report a dramatic change in the OMARmore » effect caused by the presence of strong intramolecular spin-orbit coupling in a series of rare-earth quinolate organic complex-based devices. Our data show a different OMAR lineshape compared with the OMAR lineshape of tris(8-hydroxyquinolinate) aluminum-based devices, which are well described in the literature. In addition, electronic structure calculations based on density functional theory help to establish the connection between this results and the presence of heavy central ions in the different complexes.« less

Enhanced spin-orbit coupling in dilute fluorinated graphene

NASA Astrophysics Data System (ADS)

Avsar, Ahmet; Lee, Jong Hak; Koon, Gavin Kok Wai; Özyilmaz, Barbaros

2015-12-01

The preservation and manipulation of a spin state mainly depends on the strength of the spin-orbit interaction. For pristine graphene, the intrinsic spin-orbit coupling (SOC) is only in the order of few μeV, which makes it almost impossible to be used as an active element in future electric field controlled spintronics devices. This stimulates the development of a systematic method for extrinsically enhancing the SOC of graphene. In this letter, we study the strength of SOC in weakly fluorinated graphene devices. We observe high non-local signals even without applying any external magnetic field. The magnitude of the signal increases with increasing fluorine adatom coverage. From the length dependence of the non-local transport measurements, we obtain SOC values of ˜5.1 meV and ˜9.1 meV for the devices with ˜0.005% and ˜0.06% fluorination, respectively. Such a large enhancement, together with the high charge mobility of fluorinated samples (μ ˜ 4300 cm2 V-1 s-1-2700 cm2 V-1 s-1), enables the detection of the spin Hall effect even at room temperature.

Topical review: spins and mechanics in diamond

NASA Astrophysics Data System (ADS)

Lee, Donghun; Lee, Kenneth W.; Cady, Jeffrey V.; Ovartchaiyapong, Preeti; Bleszynski Jayich, Ania C.

2017-03-01

There has been rapidly growing interest in hybrid quantum devices involving a solid-state spin and a macroscopic mechanical oscillator. Such hybrid devices create exciting opportunities to mediate interactions between disparate quantum bits (qubits) and to explore the quantum regime of macroscopic mechanical objects. In particular, a system consisting of the nitrogen-vacancy defect center (NV center) in diamond coupled to a high-quality-factor mechanical oscillator is an appealing candidate for such a hybrid quantum device, as it utilizes the highly coherent and versatile spin properties of the defect center. In this paper, we will review recent experimental progress on diamond-based hybrid quantum devices in which the spin and orbital dynamics of single defects are driven by the motion of a mechanical oscillator. In addition, we discuss prospective applications for this device, including long-range, phonon-mediated spin-spin interactions, and phonon cooling in the quantum regime. We conclude the review by evaluating the experimental limitations of current devices and identifying alternative device architectures that may reach the strong coupling regime.

Room-temperature spin-orbit torque in NiMnSb

NASA Astrophysics Data System (ADS)

Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

2016-09-01

Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

Spin-dependent heat and thermoelectric currents in a Rashba ring coupled to a photon cavity

NASA Astrophysics Data System (ADS)

Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

2018-01-01

Spin-dependent heat and thermoelectric currents in a quantum ring with Rashba spin-orbit interaction placed in a photon cavity are theoretically calculated. The quantum ring is coupled to two external leads with different temperatures. In a resonant regime, with the ring structure in resonance with the photon field, the heat and the thermoelectric currents can be controlled by the Rashba spin-orbit interaction. The heat current is suppressed in the presence of the photon field due to contribution of the two-electron and photon replica states to the transport while the thermoelectric current is not sensitive to changes in parameters of the photon field. Our study opens a possibility to use the proposed interferometric device as a tunable heat current generator in the cavity photon field.

The Spin-Orbit Resonances of the Solar System: A Mathematical Treatment Matching Physical Data

NASA Astrophysics Data System (ADS)

Antognini, Francesco; Biasco, Luca; Chierchia, Luigi

2014-06-01

In the mathematical framework of a restricted, slightly dissipative spin-orbit model, we prove the existence of periodic orbits for astronomical parameter values corresponding to all satellites of the Solar System observed in exact spin-orbit resonance.

Quantum spin Hall phase in 2D trigonal lattice

PubMed Central

Wang, Z. F.; Jin, Kyung-Hwan; Liu, Feng

2016-01-01

The quantum spin Hall (QSH) phase is an exotic phenomena in condensed-matter physics. Here we show that a minimal basis of three orbitals (s, px, py) is required to produce a QSH phase via nearest-neighbour hopping in a two-dimensional trigonal lattice. Tight-binding model analyses and calculations show that the QSH phase arises from a spin–orbit coupling (SOC)-induced s–p band inversion or p–p bandgap opening at Brillouin zone centre (Γ point), whose topological phase diagram is mapped out in the parameter space of orbital energy and SOC. Remarkably, based on first-principles calculations, this exact model of QSH phase is shown to be realizable in an experimental system of Au/GaAs(111) surface with an SOC gap of ∼73 meV, facilitating the possible room-temperature measurement. Our results will extend the search for substrate supported QSH materials to new lattice and orbital types. PMID:27599580

Single-molecule quantum dot as a Kondo simulator

NASA Astrophysics Data System (ADS)

Hiraoka, R.; Minamitani, E.; Arafune, R.; Tsukahara, N.; Watanabe, S.; Kawai, M.; Takagi, N.

2017-06-01

Structural flexibility of molecule-based systems is key to realizing the novel functionalities. Tuning the structure in the atomic scale enables us to manipulate the quantum state in the molecule-based system. Here we present the reversible Hamiltonian manipulation in a single-molecule quantum dot consisting of an iron phthalocyanine molecule attached to an Au electrode and a scanning tunnelling microscope tip. We precisely controlled the position of Fe2+ ion in the molecular cage by using the tip, and tuned the Kondo coupling between the molecular spins and the Au electrode. Then, we realized the crossover between the strong-coupling Kondo regime and the weak-coupling regime governed by spin-orbit interaction in the molecule. The results open an avenue to simulate low-energy quantum many-body physics and quantum phase transition through the molecular flexibility.

Room-Temperature Spin-Orbit Torque Switching Induced by a Topological Insulator

NASA Astrophysics Data System (ADS)

Han, Jiahao; Richardella, A.; Siddiqui, Saima A.; Finley, Joseph; Samarth, N.; Liu, Luqiao

2017-08-01

The strongly spin-momentum coupled electronic states in topological insulators (TI) have been extensively pursued to realize efficient magnetic switching. However, previous studies show a large discrepancy of the charge-spin conversion efficiency. Moreover, current-induced magnetic switching with TI can only be observed at cryogenic temperatures. We report spin-orbit torque switching in a TI-ferrimagnet heterostructure with perpendicular magnetic anisotropy at room temperature. The obtained effective spin Hall angle of TI is substantially larger than the previously studied heavy metals. Our results demonstrate robust charge-spin conversion in TI and provide a direct avenue towards applicable TI-based spintronic devices.

ϕ Meson Spin Alignment and the Azimuthal Angle Dependence of Λ (Λ) Polarization in Au+Au collisions at RHIC

NASA Astrophysics Data System (ADS)

Tu, Biao

2018-02-01

Initial large global angular momentum in non-central relativistic heavy-ion collisions can produce strong vorticity, and through the spin-orbit coupling, causes the spin of particles to align with the system's global angular momentum. We present the azimuthal angle dependent (relative to the reaction plane) polarization for Λ and Λ in mid-central Au+Au collisions at = 200 GeV. We also present the ϕ meson spin alignment parameter, ρ00 in Au+Au collisions at = 19.6, 27, 39, 62.4 and 200 GeV. The implications of the results are discussed.

The Duffin-Kemmer-Petiau oscillator

NASA Technical Reports Server (NTRS)

Nedjadi, Youcef; Barrett, Roger

1995-01-01

In view of current interest in relativistic spin-one systems and the recent work on the Dirac Oscillator, we introduce the Duffin-Kemmer-Petiau (DKP) equation obtained by using an external potential linear in r. Since, in the non-relativistic limit, the spin 1 representation leads to a harmonic oscillator with a spin-orbit coupling of the Thomas form, we call the equation the DKP oscillator. This oscillator is a relativistic generalization of the quantum harmonic oscillator for scalar and vector bosons. We show that it conserves total angular momentum and that it is exactly solvable. We calculate and discuss the eigenspectrum of the DKP oscillator in the spin 1 representation.

Theoretical investigation of electronic states and spectroscopic properties of tellurium selenide molecule employing relativistic effective core potentials.

PubMed

Chattopadhyaya, Surya; Nath, Abhijit; Das, Kalyan Kumar

2014-04-24

Ab initio based relativistic configuration interaction calculations have been performed to study the electronic states and spectroscopic properties of tellurium selenide (TeSe) - the heaviest heteronuclear diatomic group 16-16 molecule. Potential energy curves of several spin-excluded (Λ-S) electronic states of TeSe have been constructed and spectroscopic constants of low-lying bound Λ-S states within 3.85 eV are reported in the first stage of calculations. The X(3)Σ(-), a(1)Δ and b(1)Σ(+) are found as the ground, first excited and second excited state, respectively, at the Λ-S level and all these three states are mainly dominated by …π(4)π(*2) configuration. The computed ground state dissociation energy is in very good agreement with the experimental results. In the next stage of calculations, effects of spin-orbit coupling on the potential energy curves and spectroscopic properties of the species are investigated in details and compared with the existing experimental results. After inclusion of spin-orbit coupling the X(3)(1)Σ(-)(0(+)) is found as the ground-state spin component of TeSe. The computed spin-orbit splitting between two components of X(3)Σ(-) state is 1285 cm(-1). Also, significant amount of spin-orbit splitting are found between spin-orbit components (Ω-components) of several other excited states. Transition moments of some important spin-allowed and spin-forbidden transitions are calculated from configuration interaction wave functions. The spin-allowed transition B(3)Σ(-)-X(3)Σ(-) and spin-forbidden transition b(1)Σ(+)(0(+))-X(3)(1)Σ(-)(0(+)) are found to be the strongest in their respective categories. Electric dipole moments of all the bound Λ-S states along with those of the two Ω-components of X(3)Σ(-) are also calculated in the present study. Copyright © 2014 Elsevier B.V. All rights reserved.

An atomic mean-field spin-orbit approach within exact two-component theory for a non-perturbative treatment of spin-orbit coupling

NASA Astrophysics Data System (ADS)

Liu, Junzi; Cheng, Lan

2018-04-01

An atomic mean-field (AMF) spin-orbit (SO) approach within exact two-component theory (X2C) is reported, thereby exploiting the exact decoupling scheme of X2C, the one-electron approximation for the scalar-relativistic contributions, the mean-field approximation for the treatment of the two-electron SO contribution, and the local nature of the SO interactions. The Hamiltonian of the proposed SOX2CAMF scheme comprises the one-electron X2C Hamiltonian, the instantaneous two-electron Coulomb interaction, and an AMF SO term derived from spherically averaged Dirac-Coulomb Hartree-Fock calculations of atoms; no molecular relativistic two-electron integrals are required. Benchmark calculations for bond lengths, harmonic frequencies, dipole moments, and electric-field gradients for a set of diatomic molecules containing elements across the periodic table show that the SOX2CAMF scheme offers a balanced treatment for SO and scalar-relativistic effects and appears to be a promising candidate for applications to heavy-element containing systems. SOX2CAMF coupled-cluster calculations of molecular properties for bismuth compounds (BiN, BiP, BiF, BiCl, and BiI) are also presented and compared with experimental results to further demonstrate the accuracy and applicability of the SOX2CAMF scheme.

Magnetism, superconductivity, and spontaneous orbital order in iron-based superconductors: Which comes first and why?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chubukov, Andrey V.; Khodas, M.; Fernandes, Rafael M.

Magnetism and nematic order are the two nonsuperconducting orders observed in iron-based superconductors. To elucidate the interplay between them and ultimately unveil the pairing mechanism, several models have been investigated. In models with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism, which induces orbital order. In models with quenched spin degrees of freedom, charge fluctuations promote spontaneous orbital order, which induces stripe magnetism. Here, we develop an unbiased approach, in which we treat magnetic and orbital fluctuations on equal footing. Key to our approach is the inclusion of the orbital character of the low-energy electronic states into renormalizationmore » group (RG) analysis. We analyze the RG flow of the couplings and argue that the same magnetic fluctuations, which are known to promote s ± superconductivity, also promote an attraction in the orbital channel, even if the bare orbital interaction is repulsive. We next analyze the RG flow of the susceptibilities and show that, if all Fermi pockets are small, the system first develops a spontaneous orbital order, then s ± superconductivity, and magnetic order does not develop down to T=0. We argue that this scenario applies to FeSe. In systems with larger pockets, such as BaFe 2As 2 and LaFeAsO, we find that the leading instability is either towards a spin-density wave or superconductivity. We argue that in this situation nematic order is caused by composite spin fluctuations and is vestigial to stripe magnetism. Finally, our results provide a unifying description of different iron-based materials.« less

Magnetism, superconductivity, and spontaneous orbital order in iron-based superconductors: Which comes first and why?

DOE PAGES

Chubukov, Andrey V.; Khodas, M.; Fernandes, Rafael M.

2016-12-02

Magnetism and nematic order are the two nonsuperconducting orders observed in iron-based superconductors. To elucidate the interplay between them and ultimately unveil the pairing mechanism, several models have been investigated. In models with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism, which induces orbital order. In models with quenched spin degrees of freedom, charge fluctuations promote spontaneous orbital order, which induces stripe magnetism. Here, we develop an unbiased approach, in which we treat magnetic and orbital fluctuations on equal footing. Key to our approach is the inclusion of the orbital character of the low-energy electronic states into renormalizationmore » group (RG) analysis. We analyze the RG flow of the couplings and argue that the same magnetic fluctuations, which are known to promote s ± superconductivity, also promote an attraction in the orbital channel, even if the bare orbital interaction is repulsive. We next analyze the RG flow of the susceptibilities and show that, if all Fermi pockets are small, the system first develops a spontaneous orbital order, then s ± superconductivity, and magnetic order does not develop down to T=0. We argue that this scenario applies to FeSe. In systems with larger pockets, such as BaFe 2As 2 and LaFeAsO, we find that the leading instability is either towards a spin-density wave or superconductivity. We argue that in this situation nematic order is caused by composite spin fluctuations and is vestigial to stripe magnetism. Finally, our results provide a unifying description of different iron-based materials.« less

Two-component relativistic coupled-cluster methods using mean-field spin-orbit integrals

NASA Astrophysics Data System (ADS)

Liu, Junzi; Shen, Yue; Asthana, Ayush; Cheng, Lan

2018-01-01

A novel implementation of the two-component spin-orbit (SO) coupled-cluster singles and doubles (CCSD) method and the CCSD augmented with the perturbative inclusion of triple excitations [CCSD(T)] method using mean-field SO integrals is reported. The new formulation of SO-CCSD(T) features an atomic-orbital-based algorithm for the particle-particle ladder term in the CCSD equation, which not only removes the computational bottleneck associated with the large molecular-orbital integral file but also accelerates the evaluation of the particle-particle ladder term by around a factor of 4 by taking advantage of the spin-free nature of the instantaneous electron-electron Coulomb interaction. Benchmark calculations of the SO splittings for the thallium atom and a set of diatomic 2Π radicals as well as of the bond lengths and harmonic frequencies for a set of closed-shell diatomic molecules are presented. The basis-set and core-correlation effects in the calculations of these properties have been carefully analyzed.

Electric Field Controlled Spin Interference in a System with Rashba Spin-Orbit Coupling

DTIC Science & Technology

2016-08-29

conducting semi-circular channels. The strength of the confinement energy on the quantum dots is tuned by gate potentials that allow “ leakage ” of electrons...interesting applications. A detectable SO effect requires a strong electric field (as well as a semiconductor host for the electrons that satisfies a...quantum dots (which may be considered identical) are confined by an electrostatically created potential that can be tuned to allow “ leakage ” of

Magnetic anisotropy in nickel complexes as determined by combined magnetic susceptibility/magnetization/theoretical studies

NASA Astrophysics Data System (ADS)

Mašlejová, Anna; Boča, Roman; Dlháň, L.'ubor; Herchel, Radovan

2004-05-01

The zero-field splitting in nickel(II) complexes was modeled by considering all relevant operators (electron repulsion, crystal-field, spin-orbit coupling, orbital-Zeeman, and spin-Zeeman) in the complete basis set spanned by d n-atomic terms. D-values between weak and strong crystal field limits were evaluated from the crystal-field multiplets as well as using the spin Hamiltonian formalism. Importance of the anisotropic orbital reduction factors is discussed and exemplified by D/hc=-22 cm-1 as subtracted from magnetic data for [Ni(imidazole) 4(acetate) 2] complex.

Topological nodal-line fermions in spin-orbit metal PbTaSe2

PubMed Central

Bian, Guang; Chang, Tay-Rong; Sankar, Raman; Xu, Su-Yang; Zheng, Hao; Neupert, Titus; Chiu, Ching-Kai; Huang, Shin-Ming; Chang, Guoqing; Belopolski, Ilya; Sanchez, Daniel S.; Neupane, Madhab; Alidoust, Nasser; Liu, Chang; Wang, BaoKai; Lee, Chi-Cheng; Jeng, Horng-Tay; Zhang, Chenglong; Yuan, Zhujun; Jia, Shuang; Bansil, Arun; Chou, Fangcheng; Lin, Hsin; Hasan, M. Zahid

2016-01-01

Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch. While the degeneracy points in Weyl semimetals are robust against any perturbation that preserves translational symmetry, nodal lines require protection by additional crystalline symmetries such as mirror reflection. Here we report, based on a systematic theoretical study and a detailed experimental characterization, the existence of topological nodal-line states in the non-centrosymmetric compound PbTaSe2 with strong spin-orbit coupling. Remarkably, the spin-orbit nodal lines in PbTaSe2 are not only protected by the reflection symmetry but also characterized by an integer topological invariant. Our detailed angle-resolved photoemission measurements, first-principles simulations and theoretical topological analysis illustrate the physical mechanism underlying the formation of the topological nodal-line states and associated surface states for the first time, thus paving the way towards exploring the exotic properties of the topological nodal-line fermions in condensed matter systems. PMID:26829889

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

NASA Astrophysics Data System (ADS)

Miller, Richards; van Schooten, K. J.; Malissa, H.; Joshi, G.; Jamali, S.; Lupton, J. M.; Boehme, C.

2016-12-01

We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g -factors, appear to be somewhat more significant in the β-phase.

Observing the Interstellar Neutral He Gas Flow with a Variable IBEX Pointing Strategy

NASA Astrophysics Data System (ADS)

Leonard, T.; Moebius, E.; Bzowski, M.; Fuselier, S. A.; Heirtzler, D.; Kubiak, M. A.; Kucharek, H.; Lee, M. A.; McComas, D. J.; Schwadron, N.; Wurz, P.

2015-12-01

The Interstellar Neutral (ISN) gas flow can be observed at Earth's orbit due to the motion of the solar system relative to the surrounding interstellar gas. Since He is minimally influenced by ionization and charge exchange, the ISN He flow provides a sample of the pristine interstellar environment. The Interstellar Boundary Explorer (IBEX) has observed the ISN gas flow over the past 7 years from a highly elliptical orbit around the Earth. IBEX is a Sun-pointing spinning spacecraft with energetic neutral atom (ENA) detectors observing perpendicular to the spacecraft spin axis. Due to the Earth's orbital motion around the Sun, it is necessary for IBEX to perform spin axis pointing maneuvers every few days to maintain a sunward pointed spin axis. The IBEX operations team has successfully pointed the spin axis in a variety of latitude orientations during the mission, including in the ecliptic during the 2012 and 2013 seasons, about 5 degrees below the ecliptic during the 2014 season, and recently about 5 degrees above the ecliptic during the 2015 season, as well as optimizing observations with the spin axis pointed along the Earth-Sun line. These observations include a growing number of measurements near the perihelion of the interstellar atom trajectories, which allow for an improved determination of the ISN He bulk flow longitude at Earth orbit. Combining these bulk flow measurements with an analytical model (Lee et al. 2012 ApJS, 198, 10) based upon orbital mechanics improves the knowledge of the narrow ISN parameter tube, obtained with IBEX, which couples the interstellar inflow longitude, latitude, speed, and temperature.

Spin-orbit torque in a three-dimensional topological insulator-ferromagnet heterostructure: Crossover between bulk and surface transport

NASA Astrophysics Data System (ADS)

Ghosh, S.; Manchon, A.

2018-04-01

Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three-dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore our model accounts for the spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large dampinglike torque reported recently is more likely attributed to the Berry curvature of interfacial states, while spin Hall torque remains small even in the bulk-dominated regime.

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d 2Sr 2MgOsO 6

DOE PAGES

Morrow, Ryan; Taylor, Alice E.; Singh, D. J.; ...

2016-08-30

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d 2 system Sr 2MgOsO 6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr 2MgOsO 6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d 2 system of 0.60(2) μ B a significantly reduced moment from the expected valuemore » for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the moment size in this compound. In conclusion, through comparison to Sr 2ScOsO 6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d 2 systems relative to their 5d 3 counterparts, providing an explanation of the high TN found in Sr 2MgOsO 6.« less

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6

PubMed Central

Morrow, Ryan; Taylor, Alice E.; Singh, D. J.; Xiong, Jie; Rodan, Steven; Wolter, A. U. B.; Wurmehl, Sabine; Büchner, Bernd; Stone, M. B.; Kolesnikov, A. I.; Aczel, Adam A.; Christianson, A. D.; Woodward, Patrick M.

2016-01-01

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) μB –a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6. PMID:27571715

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d(2) Sr2MgOsO6.

PubMed

Morrow, Ryan; Taylor, Alice E; Singh, D J; Xiong, Jie; Rodan, Steven; Wolter, A U B; Wurmehl, Sabine; Büchner, Bernd; Stone, M B; Kolesnikov, A I; Aczel, Adam A; Christianson, A D; Woodward, Patrick M

2016-08-30

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d(2) system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d(2) system of 0.60(2) μB -a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d(2) systems relative to their 5d(3) counterparts, providing an explanation of the high TN found in Sr2MgOsO6.

Rashba-type spin splitting and the electronic structure of ultrathin Pb/MoTe2 heterostructure

NASA Astrophysics Data System (ADS)

Du, X.; Wang, Z. Y.; Huang, G. Q.

2016-11-01

The spin-polarized band structures of the Pb(111)/MoTe2 heterostructure are studied by the first-principles calculations. Due to strong spin-orbit coupling and space inversion asymmetry, large Rashba spin splitting of electronic bands appears in this hybrid system. The spin splitting is completely out-of-plane and opposite at \\bar{K} and {\\bar{K}}\\prime points. Rashba spin splitting also appears along the in-plane momentum direction around the \\bar{{{Γ }}} point due to the existence of surface potential gradient induced by charge transfer at interface. Furthermore, our calculations show that the spin-polarized bands closely approach the Fermi level in Pb/MoTe2 heterostructure, showing that this heterostructure may be a good candidate in valleytronics or spintronics.

MkMRCC, APUCC, APUBD calculations of didehydronated species: comparison among calculated through-bond effective exchange integrals for diradicals

NASA Astrophysics Data System (ADS)

Saito, Toru; Nishihara, Satomichi; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Okumura, Mitsutaka; Yamaguchi, Kizashi

2010-10-01

Mukherjee's type of multireference coupled-cluster (MkMRCC), approximate spin-projected spin-unrestricted CC (APUCC), and AP spin-unrestricted Brueckner's (APUBD) methods were applied to didehydronated ethylene, allyl cation, cis-butadiene, and naphthalene. The focus is on descriptions of magnetic properties for these diradical species such as S-T gaps and diradical characters. Several types of orbital sets were examined as reference orbitals for MkMRCC calculations, and it was found that the change of orbital sets do not give significant impacts on computational results for these species. Comparison of MkMRCC results with APUCC and APUBD results show that these two types of methods yield similar results. These results show that the quantum spin corrected UCC and UBD methods can effectively account for both nondynamical and dynamical correlation effects that are covered by the MkMRCC methods. It was also shown that appropriately parameterized hybrid density functional theory (DFT) with AP corrections (APUDFT) calculations yielded very accurate data that qualitatively agree with those of MRCC and APUBD methods. This hierarchy of methods, MRCC, APUCC, and APUDFT, is expected to constitute a series of standard ab initio approaches towards radical systems, among which we could choose one of them, depending on the size of the systems and the required accuracy.

Spin-orbit coupling induced two-electron relaxation in silicon donor pairs

NASA Astrophysics Data System (ADS)

Song, Yang; Das Sarma, S.

2017-09-01

We unravel theoretically a key intrinsic relaxation mechanism among the low-lying singlet and triplet donor-pair states in silicon, an important element in the fast-developing field of spintronics and quantum computation. Despite the perceived weak spin-orbit coupling (SOC) in Si, we find that our discovered relaxation mechanism, combined with the electron-phonon and interdonor interactions, drives the transitions in the two-electron states over a large range of donor coupling regimes. The scaling of the relaxation rate with interdonor exchange interaction J goes from J5 to J4 at the low to high temperature limits. Our analytical study draws on the symmetry analysis over combined band, donor envelope, and valley configurations. It uncovers naturally the dependence on the donor-alignment direction and triplet spin orientation, and especially on the dominant SOC source from donor impurities. While a magnetic field is not necessary for this relaxation, unlike in the single-donor spin relaxation, we discuss the crossover behavior with increasing Zeeman energy in order to facilitate comparison with experiments.

Constructive spin-orbital angular momentum coupling can twist materials to create spiral structures in optical vortex illumination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barada, Daisuke; Center for Optical Research and Education; Juman, Guzhaliayi

It was discovered that optical vortices twist isotropic and homogenous materials, e.g., azo-polymer films to form spiral structures on a nano- or micro-scale. However, the formation mechanism has not yet been established theoretically. To understand the mechanism of the spiral surface relief formation in the azo-polymer film, we theoretically investigate the optical radiation force induced in an isotropic and homogeneous material under irradiation using a continuous-wave optical vortex with arbitrary topological charge and polarization. It is revealed that the spiral surface relief formation in azo-polymer films requires the irradiation of optical vortices with a positive (negative) spin angular momentum andmore » a positive (negative) orbital angular momentum (constructive spin-orbital angular momentum coupling), i.e., the degeneracy among the optical vortices with the same total angular momentum is resolved.« less

An efficient method for hybrid density functional calculation with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wang, Maoyuan; Liu, Gui-Bin; Guo, Hong; Yao, Yugui

2018-03-01

In first-principles calculations, hybrid functional is often used to improve accuracy from local exchange correlation functionals. A drawback is that evaluating the hybrid functional needs significantly more computing effort. When spin-orbit coupling (SOC) is taken into account, the non-collinear spin structure increases computing effort by at least eight times. As a result, hybrid functional calculations with SOC are intractable in most cases. In this paper, we present an approximate solution to this problem by developing an efficient method based on a mixed linear combination of atomic orbital (LCAO) scheme. We demonstrate the power of this method using several examples and we show that the results compare very well with those of direct hybrid functional calculations with SOC, yet the method only requires a computing effort similar to that without SOC. The presented technique provides a good balance between computing efficiency and accuracy, and it can be extended to magnetic materials.

Topological Oxide Insulator in Cubic Perovskite Structure

PubMed Central

Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

2013-01-01

The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases. PMID:23575973

Anti-Weak Localization Measurements in the Ballistic Regime

NASA Astrophysics Data System (ADS)

Jayathilaka, Dilhani; Dedigama, Aruna; Murphy, Sheena; Edirisooriya, Madhavie; Goel, Niti; Mishima, Tetsuya; Santos, Michael; Mullen, Kieran

2007-03-01

Anti-weak localization dominates at low fields in systems in which spin-orbit coupling is strong. The experimental results are well described by theory [1] in low mobility systems in which the magnetic length (lB) is greater than the mean free path; however high mobility systems with strong spin-orbit interactions, such the InSb based two dimensional systems (2DESs) examined here, are not in this diffusive regime. A recently developed theory [2] addresses both the diffusive and ballistic regimes taking into account both the backscattered and non-backscattered contributions to the conductivity. We will discuss the agreement of the new theory to measurements of InSb 2DESs prepared with both strong Dresselhaus and Rashba effects. [1] S.V. Iordanskii, Yu B. Lyanda-Geller, and G.E. Pikus, JETP Lett. 60, 206 (1994). [2] L.E. Golub, Phys. Rev. B. 71, 235310 (2005).

Dzyaloshinskii-Moriya interaction in the presence of Rashba and Dresselhaus spin-orbit coupling

NASA Astrophysics Data System (ADS)

Valizadeh, Mohammad M.; Satpathy, S.

2018-03-01

Chiral order in magnetic structures is currently an area of considerable interest and leads to skyrmion structures and domain walls with certain chirality. The chiral structure originates from the Dzyaloshinskii-Moriya interaction caused by broken inversion symmetry and the spin-orbit interaction. In addition to the Rashba or Dresselhaus interactions, there may also exist substantial spin polarization in magnetic thin films. Here, we study the exchange interaction between two localized magnetic moments in the spin-polarized electron gas with both Rashba and Dresselhaus spin-orbit interaction present. Analytical expressions are found in certain limits in addition to what is known in the literature. The stability of the Bloch and Néel domain walls in magnetic thin films is discussed in light of our results.

First principle calculations of effective exchange integrals: Comparison between SR (BS) and MR computational results

NASA Astrophysics Data System (ADS)

Yamaguchi, Kizashi; Nishihara, Satomichi; Saito, Toru; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Yamada, Satoru; Isobe, Hiroshi; Okumura, Mitsutaka

2015-01-01

First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di- and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level. In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure- and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di- and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.

Von Neumann entropy in a Rashba-Dresselhaus nanodot; dynamical electronic spin-orbit entanglement

NASA Astrophysics Data System (ADS)

Safaiee, Rosa; Golshan, Mohammad Mehdi

2017-06-01

The main purpose of the present article is to report the characteristics of von Neumann entropy, thereby, the electronic hybrid entanglement, in the heterojunction of two semiconductors, with due attention to the Rashba and Dresselhaus spin-orbit interactions. To this end, we cast the von Neumann entropy in terms of spin polarization and compute its time evolution; with a vast span of applications. It is assumed that gate potentials are applied to the heterojunction, providing a two dimensional parabolic confining potential (forming an isotropic nanodot at the junction), as well as means of controlling the spin-orbit couplings. The spin degeneracy is also removed, even at electronic zero momentum, by the presence of an external magnetic field which, in turn, leads to the appearance of Landau states. We then proceed by computing the time evolution of the corresponding von Neumann entropy from a separable (spin-polarized) initial state. The von Neumann entropy, as we show, indicates that electronic hybrid entanglement does occur between spin and two-dimensional Landau levels. Our results also show that von Neumann entropy, as well as the degree of spin-orbit entanglement, periodically collapses and revives. The characteristics of such behavior; period, amplitude, etc., are shown to be determined from the controllable external agents. Moreover, it is demonstrated that the phenomenon of collapse-revivals' in the behavior of von Neumann entropy, equivalently, electronic hybrid entanglement, is accompanied by plateaus (of great importance in quantum computation schemes) whose durations are, again, controlled by the external elements. Along these lines, we also make a comparison between effects of the two spin-orbit couplings on the entanglement (von Neumann entropy) characteristics. The finer details of the electronic hybrid entanglement, which may be easily verified through spin polarization measurements, are also accreted and discussed. The novel results of the present article, with potent applications in the field of quantum information processing, provide a deeper understanding of the electronic von Neumann entropy and hybrid entanglement that occurs in two-dimensional nanodots.

Spin-orbit coupling and electric-dipole spin resonance in a nanowire double quantum dot.

PubMed

Liu, Zhi-Hai; Li, Rui; Hu, Xuedong; You, J Q

2018-02-02

We study the electric-dipole transitions for a single electron in a double quantum dot located in a semiconductor nanowire. Enabled by spin-orbit coupling (SOC), electric-dipole spin resonance (EDSR) for such an electron can be generated via two mechanisms: the SOC-induced intradot pseudospin states mixing and the interdot spin-flipped tunneling. The EDSR frequency and strength are determined by these mechanisms together. For both mechanisms the electric-dipole transition rates are strongly dependent on the external magnetic field. Their competition can be revealed by increasing the magnetic field and/or the interdot distance for the double dot. To clarify whether the strong SOC significantly impact the electron state coherence, we also calculate relaxations from excited levels via phonon emission. We show that spin-flip relaxations can be effectively suppressed by the phonon bottleneck effect even at relatively low magnetic fields because of the very large g-factor of strong SOC materials such as InSb.

KOI2138 -- a Spin-Orbit Aligned Intermediate Period Super-Earth

NASA Astrophysics Data System (ADS)

Barnes, Jason W.

2015-11-01

A planet's formation and evolution are encoded in spin-orbit alignment -- the planet's inclination relative to its star's equatorial plane. While the solar system's spin-orbit aligned planets indicate our own relatively quiescent history, many close-in giant planets show significant misalignment. Some planets even orbit retrograde! Hot Jupiters, then, have experienced fundamentally different histories than we experienced here in the solar system. In this presentation, I will show a new determination of the spin-orbit alignment of 2.1 REarth exoplanet candidate KOI2138. KOI2138 shows a gravity-darkened transit lightcurve that is consistent with spin-orbit alignment. This measurement is important because the only other super-Earth with an alignment determination (55 Cnc e, orbit period 0.74 days) is misaligned. With an orbital period of 23.55 days, KOI2138 is far enough from its star to avoid tidal orbit evolution. Therefore its orbit is likely primordial, and hence it may represent the tip of an iceberg of terrestrial, spin-orbit aligned planets that have histories that more closely resemble that of the solar system's terrestrial planets.

Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramaswamy, Rajagopalan; Qiu, Xuepeng; Dutta, Tanmay

We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.

Epitaxial strain effect on the physical properties of layered ruthenate and iridate thin films

NASA Astrophysics Data System (ADS)

Miao, Ludi

Transition metal oxides have attracted widespread attention due to their broad range of fascinating exotic phenomena such as multiferroicity, superconductivity, colossal magnetoresistance and metal-to-insulator transition. Due to the interplay between spin, charge, lattice and orbital degrees of freedom of strongly correlated d electrons, these physical properties are extremely sensitive to the external perturbations such as magnetic field, charge carrier doping and pressure, which provide a unique chance in search for novel exotic quantum states. Ruthenate systems are a typical strongly correlated system, with rich ordered states and their properties are extremely sensitive to external stimuli. Recently, the experimental observation of spin-orbit coupling induced Mott insulator in Sr2IrO4 as well as the theoretical prediction of topological insulating state in other iridates, have attracted tremendous interest in the physics of strong correlation and spin-orbit coupling in 4d/5d compounds. We observe an itinerant ferromagnetic ground state of Ca2 RuO4 film in stark contrast to the Mott-insulating state in bulk Ca2RuO4. We have also established the epitaxial strain effect on the transport and magnetic properties for the (Ca,Sr) 2RuO4 thin films. For Sr2IrO4 thin films, we will show that the Jeff = 1/2 moment orientation can be modulated by epitaxial strain. In addition, we discovered novel Ba 7Ir3O13+x thin films which exhibit colossal permittivity.

Evolution of the Carter constant for inspirals into a black hole: Effect of the black hole quadrupole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flanagan, Eanna E.; Laboratory for Elementary Particle Physics, Cornell University, Ithaca, New York 14853; Hinderer, Tanja

2007-06-15

We analyze the effect of gravitational radiation reaction on generic orbits around a body with an axisymmetric mass quadrupole moment Q to linear order in Q, to the leading post-Newtonian order, and to linear order in the mass ratio. This system admits three constants of the motion in absence of radiation reaction: energy, angular momentum along the symmetry axis, and a third constant analogous to the Carter constant. We compute instantaneous and time-averaged rates of change of these three constants. For a point particle orbiting a black hole, Ryan has computed the leading order evolution of the orbit's Carter constant,more » which is linear in the spin. Our result, when combined with an interaction quadratic in the spin (the coupling of the black hole's spin to its own radiation reaction field), gives the next to leading order evolution. The effect of the quadrupole, like that of the linear spin term, is to circularize eccentric orbits and to drive the orbital plane towards antialignment with the symmetry axis. In addition we consider a system of two point masses where one body has a single mass multipole or current multipole of order l. To linear order in the mass ratio, to linear order in the multipole, and to the leading post-Newtonian order, we show that there does not exist an analog of the Carter constant for such a system (except for the cases of an l=1 current moment and an l=2 mass moment). Thus, the existence of the Carter constant in Kerr depends on interaction effects between the different multipoles. With mild additional assumptions, this result falsifies the conjecture that all vacuum, axisymmetric spacetimes possess a third constant of the motion for geodesic motion.« less

Accurate potential energy functions, non-adiabatic and spin-orbit couplings in the ZnH(+) system.

PubMed

Liang, Guiying; Liu, Xiaoting; Zhang, Xiaomei; Xu, Haifeng; Yan, Bing

2016-03-05

A high-level ab initio calculation on the ZnH(+) cation has been carried out with the multi-reference configuration interaction method plus Davison correction (MRCI+Q). The scalar relativistic effect is included by using the Douglas-Kroll-Hess (DKH) method. The calculated potential energy curves (PECs) of the 7 Λ-S states are associated with the dissociation limits of Zn(+)((2)Sg)+H((2)Sg), Zn((1)Sg)+H(+)((1)Sg), and Zn(+)((2)Pu)+H((2)Sg), respectively (The Λ-S state is labeled as (2S+1)Λ, in which Λ is the quantum number for the projection along the internuclear axis of the total electronic orbital angular momentum and S is the total electron spin). The spectroscopic constants of the bound states are determined and in good agreement with the available theoretical and experimental results. The permanent dipole moments (PDMs) of Λ-S states and the spin-orbit (SO) matrix elements between Λ-S states are also computed. The results show that the abrupt changes of the PDMs and SO matrix elements come into being for the reason of the avoided crossing between the states with the same symmetry. In addition, the non-adiabatic couplings matrix elements between Λ-S states are also evaluated. Finally, the spin-orbit couplings (SOCs) for the low-lying states are considered with Breit-Pauli operator. The SOC effect makes the 7 Λ-S states of the ZnH(+) cation split into 12 Ω states (Ω=Λ+Sz, in which Sz is projection of the total electron spin S along the internuclear Z-axis). For the (3)0(+) state, the two energy minima exhibit in the potential, which could be attributed to the formation of the new avoided crossing point. The transition dipole moments (TDMs), Franck-Condon factors, and the radiative lifetimes of the selected transitions (2)0(+)-X0(+), (3)0(+)-X0(+), (2)1-X0(+) and (3)1-X0(+) have been reported. Copyright © 2015 Elsevier B.V. All rights reserved.

Spin injection into Pt-polymers with large spin-orbit coupling

NASA Astrophysics Data System (ADS)

Sun, Dali; McLaughlin, Ryan; Siegel, Gene; Tiwari, Ashutosh; Vardeny, Z. Valy

2014-03-01

Organic spintronics has entered a new era of devices that integrate organic light-emitting diodes (OLED) in organic spin valve (OSV) geometry (dubbed bipolar organic spin valve, or spin-OLED), for actively manipulating the device electroluminescence via the spin alignment of two ferromagnetic electrodes (Science 337, 204-209, 2012; Appl. Phys. Lett. 103, 042411, 2013). Organic semiconductors that contain heavy metal elements have been widely used as phosphorescent dopants in white-OLEDs. However such active materials are detrimental for OSV operation due to their large spin-orbit coupling (SOC) that may limit the spin diffusion length and thus spin-OLED based on organics with large SOC is a challenge. We report the successful fabrication of OSVs based on pi-conjugated polymers which contain intrachain Platinum atoms (dubbed Pt-polymers). Spin injection into the Pt-polymers is investigated by the giant magnetoresistance (GMR) effect as a function of bias voltage, temperature and polymer layer thickness. From the GMR bias voltage dependence we infer that the ``impendence mismatch'' between ferromagnetic electrodes and Pt-polymer may be suppressed due to the large SOC. Research sponsored by the NSF (Grant No. DMR-1104495) and NSF-MRSEC (DMR 1121252) at the University of Utah.

Proximity-induced mixed odd- and even-frequency pairing in monolayer NbSe2

NASA Astrophysics Data System (ADS)

Aliabad, Mojtaba Rahimi; Zare, Mohammad-Hossein

2018-06-01

Monolayer superconducting transition-metal dichalcogenide NbSe2 is a candidate for a nodal topological superconductor by magnetic field. Because of the so-called Ising spin-orbit coupling that strongly pins the electron spins to the out-of-plane direction, Cooper pairs in monolayer superconductor NbSe2 are protected against an applied in-plane magnetic field much larger than the Pauli limit. In monolayer NbSe2, in addition to the Fermi pockets at the corners of Brillouin zone with opposite crystal momentum similar to other semiconducting transition-metal dichalcogenids, there is an extra Fermi pocket around the Γ point with much smaller spin splitting, which could lead to an alternative strategy for pairing possibilities that are manipulable by a smaller magnetic field. By considering a monolayer NbSe2-ferromagnet substrate junction, we explore the modified pairing correlations on the pocket at Γ point in hole-doped monolayer NbSe2. The underlying physics is fascinating as there is a delicate interplay of the induced exchange field and the Ising spin-orbit coupling. We realize a mixed singlet-triplet superconductivity, s +f , due to the Ising spin-orbit coupling. Moreover, our results reveal the admixture state including both odd- and even-frequency components, associated with the ferromagnetic proximity effect. Different frequency symmetries of the induced pairing correlations can be realized by manipulating the magnitude and direction of the induced magnetization.

Floquet spin states in graphene under ac-driven spin-orbit interaction

NASA Astrophysics Data System (ADS)

López, A.; Sun, Z. Z.; Schliemann, J.

2012-05-01

We study the role of periodically driven time-dependent Rashba spin-orbit coupling (RSOC) on a monolayer graphene sample. After recasting the originally 4×4 system of dynamical equations as two time-reversal related two-level problems, the quasienergy spectrum and the related dynamics are investigated via various techniques and approximations. In the static case, the system is gapped at the Dirac point. The rotating wave approximation (RWA) applied to the driven system unphysically preserves this feature, while the Magnus-Floquet approach as well as a numerically exact evaluation of the Floquet equation show that this gap is dynamically closed. In addition, a sizable oscillating pattern of the out-of-plane spin polarization is found in the driven case for states that are completely unpolarized in the static limit. Evaluation of the autocorrelation function shows that the original uniform interference pattern corresponding to time-independent RSOC gets distorted. The resulting structure can be qualitatively explained as a consequence of the transitions induced by the ac driving among the static eigenstates, i.e., these transitions modulate the relative phases that add up to give the quantum revivals of the autocorrelation function. Contrary to the static case, in the driven scenario, quantum revivals (suppressions) are correlated to spin-up (down) phases.

Relativistic symmetries in the Rosen—Morse potential and tensor interaction using the Nikiforov—Uvarov method

NASA Astrophysics Data System (ADS)

Sameer, M. Ikhdair; Majid, Hamzavi

2013-04-01

Approximate analytical bound-state solutions of the Dirac particle in the fields of attractive and repulsive Rosen—Morse (RM) potentials including the Coulomb-like tensor (CLT) potential are obtained for arbitrary spin-orbit quantum number κ. The Pekeris approximation is used to deal with the spin-orbit coupling terms κ (κ± 1)r-2. In the presence of exact spin and pseudospin (p-spin) symmetries, the energy eigenvalues and the corresponding normalized two-component wave functions are found by using the parametric generalization of the Nikiforov—Uvarov (NU) method. The numerical results show that the CLT interaction removes degeneracies between the spin and p-spin state doublets.

Field-effect control of superconductivity and Rashba spin-orbit coupling in top-gated LaAlO3/SrTiO3 devices

PubMed Central

Hurand, S.; Jouan, A.; Feuillet-Palma, C.; Singh, G.; Biscaras, J.; Lesne, E.; Reyren, N.; Barthélémy, A.; Bibes, M.; Villegas, J. E.; Ulysse, C.; Lafosse, X.; Pannetier-Lecoeur, M.; Caprara, S.; Grilli, M.; Lesueur, J.; Bergeal, N.

2015-01-01

The recent development in the fabrication of artificial oxide heterostructures opens new avenues in the field of quantum materials by enabling the manipulation of the charge, spin and orbital degrees of freedom. In this context, the discovery of two-dimensional electron gases (2-DEGs) at LaAlO3/SrTiO3 interfaces, which exhibit both superconductivity and strong Rashba spin-orbit coupling (SOC), represents a major breakthrough. Here, we report on the realisation of a field-effect LaAlO3/SrTiO3 device, whose physical properties, including superconductivity and SOC, can be tuned over a wide range by a top-gate voltage. We derive a phase diagram, which emphasises a field-effect-induced superconductor-to-insulator quantum phase transition. Magneto-transport measurements show that the Rashba coupling constant increases linearly with the interfacial electric field. Our results pave the way for the realisation of mesoscopic devices, where these two properties can be manipulated on a local scale by means of top-gates. PMID:26244916

Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions

NASA Astrophysics Data System (ADS)

Scazza, F.; Hofrichter, C.; Höfer, M.; de Groot, P. C.; Bloch, I.; Fölling, S.

2014-10-01

Spin-exchanging interactions govern the properties of strongly correlated electron systems such as many magnetic materials. When orbital degrees of freedom are present, spin exchange between different orbitals often dominates, leading to the Kondo effect, heavy fermion behaviour or magnetic ordering. Ultracold ytterbium or alkaline-earth ensembles have attracted much recent interest as model systems for these effects, with two (meta-) stable electronic configurations representing independent orbitals. We report the observation of spin-exchanging contact interactions in a two-orbital SU(N)-symmetric quantum gas realized with fermionic 173Yb. We find strong inter-orbital spin exchange by spectroscopic characterization of all interaction channels and demonstrate SU(N = 6) symmetry within our measurement precision. The spin-exchange process is also directly observed through the dynamic equilibration of spin imbalances between ensembles in separate orbitals. The realization of an SU(N)-symmetric two-orbital Hubbard Hamiltonian opens the route to quantum simulations with extended symmetries and with orbital magnetic interactions, such as the Kondo lattice model.

Reducing orbital eccentricity of precessing black-hole binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buonanno, Alessandra; Taracchini, Andrea; Kidder, Lawrence E.

2011-05-15

Building initial conditions for generic binary black-hole evolutions which are not affected by initial spurious eccentricity remains a challenge for numerical-relativity simulations. This problem can be overcome by applying an eccentricity-removal procedure which consists of evolving the binary black hole for a couple of orbits, estimating the resulting eccentricity, and then restarting the simulation with corrected initial conditions. The presence of spins can complicate this procedure. As predicted by post-Newtonian theory, spin-spin interactions and precession prevent the binary from moving along an adiabatic sequence of spherical orbits, inducing oscillations in the radial separation and in the orbital frequency. For single-spinmore » binary black holes these oscillations are a direct consequence of monopole-quadrupole interactions. However, spin-induced oscillations occur at approximately twice the orbital frequency, and therefore can be distinguished and disentangled from the initial spurious eccentricity which occurs at approximately the orbital frequency. Taking this into account, we develop a new eccentricity-removal procedure based on the derivative of the orbital frequency and find that it is rather successful in reducing the eccentricity measured in the orbital frequency to values less than 10{sup -4} when moderate spins are present. We test this new procedure using numerical-relativity simulations of binary black holes with mass ratios 1.5 and 3, spin magnitude 0.5, and various spin orientations. The numerical simulations exhibit spin-induced oscillations in the dynamics at approximately twice the orbital frequency. Oscillations of similar frequency are also visible in the gravitational-wave phase and frequency of the dominant l=2, m=2 mode.« less

Spin and valley filter across line defect in silicene

NASA Astrophysics Data System (ADS)

Wang, Sake; Ren, Chongdan; Li, Yunfang; Tian, Hongyu; Lu, Weitao; Sun, Minglei

2018-05-01

We propose a new scheme to achieve an effective spin/valley filter in silicene with extended line defect on the basis of spin–valley coupling due to the intrinsic spin-orbit coupling (SOC). The transmission coefficient of the spin/valley states is seriously affected by the SOC. When a perpendicular magnetic field is applied on one side of the line defect, one valley state will experience backscattering, but the other valley will not; this leads to high valley polarization in all transmission directions. Moreover, the spin/valley polarization can be enhanced to 96% with the aid of a perpendicular electric field.

Exchange and spin-orbit induced phenomena in diluted (Ga,Mn)As from first principles

NASA Astrophysics Data System (ADS)

Kudrnovský, J.; Drchal, V.; Turek, I.

2016-08-01

Physical properties induced by exchange interactions (Curie temperature and spin stiffness) and spin-orbit coupling (anomalous Hall effect, anisotropic magnetoresistance, and Gilbert damping) in the diluted (Ga,Mn)As ferromagnetic semiconductor are studied from first principles. Recently developed Kubo-Bastin transport theory and nonlocal torque operator formulation of the Gilbert damping as formulated in the tight-binding linear muffin-tin orbital method are used. The first-principles Liechtenstein mapping is employed to construct an effective Heisenberg Hamiltonian and to estimate Curie temperature and spin stiffness in the real-space random-phase approximation. Good agreement of calculated physical quantities with experiments on well-annealed samples containing only a small amount of compensating defects is obtained.

Geometric effects resulting from square and circular confinements for a particle constrained to a space curve

NASA Astrophysics Data System (ADS)

Wang, Yong-Long; Lai, Meng-Yun; Wang, Fan; Zong, Hong-Shi; Chen, Yan-Feng

2018-04-01

Investigating the geometric effects resulting from the detailed behaviors of the confining potential, we consider square and circular confinements to constrain a particle to a space curve. We find a torsion-induced geometric potential and a curvature-induced geometric momentum just in the square case, while a geometric gauge potential solely in the circular case. In the presence of electromagnetic field, a geometrically induced magnetic moment couples with magnetic field as an induced Zeeman coupling only for the circular confinement also. As spin-orbit interaction is considered, we find some additional terms for the spin-orbit coupling, which are induced not only by torsion, but also curvature. Moreover, in the circular case, the spin also couples with an intrinsic angular momentum, which describes the azimuthal motions mapped on the space curve. As an important conclusion for the thin-layer quantization approach, some substantial geometric effects result from the confinement boundaries. Finally, these results are proved on a helical wire.

Quantum impurity models for magnetic adsorbates on superconductor surfaces

NASA Astrophysics Data System (ADS)

Žitko, Rok

2018-05-01

Magnetic atoms adsorbed on surfaces have a quenched orbital moment while their ground-state spin multiplet is partially split as a consequence of the spin-orbit coupling which, even if intrinsically weak, has a large effect due to the abrupt change of the potential at the surface. Such metal adsorbates should be modelled using quantum impurity models that include the relevant internal degrees of freedom and the interaction terms, in particular the magnetic anisotropy and the Kondo exchange coupling. When adsorbed on superconducting surfaces, these impurities have complex spectra of sub-gap excitations due to magnetic anisotropy splitting and Kondo screening. Both anisotropy splitting and Zeeman splitting due to the external magnetic field are significantly renormalized by the coupling to the substrate electrons. In this work I discuss the quantum-to-classical crossover and the applicability of classical static-local-spin picture for discussing magnetic nanostructures on superconductors.

Reorientations, relaxations, metastabilities, and multidomains of skyrmion lattices

NASA Astrophysics Data System (ADS)

Bannenberg, L. J.; Qian, F.; Dalgliesh, R. M.; Martin, N.; Chaboussant, G.; Schmidt, M.; Schlagel, D. L.; Lograsso, T. A.; Wilhelm, H.; Pappas, C.

2017-11-01

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu2OSeO3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history of the sample, which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Furthermore, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bannenberg, L. J.; Qian, F.; Dalgliesh, R. M.

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu 2OSeO 3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history ofmore » the sample, which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Moreover, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.« less

Theory of Direct Optical Measurement of Pure Spin Currents in Direct-gap Semiconductors

NASA Astrophysics Data System (ADS)

Wang, Jing; Liu, Ren-Bao; Zhu, Bang-Fen

2010-01-01

We predict that a pure spin current in a semiconductor may lead to the optical circular birefingence effect without invoking magnetization. This effect may be exploited for a direct, non-destructive measurement of the pure spin current. We derive the effective coupling between a pure spin current and a polarized light beam, and point out that it originates from the inherent spin-orbit coupling in the valence bands, rather than the Rashba or Dresselhaus effects due to inversion asymmetries. The Faraday rotation angle in GaAs is estimated, which indicates that this spin current optical birefringence is experimentally observable.

Switchable S = 1/2 and J = 1/2 Rashba bands in ferroelectric halide perovskites

PubMed Central

Kim, Minsung; Im, Jino; Freeman, Arthur J.; Ihm, Jisoon; Jin, Hosub

2014-01-01

The Rashba effect is spin degeneracy lift originated from spin–orbit coupling under inversion symmetry breaking and has been intensively studied for spintronics applications. However, easily implementable methods and corresponding materials for directional controls of Rashba splitting are still lacking. Here, we propose organic–inorganic hybrid metal halide perovskites as 3D Rashba systems driven by bulk ferroelectricity. In these materials, it is shown that the helical direction of the angular momentum texture in the Rashba band can be controlled by external electric fields via ferroelectric switching. Our tight-binding analysis and first-principles calculations indicate that and Rashba bands directly coupled to ferroelectric polarization emerge at the valence and conduction band edges, respectively. The coexistence of two contrasting Rashba bands having different compositions of the spin and orbital angular momentum is a distinctive feature of these materials. With recent experimental evidence for the ferroelectric response, the halide perovskites will be, to our knowledge, the first practical realization of the ferroelectric-coupled Rashba effect, suggesting novel applications to spintronic devices. PMID:24785294

Spin-polarized exciton quantum beating in hybrid organic-inorganic perovskites

NASA Astrophysics Data System (ADS)

Odenthal, Patrick; Talmadge, William; Gundlach, Nathan; Wang, Ruizhi; Zhang, Chuang; Sun, Dali; Yu, Zhi-Gang; Valy Vardeny, Z.; Li, Yan S.

2017-09-01

Hybrid organic-inorganic perovskites have emerged as a new class of semiconductors that exhibit excellent performance as active layers in photovoltaic solar cells. These compounds are also highly promising materials for the field of spintronics due to their large and tunable spin-orbit coupling, spin-dependent optical selection rules, and their predicted electrically tunable Rashba spin splitting. Here we demonstrate the optical orientation of excitons and optical detection of spin-polarized exciton quantum beating in polycrystalline films of the hybrid perovskite CH3NH3PbClxI3-x. Time-resolved Faraday rotation measurement in zero magnetic field reveals unexpectedly long spin lifetimes exceeding 1 ns at 4 K, despite the large spin-orbit couplings of the heavy lead and iodine atoms. The quantum beating of exciton states in transverse magnetic fields shows two distinct frequencies, corresponding to two g-factors of 2.63 and -0.33, which we assign to electrons and holes, respectively. These results provide a basic picture of the exciton states in hybrid perovskites, and suggest they hold potential for spintronic applications.

Theory of Intrinsic Spin Torque Due to Interface Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Kalitsov, Alan; Chshiev, Mairbek; Butler, William; Mryasov, Oleg

2014-03-01

The effect of intrinsic spin torque due to spin-orbit coupling (SOC) at the interface between thin ferromagnetic film and non-magnetic metal has attracted significant fundamental and applied research interest. We report quantum theory of SOC driven spin torque (SOT) within the Rashba model of SOC and two-band tight binding (TB) Hamiltonian including s-d exchange interactions (J). We employ the non-equilibrium Green Function formalism and find that SOT to the first order in SOC has symmetry consistent with the earlier quasi-classical diffusive theory. An obvious benefit of the proposed approach is the expression for the SOT given in terms of TB parameters which enables a physically transparent analysis of the dependencies of SOT on material specific parameters such as Rashba SOC constant, hopping integral, Fermi level and J. On the basis of analytical and numerical results we discuss trends in strength of SOT and its correlation with the Spin Hall conductivity. This work was supported in part by C-SPIN, STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

Spin-Orbit Mediated Interference in the Radiative and Nonradiative Channels of the La 4d Core Resonances

NASA Astrophysics Data System (ADS)

Suljoti, E.; de Groot, F. M. F.; Nagasono, M.; Glatzel, P.; Hennies, F.; Deppe, M.; Pietzsch, A.; Sonntag, B.; Föhlisch, A.; Wurth, W.

2009-09-01

Symmetrical fluorescence yield profiles and asymmetrical electron yield profiles of the preresonances at the La NIV,V x-ray absorption edge are experimentally observed in LaPO4 nanoparticles. Theoretical studies show that they are caused by interference effects. The spin-orbit interaction and the giant resonance produce symmetry entangled intermediate states that activate coherent scattering and alter the spectral distribution of the oscillator strength. The scattering amplitudes of the electron and fluorescence decays are further modified by the spin-orbit coupling in the final 5p5ɛl and 5p54f1 states.

Unanticipated spin gap measured in the frustrated quasi-FCC d3 double perovskites La2 LiXO6 (X = Ru, Os)

NASA Astrophysics Data System (ADS)

Maharaj, Dalini D.; Sala, Gabriele; Marjerrison, Casey A.; Greedan, John; Gaulin, Bruce; Stone, Matthew

There is much current interest in the influence of strong spin-orbit (SO) interactions on exotic ground state selection in new 4d and 5d magnets, particularly involving 4d5 Ir. Here we consider double perovskites of the form A2 BB'O6 which are based on heavy 4d or 5d magnetic ions, where the SO interaction is expected to be significant as it increases as ~Z4 . The double perovskite structure can accommodate a variety of magnetic ions on the B' site, providing a playground for systematic studies of the exotic ground states stabilized by strong SO coupling. Here, we report inelastic neutron scattering (INS) measurements conducted on the frustrated monoclinic magnets, La2LiXO6 (X = Ru, Os), wherein the magnetic moments decorate a quasi face-centered-cubic lattice. Our results show the development of a spin gap in the spin excitation spectrum of size ΔOs = 8 meV and ΔRu = 2.5meV concomitant with TN, which is unexpected for orbitally quenched d3 systems. We liken these results to INS results obtained for Ba2YXO6 and La2NaXO6, which were also shown to exhibit spin gaps that correlate with TN. We shall discuss trends observed in these three d3 double perovskite families which correlate strong SO coupling, spin gap and TN.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Yuyuan; Wang, Siqi; Wang, Rui

The spin-orbit coupling strength of graphene can be enhanced by depositing iridium nanoclusters. Weak localization is intensely suppressed near zero fields after the cluster deposition, rather than changing to weak anti-localization. Fitting the magnetoresistance gives the spin relaxation time, which increases by two orders with the application of a back gate. The spin relaxation time is found to be proportional to the electronic elastic scattering time, demonstrating the Elliot–Yafet spin relaxation mechanism. A sizeable Kane–Mele-like coupling strength of over 5.5 meV is determined by extrapolating the temperature dependence to zero.

Decoherence of spin states induced by Rashba coupling for an electron confined to a semiconductor quantum dot in the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Poszwa, A.

2018-05-01

We investigate quantum decoherence of spin states caused by Rashba spin-orbit (SO) coupling for an electron confined to a planar quantum dot (QD) in the presence of a magnetic field (B). The Schrödinger equation has been solved in a frame of second-order perturbation theory. The relationship between the von Neumann (vN) entropy and the spin polarization is obtained. The relation is explicitly demonstrated for the InSb semiconductor QD.

Ab initio model potential calculations on the electronic spectrum of Ni2 + -doped MgO including correlation, spin-orbit and embedding effects

NASA Astrophysics Data System (ADS)

Llusar, Rosa; Casarrubios, Marcos; Barandiarán, Zoila; Seijo, Luis

1996-10-01

An ab initio theoretical study of the optical absorption spectrum of Ni2+-doped MgO has been conducted by means of calculations in a MgO-embedded (NiO6)10-cluster. The calculations include long- and short-range embedding effects of electrostatic and quantum nature brought about by the MgO crystalline lattice, as well as electron correlation and spin-orbit effects within the (NiO6)10- cluster. The spin-orbit calculations have been performed using the spin-orbit-CI WB-AIMP method [Chem. Phys. Lett. 147, 597 (1988); J. Chem. Phys. 102, 8078 (1995)] which has been recently proposed and is applied here for the first time to the field of impurities in crystals. The WB-AIMP method is extended in order to handle correlation effects which, being necessary to produce accurate energy differences between spin-free states, are not needed for the proper calculation of spin-orbit couplings. The extension of the WB-AIMP method, which is also aimed at keeping the size of the spin-orbit-CI within reasonable limits, is based on the use of spin-free-state shifting operators. It is shown that the unreasonable spin-orbit splittings obtained for MgO:Ni2+ in spin-orbit-CI calculations correlating only 8 electrons become correct when the proposed extension is applied, so that the same CI space is used but energy corrections due to correlating up to 26 electrons are included. The results of the ligand field spectrum of MgO:Ni2+ show good overall agreement with the experimental measurements and a reassignment of the observed Eg(b3T1g) excited state is proposed and discussed.

Equation-of-motion coupled-cluster method for doubly ionized states with spin-orbit coupling.

PubMed

Wang, Zhifan; Hu, Shu; Wang, Fan; Guo, Jingwei

2015-04-14

In this work, we report implementation of the equation-of-motion coupled-cluster method for doubly ionized states (EOM-DIP-CC) with spin-orbit coupling (SOC) using a closed-shell reference. Double ionization potentials (DIPs) are calculated in the space spanned by 2h and 3h1p determinants with the EOM-DIP-CC approach at the CC singles and doubles level (CCSD). Time-reversal symmetry together with spatial symmetry is exploited to reduce computational effort. To circumvent the problem of unstable dianion references when diffuse basis functions are included, nuclear charges are scaled. Effect of this stabilization potential on DIPs is estimated based on results from calculations using a small basis set without diffuse basis functions. DIPs and excitation energies of some low-lying states for a series of open-shell atoms and molecules containing heavy elements with two unpaired electrons have been calculated with the EOM-DIP-CCSD approach. Results show that this approach is able to afford a reliable description on SOC splitting. Furthermore, the EOM-DIP-CCSD approach is shown to provide reasonable excitation energies for systems with a dianion reference when diffuse basis functions are not employed.

Equation-of-motion coupled-cluster method for doubly ionized states with spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhifan; Hu, Shu; Guo, Jingwei

2015-04-14

In this work, we report implementation of the equation-of-motion coupled-cluster method for doubly ionized states (EOM-DIP-CC) with spin-orbit coupling (SOC) using a closed-shell reference. Double ionization potentials (DIPs) are calculated in the space spanned by 2h and 3h1p determinants with the EOM-DIP-CC approach at the CC singles and doubles level (CCSD). Time-reversal symmetry together with spatial symmetry is exploited to reduce computational effort. To circumvent the problem of unstable dianion references when diffuse basis functions are included, nuclear charges are scaled. Effect of this stabilization potential on DIPs is estimated based on results from calculations using a small basis setmore » without diffuse basis functions. DIPs and excitation energies of some low-lying states for a series of open-shell atoms and molecules containing heavy elements with two unpaired electrons have been calculated with the EOM-DIP-CCSD approach. Results show that this approach is able to afford a reliable description on SOC splitting. Furthermore, the EOM-DIP-CCSD approach is shown to provide reasonable excitation energies for systems with a dianion reference when diffuse basis functions are not employed.« less

Periodic driving control of Raman-induced spin-orbit coupling in Bose-Einstein condensates: The heating mechanisms

NASA Astrophysics Data System (ADS)

Gomez Llorente, J. M.; Plata, J.

2016-06-01

We focus on a technique recently implemented for controlling the magnitude of synthetic spin-orbit coupling (SOC) in ultracold atoms in the Raman-coupling scenario. This technique uses a periodic modulation of the Raman-coupling amplitude to tune the SOC. Specifically, it has been shown that the effect of a high-frequency sinusoidal modulation of the Raman-laser intensity can be incorporated into the undriven Hamiltonian via effective parameters, whose adiabatic variation can therefore be used to tune the SOC. Here, we characterize the heating mechanisms that can be relevant to this method. We identify the main mechanism responsible for the heating observed in the experiments as basically rooted in driving-induced transfer of population to excited states. Characteristics of that process determined by the harmonic trapping, the decay of the excited states, and the technique used for preparing the system are discussed. Additional heating, rooted in departures from adiabaticity in the variation of the effective parameters, is also described. Our analytical study provides some clues that may be useful in the design of strategies for curbing the effects of heating on the efficiency of the control methods.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruhman, Jonathan; Kozii, Vladyslav; Fu, Liang

In this work, we study how an inversion-breaking quantum critical point affects the ground state of a one-dimensional electronic liquid with repulsive interaction and spin-orbit coupling. We find that regardless of the interaction strength, the critical fluctuations always lead to a gap in the electronic spin sector. The origin of the gap is a two-particle backscattering process, which becomes relevant due to renormalization of the Luttinger parameter near the critical point. The resulting spin-gapped state is topological and can be considered as a one-dimensional version of a spin-triplet superconductor. Interestingly, in the case of a ferromagnetic critical point, the Luttingermore » parameter is renormalized in the opposite manner, such that the system remains nonsuperconducting.« less

Spin-dependent dwell times of electron tunneling through double- and triple-barrier structures

NASA Astrophysics Data System (ADS)

Erić, Marko; Radovanović, Jelena; Milanović, Vitomir; Ikonić, Zoran; Indjin, Dragan

2008-04-01

We have analyzed the influence of Dresselhaus and Rashba spin-orbit couplings (caused by the bulk inversion asymmetry and the structural asymmetry, respectively) on electron tunneling through a double- and triple-barrier structures, with and without an externally applied electric field. The results indicate that the degree of structural asymmetry and external electric field can greatly affect the dwell times of electrons with opposite spin orientation. This opens up the possibilities of obtaining efficient spin separation in the time domain. The material system of choice is AlxGa1-xSb, and the presented model takes into account the position dependence of material parameters, as well as the effects of band nonparabolicity.

Numerical Researches on Dynamical Systems with Relativistic Spin

NASA Astrophysics Data System (ADS)

Han, W. B.

2010-04-01

It is well known that spinning compact binaries are one of the most important research objects in the universe. Especially, EMRIs (extreme mass ratio inspirals) involving stellar compact objects which orbit massive black holes, are considered to be primary sources of gravitational radiation (GW) which could be detected by the space-based interferometer LISA. GW signals from EMRIs can be used to test general relativity, measure the masses and spins of central black holes and study essential physics near horizons. Compared with the situation without spin, the complexity of extreme objects, most of which rotate very fast, is much higher. So the dynamics of EMRI systems are numerically and analytically studied. We focus on how the spin effects on the dynamics of these systems and the produced GW radiations. Firstly, an ideal model of spinning test particles around Kerr black hole is considered. For equatorial orbits, we present the correct expression of effective potential and analyze the stability of circular orbits. Especially, the gravitational binding energy and frame-dragging effect of extreme Kerr black hole are much bigger than those without spin. For general orbits, spin can monotonically enlarge orbital inclination and destroy the symmetry of orbits about equatorial plane. It is the most important that extreme spin can produce orbital chaos. By carefully investigating the relations between chaos and orbital parameters, we point out that chaos usually appears for orbits with small pericenter, big eccentricity and orbital inclination. It is emphasized that Poincaré section method is invalid to detect the chaos of spinning particles, and the way of systems toward chaos is the period-doubling bifurcation. Furthermore, we study how spins effect on GW radiations from spinning test particles orbiting Kerr black holes. It is found that spins can increase orbit eccentricity and then make h+ component be detected more easily. But for h× component, because spins change orbital inclination in a complicated way, it is more difficult to build GW signal templates. Secondly, based on the scalar gravity theory, a numerical relativistic model of EMRIs is constructed to consider the self-gravity and radiation reaction of low-mass objects. Finally, we develop a new method with multiple steps for Hamilton systems to meet the needs of numerical researches. This method can effectively maintain each conserved quantity of the separable Hamilton system. In addition, for constrained system with a few first integrals, we present a new numerical stabilization method named as adjustment-stabilization method, which can maintain all known conserved quantities in a given dynamical system and greatly improve the numerical accuracy. Our new method is the most complete stabilization method up to now.

Many-body physics using cold atoms

NASA Astrophysics Data System (ADS)

Sundar, Bhuvanesh

Advances in experiments on dilute ultracold atomic gases have given us access to highly tunable quantum systems. In particular, there have been substantial improvements in achieving different kinds of interaction between atoms. As a result, utracold atomic gases oer an ideal platform to simulate many-body phenomena in condensed matter physics, and engineer other novel phenomena that are a result of the exotic interactions produced between atoms. In this dissertation, I present a series of studies that explore the physics of dilute ultracold atomic gases in different settings. In each setting, I explore a different form of the inter-particle interaction. Motivated by experiments which induce artificial spin-orbit coupling for cold fermions, I explore this system in my first project. In this project, I propose a method to perform universal quantum computation using the excitations of interacting spin-orbit coupled fermions, in which effective p-wave interactions lead to the formation of a topological superfluid. Motivated by experiments which explore the physics of exotic interactions between atoms trapped inside optical cavities, I explore this system in a second project. I calculate the phase diagram of lattice bosons trapped in an optical cavity, where the cavity modes mediates effective global range checkerboard interactions between the atoms. I compare this phase diagram with one that was recently measured experimentally. In two other projects, I explore quantum simulation of condensed matter phenomena due to spin-dependent interactions between particles. I propose a method to produce tunable spin-dependent interactions between atoms, using an optical Feshbach resonance. In one project, I use these spin-dependent interactions in an ultracold Bose-Fermi system, and propose a method to produce the Kondo model. I propose an experiment to directly observe the Kondo effect in this system. In another project, I propose using lattice bosons with a large hyperfine spin, which have Feshbach-induced spin-dependent interactions, to produce a quantum dimer model. I propose an experiment to detect the ground state in this system. In a final project, I develop tools to simulate the dynamics of fermionic superfluids in which fermions interact via a short-range interaction.

Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group

NASA Astrophysics Data System (ADS)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

2018-05-01

We present a state interaction spin-orbit coupling method to calculate electron paramagnetic resonance g-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute g-tensors for the TiF3 and CuCl42 - complexes, a [2Fe-2S] model of the active center of ferredoxins, and a Mn4CaO5 model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining g-tensors in multireference calculations with a large number of open shells.