Gravity dual of spin and charge density waves

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2014-12-01

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

High resolution MR based polymer dosimetry versus film densitometry: a systematic study based on the modulation transfer function approach.

PubMed

Berg, A; Pernkopf, M; Waldhäusl, C; Schmidt, W; Moser, E

2004-09-07

Precise methods of modem radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods-ionization chambers, TLD arrangements or silicon detectors, for example-are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer dosimetry (MRPD) appears to be well suited to three-dimensional high resolution relative dosimetry but the spatial resolution based on a systematic modulation transfer function (MTF) approach has not yet been investigated. We offer a theoretical construct for addressing the spatial resolution in different dose imaging systems, i.e. the dose modulation transfer function (DMTF) approach, an experimental realization of this concept with a phantom and quantitative comparisons between two dosimetric systems: polymer gel and film dosimetry. Polymer gel samples were irradiated by Co-60 photons through an absorber grid which is characterized by periodic structures of different spatial period (a), the smallest one at width of a/2 = 280 microm. The modulation in dose under the grid is visualized via calibrated, high resolution, parameter-selective (T2) and dose images based on multi-echo MR imaging. The DMTF is obtained from the modulation depth of the spin-spin relaxation time (T2) after calibration. Voxel sizes below 0.04 mm3 could be achieved, which are significantly smaller than those reported in MR based dose imaging on polymer gels elsewhere, using a powerful gradient system and a highly sensitive small birdcage resonator on a whole-body 3T MR scanner. Dose modulations at 22% of maximum dose amplitude could be observed at about 2 line pairs per mm. The polymer DMTF results are compared to those of a typical clinical film-scanner system. This study demonstrates that MR based gel dosimetry at 200 microm pixel resolution might even be superior, with reference to relative spatial resolution, to the results of a standard film-scanner system offering a nominal scan resolution of 200 microm.

Astrophysics-independent bounds on the annual modulation of dark matter signals.

PubMed

Herrero-Garcia, Juan; Schwetz, Thomas; Zupan, Jure

2012-10-05

We show how constraints on the time integrated event rate from a given dark matter (DM) direct detection experiment can be used to bound the amplitude of the annual modulation signal in another experiment. The method requires only mild assumptions about the properties of the local DM distribution: that it is temporally stable on the scale of months and spatially homogeneous on the ecliptic. We apply the method to the annual modulation signal in DAMA/LIBRA, which we compare to the bounds derived from XENON10, XENON100, cryogenic DM search, and SIMPLE data. Assuming a DM mass of 10 GeV, we show that under the above assumptions about the DM halo, a DM interpretation of the DAMA/LIBRA signal is excluded for several classes of models: at 6.3σ (4.6σ) for elastic isospin conserving (violating) spin-independent interactions, and at 4.9σ for elastic spin-dependent interactions on protons.

Topological helical edge states in water waves over a topographical bottom

NASA Astrophysics Data System (ADS)

Wu, Shiqiao; Wu, Ying; Mei, Jun

2018-02-01

We present the discovery of topologically protected helical edge states in water wave systems, which are realized in water wave propagating over a topographical bottom whose height is modulated periodically in a two-dimensional triangular pattern. We develop an effective Hamiltonian to characterize the dispersion relation and use spin Chern numbers to classify the topology. Through full-wave simulations we unambiguously demonstrate the robustness of the helical edge states which are immune to defects and disorders so that the backscattering loss is significantly reduced. A spin splitter is designed for water wave systems, where helical edge states with different spin orientations are spatially separated with each other, and potential applications are discussed.

Optical Dependence of Electrically Detected Magnetic Resonance in Lightly Doped Si:P Devices

NASA Astrophysics Data System (ADS)

Zhu, Lihuang; van Schooten, Kipp J.; Guy, Mallory L.; Ramanathan, Chandrasekhar

2017-06-01

Using frequency-modulated electrically detected magnetic resonance (EDMR), we show that signals measured from lightly doped (1.2 - 5 ×1 015 cm-3 ) silicon devices vary significantly with the wavelength of the optical excitation used to generate the mobile carriers. We measure EDMR spectra at 4.2 K as a function of modulation frequency and applied microwave power using a 980-nm laser, a 405-nm laser, and a broadband white-light source. EDMR signals are observed from the phosphorus donor and two distinct defect species in all of the experiments. With near-infrared irradiation, we find that the EDMR signal primarily arises from donor-defect pairs, while, at higher photon energies, there are significant additional contributions from defect-defect pairs. The contribution of spins from different spatial regions to the EDMR signal is seen to vary as the optical penetration depth changes from about 120 nm at 405-nm illumination to 100 μ m at 980-nm illumination. The modulation frequency dependence of the EDMR signal shows that the energy of the optical excitation strongly modulates the kinetics of the underlying spin-dependent recombination (SDR) process. Careful tuning of the optical photon energy could therefore be used to control both the subset of spin pairs contributing to the EDMR signal and the dynamics of the SDR process.

Strong-coupling induced damping of spin-echo modulations in magic-angle-spinning NMR: Implications for J coupling measurements in disordered solids

NASA Astrophysics Data System (ADS)

Guerry, Paul; Brown, Steven P.; Smith, Mark E.

2017-10-01

In the context of improving J coupling measurements in disordered solids, strong coupling effects have been investigated in the spin-echo and refocused INADEQUATE spin-echo (REINE) modulations of three- and four-spin systems under magic-angle-spinning (MAS), using density matrix simulations and solid-state NMR experiments on a cadmium phosphate glass. Analytical models are developed for the different modulation regimes, which are shown to be distinguishable in practice using Akaike's information criterion. REINE modulations are shown to be free of the damping that occurs for spin-echo modulations when the observed spin has the same isotropic chemical shift as its neighbour. Damping also occurs when the observed spin is bonded to a strongly-coupled pair. For mid-chain units, the presence of both direct and relayed damping makes both REINE and spin-echo modulations impossible to interpret quantitatively. We nonetheless outline how a qualitative comparison of the modulation curves can provide valuable information on disordered networks, possibly also pertaining to dynamic effects therein.

Modulation of pure spin currents with a ferromagnetic insulator

NASA Astrophysics Data System (ADS)

Villamor, Estitxu; Isasa, Miren; Vélez, Saül; Bedoya-Pinto, Amilcar; Vavassori, Paolo; Hueso, Luis E.; Bergeret, F. Sebastián; Casanova, Fèlix

2015-01-01

We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y3F e5O12 (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the nonlocal resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a path towards the development of spin logics.

3He Diffusion MRI of the Lung

PubMed Central

Conradi, Mark S.; Yablonskiy, Dmitriy A.; Woods, Jason C.; Gierada, David S.; Jacob, Richard E.; Chang, Yulin V.; Choong, Cliff K.; Sukstanskii, Alex L.; Tanoli, Tariq; Lefrak, Stephen S.; Cooper, Joel D.

2007-01-01

Rationale and Objectives MR imaging of the restricted diffusion of laser-polarized 3He gas provides unique insights into the changes in lung microstructure in emphysema. Results We discuss measurements of ventilation (spin density), mean diffusivity, and the anisotropy of diffusion, which yields the mean acinar airway radius. In addition, the use of spatially modulated longitudinal magnetization allows diffusion to be measured over longer distances and times, with sensitivity to collateral ventilation paths. Early results are also presented for spin density and diffusivity maps made with a perfluorinated inert gas, C3F8. Methods Techniques for purging and imaging excised lungs are discussed. PMID:16253852

Spin wave mode coexistence on the nanoscale: A consequence of the Oersted field induced asymmetric energy landscape

NASA Astrophysics Data System (ADS)

Dumas, Randy

2014-03-01

The emerging field of magnonics relies on the systematic generation, manipulation, and detection of spin waves (SWs). Nanocontact spin torque oscillators (NC-STOs) provide an ideal platform to study spin transfer torque induced SW emission. In analogy to two species competing for the same food supply it has been argued that only one SW mode can survive in the steady state. However, as evidenced in many experiments clear signatures of mode-hopping are often observed. Here, we present a third possibility, namely that under the correct experimental conditions, mode coexistencecan be realized in NC-STOs. Micromagnetic simulations reveal that the SW modes are spatially separated under the NC. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field in the vicinity of the NC and further promoted by SW localization. Finally, both simulation and experiment reveal a weak low frequency signal exactly at the difference of the mode frequencies, consistent with inter-modulation of two coexistent modes. The Swedish Research Council, The Swedish Foundation for Strategic Research, and the Knut and Alice Wallenberg Foundation are acknowledged. ANL is a US DOE Science Laboratory operated under contract no. DE-AC02-06CH11357 by UChicago Argonne, LLC.

A large-alphabet three-party quantum key distribution protocol based on orbital and spin angular momenta hybrid entanglement

NASA Astrophysics Data System (ADS)

Lai, Hong; Luo, Mingxing; Zhang, Jun; Pieprzyk, Josef; Pan, Lei; Orgun, Mehmet A.

2018-07-01

The orthogonality of the orbital angular momentum (OAM) eigenstates enables a single photon carry an arbitrary number of bits. Moreover, additional degrees of freedom (DOFs) of OAM can span a high-dimensional Hilbert space, which could greatly increase information capacity and security. Moreover, the use of the spin angular momentum-OAM hybrid entangled state can increase Shannon dimensionality, because photons can be hybrid entangled in multiple DOFs. Based on these observations, we develop a hybrid entanglement quantum key distribution (QKD) protocol to achieve three-party quantum key distribution without classical message exchanges. In our proposed protocol, a communicating party uses a spatial light modulator (SLM) and a specific phase hologram to modulate photons' OAM state. Similarly, the other communicating parties use their SLMs and the fixed different phase holograms to modulate the OAM entangled photon pairs, producing the shared key among the parties Alice, Bob and Charlie without classical message exchanges. More importantly, when the same operation is repeated for every party, our protocol could be extended to a multiple-party QKD protocol.

300 MHz continuous wave electron paramagnetic resonance spectrometer for small animal in vivo imaging

NASA Astrophysics Data System (ADS)

Koscielniak, J.; Devasahayam, N.; Moni, M. S.; Kuppusamy, P.; Yamada, K.; Mitchell, J. B.; Krishna, M. C.; Subramanian, S.

2000-11-01

Design and construction of an electron paramagnetic resonance (EPR) spectrometer, operating in the continuous wave mode in the radio frequency (rf) region, and capable of performing spectroscopy and in vivo imaging of paramagnetic spin probes is described. A resonant frequency of 300 MHz was chosen to provide the required sensitivity at nontoxic levels of commonly used spin probes and penetration of the rf in small animals. Three major components, the magnet, the radio frequency signal detection bridge, and the data acquisition module are described in this article. Integration of a rapid scan capability to reduce imaging time is also described. Two- and three-dimensional EPR images of the spin probe distribution in phantom objects as well as from in vivo experiments are reported. From the EPR images, morphology of some internal organs could be recognized. EPR images of the spin probe distribution in mice suggest differences in perfusion of the spin probe between normal and tumor regions. Addition of a spectral dimension to spatial images should enable differentiation of oxygen status in normal and pathological conditions.

Visualization of anomalous Ettingshausen effect in a ferromagnetic film: Direct evidence of different symmetry from spin Peltier effect

NASA Astrophysics Data System (ADS)

Seki, T.; Iguchi, R.; Takanashi, K.; Uchida, K.

2018-04-01

Spatial distribution of temperature modulation due to the anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt/yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE strongly depends on the direction of magnetization, leading to the remarkable different temperature profiles in the FePt thin film between the in-plane and perpendicularly magnetized configurations.

Thermal imaging of spin Peltier effect

NASA Astrophysics Data System (ADS)

Daimon, Shunsuke; Iguchi, Ryo; Hioki, Tomosato; Saitoh, Eiji; Uchida, Ken-Ichi

2016-12-01

The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The `spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.

Three-dimensional hologram display system

NASA Technical Reports Server (NTRS)

Mintz, Frederick (Inventor); Chao, Tien-Hsin (Inventor); Bryant, Nevin (Inventor); Tsou, Peter (Inventor)

2009-01-01

The present invention relates to a three-dimensional (3D) hologram display system. The 3D hologram display system includes a projector device for projecting an image upon a display medium to form a 3D hologram. The 3D hologram is formed such that a viewer can view the holographic image from multiple angles up to 360 degrees. Multiple display media are described, namely a spinning diffusive screen, a circular diffuser screen, and an aerogel. The spinning diffusive screen utilizes spatial light modulators to control the image such that the 3D image is displayed on the rotating screen in a time-multiplexing manner. The circular diffuser screen includes multiple, simultaneously-operated projectors to project the image onto the circular diffuser screen from a plurality of locations, thereby forming the 3D image. The aerogel can use the projection device described as applicable to either the spinning diffusive screen or the circular diffuser screen.

Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Ando, Yuichiro; Kameno, Makoto; Tahara, Takayuki; Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-09-01

Spin transport in nondegenerate semiconductors is expected to pave the way to the creation of spin transistors, spin logic devices, and reconfigurable logic circuits, because room-temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in nondegenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observe the modulation of the Hanle-type spin-precession signals, which is a characteristic spin dynamics in nondegenerate semiconductors. We obtain long spin transport of more than 20 μm and spin rotation greater than 4π at RT. We also observe gate-induced modulation of spin-transport signals at RT. The modulation of the spin diffusion length as a function of a gate voltage is successfully observed, which we attribute to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to lead to the creation of practical Si-based spin MOSFETs.

Feasibility test of a solid state spin-scan photo-imaging system

NASA Technical Reports Server (NTRS)

Laverty, N. P.

1973-01-01

The feasibility of using a solid-state photo-imaging system to obtain resolution imagery from a Pioneer-type spinning spacecraft in future exploratory missions to the outer planets is discussed. Evaluation of the photo-imaging system performance, based on electrical video signal analysis recorded on magnetic tape, shows that the signal-to-noise (S/N) ratios obtained at low spatial frequencies exceed the anticipated performance and that measured modulation transfer functions exhibited some degradation in comparison with the estimated values, primarily owing to the difficulty in obtaining a precise focus of the optical system in the laboratory with the test patterns in close proximity to the objective lens. A preliminary flight model design of the photo-imaging system is developed based on the use of currently available phototransistor arrays. Image quality estimates that will be obtained are presented in terms of S/N ratios and spatial resolution for the various planets and satellites. Parametric design tradeoffs are also defined.

Large current modulation and tunneling magnetoresistance change by a side-gate electric field in a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor.

PubMed

Kanaki, Toshiki; Yamasaki, Hiroki; Koyama, Tomohiro; Chiba, Daichi; Ohya, Shinobu; Tanaka, Masaaki

2018-05-08

A vertical spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) is a promising low-power device for the post scaling era. Here, using a ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs channel layer, we demonstrate a large drain-source current I DS modulation by a gate-source voltage V GS with a modulation ratio up to 130%, which is the largest value that has ever been reported for vertical spin field-effect transistors thus far. We find that the electric field effect on indirect tunneling via defect states in the GaAs channel layer is responsible for the large I DS modulation. This device shows a tunneling magnetoresistance (TMR) ratio up to ~7%, which is larger than that of the planar-type spin MOSFETs, indicating that I DS can be controlled by the magnetization configuration. Furthermore, we find that the TMR ratio can be modulated by V GS . This result mainly originates from the electric field modulation of the magnetic anisotropy of the GaMnAs ferromagnetic electrodes as well as the potential modulation of the nonmagnetic semiconductor GaAs channel layer. Our findings provide important progress towards high-performance vertical spin MOSFETs.

Phase modulation in dipolar-coupled A 2 spin systems: effect of maximum state mixing in 1H NMR in vivo

NASA Astrophysics Data System (ADS)

Schröder, Leif; Schmitz, Christian; Bachert, Peter

2004-12-01

Coupling constants of nuclear spin systems can be determined from phase modulation of multiplet resonances. Strongly coupled systems such as citrate in prostatic tissue exhibit a more complex modulation than AX connectivities, because of substantial mixing of quantum states. An extreme limit is the coupling of n isochronous spins (A n system). It is observable only for directly connected spins like the methylene protons of creatine and phosphocreatine which experience residual dipolar coupling in intact muscle tissue in vivo. We will demonstrate that phase modulation of this "pseudo-strong" system is quite simple compared to those of AB systems. Theory predicts that the spin-echo experiment yields conditions as in the case of weak interactions, in particular, the phase modulation depends linearly on the line splitting and the echo time.

Spin-Current-Controlled Modulation of the Magnon Spin Conductance in a Three-Terminal Magnon Transistor

NASA Astrophysics Data System (ADS)

Cornelissen, L. J.; Liu, J.; van Wees, B. J.; Duine, R. A.

2018-03-01

Efficient manipulation of magnon spin transport is crucial for developing magnon-based spintronic devices. In this Letter, we provide proof of principle of a method for modulating the diffusive transport of thermal magnons in an yttrium iron garnet channel between injector and detector contacts. The magnon spin conductance of the channel is altered by increasing or decreasing the magnon chemical potential via spin Hall injection of magnons by a third modulator electrode. We obtain a modulation efficiency of 1.6 %/mA at T =250 K . Finite element modeling shows that this could be increased to well above 10 %/mA by reducing the thickness of the channel, providing interesting prospects for the development of thermal-magnon-based logic circuits.

Concept for room temperature single-spin tunneling force microscopy with atomic spatial resolution

NASA Astrophysics Data System (ADS)

Payne, Adam

A study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single electron tunneling between two electrically isolated paramagnetic states. Single-spin magnetic resonance detection is possible by measuring the force detected tunneling charge noise on and off spin resonance. Simulation results of this charge noise, based upon physical models of the tunneling and spin physics, are directly compared to measured atomic force microscopy (AFM) system noise. The results show that the approach could provide single-spin measurement of electrically isolated defect states with atomic spatial resolution at room temperature.

Evolution of Spin and Superorbital Modulation in 4U 0114+650

NASA Astrophysics Data System (ADS)

Hu, Chin-Ping; Ng, Chi-Yung; Chou, Yi

2016-09-01

We report on a systematic analysis of the spin and superorbital modulations of the high-mass X-ray binary 4U 0114+650, which consists of the slowest spinning neutron star known. Utilizing dynamic power spectra, we found that the spin period varied dramatically during the RXTE ASM and Swift BAT observations. This variation consists of a long-term spin-up trend, and two ~1,000 day and one ~600 day random walk epochs previously, MJD 51,000, ~MJD 51,400-52,000, and ~MJD 55,100-56,100. We further found that the events appear together with depressions of superorbital modulation amplitude. This provides evidence of the existence of an accretion disk, although the physical mechanism of superorbital modulation remains unclear. Furthermore, the decrease of the superorbital modulation amplitude may be associated with the decrease of mass accretion rate from the disk, and may distribute the accretion torque of the neutron star randomly in time.

Direct current modulation of spin-Hall-induced spin torque ferromagnetic resonance in platinum/permalloy bilayer thin films

NASA Astrophysics Data System (ADS)

Hirayama, Shigeyuki; Mitani, Seiji; Otani, YoshiChika; Kasai, Shinya

2018-06-01

We examined the spin-Hall-induced spin torque ferromagnetic resonance (ST-FMR) in platinum/permalloy bilayer thin films under bias direct current (DC). The bias DC modulated the symmetric components of the ST-FMR spectra, while no dominant modulation was found in the antisymmetric components. A detailed analysis in combination with simple model calculations clarified that the major origin of the modulation can be attributed to the DC resistance change under the precessional motion of magnetization. This effect is the second order contribution for the precession angle, even though the contribution can be comparable to the rectification voltage under some specific conditions.

Spin-Current-Controlled Modulation of the Magnon Spin Conductance in a Three-Terminal Magnon Transistor.

PubMed

Cornelissen, L J; Liu, J; van Wees, B J; Duine, R A

2018-03-02

Efficient manipulation of magnon spin transport is crucial for developing magnon-based spintronic devices. In this Letter, we provide proof of principle of a method for modulating the diffusive transport of thermal magnons in an yttrium iron garnet channel between injector and detector contacts. The magnon spin conductance of the channel is altered by increasing or decreasing the magnon chemical potential via spin Hall injection of magnons by a third modulator electrode. We obtain a modulation efficiency of 1.6%/mA at T=250  K. Finite element modeling shows that this could be increased to well above 10%/mA by reducing the thickness of the channel, providing interesting prospects for the development of thermal-magnon-based logic circuits.

Polaron spin echo envelope modulations in an organic semiconducting polymer

DOE PAGES

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

Here, we present a theoretical analysis of the electron spin echo envelope modulation (ESEEM) spectra of polarons in semiconducting π -conjugated polymers. We show that the contact hyperfine coupling and the dipolar interaction between the polaron and the proton spins give rise to different features in the ESEEM spectra. Our theory enables direct selective probe of different groups of nuclear spins, which affect the polaron spin dynamics. Namely, we demonstrate how the signal from the distant protons (coupled to the polaron spin via dipolar interactions) can be distinguished from the signal coming from the protons residing on the polaron sitemore » (coupled to the polaron spin via contact hyperfine interaction). We propose a method for directly probing the contact hyperfine interaction, that would enable detailed study of the polaron orbital state and its immediate environment. Lastly, we also analyze the decay of the spin echo modulation, and its connection to the polaron transport.« less

EPR oximetry in three spatial dimensions using sparse spin distribution

NASA Astrophysics Data System (ADS)

Som, Subhojit; Potter, Lee C.; Ahmad, Rizwan; Vikram, Deepti S.; Kuppusamy, Periannan

2008-08-01

A method is presented to use continuous wave electron paramagnetic resonance imaging for rapid measurement of oxygen partial pressure in three spatial dimensions. A particulate paramagnetic probe is employed to create a sparse distribution of spins in a volume of interest. Information encoding location and spectral linewidth is collected by varying the spatial orientation and strength of an applied magnetic gradient field. Data processing exploits the spatial sparseness of spins to detect voxels with nonzero spin and to estimate the spectral linewidth for those voxels. The parsimonious representation of spin locations and linewidths permits an order of magnitude reduction in data acquisition time, compared to four-dimensional tomographic reconstruction using traditional spectral-spatial imaging. The proposed oximetry method is experimentally demonstrated for a lithium octa- n-butoxy naphthalocyanine (LiNc-BuO) probe using an L-band EPR spectrometer.

Rabi oscillation and electron-spin-echo envelope modulation of the photoexcited triplet spin system in silicon

NASA Astrophysics Data System (ADS)

Akhtar, Waseem; Sekiguchi, Takeharu; Itahashi, Tatsumasa; Filidou, Vasileia; Morton, John J. L.; Vlasenko, Leonid; Itoh, Kohei M.

2012-09-01

We report on a pulsed electron paramagnetic resonance (EPR) study of the photoexcited triplet state (S=1) of oxygen-vacancy centers in silicon. Rabi oscillations between the triplet sublevels are observed using coherent manipulation with a resonant microwave pulse. The Hahn echo and stimulated echo decay profiles are superimposed with strong modulations known as electron-spin-echo envelope modulation (ESEEM). The ESEEM spectra reveal a weak but anisotropic hyperfine coupling between the triplet electron spin and a 29Si nuclear spin (I=1/2) residing at a nearby lattice site, that cannot be resolved in conventional field-swept EPR spectra.

Thermodynamic properties of Fermi gases in states with defined many-body spins

NASA Astrophysics Data System (ADS)

Yurovsky, Vladimir

2016-05-01

Zero-range interactions in cold spin- 1 / 2 Fermi gases can be described by single interaction strength, since collisions of atoms in the same spin state are forbidden by the Pauli principle. In a spin-independent trap potential (even in the presence of a homogeneous spin-dependent external field), the gas can persist in a state with the given many-body spin, since the spin operator commutes with the Hamiltonian. Spin and spatial degrees of freedom in such systems are separated, and the spin and spatial wavefunctions form non-Abelian irreducible representations of the symmetric group, unless the total spin is S = N / 2 for N atoms (see). Although the total wavefunction, being a linear combination of products of the spin and spatial functions, is permutation-antisymmetric, the non-Abelian permutation symmetry is disclosed in the matrix elements and, as demonstrated here, in thermodynamic properties. The effects include modification of the specific heat and compressibility of the gas.

Correction of mid-spatial-frequency errors by smoothing in spin motion for CCOS

NASA Astrophysics Data System (ADS)

Zhang, Yizhong; Wei, Chaoyang; Shao, Jianda; Xu, Xueke; Liu, Shijie; Hu, Chen; Zhang, Haichao; Gu, Haojin

2015-08-01

Smoothing is a convenient and efficient way to correct mid-spatial-frequency errors. Quantifying the smoothing effect allows improvements in efficiency for finishing precision optics. A series experiments in spin motion are performed to study the smoothing effects about correcting mid-spatial-frequency errors. Some of them use a same pitch tool at different spinning speed, and others at a same spinning speed with different tools. Introduced and improved Shu's model to describe and compare the smoothing efficiency with different spinning speed and different tools. From the experimental results, the mid-spatial-frequency errors on the initial surface were nearly smoothed out after the process in spin motion and the number of smoothing times can be estimated by the model before the process. Meanwhile this method was also applied to smooth the aspherical component, which has an obvious mid-spatial-frequency error after Magnetorheological Finishing processing. As a result, a high precision aspheric optical component was obtained with PV=0.1λ and RMS=0.01λ.

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.

Modulated magnetic structure of F e3P O7 as seen by 57Fe Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Sobolev, A. V.; Akulenko, A. A.; Glazkova, I. S.; Pankratov, D. A.; Presniakov, I. A.

2018-03-01

The paper reports results of the 57Fe Mössbauer measurements on an F e3P O4O3 powder sample recorded at various temperatures, including the point of magnetic phase transition TN≈163 K . The spectra measured above TN consist of a quadrupole doublet with high quadrupole splitting of Δ300 K≈1.10 mm /s , emphasizing that F e3 + ions are located in crystal positions with a strong electric-field gradient (EFG). To predict the sign and orientation of the main components of the EFG tensor, we calculated the EFG using the density-functional-theory approach. In the temperature range T

What happens when spins meet for ionizing radiation dosimetry?

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

Pavoni, Juliana F.; Baffa, Oswaldo, E-mail: baffa@usp.br; Neves-Junior, Wellington F. P.

2016-07-07

Electron spin resonance (ESR) and magnetic resonance imaging (MRI) can be used to measure radiation dose deposited in different milieu through its effects. Radiation can break chemical bonds and if they produce stable free radicals, ESR can measure their concentration through their spins and a dose can be inferred. Ionizing radiation can also promote polymerization and in this case proton relaxation times can be measured and an image weighed by T2 can be produced giving spatial information about dose. A review of the basics of these applications is presented concluding with an end-to-end test using a composite Gel-Alanine phantom tomore » validate 3-dimensionally dose distribution delivered in a simulation of Volume Modulated Arch Therapy on the simultaneous treatment of multiple brain metastases. The results obtained with the gel and alanine dosimeters are consistent with the expected by the treatment planning system, showing the potential of this multidosimetric approach and validating dosimetrically the multiple brain metastases treatment using VMAT.« less

What happens when spins meet for ionizing radiation dosimetry?

NASA Astrophysics Data System (ADS)

Pavoni, Juliana F.; Neves-Junior, Wellington F. P.; Baffa, Oswaldo

2016-07-01

Electron spin resonance (ESR) and magnetic resonance imaging (MRI) can be used to measure radiation dose deposited in different milieu through its effects. Radiation can break chemical bonds and if they produce stable free radicals, ESR can measure their concentration through their spins and a dose can be inferred. Ionizing radiation can also promote polymerization and in this case proton relaxation times can be measured and an image weighed by T2 can be produced giving spatial information about dose. A review of the basics of these applications is presented concluding with an end-to-end test using a composite Gel-Alanine phantom to validate 3-dimensionally dose distribution delivered in a simulation of Volume Modulated Arch Therapy on the simultaneous treatment of multiple brain metastases. The results obtained with the gel and alanine dosimeters are consistent with the expected by the treatment planning system, showing the potential of this multidosimetric approach and validating dosimetrically the multiple brain metastases treatment using VMAT.

Spin-wave energy dispersion of a frustrated spin-½ Heisenberg antiferromagnet on a stacked square lattice.

PubMed

Majumdar, Kingshuk

2011-03-23

The effects of interlayer coupling and spatial anisotropy on the spin-wave excitation spectra of a three-dimensional spatially anisotropic, frustrated spin-½ Heisenberg antiferromagnet (HAFM) are investigated for the two ordered phases using second-order spin-wave expansion. We show that the second-order corrections to the spin-wave energies are significant and find that the energy spectra of the three-dimensional HAFM have similar qualitative features to the energy spectra of the two-dimensional HAFM on a square lattice. We also discuss the features that can provide experimental measures for the strength of the interlayer coupling, spatial anisotropy parameter, and magnetic frustration.

Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond

NASA Astrophysics Data System (ADS)

Ajoy, A.; Bissbort, U.; Lukin, M. D.; Walsworth, R. L.; Cappellaro, P.

2015-01-01

Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution. Here, we propose a method that, by exploiting the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin, can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. We propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.

Use of earth field spin echo NMR to search for liquid minerals

DOEpatents

Stoeffl, Wolfgang

2001-01-01

An instrument for measuring the spatial, qualitative and quantitative parameters of an underground nuclear magnetic resonance (NMR) active liquid mineral deposit, including oil and water. A phased array of excitation and receiver antennas on the surface and/or in a borehole excites the NMR active nuclei in the deposit, and using known techniques from magnetic resonance imaging (MRI), the spatial and quantitative distribution of the deposit can be measured. A surface array may utilize, for example, four large (50-500 diameter) diameter wire loops laid on the ground surface, and a weak (1.5-2.5 kHz) alternating current (AC) field applied, matching the NMR frequency of hydrogen in the rather flat and uniform earth magnetic field. For a short duration (a few seconds) an additional gradient field can be generated, superimposed to the earth field, by applying direct current (DC) to the grid (wire loops), enhancing the position sensitivity of the spin-echo and also suppressing large surface water signals by shifting them to a different frequency. The surface coil excitation can be combined with downhole receivers, which are much more radio-quiet compared to surface receivers, and this combination also enhances the position resolution of the MRI significantly. A downhole receiver module, for example, may have a 5.5 inch diameter and fit in a standard six inch borehole having a one-quarter inch thick stainless steel casing. The receiver module may include more than one receiver units for improved penetration and better position resolution.

Electrical detection of electron-spin-echo envelope modulations in thin-film silicon solar cells

NASA Astrophysics Data System (ADS)

Fehr, M.; Behrends, J.; Haas, S.; Rech, B.; Lips, K.; Schnegg, A.

2011-11-01

Electrically detected electron-spin-echo envelope modulations (ED-ESEEM) were employed to detect hyperfine interactions between nuclear spins and paramagnetic sites, determining spin-dependent transport processes in multilayer thin-film microcrystalline silicon solar cells. Electrical detection in combination with a modified Hahn-echo sequence was used to measure echo modulations induced by 29Si, 31P, and 1H nuclei weakly coupled to electron spins of paramagnetic sites in the amorphous and microcrystalline solar cell layers. In the case of CE centers in the μc-Si:H i-layer, the absence of 1H ESEEM modulations indicates that the adjacencies of CE centers are depleted from hydrogen atoms. On the basis of this result, we discuss several models for the microscopic origin of the CE center and conclusively assign those centers to coherent twin boundaries inside of crystalline grains in μc-Si:H.

Silk screen based dual spin-filter module for perfusion culture of adherent and non-adherent mammalian cells.

PubMed

Kamthan, Shweta; Gomes, James; Roychoudhury, Pradip K

2014-08-01

Spin-filters have been primarily used for producing therapeutic proteins from mammalian cells. However, disposability and/or high filter clogging of the existing spin-filter systems affect the process economy and productivity. Hence, to address these drawbacks a reusable dual spin-filter module for perfusion culture of adherent and non-adherent mammalian cells was designed. Two non-woven Bombyx mori silk layers were used as filter screen; the outer layer was conducive to cell attachment whilst the inner was non-conducive. Adherent cells can be cultured either in suspended mode using its inner single module or as monolayer of cells using its dual concentric module. We achieved 30 % higher urokinase productivity as compared to the stainless-steel spin-filter during perfusion experiments of adherent human kidney cells in suspended mode. This was due to the hydrophobic and negatively-charged silk screen that allows clog-free perfusion culture for prolonged periods.

High Performance Nuclear Magnetic Resonance Imaging Using Magnetic Resonance Force Microscopy

DTIC Science & Technology

2013-12-12

Micron- Size Ferromagnet . Physical Review Letters, 92(3) 037205 (2004) [22] A. Z. Genack and A. G. Redeld. Theory of nuclear spin diusion in a...perform spatially resolved scanned probe studies of spin dynamics in nanoscale ensembles of few electron spins of varying size . Our research culminated...perform spatially resolved scanned probe studies of spin dynamics in nanoscale ensembles of few electron spins of varying size . Our research culminated

A spin-modulated telescope for measurement of cosmic microwave background anisotropy

NASA Astrophysics Data System (ADS)

Staren, John William

The measurement of anisotropy in the Cosmic Microwave Background (CMB) advances our knowledge of the early Universe from which the radiation originated. The angular power spectrum of CMB anisotropy at sub-degree scales depends heavily on comsological parameters such as Ob, O 0 and H0. In pursuit of critical power spectrum measurements over a range of angular scales, a spin-modulated telescope with a single cryogenic amplifier used in a total power radiometer is designed, built and tested. The new technique of spin-modulation with a spinning flat mirror canted 2.5° relative to its spin axis modulates the beam in a 10° oval pattern on the sky at 2.5 Hz. This rapid two-dimensional modulation of the beam is tested at balloon altitudes to minimize the atmospheric offset and determine the efficacy of the scan and telescope design. Maps of over 600 and 400 square degrees are made of regions observed using the spin-modulation and a 20° azimuth scan. These maps yield a 95% confidence level flat band power upper limit of DeltaTℓ = Tcmb(ℓ(ℓ + 1)Cℓ/2pi)0.5 < 77 muK at ℓ = 38 and are free of systematics effects and striping due to long-term drifts in our amplifier to the levels tested here. Planning for the next telescope, with multiple amplifiers, is performed to ensure its success.

Multiple stable states of a periodically driven electron spin in a quantum dot using circularly polarized light

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2011-06-01

The periodical modulation of circularly polarized light with a frequency close to the electron spin resonance frequency induces a sharp change of the single electron spin orientation. Hyperfine interaction provides a feedback, thus fixing the precession frequency of the electron spin in the external and the Overhauser field near the modulation frequency. The nuclear polarization is bidirectional and the electron-nuclear spin system (ENSS) possesses a few stable states. The same physics underlie the frequency-locking effect for two-color and mode-locked excitations. However, the pulsed excitation with mode-locked laser brings about the multitudes of stable states in ENSS in a quantum dot. The resulting precession frequencies of the electron spin differ in these states by the multiple of the modulation frequency. Under such conditions ENSS represents a digital frequency converter with more than 100 stable channels.

Evolution of Spin, Orbital, and Superorbital Modulations of 4U 0114+650

NASA Astrophysics Data System (ADS)

Hu, Chin-Ping; Chou, Yi; Ng, C.-Y.; Lin, Lupin Chun-Che; Yen, David Chien-Chang

2017-07-01

We report a systematic analysis of the spin, orbital, and superorbital modulations of 4U 0114+650, a high-mass X-ray binary that consists of one of the slowest spinning neutron stars. Using the dynamic power spectrum, we found that the spin period varied dramatically and is anticorrelated with the long-term X-ray flux variation that can be observed using the Rossi X-ray Timing Explorer ASM, Swift BAT, and the Monitor of All-sky X-ray Image. The spin-up rate over the entire data set is consistent with previously reported values; however, the local spin-up rate is considerably higher. The corresponding local spin-up timescale is comparable to the local spin-up rate of OAO 1657-415, indicating that 4U 0114+650 could also have a transient disk. Moreover, the spin period evolution shows two ˜1000-day spin-down/random-walk epochs that appeared together with depressions of the superorbital modulation amplitude. This implies that the superorbital modulation was closely related to the presence of the accretion disk, which is not favored in the spin-down/random-walk epochs because the accretion is dominated by the direct wind accretion. The orbital period is stable during the entire time span; however, the orbital profile significantly changes with time. We found that the depth of the dip near the inferior conjunction of the companion is highly variable, which disfavors the eclipsing scenario. Moreover, the dip was less obvious during the spin-down/random-walk epochs, indicating its correlation with the accretion disk. Further monitoring in both X-ray and optical bands could reveal the establishment of the accretion disk in this system.

Evolution of Spin, Orbital, and Superorbital Modulations of 4U 0114+650

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

Hu, Chin-Ping; Ng, C.-Y.; Chou, Yi

2017-07-20

We report a systematic analysis of the spin, orbital, and superorbital modulations of 4U 0114+650, a high-mass X-ray binary that consists of one of the slowest spinning neutron stars. Using the dynamic power spectrum, we found that the spin period varied dramatically and is anticorrelated with the long-term X-ray flux variation that can be observed using the Rossi X-ray Timing Explorer ASM, Swift BAT, and the Monitor of All-sky X-ray Image. The spin-up rate over the entire data set is consistent with previously reported values; however, the local spin-up rate is considerably higher. The corresponding local spin-up timescale is comparablemore » to the local spin-up rate of OAO 1657−415, indicating that 4U 0114+650 could also have a transient disk. Moreover, the spin period evolution shows two ∼1000-day spin-down/random-walk epochs that appeared together with depressions of the superorbital modulation amplitude. This implies that the superorbital modulation was closely related to the presence of the accretion disk, which is not favored in the spin-down/random-walk epochs because the accretion is dominated by the direct wind accretion. The orbital period is stable during the entire time span; however, the orbital profile significantly changes with time. We found that the depth of the dip near the inferior conjunction of the companion is highly variable, which disfavors the eclipsing scenario. Moreover, the dip was less obvious during the spin-down/random-walk epochs, indicating its correlation with the accretion disk. Further monitoring in both X-ray and optical bands could reveal the establishment of the accretion disk in this system.« less

Quantum entanglement and spin control in silicon nanocrystal.

PubMed

Berec, Vesna

2012-01-01

Selective coherence control and electrically mediated exchange coupling of single electron spin between triplet and singlet states using numerically derived optimal control of proton pulses is demonstrated. We obtained spatial confinement below size of the Bohr radius for proton spin chain FWHM. Precise manipulation of individual spins and polarization of electron spin states are analyzed via proton induced emission and controlled population of energy shells in pure (29)Si nanocrystal. Entangled quantum states of channeled proton trajectories are mapped in transverse and angular phase space of (29)Si <100> axial channel alignment in order to avoid transversal excitations. Proton density and proton energy as impact parameter functions are characterized in single particle density matrix via discretization of diagonal and nearest off-diagonal elements. We combined high field and low densities (1 MeV/92 nm) to create inseparable quantum state by superimposing the hyperpolarizationed proton spin chain with electron spin of (29)Si. Quantum discretization of density of states (DOS) was performed by the Monte Carlo simulation method using numerical solutions of proton equations of motion. Distribution of gaussian coherent states is obtained by continuous modulation of individual spin phase and amplitude. Obtained results allow precise engineering and faithful mapping of spin states. This would provide the effective quantum key distribution (QKD) and transmission of quantum information over remote distances between quantum memory centers for scalable quantum communication network. Furthermore, obtained results give insights in application of channeled protons subatomic microscopy as a complete versatile scanning-probe system capable of both quantum engineering of charged particle states and characterization of quantum states below diffraction limit linear and in-depth resolution.PACS NUMBERS: 03.65.Ud, 03.67.Bg, 61.85.+p, 67.30.hj.

Current-induced modulation of backward spin-waves in metallic microstructures

NASA Astrophysics Data System (ADS)

Sato, Nana; Lee, Seo-Won; Lee, Kyung-Jin; Sekiguchi, Koji

2017-03-01

We performed a propagating spin-wave spectroscopy for backward spin-waves in ferromagnetic metallic microstructures in the presence of electric-current. Even with the smaller current injection of 5× {{10}10} A m-2 into ferromagnetic microwires, the backward spin-waves exhibit a gigantic 200 MHz frequency shift and a 15% amplitude change, showing 60 times larger modulation compared to previous reports. Systematic experiments by measuring dependences on a film thickness of mirowire, on the wave-vector of spin-wave, and on the magnitude of bias field, we revealed that for the backward spin-waves a distribution of internal magnetic field generated by electric-current efficiently modulates the frequency and amplitude of spin-waves. The gigantic frequency and amplitude changes were reproduced by a micromagnetics simulation, predicting that the current-injection of 5× {{10}11} A m-2 allows 3 GHz frequency shift. The effective coupling between electric-current and backward spin-waves has a potential to build up a logic control method which encodes signals into the phase and amplitude of spin-waves. The metallic magnonics cooperating with electronics could suggest highly integrated magnonic circuits both in Boolean and non-Boolean principles.

Spatially resolved NMR spectra for the Swiss cheese model in heavy fermion PuCoGa5 superconductor

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Zhu, Jian-Xin; Balatsky, A. V.; Graf, M. J.

2011-03-01

Spatially resolved NMR experiments, which probe the local electronic excitations, play a vital role for studying the pairing symmetry of unconventional superconductors. Here we calculate the spatial modulation of the NMR spin-lattice relaxation rate (1/T1) for the Swiss cheese model as a function of impurity concentration in PuCoGa5 superconductor. The local suppression of the superconducting order parameter due to impurities is related to the number of holes in the Swiss cheese model. Our results indicate that Friedel-like oscillations,as seen in the local-density of states near an impurity, are also present in the behavior of 1/T1 as one moves away from the impurity site. We demonstrate that the gap nodes, which are filled by disorder, can be probed by NMR through the local information encoded in the spectra. The advantage of spatially resolved NMR compared to STM measurements is that the former probe is not sensitive to surface states. Work is supported by US DOE.

Chemical modulation of electronic structure at the excited state

NASA Astrophysics Data System (ADS)

Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

2017-12-01

Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

Magnetic modulation of inverse spin Hall effect in lateral spin-valves

NASA Astrophysics Data System (ADS)

Andrianov, T.; Vedyaev, A.; Dieny, B.

2018-05-01

We analytically investigated the spin-dependent transport properties in a lateral spin-valve device comprising pinned ferromagnetic electrodes allowing the injection of a spin current in a spin conducting channel where spin orbit scattering takes place. This produces an inverse spin Hall (ISHE) voltage across the thickness of the spin conducting channel. It is shown that by adding an extra soft ferromagnetic electrode with rotatable magnetization along the spin conducting channel, the ISHE generated voltage can be magnetically modulated by changing the magnetization orientation of this additional electrode. The dependence of the ISHE voltage on the direction of magnetization of the ferromagnetic electrode with rotatable magnetization was calculated in various configurations. Our results suggest that such structures could be considered as magnetic field sensors in situations where the total thickness of the sensor is constrained such as in hard disk drive readers.

Anomalous modulation of spin torque-induced ferromagnetic resonance caused by direct currents in permalloy/platinum bilayer thin films

NASA Astrophysics Data System (ADS)

Hirayama, Shigeyuki; Mitani, Seiji; Otani, YoshiChika; Kasai, Shinya

2018-01-01

We systematically investigated the spin-torque ferromagnetic resonance (ST-FMR) in permalloy/Pt bilayer thin films under bias direct currents. According to the conventional ST-FMR theory, the half widths of the resonant peaks in the spectra can be modulated by bias currents, which give a reliable value of the spin injection efficiency of the spin Hall effect. On the other hand, the symmetric components of the spectra show an unexpected strong bias current dependence, while the asymmetric components are free from the modulation. These findings suggest that some contributions are missing in the ST-FMR analysis of the ferromagnetic/nonmagnetic metal bilayer thin films.

Antidamping spin-orbit torques in epitaxial-Py(100)/β-Ta

NASA Astrophysics Data System (ADS)

Tiwari, Dhananjay; Behera, Nilamani; Kumar, Akash; Dürrenfeld, Philipp; Chaudhary, Sujeet; Pandya, D. K.; Åkerman, Johan; Muduli, P. K.

2017-12-01

We perform spin torque ferromagnetic resonance measurements on the Si(100)/TiN(100)/epi-Py(100)/β-Ta system. We demonstrate current induced modulation of the Gilbert damping constant, which is about 30% for a current density of 6.25 × 109 A/m2. We show that the observed modulation of the Gilbert damping constant cannot be explained by spin transfer torques arising from the spin Hall effect of the β-Ta layer. An additional mechanism such as antidamping spin-orbit torque resulting from the interface or the crystalline structure of Py thin films needs to be considered.

Atomic-resolution single-spin magnetic resonance detection concept based on tunneling force microscopy

NASA Astrophysics Data System (ADS)

Payne, A.; Ambal, K.; Boehme, C.; Williams, C. C.

2015-05-01

A study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single-electron tunneling between two electrically isolated paramagnetic states. Single-spin magnetic resonance detection is possible by measuring the force detected tunneling charge noise on and off spin resonance. Simulation results of this charge noise, based upon physical models of the tunneling and spin physics, are directly compared to measured atomic force microscopy system noise. The results show that the approach could provide single-spin measurement of electrically isolated qubit states with atomic spatial resolution at room temperature.

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.

Spin Transport in Electric-Barrier-Modulated Ferromagnetic/Normal/Ferromagnetic Monolayer Zigzag MoS2 Nanoribbon Junction

NASA Astrophysics Data System (ADS)

Xia, Y.-Y.; Yuan, R.-Y.; Yang, Q.-J.; Sun, Q.; Zheng, J.; Guo, Y.

In this paper, with the three-band tight-binding model and non-equilibrium Green’s function technique, we investigate spin transport in electric-barrier-modulated Ferromagnetic/Normal/Ferromagnetic (F/N/F) monolayer (ML) zigzag MoS2 nanoribbon junction. The results demonstrate that once the double electric barriers structure emerges, the oscillations of spin conductances become violent, especially for spin-down conductance, the numbers of resonant peaks increase obviously, thus we can obtain 100% spin polarization in the low energy region. It is also found that with the intensity of the exchange field enhancement, the resonant peaks of spin-up and spin-down conductances move in the opposite direction in a certain energy region. As a consequence, the spin-down conductance can be filtered out completely. The findings here indicate that the present structure may be considered as a good candidate for spin filter.

Spin-controlled ultrafast vertical-cavity surface-emitting lasers

NASA Astrophysics Data System (ADS)

Höpfner, Henning; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.

2014-05-01

Spin-controlled semiconductor lasers are highly attractive spintronic devices providing characteristics superior to their conventional purely charge-based counterparts. In particular, spin-controlled vertical-cavity surface emitting lasers (spin-VCSELs) promise to offer lower thresholds, enhanced emission intensity, spin amplification, full polarization control, chirp control and ultrafast dynamics. Most important, the ability to control and modulate the polarization state of the laser emission with extraordinarily high frequencies is very attractive for many applications like broadband optical communication and ultrafast optical switches. We present a novel concept for ultrafast spin-VCSELs which has the potential to overcome the conventional speed limitation for directly modulated lasers by the relaxation oscillation frequency and to reach modulation frequencies significantly above 100 GHz. The concept is based on the coupled spin-photon dynamics in birefringent micro-cavity lasers. By injecting spin-polarized carriers in the VCSEL, oscillations of the coupled spin-photon system can by induced which lead to oscillations of the polarization state of the laser emission. These oscillations are decoupled from conventional relaxation oscillations of the carrier-photon system and can be much faster than these. Utilizing these polarization oscillations is thus a very promising approach to develop ultrafast spin-VCSELs for high speed optical data communication in the near future. Different aspects of the spin and polarization dynamics, its connection to birefringence and bistability in the cavity, controlled switching of the oscillations, and the limitations of this novel approach will be analysed theoretically and experimentally for spin-polarized VCSELs at room temperature.

Dynamics of a localized spin excitation close to the spin-helix regime

NASA Astrophysics Data System (ADS)

Salis, Gian; Walser, Matthias; Altmann, Patrick; Reichl, Christian; Wegscheider, Werner

2014-03-01

The time evolution of a local spin excitation in a (001)-confined two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit interactions of similar strength is investigated theoretically and compared with experimental data. Specifically, the consequences of a finite spatial extension of the initial spin polarization are studied for non-balanced Rashba and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction. We show that the initial out-of-plane spin polarization evolves into a helical spin pattern with a wave number that gradually approaches the value q0 of the persistent spin helix mode. In addition to an exponential decay of the spin polarization that is proportional to both the spin-orbit imbalance and the cubic Dresselhaus term, the finite width w of the spin excitation reduces the spin polarization by a factor that approaches exp(-q02w2 / 2) at longer times. This result bridges the gap between the formation of a long-lived helical spin mode and a spatially homogeneous spin decay described by the Dyakonov-Perel mechanism. This work is financially supported by NCCR QSIT.

Investigation of Kibble-Zurek Quench Dynamics in a Spin-1 Ferromagnetic BEC

NASA Astrophysics Data System (ADS)

Anquez, Martin; Robbins, Bryce; Hoang, Thai; Yang, Xiaoyun; Land, Benjamin; Hamley, Christopher; Chapman, Michael

2014-05-01

We study the temporal evolution of spin populations in small spin-1 87Rb condensates following a slow quench. A ferromagnetic spin-1 BEC exhibits a second-order gapless (quantum) phase transition due to a competition between the magnetic and collisional spin interaction energies. The dynamics of slow quenches through the critical point are predicted to exhibit universal power-law scaling as a function of quench speed. In spatially extended condensates, these excitations are revealed as spatial spin domains. In small condensates, the excitations are manifest in the temporal evolution of the spin populations, illustrating a Kibble-Zurek type scaling. We will present the results of our investigation and compare them to full quantum simulations of the system.

Spin power and efficiency in an Aharnov-Bohm ring with an embedded magnetic impurity quantum dot

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

Yang, Xi; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn; Collaborative Innovation Center of Quantum Matter, Beijing

2015-05-11

Spin thermoelectric effects in an Aharnov-Bohm ring with a magnetic impurity quantum dot (QD) are theoretically investigated by using the nonequilibrium Green's function method. It is found that due to the exchange coupling between the impurity and the electrons in QD, spin output power, and efficiency can be significant and be further modulated by the gate voltage. The spin thermoelectric effect can be modulated effectively by adjusting the Rashba spin-orbit interaction (RSOI) and the magnetic flux. The spin power and efficiency show zigzag oscillations, and thus spin thermoelectric effect can be switched by adjusting the magnetic flux phase factor andmore » RSOI ones. In addition, the spin efficiency can be significantly enhanced by the coexistence of the RSOI and the magnetic flux, and the maximal value of normalized spin efficiency η{sub max}/η{sub C} = 0.35 is obtained. Our results show that such a QD ring device may be used as a manipulative spin thermoelectric generator.« less

Spin-dependent transport and current modulation in a current-in-plane spin-valve field-effect transistor

NASA Astrophysics Data System (ADS)

Kanaki, Toshiki; Koyama, Tomohiro; Chiba, Daichi; Ohya, Shinobu; Tanaka, Masaaki

2016-10-01

We propose a current-in-plane spin-valve field-effect transistor (CIP-SV-FET), which is composed of a ferromagnet/nonferromagnet/ferromagnet trilayer structure and a gate electrode. This is a promising device alternative to spin metal-oxide-semiconductor field-effect transistors. Here, we fabricate a ferromagnetic-semiconductor GaMnAs-based CIP-SV-FET and demonstrate its basic operation of the resistance modulation both by the magnetization configuration and by the gate electric field. Furthermore, we present the electric-field-assisted magnetization reversal in this device.

All-electric spin modulator based on a two-dimensional topological insulator

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

Xiao, Xianbo; Ai, Guoping; Liu, Ying

2016-01-18

We propose and investigate a spin modulator device consisting of two ferromagnetic leads connected by a two-dimensional topological insulator as the channel material. It exploits the unique features of the topological spin-helical edge states, such that the injected carriers with a non-collinear spin-polarization direction would travel through both edges and show interference effect. The conductance of the device can be controlled in a simple and all-electric manner by a side-gate voltage, which effectively rotates the spin-polarization of the carrier. At low voltages, the rotation angle is linear in the gate voltage, and the device can function as a good spin-polarizationmore » rotator by replacing the drain electrode with a non-magnetic material.« less

A Study of Dip-Coatable, High-Capacitance Ion Gel Dielectrics for 3D EWOD Device Fabrication

PubMed Central

Clement, Carlos E.; Jiang, Dongyue; Thio, Si Kuan; Park, Sung-Yong

2017-01-01

We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance (c ≈ 10 μF/cm2) than that of conventional dielectrics such as SiO2. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules. Not only does the spin-coating process require multiple repetitions per module, but the ion gel layer also comes in risks of damage or contamination due to handling errors caused during assembly. In addition, it was observed that the chemical formulation previously used for the spin-coating method causes the surface defects on the dip-coated gel layers and thus leads to poor EWOD performance. In this paper, we alternatively propose a dip-coating method with modified gel solutions to obtain defect-free, functional ion gel layers without the issues arising from the spin-coating method for 3D device fabrication. A dip-coating approach offers a single-step coating solution with the benefits of simplicity, scalability, and high throughput for deposition of high-capacitance gel layers on non-planar EWOD devices. An ion gel solution was prepared by combining the [EMIM][TFSI] ionic liquid and the [P(VDF-HFP)] copolymer at various wt % ratios in acetone solvent. Experimental studies were conducted to fully understand the effects of chemical composition ratios in the gel solution and how varying thicknesses of ion gel and Teflon layers affects EWOD performance. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. Each prism module has been individually controlled to achieve spatial beam steering without the need for bulky mechanical moving parts. PMID:28772400

A Study of Dip-Coatable, High-Capacitance Ion Gel Dielectrics for 3D EWOD Device Fabrication.

PubMed

Clement, Carlos E; Jiang, Dongyue; Thio, Si Kuan; Park, Sung-Yong

2017-01-05

We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance ( c ≈ 10 μF/cm²) than that of conventional dielectrics such as SiO₂. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules. Not only does the spin-coating process require multiple repetitions per module, but the ion gel layer also comes in risks of damage or contamination due to handling errors caused during assembly. In addition, it was observed that the chemical formulation previously used for the spin-coating method causes the surface defects on the dip-coated gel layers and thus leads to poor EWOD performance. In this paper, we alternatively propose a dip-coating method with modified gel solutions to obtain defect-free, functional ion gel layers without the issues arising from the spin-coating method for 3D device fabrication. A dip-coating approach offers a single-step coating solution with the benefits of simplicity, scalability, and high throughput for deposition of high-capacitance gel layers on non-planar EWOD devices. An ion gel solution was prepared by combining the [EMIM][TFSI] ionic liquid and the [P(VDF-HFP)] copolymer at various wt % ratios in acetone solvent. Experimental studies were conducted to fully understand the effects of chemical composition ratios in the gel solution and how varying thicknesses of ion gel and Teflon layers affects EWOD performance. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. Each prism module has been individually controlled to achieve spatial beam steering without the need for bulky mechanical moving parts.

Modulating the spin transport behaviors in ZBNCNRs by edge hydrogenation and position of BN chain

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

Ouyang, Jun; Long, Mengqiu, E-mail: mqlong@csu.edu.cn, E-mail: ygao@csu.edu.cn; Zhang, Dan

2016-03-15

Using the density functional theory and the nonequilibrium Green’s function method, we study the spin transport behaviors in zigzag boron-nitrogen-carbon nanoribbons (ZBNCNRs) by modulating the edge hydrogenation and the position of B-N nanoribbons (BNNRs) chain. The different edge hydrogenations of the ZBNCNRs and the different position relationships of the BNNRs have been considered systematically. Our results show that the metallic, semimetallic and semiconductive properties of the ZBNCNRs can be modulated by the different edge hydrogenations and different position relationships of BN chains. And our proposaled ZBNCNRs devices act as perfect spin-filters with nearly 100% spin polarization. These effects would havemore » potential applications for boron-nitrogen-carbon-based nanomaterials in spintronics nano-devices.« less

Polar-Core Spin Vortex of Quasi-2D Spin-2 Condensate in a Flat-Bottomed Optical Trap

NASA Astrophysics Data System (ADS)

Zheng, Gong-Ping; Chang, Gao-Zhan; Li, Pin; Li, Ting

2017-10-01

Motivated by the recent experiments realized in a flat-bottomed optical trap [Science 347 (2015) 167; Nat. Commun. 6 (2015) 6162], we study the ground state of polar-core spin vortex of quasi-2D spin-2 condensate in a homogeneous trap plus a weak magnetic field. The exact spatial distribution of local spin is obtained and the vortex core are observed to decrease with the growth of the effective spin-spin interaction. For the larger effective spin-spin interaction, the spatial distribution of spin magnitude in spin-2 condensate we obtained agrees well with that of spin-1 condensate in a homogeneous trap, where a polar-core spin vortex was schematically demonstrated as a fully-magnetized planar spin texture with a zero-spin core. The effective spin-spin interaction is proportional to both the bare spin-spin interaction and the radius of the homogeneous trap, simultaneously. Thus the polar-core spin vortex we obtained can be easily controlled by the radius of the trap. Supported by the National Natural Science Foundation of China under Grant No. 11274095, the Key Scientific Research Project of Henan Province of China under Grant No. 16A140011, and the High Performance Computing Center of Henan Normal University

The role of spin–rotation coupling in the non-exponential decay of hydrogen-like heavy ions

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

Lambiase, Gaetano, E-mail: lambiase@sa.infn.it; INFN, Sezione di Napoli; International Institute for Advanced Scientific Studies, 89019 Vietri sul Mare

2013-05-15

Recent experiments carried out at the storage ring of GSI in Darmstadt reveal an unexpected oscillation in the orbital electron capture and subsequent decay of hydrogen-like {sup 140}Pr{sup 58+}, {sup 142}Pm{sup 60+} and {sup 122}I{sup 52+}. The modulations have periods of 7.069(8) s, 7.10(22) s and 6.1 s respectively in the laboratory frame and are superimposed on the expected exponential decays. In this paper we propose a semiclassical model in which the observed modulations arise from the coupling of rotation to the spins of electron and nucleus. We show that the modulations are connected to quantum beats and to themore » effect of the Thomas precession on the spins of bound electron and nucleus, the magnetic moment precessions of electron and nucleus and their cyclotron frequencies. We also show that the spin–spin coupling of electron and nucleus, though dominant relative to the magnetic moment coupling of electron and nucleus with the storage ring magnetic field, does not contribute to the modulation because these terms average out during the time of flight of the ions, or cancel out. The model also predicts that the anomaly cannot be observed if the motion of the ions is rectilinear, or if the ions are stopped in a target (decay of neutral atoms in solid environments). It also supports the notion that no modulation occurs for the β{sup +}-decay branch. -- Highlights: ► Spin precession of the spin of nucleus and electron in storage ring. ► Coupling of rotation to the spin of electron and nucleus. ► Modulation in the decay probability of the heavy ions induced by quantum beats. ► Comparison with experimental data.« less

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

NASA Astrophysics Data System (ADS)

Caffrey, Nuala M.; Ferriani, Paolo; Marocchi, Simone; Heinze, Stefan

2013-10-01

Using first-principles calculations, we show that the magnetic properties of a two-dimensional antiferromagnetic transition-metal surface are modified on the atomic scale by the adsorption of small organic molecules. We consider benzene (C6H6), cyclooctatetraene (C8H8), and a small transition-metal-benzene complex (BzV) adsorbed on a single atomic layer of Mn deposited on the W(110) surface—a surface which exhibits a nearly antiferromagnetic alignment of the magnetic moments in adjacent Mn rows. Due to the spin dependent hybridization of the molecular pz orbitals with the d states of the Mn monolayer, there is a significant reduction of the magnetic moments in the Mn film. Furthermore, the spin polarization at this organic-antiferromagnetic interface is found to be modulated on the atomic scale, both enhanced and inverted, as a result of the molecular adsorption. We show that this effect can be resolved by spin-polarized scanning tunneling microscopy (SP-STM). Our simulated SP-STM images display a spatially dependent spin resolved vacuum charge density above an adsorbed molecule—i.e., different regions above the molecule sustain different signs of spin polarization. While states with s and p symmetry dominate the vacuum charge density in the vicinity of the Fermi energy for the clean magnetic surface, we demonstrate that after a molecule is adsorbed those d states, which are normally suppressed due to their symmetry, can play a crucial role in the vacuum due to their interaction with the molecular orbitals. We also model the effect of small deviations from perfect antiferromagnetic ordering, induced by the slight canting of magnetic moments due to the spin spiral ground state of Mn/W(110).

The State of the Art in (Cd,Mn)Te Heterostructures: Fundamentals and Applications

NASA Astrophysics Data System (ADS)

Wojtowicz, Tomasz

In my talk I will review recent progress in the MBE technology of (Cd,Mn)Te nanostructures containing two dimensional electron gas (2DEG) that led to the first ever observation of fractional quantum Hall effect in magnetic system. This opens new directions in spintronics. I will first discuss already demonstrated applications of such high mobility magnetic-2DEG system for: a) THz and microwave radiation induced zero-bias generation of pure spin currents and very efficient magnetic field induced conversion of them into spin polarized electric current; b) clear demonstration of THz radiation from spin-waves excited via efficient Raman generation process; c) experimental demonstration of working principles of a new type of spin transistor based on controlling the spin transmission via tunable Landau-Zener transitions in spatially modulated spin-split bands. I will also explain the possibility to use magnetic-2DEG for developing of a new system where non-Abelian excitations can not only be created, but also manipulated in a two-dimensional plane. The system is based on high mobility CdTe quantum wells with engineered placement of Mn atoms, where sign of the Lande g-factor can be locally controlled by electrostatic gates at high magnetic fields. Such a system may allow for building a new platform for topologically protected quantum information processing. I will also present results demonstrating electrostatic control of 2D gas polarization in a quantum Hall regime. The research was partially supported by National Science Centre (Poland) Grant DEC-2012/06/A/ST3/00247 and by ONR Grant N000141410339.

Generation of dark and bright spin wave envelope soliton trains through self-modulational instability in magnetic films.

PubMed

Wu, Mingzhong; Kalinikos, Boris A; Patton, Carl E

2004-10-08

The generation of dark spin wave envelope soliton trains from a continuous wave input signal due to spontaneous modulational instability has been observed for the first time. The dark soliton trains were formed from high dispersion dipole-exchange spin waves propagated in a thin yttrium iron garnet film with pinned surface spins at frequencies situated near the dipole gaps in the dipole-exchange spin wave spectrum. Dark and bright soliton trains were generated for one and the same film through placement of the input carrier frequency in regions of negative and positive dispersion, respectively. Two unreported effects in soliton dynamics, hysteresis and period doubling, were also observed.

Image routing via atomic spin coherence

PubMed Central

Wang, Lei; Sun, Jia-Xiang; Luo, Meng-Xi; Sun, Yuan-Hang; Wang, Xiao-Xiao; Chen, Yi; Kang, Zhi-Hui; Wang, Hai-Hua; Wu, Jin-Hui; Gao, Jin-Yue

2015-01-01

Coherent storage of optical image in a coherently-driven medium is a promising method with possible applications in many fields. In this work, we experimentally report a controllable spatial-frequency routing of image via atomic spin coherence in a solid-state medium driven by electromagnetically induced transparency (EIT). Under the EIT-based light-storage regime, a transverse spatial image carried by the probe field is stored into atomic spin coherence. By manipulating the frequency and spatial propagation direction of the read control field, the stored image is transferred into a new spatial-frequency channel. When two read control fields are used to retrieve the stored information, the image information is converted into a superposition of two spatial-frequency modes. Through this technique, the image is manipulated coherently and all-optically in a controlled fashion. PMID:26658846

Controlled finite momentum pairing and spatially varying order parameter in proximitized HgTe quantum wells

NASA Astrophysics Data System (ADS)

Hart, Sean; Ren, Hechen; Kosowsky, Michael; Ben-Shach, Gilad; Leubner, Philipp; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; Halperin, Bertrand; Yacoby, Amir

Conventional s-wave superconductivity arises from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs with zero net momentum. Recent studies have focused on coupling s-wave superconductors to systems with an unusual configuration of electronic spin and momentum at the Fermi surface, where the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements on Josephson junctions based on HgTe quantum wells coupled to aluminum or niobium superconductors, and subject to a magnetic field in the plane of the quantum well. We observe that the in-plane magnetic field modulates the Fraunhofer interference pattern, and that this modulation depends both on electron density and on the direction of the in-plane field with respect to the junction. However, the orientation of the junction with respect to the underlying crystal lattice does not impact the measurements. These findings suggest that spin-orbit coupling plays a role in the observed behavior, and that measurements of Josephson junctions in the presence of an in-plane field can elucidate the Fermi surface properties of the weak link material. NSF DMR-1206016; STC Center for Integrated Quantum Materials under NSF Grant No. DMR-1231319; NSF GRFP under Grant DGE1144152, Microsoft Corporation Project Q.

Modulation of spin dynamics via voltage control of spin-lattice coupling in multiferroics

DOE PAGES

Zhu, Mingmin; Zhou, Ziyao; Peng, Bin; ...

2017-02-03

Our work aims at magnonics manipulation by the magnetoelectric coupling effect and is motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La 0.7Sr 0.3MnO 3/0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage-induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin-lattice coupling effect, i.e., varying exchange stiffness due to voltage-induced anisotropic lattice changes, has been establishedmore » to explain experiment results with good agreement. In addition, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin-lattice coupling effect provides a platform for realizing energy-efficient, tunable magnonics devices.« less

Saturation capability of short phase modulated pulses facilitates the measurement of longitudinal relaxation times of quadrupolar nuclei.

PubMed

Makrinich, Maria; Gupta, Rupal; Polenova, Tatyana; Goldbourt, Amir

The ability of various pulse types, which are commonly applied for distance measurements, to saturate or invert quadrupolar spin polarization has been compared by observing their effect on magnetization recovery curves under magic-angle spinning. A selective central transition inversion pulse yields a bi-exponential recovery for a diamagnetic sample with a spin-3/2, consistent with the existence of two processes: the fluctuations of the electric field gradients with identical single (W 1 ) and double (W 2 ) quantum quadrupolar-driven relaxation rates, and spin exchange between the central transition of one spin and satellite transitions of a dipolar-coupled similar spin. Using a phase modulated pulse, developed for distance measurements in quadrupolar spins (Nimerovsky et al., JMR 244, 2014, 107-113) and suggested for achieving the complete saturation of all quadrupolar spin energy levels, a mono-exponential relaxation model fits the data, compatible with elimination of the spin exchange processes. Other pulses such as an adiabatic pulse lasting one-third of a rotor period, and a two-rotor-period long continuous-wave pulse, both used for distance measurements under special experimental conditions, yield good fits to bi-exponential functions with varying coefficients and time constants due to variations in initial conditions. Those values are a measure of the extent of saturation obtained from these pulses. An empirical fit of the recovery curves to a stretched exponential function can provide general recovery times. A stretching parameter very close to unity, as obtained for a phase modulated pulse but not for other cases, suggests that in this case recovery times and longitudinal relaxation times are similar. The results are experimentally demonstrated for compounds containing 11 B (spin-3/2) and 51 V (spin-7/2). We propose that accurate spin lattice relaxation rates can be measured by a short phase modulated pulse (<1-2ms), similarly to the "true T 1 " measured by saturation with an asynchronous pulse train (Yesinowski, JMR 252, 2015, 135-144). Copyright © 2017 Elsevier Inc. All rights reserved.

Basis for calculating cross sections for nuclear magnetic resonance spin-modulated polarized neutron scattering.

PubMed

Kotlarchyk, Michael; Thurston, George M

2016-12-28

In this work we study the potential for utilizing the scattering of polarized neutrons from nuclei whose spin has been modulated using nuclear magnetic resonance (NMR). From first principles, we present an in-depth development of the differential scattering cross sections that would arise in such measurements from a hypothetical target system containing nuclei with non-zero spins. In particular, we investigate the modulation of the polarized scattering cross sections following the application of radio frequency pulses that impart initial transverse rotations to selected sets of spin-1/2 nuclei. The long-term aim is to provide a foundational treatment of the scattering cross section associated with enhancing scattering signals from selected nuclei using NMR techniques, thus employing minimal chemical or isotopic alterations, so as to advance the knowledge of macromolecular or liquid structure.

Detecting π-phase superfluids with p-wave symmetry in a quasi-1D optical lattice

NASA Astrophysics Data System (ADS)

Liu, Bo; Li, Xiaopeng; Hulet, Randall G.; Liu, W. Vincent

2016-05-01

We propose an experimental protocol to create a p-wave superfluid in a spin-polarized cold Fermi gas tuned by an s-wave Feshbach resonance. A crucial ingredient is to add an anisotropic 3D optical lattice and tune the fillings of two spins to the s and p band, respectively. The pairing order parameter is confirmed to inherit p-wave symmetry in its center-of-mass motion. We find that it can further develop into a state of unexpected π-phase modulation in a broad parameter regime. Experimental signatures are predicted in the momentum distributions, density of states and spatial densities for a realistic experimental setup. The π-phase p-wave superfluid is reminiscent of the π-state in superconductor-ferromagnet heterostructures but differs in symmetry and physical origin. The spatially-varying phases of the superfluid gap provide a novel approach to synthetic magnetic fields for neutral atoms. It would represent another example of p-wave pairing, first discovered in He-3 liquids. Work supported in part by U.S. ARO, AFOSR, NSF, ONR, Charles E. Kaufman Foundation, and The Pittsburgh Foundation, LPS-MPO-CMTC, JQI-NSF-PFC, ARO-Atomtronics-MURI, the Welch Foundation, ARO-MURI and NSF of China.

Simple Z2 lattice gauge theories at finite fermion density

NASA Astrophysics Data System (ADS)

Prosko, Christian; Lee, Shu-Ping; Maciejko, Joseph

2017-11-01

Lattice gauge theories are a powerful language to theoretically describe a variety of strongly correlated systems, including frustrated magnets, high-Tc superconductors, and topological phases. However, in many cases gauge fields couple to gapless matter degrees of freedom, and such theories become notoriously difficult to analyze quantitatively. In this paper we study several examples of Z2 lattice gauge theories with gapless fermions at finite density, in one and two spatial dimensions, that are either exactly soluble or whose solution reduces to that of a known problem. We consider complex fermions (spinless and spinful) as well as Majorana fermions and study both theories where Gauss' law is strictly imposed and those where all background charge sectors are kept in the physical Hilbert space. We use a combination of duality mappings and the Z2 slave-spin representation to map our gauge theories to models of gauge-invariant fermions that are either free, or with on-site interactions of the Hubbard or Falicov-Kimball type that are amenable to further analysis. In 1D, the phase diagrams of these theories include free-fermion metals, insulators, and superconductors, Luttinger liquids, and correlated insulators. In 2D, we find a variety of gapped and gapless phases, the latter including uniform and spatially modulated flux phases featuring emergent Dirac fermions, some violating Luttinger's theorem.

Temporal and Spatial Variances in Arterial Spin-Labeling Are Inversely Related to Large-Artery Blood Velocity.

PubMed

Robertson, A D; Matta, G; Basile, V S; Black, S E; Macgowan, C K; Detre, J A; MacIntosh, B J

2017-08-01

The relationship between extracranial large-artery characteristics and arterial spin-labeling MR imaging may influence the quality of arterial spin-labeling-CBF images for older adults with and without vascular pathology. We hypothesized that extracranial arterial blood velocity can explain between-person differences in arterial spin-labeling data systematically across clinical populations. We performed consecutive pseudocontinuous arterial spin-labeling and phase-contrast MR imaging on 82 individuals (20-88 years of age, 50% women), including healthy young adults, healthy older adults, and older adults with cerebral small vessel disease or chronic stroke infarcts. We examined associations between extracranial phase-contrast hemodynamics and intracranial arterial spin-labeling characteristics, which were defined by labeling efficiency, temporal signal-to-noise ratio, and spatial coefficient of variation. Large-artery blood velocity was inversely associated with labeling efficiency ( P = .007), temporal SNR ( P < .001), and spatial coefficient of variation ( P = .05) of arterial spin-labeling, after accounting for age, sex, and group. Correction for labeling efficiency on an individual basis led to additional group differences in GM-CBF compared to correction using a constant labeling efficiency. Between-subject arterial spin-labeling variance was partially explained by extracranial velocity but not cross-sectional area. Choosing arterial spin-labeling timing parameters with on-line knowledge of blood velocity may improve CBF quantification. © 2017 by American Journal of Neuroradiology.

Transient nutation electron spin resonance spectroscopy on spin-correlated radical pairs: A theoretical analysis on hyperfine-induced nuclear modulations

NASA Astrophysics Data System (ADS)

Weber, Stefan; Kothe, Gerd; Norris, James R.

1997-04-01

The influence of anisotropic hyperfine interaction on transient nutation electron paramagnetic resonance (EPR) of light-induced spin-correlated radical pairs is studied theoretically using the density operator formalism. Analytical expressions for the time evolution of the transient EPR signal during selective microwave excitation of single transitions are derived for a model system comprised of a weakly coupled radical pair and one hyperfine-coupled nucleus with I=1/2. Zero-quantum electron coherence and single-quantum nuclear coherence are created as a result of the sudden light-induced generation of the radical pair state from a singlet-state precursor. Depending on the relative sizes of the nuclear Zeeman frequency and the secular and pseudo-secular parts of the hyperfine coupling, transitions between levels with different nuclear spin orientations are predicted to modulate the time-dependent EPR signal. These modulations are in addition to the well-known transient nutations and electron zero-quantum precessions. Our calculations provide insight into the mechanism of recent experimental observations of coherent nuclear modulations in the time-resolved EPR signals of doublets and radical pairs. Two distinct mechanisms of the modulations are presented for various microwave magnetic field strengths. The first modulation scheme arises from electron and nuclear coherences initiated by the laser excitation pulse and is "read out" by the weak microwave magnetic field. While the relative modulation depth of these oscillations with respect to the signal intensity is independent of the Rabi frequency, ω1, the frequencies of this coherence phenomenon are modulated by the effective microwave amplitude and determined by the nuclear Zeeman interaction and hyperfine coupling constants as well as the electron-electron spin exchange and dipolar interactions between the two radical pair halves. In a second mechanism the modulations are both created and detected by the microwave radiation. Here, the laser pulse merely defines the beginning of the microwave-induced coherent time evolution. This second mechanism appears the most consistent with current experimental observations.

A novel Cs-(129)Xe atomic spin gyroscope with closed-loop Faraday modulation.

PubMed

Fang, Jiancheng; Wan, Shuangai; Qin, Jie; Zhang, Chen; Quan, Wei; Yuan, Heng; Dong, Haifeng

2013-08-01

We report a novel Cs-(129)Xe atomic spin gyroscope (ASG) with closed-loop Faraday modulation method. This ASG requires approximately 30 min to start-up and 110 °C to operate. A closed-loop Faraday modulation method for measurement of the optical rotation was used in this ASG. This method uses an additional Faraday modulator to suppress the laser intensity fluctuation and Faraday modulator thermal induced fluctuation. We theoretically and experimentally validate this method in the Cs-(129)Xe ASG and achieved a bias stability of approximately 3.25 °∕h.

Modulated spin orbit torque in a Pt/Co/Pt/YIG multilayer by nonequilibrium proximity effect

NASA Astrophysics Data System (ADS)

Liu, Q. B.; Meng, K. K.; Cai, Y. Z.; Qian, X. H.; Wu, Y. C.; Zheng, S. Q.; Jiang, Y.

2018-01-01

We have compared the spin orbit torque (SOT) induced magnetization switching in Pt/Co/Pt/Y3Fe5O12 (YIG) and Pt/Co/Pt/SiO2 multilayers. The critical switching current in Pt/Co/Pt/YIG is almost half of that in Pt/Co/Pt/SiO2. Through harmonic measurements, we demonstrated the enhancement of the effective spin Hall angle in Pt/Co/Pt/YIG. The increased efficiency of SOT is ascribed to the nonequilibrium proximity effect at the Pt/YIG interface, which suppresses the spin current reflection and enhances the effective spin accumulation at the Co/Pt interface. Our method can effectively reduce the switching current density and provide another way to modulate SOT.

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.

Origin of the positive spin- 1 2 photoluminescence-detected magnetic resonance in π-conjugated materials and devices

DOE PAGES

Chen, Ying; Cai, Min; Hellerich, Emily; ...

2015-09-02

The spin-1/2 single-modulation (SM) and double-modulation (DM) photoluminescence (PL) detected magnetic resonance (PLDMR) in poly(2-methoxy-5-(2'-ethyl)–hexoxy-1,4- phenylene vinylene) (MEH-PPV) films and poly(3-hexylthiophene) (P3HT) films is described, analyzed, and discussed. In particular, the models based on spin-dependent recombination of charge pairs (SDR) and triplet-polaron quenching (TPQ) are evaluated. By analyzing the dependence of the resonance amplitude on the microwave chopping (modulation) frequency using rate equations, it is demonstrated that the TPQ model can well explain the observed resonance behavior, while SDR model cannot reproduce the results of the observed DM-PLDMR. As a result, the observed spin-1/2 PLDMR is assigned to TPQ rathermore » than SDR, even though the latter may also be present.« less

Photonic Interrogation and Control of Nano Processes

NASA Technical Reports Server (NTRS)

Jassemnejad, Baha

2003-01-01

My research activities for the summer of 2003 consisted of two projects: One project was concerned with determining a method for predicting the static and dynamic assembly properties of nano-structures using laser tweezers. The other project was to investigate the generation of Laguerre-Gaussian modes using a spatial light modulator incorporated into an optical tweezers system. Concerning the first project, I initially pursued the approach suggested by my NASA colleague Dr. Art Decker. This approach involved mimicking the model of the structure of atomic nucleus for the assembly of 1 to 100 atoms using allowed quadruple transitions induced by orbital angular momentums of a Laguerre- Gaussian (Doughnut) laser mode. After realizing the inaptness of the nuclear model with the nanostructure model as far as the binding forces and transitions were concerned, I focused on using quantum dot modei. This model was not attuned also for the host lattice influences the electronic structure of the quantum dot. Thus one other option that I decided to pursue was the approach of molecular quantum mechanics. In this approach the nanostructure is treated as a large (10-100 nm) molecule constructed from single element or multi-elements. Subsequent to consultation with Dr. Fred Morales, a chemical engineer at NASA GRC, and Dr. David Ball, a computational chemist at Cleveland State University, I acquired a molecular-quantum computation software, Hyperchem 7.0. This software allows simulation of different molecular structures as far as their static and dynamic behaviors are concerned. The time that I spent on this project was about eight weeks. Once this suitable approach was identified, I realized the need to collaborate with a computational quantum chemist to pursue searching for stable nanostructures in the range of 10-100 nm that we can be assembled using laser tweezers. The second project was about generating laser tweezers that possess orbital angular momentum. As shown, we were able to generate laser tweezers modes of different orbital angular momentum using a spatial light modulator incorporated into a laser tweezers system. The motivation for investigating these types of modes stems from being able to spin particles at high speeds and also to orient two particles in separate traps and then join them together. Also, there has been recent intense interest on fundamental physics research on orbital angular momentum of light. The fact that circularly polarized light may have associated with it angular momentum that relates to the spin of individual photons (spin 0 for the plane polarized light, spin +1 for the right-circularly polarized light and spin -1 for the left-circularly polarized light) was first demonstrated by Beth in 1936. Orbital angular momentum is, however, distinct from spin in that the spin angular momentum of light is intrinsically linked to the behavior of the electric field in the light whereas orbital angular momentum is a consequence of inclined wavefronts. In 1992 L. Allen, et al showed that the Laguerre-Gaussian (LG) modes could possess well-defined orbital angular momentum that can exceed 1 planck's constant, i.e. l plancks constant per photon, where l is the azimuthal index of the mode.

Design of Transverse Spinning of Light with Globally Unique Handedness

NASA Astrophysics Data System (ADS)

Piao, Xianji; Yu, Sunkyu; Park, Namkyoo

2018-05-01

Access to the transverse spin of light has unlocked new regimes in topological photonics. To achieve the transverse spin from nonzero longitudinal fields, various platforms that derive transversely confined waves based on focusing, interference, or evanescent waves have been suggested. Nonetheless, because of the transverse confinement inherently accompanying sign reversal of the field derivative, the resulting transverse spin handedness of each field experiences spatial inversion, which leads to a mismatch between the intensities of the field and its spin component and hinders the global observation of the transverse spin. Here, we reveal a globally pure transverse spin of the electric field in which the field intensity signifies the spin distribution. Starting from the target spin mode for the inverse design of required spatial profiles of anisotropic permittivities, we show that the elliptic-hyperbolic transition around the epsilon-near-zero permittivity allows for the global conservation of transverse spin handedness of the electric field across the topological interface between anisotropic metamaterials. Extending to the non-Hermitian regime, we develop annihilated transverse spin modes to cover the entire Poincaré sphere of the meridional plane. This result realizes the complete optical analogy of three-dimensional quantum spin states.

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.

Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Mohseni, S. Morteza; Yazdi, H. F.; Hamdi, M.; Brächer, T.; Mohseni, S. Majid

2018-03-01

Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave mode co-existence including a non-linear self-localized spin-wave bullet and a propagating mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two propagating spin wave modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.

Design and commissioning of an aberration-corrected ultrafast spin-polarized low energy electron microscope with multiple electron sources.

PubMed

Wan, Weishi; Yu, Lei; Zhu, Lin; Yang, Xiaodong; Wei, Zheng; Liu, Jefferson Zhe; Feng, Jun; Kunze, Kai; Schaff, Oliver; Tromp, Ruud; Tang, Wen-Xin

2017-03-01

We describe the design and commissioning of a novel aberration-corrected low energy electron microscope (AC-LEEM). A third magnetic prism array (MPA) is added to the standard AC-LEEM with two prism arrays, allowing the incorporation of an ultrafast spin-polarized electron source alongside the standard cold field emission electron source, without degrading spatial resolution. The high degree of symmetries of the AC-LEEM are utilized while we design the electron optics of the ultrafast spin-polarized electron source, so as to minimize the deleterious effect of time broadening, while maintaining full control of electron spin. A spatial resolution of 2nm and temporal resolution of 10ps (ps) are expected in the future time resolved aberration-corrected spin-polarized LEEM (TR-AC-SPLEEM). The commissioning of the three-prism AC-LEEM has been successfully finished with the cold field emission source, with a spatial resolution below 2nm. Copyright © 2017 Elsevier B.V. All rights reserved.

Orbital and spin parts of energy currents for electromagnetic waves through spatially inhomogeneous media

NASA Astrophysics Data System (ADS)

Lee, Hyoung-In; Mok, Jinsik

2018-05-01

We investigate electromagnetic waves propagating through non-magnetic and loss-free dielectric media, but with spatially inhomogeneous refractive indices. We derive hence a set of analytic formulae for conservation laws and energy-current (Poynting) vector. As a result, we deduce that the energy-current vector cannot be neatly separated into its orbital and spin parts in contrast to the cases with spatially homogeneous media. In addition, we present physical interpretations of the two additional terms due to spatial material inhomogeneity.

Numerical simulations of motion-insensitive diffusion imaging based on the distant dipolar field effects.

PubMed

Lin, Tao; Sun, Huijun; Chen, Zhong; You, Rongyi; Zhong, Jianhui

2007-12-01

Diffusion weighting in MRI is commonly achieved with the pulsed-gradient spin-echo (PGSE) method. When combined with spin-warping image formation, this method often results in ghosts due to the sample's macroscopic motion. It has been shown experimentally (Kennedy and Zhong, MRM 2004;52:1-6) that these motion artifacts can be effectively eliminated by the distant dipolar field (DDF) method, which relies on the refocusing of spatially modulated transverse magnetization by the DDF within the sample itself. In this report, diffusion-weighted images (DWIs) using both DDF and PGSE methods in the presence of macroscopic sample motion were simulated. Numerical simulation results quantify the dependence of signals in DWI on several key motion parameters and demonstrate that the DDF DWIs are much less sensitive to macroscopic sample motion than the traditional PGSE DWIs. The results also show that the dipolar correlation distance (d(c)) can alter contrast in DDF DWIs. The simulated results are in good agreement with the experimental results reported previously.

Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

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

Clément, P.-Y.; Baraduc, C., E-mail: claire.baraduc@cea.fr; Chshiev, M.

2015-09-07

Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pavemore » the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.« less

Coherent manipulation of spin correlations in the Hubbard model

NASA Astrophysics Data System (ADS)

Wurz, N.; Chan, C. F.; Gall, M.; Drewes, J. H.; Cocchi, E.; Miller, L. A.; Pertot, D.; Brennecke, F.; Köhl, M.

2018-05-01

We coherently manipulate spin correlations in a two-component atomic Fermi gas loaded into an optical lattice using spatially and time-resolved Ramsey spectroscopy combined with high-resolution in situ imaging. This technique allows us not only to imprint spin patterns but also to probe the static magnetic structure factor at an arbitrary wave vector, in particular, the staggered structure factor. From a measurement along the diagonal of the first Brillouin zone of the optical lattice, we determine the magnetic correlation length and the individual spatial spin correlators. At half filling, the staggered magnetic structure factor serves as a sensitive thermometer, which we employ to study the equilibration in the spin and density sector during a slow quench of the lattice depth.

A universal quantum module for quantum communication, computation, and metrology

NASA Astrophysics Data System (ADS)

Hanks, Michael; Lo Piparo, Nicolò; Trupke, Michael; Schmiedmayer, Jorg; Munro, William J.; Nemoto, Kae

2017-08-01

In this work, we describe a simple module that could be ubiquitous for quantum information based applications. The basic modules comprises a single NV- center in diamond embedded in an optical cavity, where the cavity mediates interactions between photons and the electron spin (enabling entanglement distribution and efficient readout), while the nuclear spins constitutes a long-lived quantum memories capable of storing and processing quantum information. We discuss how a network of connected modules can be used for distributed metrology, communication and computation applications. Finally, we investigate the possible use of alternative diamond centers (SiV/GeV) within the module and illustrate potential advantages.

Intrinsic anharmonic effects on the phonon frequencies and effective spin-spin interactions in a quantum simulator made from trapped ions in a linear Paul trap

NASA Astrophysics Data System (ADS)

McAneny, M.; Freericks, J. K.

2014-11-01

The Coulomb repulsion between ions in a linear Paul trap gives rise to anharmonic terms in the potential energy when expanded about the equilibrium positions. We examine the effect of these anharmonic terms on the accuracy of a quantum simulator made from trapped ions. To be concrete, we consider a linear chain of Yb171+ ions stabilized close to the zigzag transition. We find that for typical experimental temperatures, frequencies change by no more than a factor of 0.01 % due to the anharmonic couplings. Furthermore, shifts in the effective spin-spin interactions (driven by a spin-dependent optical dipole force) are also, in general, less than 0.01 % for detunings to the blue of the transverse center-of-mass frequency. However, detuning the spin interactions near other frequencies can lead to non-negligible anharmonic contributions to the effective spin-spin interactions. We also examine an odd behavior exhibited by the harmonic spin-spin interactions for a range of intermediate detunings, where nearest-neighbor spins with a larger spatial separation on the ion chain interact more strongly than nearest neighbors with a smaller spatial separation.

Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets

NASA Astrophysics Data System (ADS)

Schneider, S.; Wolf, D.; Stolt, M. J.; Jin, S.; Pohl, D.; Rellinghaus, B.; Schmidt, M.; Büchner, B.; Goennenwein, S. T. B.; Nielsch, K.; Lubk, A.

2018-05-01

Envisaged applications of Skyrmions in magnetic memory and logic devices crucially depend on the stability and mobility of these topologically nontrivial magnetic textures in thin films. We present for the first time quantitative maps of the magnetic induction that provide evidence for a 3D modulation of the Skyrmionic spin texture. The projected in-plane magnetic induction maps as determined from in-line and off-axis electron holography carry the clear signature of Bloch Skyrmions. However, the magnitude of this induction is much smaller than the values expected for homogeneous Bloch Skyrmions that extend throughout the thickness of the film. This finding can only be understood if the underlying spin textures are modulated along the out-of-plane z direction. The projection of (the in-plane magnetic induction of) helices is further found to exhibit thickness-dependent lateral shifts, which show that this z modulation is accompanied by an (in-plane) modulation along the x and y directions.

Role of spin diffusion in current-induced domain wall motion for disordered ferromagnets

NASA Astrophysics Data System (ADS)

Akosa, Collins Ashu; Kim, Won-Seok; Bisig, André; Kläui, Mathias; Lee, Kyung-Jin; Manchon, Aurélien

2015-03-01

Current-induced spin transfer torque and magnetization dynamics in the presence of spin diffusion in disordered magnetic textures is studied theoretically. We demonstrate using tight-binding calculations that weak, spin-conserving impurity scattering dramatically enhances the nonadiabaticity. To further explore this mechanism, a phenomenological drift-diffusion model for incoherent spin transport is investigated. We show that incoherent spin diffusion indeed produces an additional spatially dependent torque of the form ˜∇2[m ×(u .∇ ) m ] +ξ ∇2[(u .∇ ) m ] , where m is the local magnetization direction, u is the direction of injected current, and ξ is a parameter characterizing the spin dynamics (precession, dephasing, and spin-flip). This torque, which scales as the inverse square of the domain wall width, only weakly enhances the longitudinal velocity of a transverse domain wall but significantly enhances the transverse velocity of vortex walls. The spatial-dependent spin transfer torque uncovered in this study is expected to have significant impact on the current-driven motion of abrupt two-dimensional textures such as vortices, skyrmions, and merons.

Evaluation Method for Fieldlike-Torque Efficiency by Modulation of the Resonance Field

NASA Astrophysics Data System (ADS)

Kim, Changsoo; Kim, Dongseuk; Chun, Byong Sun; Moon, Kyoung-Woong; Hwang, Chanyong

2018-05-01

The spin Hall effect has attracted a lot of interest in spintronics because it offers the possibility of a faster switching route with an electric current than with a spin-transfer-torque device. Recently, fieldlike spin-orbit torque has been shown to play an important role in the magnetization switching mechanism. However, there is no simple method for observing the fieldlike spin-orbit torque efficiency. We suggest a method for measuring fieldlike spin-orbit torque using a linear change in the resonance field in spectra of direct-current (dc)-tuned spin-torque ferromagnetic resonance. The fieldlike spin-orbit torque efficiency can be obtained in both a macrospin simulation and in experiments by simply subtracting the Oersted field from the shifted amount of resonance field. This method analyzes the effect of fieldlike torque using dc in a normal metal; therefore, only the dc resistivity and the dimensions of each layer are considered in estimating the fieldlike spin-torque efficiency. The evaluation of fieldlike-torque efficiency of a newly emerging material by modulation of the resonance field provides a shortcut in the development of an alternative magnetization switching device.

Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

2016-10-01

Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

Demonstrating ultrafast polarization dynamics in spin-VCSELs

NASA Astrophysics Data System (ADS)

Lindemann, Markus; Pusch, Tobias; Michalzik, Rainer; Gerhardt, Nils C.; Hofmann, Martin R.

2018-02-01

Vertical-cavity surface-emitting lasers (VCSELs) are used for short-haul optical data transmission with increasing bit rates. The optimization involves both enhanced device designs and the use of higher-order modulation formats. In order to improve the modulation bandwidth substantially, the presented work employs spin-pumped VCSELs (spin-VCSELs) and their polarization dynamics instead of relying on intensity-modulated devices. In spin-VCSELs, the polarization state of the emitted light is controllable via spin injection. By optical spin pumping a single-mode VCSEL is forced to emit light composed of both orthogonal linearly polarized fundamental modes. The frequencies of these two modes differ slightly by a value determined by the cavity birefringence. As a result, the circular polarization degree oscillates with their beat frequency, i.e., with the birefringence-induced mode splitting. We used this phenomenon to show so-called polarization oscillations, which are generated by pulsed spin injection. Their frequency represents the polarization dynamics resonance frequency and can be tuned over a wide range via the birefringence, nearly independent from any other laser parameter. In previous work we demonstrated a maximum birefringence-induced mode splitting of more than 250 GHz. In this work, compared to previous publications, we show an almost doubled polarization oscillation frequency of more than 80 GHz. Furthermore, we discuss concepts to achieve even higher values far above 100 GHz.

Dielectric magnetic microparticles as photomagnonic cavities: Enhancing the modulation of near-infrared light by spin waves

NASA Astrophysics Data System (ADS)

Almpanis, Evangelos

2018-05-01

The coupling between spin waves and optical Mie resonances inside a dielectric magnetic spherical particle, which acts simultaneously as a photonic and magnonic (photomagnonic) cavity, is investigated by means of numerical calculations accurate to arbitrary order in the magnetooptical coupling coefficient. Isolated dielectric magnetic particles with diameters of just a few microns support high-Q optical Mie resonances at near-infrared frequencies and localized spin waves, providing an ultrasmall and compact platform in the emerging field of cavity optomagnonics. Our results predict the occurrence of strong interaction effects, beyond the linear-response approximation, which lead to enhanced modulation of near-infrared light by spin waves through multimagnon absorption and emission mechanisms.

Final Technical Report for DE-SC0008149

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

Buchanan, Kristen

The major goal of this project is to study spin waves in magnetic thin films, especially how spin waves respond to external stimuli. This is expected to lead to new insight into dynamic processes and new ideas for methods to control spin waves. Experimental studies are being done primarily using time- and spatially-resolved Brillouin light scattering (BLS) measurements on extended and patterned magnetic thin films. BLS is a versatile tool that provides a non-invasive probe of spin dynamics with frequencies of ~1 GHz to well over 100 GHz, diffraction-limited spatial resolution, 250-ps temporal resolution, and it is sensitive enough tomore » detect thermal magnons.« less

Approximate methods for the fast computation of EPR and ST-EPR spectra. V. Application of the perturbation approach to the problem of anisotropic motion

NASA Astrophysics Data System (ADS)

Robinson, B. H.; Dalton, L. R.

1981-01-01

The modulation perturbation treatment of Galloway and Dalton is applied to the solution of the stochastic Liouville equation for the spin density matrix which incorporates an anisotropic rotational diffusion operator. Pseudosecular and saturation terms of the spin hamiltonian are explicitly considered as is the interaction of the electron spins with the applied Zeeman modulation field. The modulation perturbation treatment results in a factor of four improvement in computational speed relative to inversion of the full supermatrix with little or no loss of computational accuracy. The theoretical simulations of EPR and ST-EPR spectra are in nearly quantitative agreement with experimental spectra taken under high resolution conditions.

Designing exotic many-body states of atomic spin and motion in photonic crystals.

PubMed

Manzoni, Marco T; Mathey, Ludwig; Chang, Darrick E

2017-03-08

Cold atoms coupled to photonic crystals constitute an exciting platform for exploring quantum many-body physics. For example, such systems offer the potential to realize strong photon-mediated forces between atoms, which depend on the atomic internal (spin) states, and where both the motional and spin degrees of freedom can exhibit long coherence times. An intriguing question then is whether exotic phases could arise, wherein crystalline or other spatial patterns and spin correlations are fundamentally tied together, an effect that is atypical in condensed matter systems. Here, we analyse one realistic model Hamiltonian in detail. We show that this previously unexplored system exhibits a rich phase diagram of emergent orders, including spatially dimerized spin-entangled pairs, a fluid of composite particles comprised of joint spin-phonon excitations, phonon-induced Néel ordering, and a fractional magnetization plateau associated with trimer formation.

A two-dimensional spin field-effect switch

NASA Astrophysics Data System (ADS)

Casanova, Felix

The integration of the spin degree of freedom in charge-based electronic devices has revolutionised both sensing and memory capability in microelectronics. Further development in spintronic devices requires electrical manipulation of spin current for logic operations. The mainstream approach followed so far, inspired by the seminal proposal of the Datta and Das spin modulator, has relied on the spin-orbit field as a medium for electrical control of the spin state. However, the still standing challenge is to find a material whose spin-orbit coupling (SOC) is weak enough to transport spins over long distances, while also being strong enough to allow their electrical manipulation. In our recent work, we demonstrate a radically different approach by engineering a van der Waals heterostructure from atomically thin crystals, and which combines the superior spin transport properties of graphene with the strong SOC of MoS2, a transition metal dichalcogenide with semiconducting properties. The spin transport in the graphene channel is modulated between ON and OFF states by tuning the spin absorption into the MoS2 layer with a gate electrode. Our demonstration of a spin field-effect switch using two-dimensional (2D) materials identifies a new route towards spin logic operations for beyond CMOS technology. Furthermore, the van der Waals heterostructure at the core of our experiments opens the path for fundamental research of exotic transport properties predicted for transition metal dichalcogenides, in which electrical spin injection has so far been elusive.

Tunable Spin dependent beam shift by simultaneously tailoring geometric and dynamical phases of light in inhomogeneous anisotropic medium

PubMed Central

Pal, Mandira; Banerjee, Chitram; Chandel, Shubham; Bag, Ankan; Majumder, Shovan K.; Ghosh, Nirmalya

2016-01-01

Spin orbit interaction and the resulting Spin Hall effect of light are under recent intensive investigations because of their fundamental nature and potential applications. Here, we report an interesting manifestation of spin Hall effect of light and demonstrate its tunability in an inhomogeneous anisotropic medium exhibiting spatially varying retardance level. In our system, the beam shift occurs only for one circular polarization mode keeping the other orthogonal mode unaffected, which is shown to arise due to the combined spatial gradients of the geometric phase and the dynamical phase of light. The constituent two orthogonal circular polarization modes of an input linearly polarized light evolve in different trajectories, eventually manifesting as a large and tunable spin separation. The spin dependent beam shift and the demonstrated principle of simultaneously tailoring space-varying geometric and dynamical phase of light for achieving its tunability (of both magnitude and direction), may provide an attractive route towards development of spin-optical devices. PMID:28004825

Bending and breaking of stripes in a charge ordered manganite.

PubMed

Savitzky, Benjamin H; El Baggari, Ismail; Admasu, Alemayehu S; Kim, Jaewook; Cheong, Sang-Wook; Hovden, Robert; Kourkoutis, Lena F

2017-12-01

In charge-ordered phases, broken translational symmetry emerges from couplings between charge, spin, lattice, or orbital degrees of freedom, giving rise to remarkable phenomena such as colossal magnetoresistance and metal-insulator transitions. The role of the lattice in charge-ordered states remains particularly enigmatic, soliciting characterization of the microscopic lattice behavior. Here we directly map picometer scale periodic lattice displacements at individual atomic columns in the room temperature charge-ordered manganite Bi 0.35 Sr 0.18 Ca 0.47 MnO 3 using aberration-corrected scanning transmission electron microscopy. We measure transverse, displacive lattice modulations of the cations, distinct from existing manganite charge-order models. We reveal locally unidirectional striped domains as small as ~5 nm, despite apparent bidirectionality over larger length scales. Further, we observe a direct link between disorder in one lattice modulation, in the form of dislocations and shear deformations, and nascent order in the perpendicular modulation. By examining the defects and symmetries of periodic lattice displacements near the charge ordering phase transition, we directly visualize the local competition underpinning spatial heterogeneity in a complex oxide.

Magnetic proximity control of spin currents and giant spin accumulation in graphene

NASA Astrophysics Data System (ADS)

Singh, Simranjeet

Two dimensional (2D) materials provide a unique platform to explore the full potential of magnetic proximity driven phenomena. We will present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to the ferromagnetic-insulator (FMI) magnetization in graphene/FMI heterostructures. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. We also discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the non-local spin signals in graphene, which is due to spin relaxation by thermally-induced transverse fluctuations of the FMI magnetization. Additionally, it has been a challenge to grow a smooth, robust and pin-hole free tunnel barriers on graphene, which can withstand large current densities for efficient electrical spin injection. We have experimentally demonstrated giant spin accumulation in graphene lateral spin valves employing SrO tunnel barriers. Nonlocal spin signals, as large as 2 mV, are observed in graphene lateral spin valves at room temperature. This high spin accumulations observed using SrO tunnel barriers puts graphene on the roadmap for exploring the possibility of achieving a non-local magnetization switching due to the spin torque from electrically injected spins. Financial support from ONR (No. N00014-14-1-0350), NSF (No. DMR-1310661), and C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.

Spin selective filtering of polariton condensate flow

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

Gao, T.; Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Crete; Antón, C.

2015-07-06

Spin-selective spatial filtering of propagating polariton condensates, using a controllable spin-dependent gating barrier, in a one-dimensional semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam provides the source of propagating polaritons, while a second circularly polarized weak beam imprints a spin dependent potential barrier, which gates the polariton flow and generates polariton spin currents. A complete spin-based control over the blocked and transmitted polaritons is obtained by varying the gate polarization.

Spectral methods for the spin-2 equation near the cylinder at spatial infinity

NASA Astrophysics Data System (ADS)

Macedo, Rodrigo P.; Valiente Kroon, Juan A.

2018-06-01

We solve, numerically, the massless spin-2 equations, written in terms of a gauge based on the properties of conformal geodesics, in a neighbourhood of spatial infinity using spectral methods in both space and time. This strategy allows us to compute the solutions to these equations up to the critical sets where null infinity intersects with spatial infinity. Moreover, we use the convergence rates of the numerical solutions to read-off their regularity properties.

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.

rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

NASA Astrophysics Data System (ADS)

Newton, Hayley; Walkup, Laura L.; Whiting, Nicholas; West, Linda; Carriere, James; Havermeyer, Frank; Ho, Lawrence; Morris, Peter; Goodson, Boyd M.; Barlow, Michael J.

2014-05-01

Spin-exchange optical pumping (SEOP) has been widely used to produce enhancements in nuclear spin polarisation for hyperpolarised noble gases. However, some key fundamental physical processes underlying SEOP remain poorly understood, particularly in regards to how pump laser energy absorbed during SEOP is thermalised, distributed and dissipated. This study uses in situ ultra-low frequency Raman spectroscopy to probe rotational temperatures of nitrogen buffer gas during optical pumping under conditions of high resonant laser flux and binary Xe/N2 gas mixtures. We compare two methods of collecting the Raman scattering signal from the SEOP cell: a conventional orthogonal arrangement combining intrinsic spatial filtering with the utilisation of the internal baffles of the Raman spectrometer, eliminating probe laser light and Rayleigh scattering, versus a new in-line modular design that uses ultra-narrowband notch filters to remove such unwanted contributions. We report a ~23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell.

Non-flipping 13C spins near an NV center in diamond: hyperfine and spatial characteristics by density functional theory simulation of the C510[NV]H252 cluster

NASA Astrophysics Data System (ADS)

Nizovtsev, A. P.; Kilin, S. Ya; Pushkarchuk, A. L.; Pushkarchuk, V. A.; Kuten, S. A.; Zhikol, O. A.; Schmitt, S.; Unden, T.; Jelezko, F.

2018-02-01

Single NV centers in diamond coupled by hyperfine interaction (hfi) to neighboring 13C nuclear spins are now widely used in emerging quantum technologies as elements of quantum memory adjusted to a nitrogen-vacancy (NV) center electron spin qubit. For nuclear spins with low flip-flop rate, single shot readout was demonstrated under ambient conditions. Here we report on a systematic search for such stable NV-13C systems using density functional theory to simulate the hfi and spatial characteristics of all possible NV-13C complexes in the H-terminated cluster C510[NV]-H252 hosting the NV center. Along with the expected stable ‘NV-axial-13C’ systems wherein the 13C nuclear spin is located on the NV axis, we found for the first time new families of positions for the 13C nuclear spin exhibiting negligible hfi-induced flipping rates due to near-symmetric local spin density distribution. Spatially, these positions are located in the diamond bilayer passing through the vacancy of the NV center and being perpendicular to the NV axis. Analysis of available publications showed that, apparently, some of the predicted non-axial near-stable NV-13C systems have already been observed experimentally. A special experiment performed on one of these systems confirmed the prediction made.

Hardy's argument and successive spin-s measurements

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

Ahanj, Ali

2010-07-15

We consider a hidden-variable theoretic description of successive measurements of noncommuting spin observables on an input spin-s state. In this scenario, the hidden-variable theory leads to a Hardy-type argument that quantum predictions violate it. We show that the maximum probability of success of Hardy's argument in quantum theory is ((1/2)){sup 4s}, which is more than in the spatial case.

Modulating effect of new potential antimelanomic agents, spin-labeled triazenes and nitrosoureas on the DOPA-oxidase activity of tyrosinase.

PubMed

Gadjeva, V; Zheleva, A; Raikova, E

1999-07-01

The modulating effect of newly synthesized alkylating spin labeled triazene and spin labeled nitrosourea derivatives on the DOPA-oxidase activity of mushroom tyrosinase has been investigated by Bumett's spectrophotometric method (Burnett et al., 1967). All spin labeled triazenes have exhibited activating effect on DOPA-oxidase activity of tyrosinase, whereas clinically used triazene (DTIC), which does not contain nitroxide moiety, have showed inhibiting effect. At the same experimental conditions the spin labeled aminoacid nitrosoureas have showed dual effect - activating, in the beginning of the enzyme reaction and inhibiting later on. It is deduced that the activating effect of the spin labeled compounds is due to the nitroxide moiety and the inhibiting effect of all compounds depends on their half-life time. This study might contribute to make more clear the mechanism of action of the new compounds and on the other hand would come in quite useful as a preliminary prognosis for their antimelanomic activity.

SNR-optimized phase-sensitive dual-acquisition turbo spin echo imaging: a fast alternative to FLAIR.

PubMed

Lee, Hyunyeol; Park, Jaeseok

2013-07-01

Phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo imaging was recently introduced, producing high-resolution isotropic cerebrospinal fluid attenuated brain images without long inversion recovery preparation. Despite the advantages, the weighted-averaging-based technique suffers from noise amplification resulting from different levels of cerebrospinal fluid signal modulations over the two acquisitions. The purpose of this work is to develop a signal-to-noise ratio-optimized version of the phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo. Variable refocusing flip angles in the first acquisition are calculated using a three-step prescribed signal evolution while those in the second acquisition are calculated using a two-step pseudo-steady state signal transition with a high flip-angle pseudo-steady state at a later portion of the echo train, balancing the levels of cerebrospinal fluid signals in both the acquisitions. Low spatial frequency signals are sampled during the high flip-angle pseudo-steady state to further suppress noise. Numerical simulations of the Bloch equations were performed to evaluate signal evolutions of brain tissues along the echo train and optimize imaging parameters. In vivo studies demonstrate that compared with conventional phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo, the proposed optimization yields 74% increase in apparent signal-to-noise ratio for gray matter and 32% decrease in imaging time. The proposed method can be a potential alternative to conventional fluid-attenuated imaging. Copyright © 2012 Wiley Periodicals, Inc.

Spin wave scattering and interference in ferromagnetic cross

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

Nanayakkara, Kasuni; Kozhanov, Alexander; Center for Nano Optics, Georgia State University, Atlanta, Georgia 30303

2015-10-28

Magnetostatic spin wave scattering and interference across a CoTaZr ferromagnetic spin wave waveguide cross junction were investigated experimentally and by micromagnetic simulations. It is observed that the phase of the scattered waves is dependent on the wavelength, geometry of the junction, and scattering direction. It is found that destructive and constructive interference of the spin waves generates switching characteristics modulated by the input phase of the spin waves. Micromagnetic simulations are used to analyze experimental data and simulate the spin wave scattering and interference.

Middle School Students' Reasoning about 3-Dimensional Objects: A Case Study

ERIC Educational Resources Information Center

Okumus, Samet

2016-01-01

According to the National Council of Teacher of Mathematics (NCTM) (2000), K-12 students should be given an opportunity to develop their spatial reasoning abilities. One of the topics that may allow students to develop their spatial skills is forming 3-dimensional objects using spinning and extrusion methods. Also, extrusion and spinning methods…

Non-thermal optical excitation of terahertz-spin precession in a magneto-optical insulator

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

Parchenko, Sergii; Maziewski, Andrzej; Stupakiewicz, Andrzej, E-mail: and@uwb.edu.pl

2016-01-18

We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical devices.

Spin-Based Devices for Magneto-Optoelectronic Integrated Circuits

DTIC Science & Technology

2009-04-29

bulk material and matches that in quantum wells. While these simple linear relationships hold for spin-polarized light-emitting diodes (spin-LEDs...temperature. The quantum efficiency and hence r| increases with decreasing temperature. The individual circuit elements, 33 therefore, exhibit the...Injection, Threshold Reduction and Output Circular Polarization Modulation in Quantum Well and Quantum Dot Semiconductor Spin Polarized Lasers working

Probing quantum frustrated systems via factorization of the ground state.

PubMed

Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio

2010-05-21

The existence of definite orders in frustrated quantum systems is related rigorously to the occurrence of fully factorized ground states below a threshold value of the frustration. Ground-state separability thus provides a natural measure of frustration: strongly frustrated systems are those that cannot accommodate for classical-like solutions. The exact form of the factorized ground states and the critical frustration are determined for various classes of nonexactly solvable spin models with different spatial ranges of the interactions. For weak frustration, the existence of disentangling transitions determines the range of applicability of mean-field descriptions in biological and physical problems such as stochastic gene expression and the stability of long-period modulated structures.

Spin dynamics in the modulation frame: application to homonuclear recoupling in magic angle spinning solid-state NMR.

PubMed

De Paëpe, Gaël; Lewandowski, Józef R; Griffin, Robert G

2008-03-28

We introduce a family of solid-state NMR pulse sequences that generalizes the concept of second averaging in the modulation frame and therefore provides a new approach to perform magic angle spinning dipolar recoupling experiments. Here, we focus on two particular recoupling mechanisms-cosine modulated rotary resonance (CMpRR) and cosine modulated recoupling with isotropic chemical shift reintroduction (COMICS). The first technique, CMpRR, is based on a cosine modulation of the rf phase and yields broadband double-quantum (DQ) (13)C recoupling using >70 kHz omega(1,C)/2pi rf field for the spinning frequency omega(r)/2=10-30 kHz and (1)H Larmor frequency omega(0,H)/2pi up to 900 MHz. Importantly, for p>or=5, CMpRR recouples efficiently in the absence of (1)H decoupling. Extension to lower p values (3.5

Measuring oxygen tension modulation, induced by a new pre-radiotherapy therapeutic, in a mammary window chamber mouse model

NASA Astrophysics Data System (ADS)

Schafer, Rachel; Gmitro, Arthur F.

2015-03-01

Tumor regions under hypoxic or low oxygen conditions respond less effectively to many treatment strategies, including radiation therapy. A novel investigational therapeutic, NVX-108 (NuvOx Pharma), has been developed to increase delivery of oxygen through the use of a nano-emulsion of dodecofluoropentane. By raising pO2 levels prior to delivering radiation, treatment efficacy may be improved. To aid in evaluating the novel drug, oxygen tension was quantitatively measured, spatially and temporally, to record the effect of administrating NVX-108 in an orthotopic mammary window chamber mouse model of breast cancer. The oxygen tension was measured through the use of an oxygen-sensitive coating, comprised of phosphorescent platinum porphyrin dye embedded in a polystyrene matrix. The coating, applied to the surface of the coverslip of the window chamber through spin coating, is placed in contact with the mammary fat pad to record the oxygenation status of the surface tissue layer. Prior to implantation of the window chamber, a tumor is grown in the SCID mouse model by injection of MCF-7 cells into the mammary fat pad. Two-dimensional spatial distributions of the pO2 levels were obtained through conversion of measured maps of phosphorescent lifetime. The resulting information on the spatial and temporal variation of the induced oxygen modulation could provide valuable insight into the optimal timing between administration of NVX-108 and radiation treatment to provide the most effective treatment outcome.

Dynamic nuclear polarization using frequency modulation at 3.34 T.

PubMed

Hovav, Y; Feintuch, A; Vega, S; Goldfarb, D

2014-01-01

During dynamic nuclear polarization (DNP) experiments polarization is transferred from unpaired electrons to their neighboring nuclear spins, resulting in dramatic enhancement of the NMR signals. While in most cases this is achieved by continuous wave (cw) irradiation applied to samples in fixed external magnetic fields, here we show that DNP enhancement of static samples can improve by modulating the microwave (MW) frequency at a constant field of 3.34 T. The efficiency of triangular shaped modulation is explored by monitoring the (1)H signal enhancement in frozen solutions containing different TEMPOL radical concentrations at different temperatures. The optimal modulation parameters are examined experimentally and under the most favorable conditions a threefold enhancement is obtained with respect to constant frequency DNP in samples with low radical concentrations. The results are interpreted using numerical simulations on small spin systems. In particular, it is shown experimentally and explained theoretically that: (i) The optimal modulation frequency is higher than the electron spin-lattice relaxation rate. (ii) The optimal modulation amplitude must be smaller than the nuclear Larmor frequency and the EPR line-width, as expected. (iii) The MW frequencies corresponding to the enhancement maxima and minima are shifted away from one another when using frequency modulation, relative to the constant frequency experiments. Copyright © 2013 Elsevier Inc. All rights reserved.

Spin correlations and spin-wave excitations in Dirac-Weyl semimetals

NASA Astrophysics Data System (ADS)

Araki, Yasufumi; Nomura, Kentaro

We study correlations among magnetic dopants in three-dimensional Dirac and Weyl semimetals. Effective field theory for localized magnetic moments is derived by integrating out the itinerant electron degrees of freedom. We find that spin correlation in the spatial direction parallel to local magnetization is more rigid than that in the perpendicular direction, reflecting spin-momentum locking nature of the Dirac Hamiltonian. Such an anisotropy becomes stronger for Fermi level close to the Dirac points, due to Van Vleck paramagnetism triggered by spin-orbit coupling. One can expect topologically nontrivial spin textures under this anisotropy, such as a hedgehog around a single point, or a radial vortex around an axis, as well as a uniform ferromagnetic order. We further investigate the characteristics of spin waves in the ferromagnetic state. Spin-wave dispersion also shows a spatial anisotropy, which is less dispersed in the direction transverse to the magnetization than that in the longitudinal direction. The spin-wave dispersion anisotropy can be traced back to the rigidity and flexibility of spin correlations discussed above. This work was supported by Grant-in-Aid for Scientific Research (Grants No.15H05854, No.26107505, and No.26400308) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Spatially distributed multipartite entanglement enables EPR steering of atomic clouds

NASA Astrophysics Data System (ADS)

Kunkel, Philipp; Prüfer, Maximilian; Strobel, Helmut; Linnemann, Daniel; Frölian, Anika; Gasenzer, Thomas; Gärttner, Martin; Oberthaler, Markus K.

2018-04-01

A key resource for distributed quantum-enhanced protocols is entanglement between spatially separated modes. However, the robust generation and detection of entanglement between spatially separated regions of an ultracold atomic system remain a challenge. We used spin mixing in a tightly confined Bose-Einstein condensate to generate an entangled state of indistinguishable particles in a single spatial mode. We show experimentally that this entanglement can be spatially distributed by self-similar expansion of the atomic cloud. We used spatially resolved spin read-out to reveal a particularly strong form of quantum correlations known as Einstein-Podolsky-Rosen (EPR) steering between distinct parts of the expanded cloud. Based on the strength of EPR steering, we constructed a witness, which confirmed genuine 5-partite entanglement.

Systems and methods for knowledge discovery in spatial data

DOEpatents

Obradovic, Zoran; Fiez, Timothy E.; Vucetic, Slobodan; Lazarevic, Aleksandar; Pokrajac, Dragoljub; Hoskinson, Reed L.

2005-03-08

Systems and methods are provided for knowledge discovery in spatial data as well as to systems and methods for optimizing recipes used in spatial environments such as may be found in precision agriculture. A spatial data analysis and modeling module is provided which allows users to interactively and flexibly analyze and mine spatial data. The spatial data analysis and modeling module applies spatial data mining algorithms through a number of steps. The data loading and generation module obtains or generates spatial data and allows for basic partitioning. The inspection module provides basic statistical analysis. The preprocessing module smoothes and cleans the data and allows for basic manipulation of the data. The partitioning module provides for more advanced data partitioning. The prediction module applies regression and classification algorithms on the spatial data. The integration module enhances prediction methods by combining and integrating models. The recommendation module provides the user with site-specific recommendations as to how to optimize a recipe for a spatial environment such as a fertilizer recipe for an agricultural field.

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.

Soil Transport Implement

NASA Technical Reports Server (NTRS)

Dixon, William; Fan, William; Lloyd, Joey; Pham, Nam-Anh; Stevens, Michael

1988-01-01

The design of the Soil Transport Implement (STI) for SKITTER is presented. The purpose of STI is to provide a protective layer of lunar soil for the lunar modules. The objective is to cover the lunar module with a layer of soil approximately two meters thick within a two week period. The amount of soil required to cover the module is roughly 77 dump truck loads or three million earth pounds. A spinning disk is employed to accomplish its task. STI is an autonomous, teleoperated system. The design incorporates the latest advances in composite materials and high strength, light weight alloys to achieve a high strength to weight ratio. The preliminary design should only be used to assess the feasibility of employing a spinning wheel as a soil transport implement. A mathematical model of the spinning wheel was used to evaluate the performance of this design.

Phase modulated 2D HSQC-TOCSY for unambiguous assignment of overlapping spin systems

NASA Astrophysics Data System (ADS)

Singh, Amrinder; Dubey, Abhinav; Adiga, Satish K.; Atreya, Hanudatta S.

2018-01-01

We present a new method that allows one to unambiguously resolve overlapping spin systems often encountered in biomolecular systems such as peptides and proteins or in samples containing a mixture of different molecules such as in metabolomics. We address this problem using the recently proposed phase modulation approach. By evolving the 1H chemical shifts in a conventional two dimensional (2D) HSQC-TOCSY experiment for a fixed delay period, the phase/intensity of set of cross peaks belonging to one spin system are modulated differentially relative to those of its overlapping counterpart, resulting in their discrimination and recognition. The method thus accelerates the process of identification and resonance assignment of individual compounds in complex mixtures. This approach facilitated the assignment of molecules in the embryo culture medium used in human assisted reproductive technology.

Electric-field assisted spin torque nano-oscillator and binary frequency shift keying modulation

NASA Astrophysics Data System (ADS)

Zhang, Xiangli; Chen, Hao-Hsuan; Zhang, Zongzhi; Liu, Yaowen

2018-04-01

Electric-controlled magnetization precession introduces technologically relevant possibility for developing spin torque nano-oscillators (STNO) with potential applications in microwave emission. Using the perpendicularly magnetized magnetic tunnel junction (MTJ), we show that the magnetization oscillation frequency can be tuned by the co-action of electric field and spin polarized current. The dynamical phase diagram of MTJ-based STNO is analytically predicted through coordinate transformation from the laboratory frame to the rotation frame, by which the nonstationary out-of-plane magnetization precession process is therefore transformed into the stationary process in the rotation frame. Furthermore, using this STNO as a microwave source, we numerically demonstrate that the bit signal can be transmitted by a binary frequency shift keying (BFSK) modulation technique. The BFSK scheme shows good modulation features with no transient state.

Solid-state selective (13)C excitation and spin diffusion NMR to resolve spatial dimensions in plant cell walls.

PubMed

Foston, Marcus; Katahira, Rui; Gjersing, Erica; Davis, Mark F; Ragauskas, Arthur J

2012-02-15

The average spatial dimensions between major biopolymers within the plant cell wall can be resolved using a solid-state NMR technique referred to as a (13)C cross-polarization (CP) SELDOM (selectively by destruction of magnetization) with a mixing time delay for spin diffusion. Selective excitation of specific aromatic lignin carbons indicates that lignin is in close proximity to hemicellulose followed by amorphous and finally crystalline cellulose. (13)C spin diffusion time constants (T(SD)) were extracted using a two-site spin diffusion theory developed for (13)C nuclei under magic angle spinning (MAS) conditions. These time constants were then used to calculate an average lower-limit spin diffusion length between chemical groups within the plant cell wall. The results on untreated (13)C enriched corn stover stem reveal that the lignin carbons are, on average, located at distances ∼0.7-2.0 nm from the carbons in hemicellulose and cellulose, whereas the pretreated material had larger separations.

Probing density and spin correlations in two-dimensional Hubbard model with ultracold fermions

NASA Astrophysics Data System (ADS)

Chan, Chun Fai; Drewes, Jan Henning; Gall, Marcell; Wurz, Nicola; Cocchi, Eugenio; Miller, Luke; Pertot, Daniel; Brennecke, Ferdinand; Koehl, Michael

2017-04-01

Quantum gases of interacting fermionic atoms in optical lattices is a promising candidate to study strongly correlated quantum phases of the Hubbard model such as the Mott-insulator, spin-ordered phases, or in particular d-wave superconductivity. We experimentally realise the two-dimensional Hubbard model by loading a quantum degenerate Fermi gas of 40 K atoms into a three-dimensional optical lattice geometry. High-resolution absorption imaging in combination with radiofrequency spectroscopy is applied to spatially resolve the atomic distribution in a single 2D layer. We investigate in local measurements of spatial correlations in both the density and spin sector as a function of filling, temperature and interaction strength. In the density sector, we compare the local density fluctuations and the global thermodynamic quantities, and in the spin sector, we observe the onset of non-local spin correlation, signalling the emergence of the anti-ferromagnetic phase. We would report our recent experimental endeavours to investigate further down in temperature in the spin sector.

Miniature Magnet for Electron Spin Resonance Experiments

ERIC Educational Resources Information Center

Rupp, L. W.; And Others

1976-01-01

Describes commercially available permanent magnets that have been incorporated in a compact and inexpensive structure providing both field sweep and modulation suitable for electron spin resonance at microwave frequencies. (MLH)

Reduction of phase noise in nanowire spin orbit torque oscillators

PubMed Central

Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N.; Krivorotov, Ilya N.

2015-01-01

Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity. PMID:26592432

Spin waves in micro-structured yttrium iron garnet nanometer-thick films

DOE PAGES

Jungfleisch, Matthias B.; Zhang, Wei; Jiang, Wanjun; ...

2015-03-24

Here, we investigated the spin-wave propagation in a micro-structured yttrium iron garnet waveguide of 40 nm thickness. Utilizing spatially-resolved Brillouin light scattering microscopy, an exponential decay of the spinwave amplitude of 10 μm was observed. This leads to an estimated Gilbert damping constant of α = (8.79 ± 0.73) x 10 $-$4, which is larger than damping values obtained through ferromagnetic resonance measurements in unstructured films. Furthermore, we compared the theoretically calculated spatial interference of waveguide modes to the spin-wave pattern observed experimentally by means of Brillouin light scattering spectroscopy.

Magnetoelectric antiferromagnets as platforms for the manipulation of solitons

NASA Astrophysics Data System (ADS)

Zarzuela, Ricardo; Kim, Se Kwon; Tserkovnyak, Yaroslav

2018-01-01

We study the magnetic dynamics of magnetoelectric antiferromagnetic thin films, where an unconventional boundary ferromagnetism coexists with the bulk Néel phase below the Néel temperature. The spin exchange between the two order parameters yields an effective low-energy theory that is formally equivalent to that of a ferrimagnet. Dynamics of domain walls and skyrmions are analyzed within the collective-variable approach, from which we conclude that they behave as massive particles moving in a viscous medium subjected to a gyrotropic force. We find that the film thickness can be used as a control parameter for the motion of these solitons. In this regard, it is shown that an external magnetic field can drive the dynamics of domain walls, whose terminal velocity is tunable with the sample thickness. Furthermore, the classification of the skyrmion dynamics is sensitive to the spatial modulation of the sample thickness, which can be easily engineered with the present (thin-film) deposition techniques. Current-driven spin transfer can trigger drifting orbits of skyrmions, which can be utilized as racetracks for these magnetic textures.

Dark Matter Search Results from the PICO-60 CF$$_3$$I Bubble Chamber

DOE PAGES

Amole, C.; Ardid, M.; Asner, D. M.; ...

2016-03-01

We reported new data from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of CF 3I and located in the SNOLAB underground laboratory. PICO-60 is the largest bubble chamber to search for dark matter to date. With an analyzed exposure of 92.8 live-days, PICO-60 exhibits the same excellent background rejection observed in smaller bubble chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic calorimetry, similar but not identical to that reported recently in a C 3F 8 bubble chamber. PICO-60 also observes a large population of unknown background events, exhibiting acoustic, spatial, and timingmore » behaviors inconsistent with those expected from a dark matter signal. We found these behaviors allow for analysis cuts to remove all background events while retaining 48.2%of the exposure. Stringent limits on WIMPs interacting via spin-dependent proton and spin-independent processes are set, and the interpretation of the DAMA/LIBRA modulation signal as dark matter interacting with iodine nuclei is ruled out.« less

Dark matter search results from the PICO-60 CF 3 I bubble chamber

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

Amole, C.; Ardid, M.; Asner, D. M.

2016-03-01

New data are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of CF3I and located in the SNOLAB underground laboratory. PICO-60 is the largest bubble chamber to search for dark matter to date. With an analyzed exposure of 92.8 livedays, PICO-60 exhibits the same excellent background rejection observed in smaller bubble chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic calorimetry, similar but not identical to that reported recently in a C3F8 bubble chamber. PICO-60 also observes a large population of unknown background events, exhibiting acoustic, spatial, and timing behaviors inconsistent withmore » those expected from a dark matter signal. These behaviors allow for analysis cuts to remove all background events while retaining 48.2% of the exposure. Stringent limits on weakly interacting massive particles interacting via spin-dependent proton and spin-independent processes are set, and most interpretations of the DAMA/LIBRA modulation signal as dark matter interacting with iodine nuclei are ruled out.« less

Electric-field control of a hydrogenic donor's spin in a semiconductor

NASA Astrophysics Data System (ADS)

de, Amrit; Pryor, Craig E.; Flatté, Michael E.

2009-03-01

The orbital wave function of an electron bound to a single donor in a semiconductor can be modulated by an applied AC electric field, which affects the electron spin dynamics via the spin-orbit interaction. Numerical calculations of the spin dynamics of a single hydrogenic donor (Si) using a real-space multi-band k.p formalism show that in addition to breaking the high symmetry of the hydrogenic donor state, the g-tensor has a strong nonlinear dependence on the applied fields. By explicitly integrating the time dependent Schr"odinger equation it is seen that Rabi oscillations can be obtained for electric fields modulated at sub-harmonics of the Larmor frequency. The Rabi frequencies obtained from sub-harmonic modulation depend on the magnitudes of the AC and DC components of the electric field. For a purely AC field, the highest Rabi frequency is obtained when E is driven at the 2nd sub-harmonic of the Larmor frequency. Apart from suggesting ways to measure g-tensor anisotropies and nonlinearities, these results also suggest the possibility of direct frequency domain measurements of Rabi frequencies.

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

Yoshizumi, K.; Sasaki, A.; Kohda, M.

We demonstrate gate-controlled switching between persistent spin helix (PSH) state and inverse PSH state, which are detected by quantum interference effect on magneto-conductance. These special symmetric spin states showing weak localization effect give rise to a long spin coherence when the strength of Rashba spin-orbit interaction (SOI) is close to that of Dresselhaus SOI. Furthermore, in the middle of two persistent spin helix states, where the Rashba SOI can be negligible, the bulk Dresselhaus SOI parameter in a modulation doped InGaAs/InAlAs quantum well is determined.

High-frequency polarization dynamics in spin-lasers: pushing the limits

NASA Astrophysics Data System (ADS)

Gerhardt, Nils C.; Lindemann, Markus; Pusch, Tobias; Michalzik, Rainer; Hofmann, Martin R.

2017-09-01

While the high-frequency performance of conventional lasers is limited by the coupled carrier-photon dynamics, spin-polarized lasers have a high potential to overcome this limitation and to push the direct modulation bandwidth beyond 100 GHz. The key is to utilize the ultrafast polarization dynamics in spin-polarized vertical cavity surface-emitting lasers (spin-VCSELs) which is decoupled from the intensity dynamics and its fundamental limitations. The polarization dynamics in such devices, characterized by the polarization oscillation resonance frequency, is mainly determined by the amount of birefringence in the cavity. Using an approach for manipulating the birefringence via mechanical strain we were able to increase the polarization dynamics to resonance frequencies of more than 40 GHz. Up to now these values are only limited by the setup to induce birefringence and do not reflect any fundamental limitations. Taking our record results for the birefringence-induced mode splitting of more than 250 GHz into account, the concept has the potential to provide polarization modulation in spin-VCSELs with modulation frequencies far beyond 100 GHz. This makes them ideal devices for next-generation fast optical interconnects. In this paper we present experimental results for ultrafast polarization dynamics up to 50 GHz and compare them to numerical simulations.

Demonstration of polarization-insensitive spatial light modulation using a single polarization-sensitive spatial light modulator.

PubMed

Liu, Jun; Wang, Jian

2015-07-06

We present a simple configuration incorporating a single polarization-sensitive phase-only liquid crystal spatial light modulator (LC-SLM) to facilitate polarization-insensitive spatial light modulation. The polarization-insensitive configuration is formed by a polarization beam splitter (PBS), a polarization-sensitive phase-only LC-SLM, a half-wave plate (HWP), and a mirror in a loop structure. We experimentally demonstrate polarization-insensitive spatial light modulations for incident linearly polarized beams with different polarization states and polarization-multiplexed beams. Polarization-insensitive spatial light modulations generating orbital angular momentum (OAM) beams are demonstrated in the experiment. The designed polarization-insensitive configuration may find promising applications in spatial light modulations accommodating diverse incident polarizations.

Spin relaxation 1/f noise in graphene

NASA Astrophysics Data System (ADS)

Omar, S.; Guimarães, M. H. D.; Kaverzin, A.; van Wees, B. J.; Vera-Marun, I. J.

2017-02-01

We report the first measurement of 1/f type noise associated with electronic spin transport, using single layer graphene as a prototypical material with a large and tunable Hooge parameter. We identify the presence of two contributions to the measured spin-dependent noise: contact polarization noise from the ferromagnetic electrodes, which can be filtered out using the cross-correlation method, and the noise originated from the spin relaxation processes. The noise magnitude for spin and charge transport differs by three orders of magnitude, implying different scattering mechanisms for the 1/f fluctuations in the charge and spin transport processes. A modulation of the spin-dependent noise magnitude by changing the spin relaxation length and time indicates that the spin-flip processes dominate the spin-dependent noise.

Spin-dependent Seebeck effects in a graphene superlattice p-n junction with different shapes

NASA Astrophysics Data System (ADS)

Zhou, Benhu; Zhou, Benliang; Yao, Yagang; Zhou, Guanghui; Hu, Ming

2017-10-01

We theoretically calculate the spin-dependent transmission probability and spin Seebeck coefficient for a zigzag-edge graphene nanoribbon p-n junction with periodically attached stubs under a perpendicular magnetic field and a ferromagnetic insulator. By using the nonequilibrium Green’s function method combining with the tight-binding Hamiltonian, it is demonstrated that the spin-dependent transmission probability and spin Seebeck coefficient for two types of superlattices can be modulated by the potential drop, the magnetization strength, the number of periods of the superlattice, the strength of the perpendicular magnetic field, and the Anderson disorder strength. Interestingly, a metal to semiconductor transition occurs as the number of the superlattice for a crossed superlattice p-n junction increases, and its spin Seebeck coefficient is much larger than that for the T-shaped one around the zero Fermi energy. Furthermore, the spin Seebeck coefficient for crossed systems can be much pronounced and their maximum absolute value can reach 528 μV K-1 by choosing optimized parameters. Besides, the spin Seebeck coefficient for crossed p-n junction is strongly enhanced around the zero Fermi energy for a weak magnetic field. Our results provide theoretical references for modulating the thermoelectric properties of a graphene superlattice p-n junction by tuning its geometric structure and physical parameters.

Anomalous spin-dependent tunneling statistics in Fe/MgO/Fe junctions induced by disorder at the interface

NASA Astrophysics Data System (ADS)

Yan, Jiawei; Wang, Shizhuo; Xia, Ke; Ke, Youqi

2018-01-01

We present first-principles analysis of interfacial disorder effects on spin-dependent tunneling statistics in thin Fe/MgO/Fe magnetic tunnel junctions. We find that interfacial disorder scattering can significantly modulate the tunneling statistics in the minority spin of the parallel configuration (PC) while all other spin channels remain dominated by the Poissonian process. For the minority-spin channel of PC, interfacial disorder scattering favors the formation of resonant tunneling channels by lifting the limitation of symmetry conservation at low concentration, presenting an important sub-Poissonian process in PC, but is destructive to the open channels at high concentration. We find that the important modulation of tunneling statistics is independent of the type of interfacial disorder. A bimodal distribution function of transmission with disorder dependence is introduced and fits very well our first-principles results. The increase of MgO thickness can quickly change the tunneling from a sub-Poissonian to Poissonian dominated process in the minority spin of PC with disorder. Our results provide a sensitive detection method of an ultralow concentration of interfacial defects.

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.

Qualification test of a MPPC-based PET module for future MRI-PET scanners

NASA Astrophysics Data System (ADS)

Kurei, Y.; Kataoka, J.; Kato, T.; Fujita, T.; Funamoto, H.; Tsujikawa, T.; Yamamoto, S.

2014-11-01

We have developed a high-resolution, compact Positron Emission Tomography (PET) module for future use in MRI-PET scanners. The module consists of large-area, 4×4 ch MPPC arrays (Hamamatsu S11827-3344MG) optically coupled with Ce:LYSO scintillators fabricated into 12×12 matrices of 1×1 mm2 pixels. At this stage, a pair of module and coincidence circuits was assembled into an experimental prototype gantry arranged in a ring of 90 mm in diameter to form the MPPC-based PET system. The PET detector ring was then positioned around the RF coil of the 4.7 T MRI system. We took an image of a point 22Na source under fast spin echo (FSE) and gradient echo (GE), in order to measure interference between the MPPC-based PET and the MRI. We only found a slight degradation in the spatial resolution of the PET image from 1.63 to 1.70 mm (FWHM; x-direction), or 1.48-1.55 mm (FWHM; y-direction) when operating with the MRI, while the signal-to-noise ratio (SNR) of the MRI image was only degraded by 5%. These results encouraged us to develop a more advanced version of the MRI-PET gantry with eight MPPC-based PET modules, whose detailed design and first qualification test are also presented in this paper.

Research of spin-orbit interaction in organic conjugated polymers

NASA Astrophysics Data System (ADS)

Li, H.; Zhou, M. Y.; Wu, S. Y.; Liang, X. R.

2017-06-01

The effect of spin-orbit interaction on the one-dimensional organic polymer was investigated theoretically. Spin-orbital interaction led to the spatial separation of energy band but did not eliminate spin degeneration, which was different from energy level splitting in the Zeeman Effect. Spin-orbit interaction had little effect on the energy band structure, charge density, and lattice position, etc.; Spin precession was obtained when a polaron was transported along the polymer chain, which theoretically proved that it was feasible to control the spin precession of polaron in organic polymers by the use of external electric field.

Fine structure and optical pumping of spins in individual semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Bracker, Allan S.; Gammon, Daniel; Korenev, Vladimir L.

2008-11-01

We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information.

Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study.

PubMed

Pogrebna, A; Mertelj, T; Vujičić, N; Cao, G; Xu, Z A; Mihailovic, D

2015-01-13

Ferromagnetism and superconductivity are antagonistic phenomena. Their coexistence implies either a modulated ferromagnetic order parameter on a lengthscale shorter than the superconducting coherence length or a weak exchange coupling between the itinerant superconducting electrons and the localized ordered spins. In some iron based pnictide superconductors the coexistence of ferromagnetism and superconductivity has been clearly demonstrated. The nature of the coexistence, however, remains elusive since no clear understanding of the spin structure in the superconducting state has been reached and the reports on the coupling strength are controversial. We show, by a direct optical pump-probe experiment, that the coupling is weak, since the transfer of the excess energy from the itinerant electrons to ordered localized spins is much slower than the electron-phonon relaxation, implying the coexistence without the short-lengthscale ferromagnetic order parameter modulation. Remarkably, the polarization analysis of the coherently excited spin wave response points towards a simple ferromagnetic ordering of spins with two distinct types of ferromagnetic domains.

Demonstration of polarization-insensitive spatial light modulation using a single polarization-sensitive spatial light modulator

PubMed Central

Liu, Jun; Wang, Jian

2015-01-01

We present a simple configuration incorporating a single polarization-sensitive phase-only liquid crystal spatial light modulator (LC-SLM) to facilitate polarization-insensitive spatial light modulation. The polarization-insensitive configuration is formed by a polarization beam splitter (PBS), a polarization-sensitive phase-only LC-SLM, a half-wave plate (HWP), and a mirror in a loop structure. We experimentally demonstrate polarization-insensitive spatial light modulations for incident linearly polarized beams with different polarization states and polarization-multiplexed beams. Polarization-insensitive spatial light modulations generating orbital angular momentum (OAM) beams are demonstrated in the experiment. The designed polarization-insensitive configuration may find promising applications in spatial light modulations accommodating diverse incident polarizations. PMID:26146032

Transmutation of skyrmions to half-solitons driven by the nonlinear optical spin Hall effect.

PubMed

Flayac, H; Solnyshkov, D D; Shelykh, I A; Malpuech, G

2013-01-04

We show that the spin domains, generated in the linear optical spin Hall effect by the analog of spin-orbit interaction for exciton polaritons, are associated with the formation of a Skyrmion lattice. In the nonlinear regime, the spin anisotropy of the polariton-polariton interactions results in a spatial compression of the domains and in a transmutation of the Skyrmions into oblique half-solitons. This phase transition is associated with both the focusing of the spin currents and the emergence of a strongly anisotropic emission pattern.

Characterization of heteronuclear decoupling through proton spin dynamics in solid-state nuclear magnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

De Paëpe, Gaël; Eléna, Bénédicte; Emsley, Lyndon

2004-08-01

The work presented here aims at understanding the performance of phase modulated heteronuclear decoupling sequences such as Cosine Modulation or Two Pulse Phase Modulation. To that end we provide an analytical description of the intrinsic behavior of Cosine Modulation decoupling with respect to radio-frequency-inhomogeneity and the proton-proton dipolar coupling network. We discover through a Modulation Frame average Hamiltonian analysis that best decoupling is obtained under conditions where the heteronuclear interactions are removed but notably where homonuclear couplings are recoupled at a homonuclear Rotary Resonance (HORROR) condition in the Modulation Frame. These conclusions are supported by extensive experimental investigations, and notably through the introduction of proton nutation experiments to characterize spin dynamics in solids under decoupling conditions. The theoretical framework presented in this paper allows the prediction of the optimum parameters for a given set of experimental conditions.

Efficient spectroscopic imaging by an optimized encoding of pre-targeted resonances

PubMed Central

Zhang, Zhiyong; Shemesh, Noam; Frydman, Lucio

2016-01-01

A “relaxation-enhanced” (RE) selective-excitation approach to acquire in vivo localized spectra with flat baselines and very good signal-to-noise ratios –particularly at high fields– has been recently proposed. As RE MRS targets a subset of a priori known resonances, new possibilities arise to acquire spectroscopic imaging data in a faster, more efficient manner. Hereby we present one such opportunity based on what we denominate Relaxation-Enhanced Chemical-shift-Encoded Spectroscopically-Separated (RECESS) imaging. RECESS delivers spectral/spatial correlations of various metabolites, by collecting a gradient echo train whose timing is defined by the chemical shifts of the various selectively excited resonances to be disentangled. Different sites thus impart distinct, coherent phase modulations on the images; condition number considerations allow one to disentangle these contributions of the various sites by a simple matrix inversion. The efficiency of the ensuing spectral/spatial correlation method is high enough to enable the examination of additional spatial axes via their phase encoding in CPMG-like spin-echo trains. The ensuing single-shot 1D spectral / 2D spatial RECESS method thus accelerates the acquisition of quality MRSI data by factors that, depending on the sensitivity, range between 2 and 50. This is illustrated with a number of phantom, of ex vivo and of in vivo acquisitions. PMID:26910285

Improved Estimation of Electron Temperature from Rocket-borne Impedance Probes

NASA Astrophysics Data System (ADS)

Rowland, D. E.; Wolfinger, K.; Stamm, J. D.

2017-12-01

The impedance probe technique is a well known method for determining high accuracy measurements of electron number density in the Earth's ionosphere. We present analysis of impedance probe data from several sounding rockets at low, mid-, and auroral latitudes, including high cadence estimates of the electron temperature, derived from analytical fits to the antenna impedance curves. These estimates compare favorably with independent estimates from Langmuir Probes, but at much higher temporal and spatial resolution, providing a capability to resolve small-scale temperature fluctuations. We also present some considerations for the design of impedance probes, including assessment of the effects of resonance damping due to rocket motion, effects of wake and spin modulation, and aspect angle to the magnetic field.

Inter-Vendor Reproducibility of Pseudo-Continuous Arterial Spin Labeling at 3 Tesla

PubMed Central

Mutsaerts, Henri J. M. M.; Steketee, Rebecca M. E.; Heijtel, Dennis F. R.; Kuijer, Joost P. A.; van Osch, Matthias J. P.; Majoie, Charles B. L. M.; Smits, Marion; Nederveen, Aart J.

2014-01-01

Purpose Prior to the implementation of arterial spin labeling (ASL) in clinical multi-center studies, it is important to establish its status quo inter-vendor reproducibility. This study evaluates and compares the intra- and inter-vendor reproducibility of pseudo-continuous ASL (pCASL) as clinically implemented by GE and Philips. Material and Methods 22 healthy volunteers were scanned twice on both a 3T GE and a 3T Philips scanner. The main difference in implementation between the vendors was the readout module: spiral 3D fast spin echo vs. 2D gradient-echo echo-planar imaging respectively. Mean and variation of cerebral blood flow (CBF) were compared for the total gray matter (GM) and white matter (WM), and on a voxel-level. Results Whereas the mean GM CBF of both vendors was almost equal (p = 1.0), the mean WM CBF was significantly different (p<0.01). The inter-vendor GM variation did not differ from the intra-vendor GM variation (p = 0.3 and p = 0.5 for GE and Philips respectively). Spatial inter-vendor CBF and variation differences were observed in several GM regions and in the WM. Conclusion These results show that total GM CBF-values can be exchanged between vendors. For the inter-vendor comparison of GM regions or WM, these results encourage further standardization of ASL implementation among vendors. PMID:25090654

Inter-vendor reproducibility of pseudo-continuous arterial spin labeling at 3 Tesla.

PubMed

Mutsaerts, Henri J M M; Steketee, Rebecca M E; Heijtel, Dennis F R; Kuijer, Joost P A; van Osch, Matthias J P; Majoie, Charles B L M; Smits, Marion; Nederveen, Aart J

2014-01-01

Prior to the implementation of arterial spin labeling (ASL) in clinical multi-center studies, it is important to establish its status quo inter-vendor reproducibility. This study evaluates and compares the intra- and inter-vendor reproducibility of pseudo-continuous ASL (pCASL) as clinically implemented by GE and Philips. 22 healthy volunteers were scanned twice on both a 3T GE and a 3T Philips scanner. The main difference in implementation between the vendors was the readout module: spiral 3D fast spin echo vs. 2D gradient-echo echo-planar imaging respectively. Mean and variation of cerebral blood flow (CBF) were compared for the total gray matter (GM) and white matter (WM), and on a voxel-level. Whereas the mean GM CBF of both vendors was almost equal (p = 1.0), the mean WM CBF was significantly different (p<0.01). The inter-vendor GM variation did not differ from the intra-vendor GM variation (p = 0.3 and p = 0.5 for GE and Philips respectively). Spatial inter-vendor CBF and variation differences were observed in several GM regions and in the WM. These results show that total GM CBF-values can be exchanged between vendors. For the inter-vendor comparison of GM regions or WM, these results encourage further standardization of ASL implementation among vendors.

Macrorealism from entropic Leggett-Garg inequalities

NASA Astrophysics Data System (ADS)

Devi, A. R. Usha; Karthik, H. S.; Sudha; Rajagopal, A. K.

2013-05-01

We formulate entropic Leggett-Garg inequalities, which place constraints on the statistical outcomes of temporal correlations of observables. The information theoretic inequalities are satisfied if macrorealism holds. We show that the quantum statistics underlying correlations between time-separated spin component of a quantum rotor mimics that of spin correlations in two spatially separated spin-s particles sharing a state of zero total spin. This brings forth the violation of the entropic Leggett-Garg inequality by a rotating quantum spin-s system in a similar manner as does the entropic Bell inequality [S. L. Braunstein and C. M. Caves, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.61.662 61, 662 (1988)] by a pair of spin-s particles forming a composite spin singlet state.

Spatial and Spin Symmetry Breaking in Semidefinite-Programming-Based Hartree-Fock Theory.

PubMed

Nascimento, Daniel R; DePrince, A Eugene

2018-05-08

The Hartree-Fock problem was recently recast as a semidefinite optimization over the space of rank-constrained two-body reduced-density matrices (RDMs) [ Phys. Rev. A 2014 , 89 , 010502(R) ]. This formulation of the problem transfers the nonconvexity of the Hartree-Fock energy functional to the rank constraint on the two-body RDM. We consider an equivalent optimization over the space of positive semidefinite one-electron RDMs (1-RDMs) that retains the nonconvexity of the Hartree-Fock energy expression. The optimized 1-RDM satisfies ensemble N-representability conditions, and ensemble spin-state conditions may be imposed as well. The spin-state conditions place additional linear and nonlinear constraints on the 1-RDM. We apply this RDM-based approach to several molecular systems and explore its spatial (point group) and spin ( Ŝ 2 and Ŝ 3 ) symmetry breaking properties. When imposing Ŝ 2 and Ŝ 3 symmetry but relaxing point group symmetry, the procedure often locates spatial-symmetry-broken solutions that are difficult to identify using standard algorithms. For example, the RDM-based approach yields a smooth, spatial-symmetry-broken potential energy curve for the well-known Be-H 2 insertion pathway. We also demonstrate numerically that, upon relaxation of Ŝ 2 and Ŝ 3 symmetry constraints, the RDM-based approach is equivalent to real-valued generalized Hartree-Fock theory.

The classical and quantum dynamics of molecular spins on graphene.

PubMed

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2016-02-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain's threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

The classical and quantum dynamics of molecular spins on graphene

NASA Astrophysics Data System (ADS)

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2016-02-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics and electrical spin manipulation. However, the influence of the graphene environment on the spin systems has yet to be unravelled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. Whereas the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly developed model. Coupling to Dirac electrons introduces a dominant quantum relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully coherent, resonant spin tunnelling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin manipulation in graphene nanodevices.

Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics

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

Pikin, S. A., E-mail: pikin@ns.crys.ras.ru

2016-05-15

It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the Néel temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vectormore » coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.« less

Low-Temperature Dynamic Nuclear Polarization at 9.4 Tesla With a 30 Milliwatt Microwave Source

PubMed Central

Thurber, Kent R.; Yau, Wai-Ming; Tycko, Robert

2010-01-01

Dynamic nuclear polarization (DNP) can provide large signal enhancements in nuclear magnetic resonance (NMR) by transfer of polarization from electron spins to nuclear spins. We discuss several aspects of DNP experiments at 9.4 Tesla (400 MHz resonant frequency for 1H, 264 GHz for electron spins in organic radicals) in the 7–80 K temperature range, using a 30 mW, frequency-tunable microwave source and a quasi-optical microwave bridge for polarization control and low-loss microwave transmission. In experiments on frozen glycerol/water doped with nitroxide radicals, DNP signal enhancements up to a factor of 80 are observed (relative to 1H NMR signals with thermal equilibrium spin polarization). The largest sensitivity enhancements are observed with a new triradical dopant, DOTOPA-TEMPO. Field modulation with a 10 G root-mean-squared amplitude during DNP increases the nuclear spin polarizations by up to 135%. Dependencies of 1H NMR signal amplitudes, nuclear spin relaxation times, and DNP build-up times on the dopant and its concentration, temperature, microwave power, and modulation frequency are reported and discussed. The benefits of low-temperature DNP can be dramatic: the 1H spin polarization is increased approximately 1000-fold at 7 K with DNP, relative to thermal polarization at 80 K. PMID:20392658

Surface Plasmon-Mediated Nanoscale Localization of Laser-Driven sub-Terahertz Spin Dynamics in Magnetic Dielectrics.

PubMed

Chekhov, Alexander L; Stognij, Alexander I; Satoh, Takuya; Murzina, Tatiana V; Razdolski, Ilya; Stupakiewicz, Andrzej

2018-05-09

We report spatial localization of the effective magnetic field generated via the inverse Faraday effect employing surface plasmon polaritons (SPPs) at Au/garnet interface. Analyzing both numerically and analytically the electric field of the SPPs at this interface, we corroborate our study with a proof-of-concept experiment showing efficient SPP-driven excitation of coherent spin precession with 0.41 THz frequency. We argue that the subdiffractional confinement of the SPP electric field enables strong spatial localization of the SPP-mediated excitation of spin dynamics. We demonstrate two orders of magnitude enhancement of the excitation efficiency at the surface plasmon resonance within a 100 nm layer of a dielectric garnet. Our findings broaden the horizons of ultrafast spin-plasmonics and open pathways toward nonthermal opto-magnetic recording on the nanoscale.

Spatially resolved nuclear spin relaxation, electron spin relaxation and light absorption in swift heavy ion irradiated LiF crystals.

PubMed

Stork, H; Dinse, K-P; Ditter, M; Fujara, F; Masierak, W; Neumann, R; Schuster, B; Schwartz, K; Trautmann, C

2010-05-12

Spatially resolved (19)F and (7)Li spin-lattice relaxation rates are measured for LiF single crystals after irradiation with two kinds of swift heavy ions ((12)C of 133 MeV and (208)Pb of 1.78 GeV incident energy). Like in earlier studies on (130)Xe and (238)U irradiated LiF crystals, we found a strong enhancement of the nuclear spin-lattice relaxation rate within the ion penetration depth and a slight--but still significant--enhancement beyond. By evaluating the nuclear relaxation rate enhancement within the ion range after irradiation with different projectiles, a universal relationship between the spin-lattice relaxation rate and the dose is deduced. The results of accompanying X-band electron paramagnetic resonance relaxation measurements and optical absorption spectroscopy are included in a physical interpretation of this relationship. Also the reason for the enhanced relaxation rate beyond the ion range is further discussed.

Critical Spin Superflow in a Spinor Bose-Einstein Condensate

NASA Astrophysics Data System (ADS)

Kim, Joon Hyun; Seo, Sang Won; Shin, Y.

2017-11-01

We investigate the critical dynamics of spin superflow in an easy-plane antiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are induced in a trapped condensate by applying a linear magnetic field gradient and we observe that the damping rate increases rapidly as the field gradient increases above a certain critical value. The onset of dissipation is found to be associated with the generation of dark-bright solitons due to the modulation instability of the counterflow of two spin components. Spin turbulence emerges as the solitons decay because of their snake instability. We identify another critical point for spin superflow, in which transverse magnon excitations are dynamically generated via spin-exchanging collisions, which leads to the transient formation of axial polar spin domains.

Building Complex Kondo Impurities by Manipulating Entangled Spin Chains.

PubMed

Choi, Deung-Jang; Robles, Roberto; Yan, Shichao; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Gauyacq, Jean-Pierre; Lorente, Nicolás; Ternes, Markus; Loth, Sebastian

2017-10-11

The creation of molecule-like structures in which magnetic atoms interact controllably is full of potential for the study of complex or strongly correlated systems. Here, we create spin chains in which a strongly correlated Kondo state emerges from magnetic coupling of transition-metal atoms. We build chains up to ten atoms in length by placing Fe and Mn atoms on a Cu 2 N surface with a scanning tunneling microscope. The atoms couple antiferromagnetically via superexchange interaction through the nitrogen atom network of the surface. The emergent Kondo resonance is spatially distributed along the chain. Its strength can be controlled by mixing atoms of different transition metal elements and manipulating their spatial distribution. We show that the Kondo screening of the full chain by the electrons of the nonmagnetic substrate depends on the interatomic entanglement of the spins in the chain, demonstrating the prerequisites to build and probe spatially extended strongly correlated nanostructures.

Generation of Quality Pulses for Control of Qubit/Quantum Memory Spin States: Experimental and Simulation

DTIC Science & Technology

2016-09-01

magnetic and nuclear spins of an entangled ensemble or of single spins or photons . These quantum states can be controlled by resonant microwave...3 3.1 SIMULATION MODEL USING MATLAB /SIMULINK...4 3.1 SIMULATION MODEL USING MATLAB ®/SIMULINK Figure 7 presents the Simulink simulation example of I/Q modulation followed by a switch

Spin transport in lateral structures with semiconducting channel

NASA Astrophysics Data System (ADS)

Zainuddin, Abu Naser

Spintronics is an emerging field of electronics with the potential to be used in future integrated circuits. Spintronic devices are already making their mark in storage technologies in recent times and there are proposals for using spintronic effects in logic technologies as well. So far, major improvement in spintronic effects, for example, the `spin-valve' effect, is being achieved in metals or insulators as channel materials. But not much progress is made in semiconductors owing to the difficulty in injecting spins into them, which has only very recently been overcome with the combined efforts of many research groups around the world. The key motivations for semiconductor spintronics are their ease in integration with the existing semiconductor technology along with the gate controllability. At present semiconductor based spintronic devices are mostly lateral and are showing a very poor performance compared to their metal or insulator based vertical counterparts. The objective of this thesis is to analyze these devices based on spin-transport models and simulations. At first a lateral spin-valve device is modeled with the spin-diffusion equation based semiclassical approach. Identifying the important issues regarding the device performance, a compact circuit equivalent model is presented which would help to improve the device design. It is found that the regions outside the current path also have a significant influence on the device performance under certain conditions, which is ordinarily neglected when only charge transport is considered. Next, a modified spin-valve structure is studied where the spin signal is controlled with a gate in between the injecting and detecting contacts. The gate is used to modulate the rashba spin-orbit coupling of the channel which, in turn, modulates the spin-valve signal. The idea of gate controlled spin manipulation was originally proposed by Datta and Das back in 1990 and is called 'Datta-Das' effect. In this thesis, we have extended the model described in the original proposal to include the influence of channel dimensions on the nature of electron flow and the contact dimensions on the magnitude and phase of the spin-valve signal. In order to capture the spin-orbit effect a non-equilibrium Green's function (NEGF) based quantum transport model for spin-valve device have been developed which is also explained with simple theoretical treatment based on stationary phase approximation. The model is also compared against a recent experiment that demonstrated such gate modulated spin-valve effect. This thesis also evaluates the possibility of gate controlled magnetization reversal or spin-torque effect as a means to validate this, so called, 'Datta-Das' effect on a more solid footing. Finally, the scope for utilizing topological insulator material in semiconductor spintronics is discussed as a possible future work for this thesis.

Strain-assisted optomechanical coupling of polariton condensate spin to a micromechanical resonator

NASA Astrophysics Data System (ADS)

Be'er, O.; Ohadi, H.; del Valle-Inclan Redondo, Y.; Ramsay, A. J.; Tsintzos, S. I.; Hatzopoulos, Z.; Savvidis, P. G.; Baumberg, J. J.

2017-12-01

We report spin and intensity coupling of an exciton-polariton condensate to the mechanical vibrations of a circular membrane microcavity. We optically drive the microcavity resonator at the lowest mechanical resonance frequency while creating an optically trapped spin-polarized polariton condensate in different locations on the microcavity and observe spin and intensity oscillations of the condensate at the vibration frequency of the resonator. Spin oscillations are induced by vibrational strain driving, whilst the modulation of the optical trap due to the displacement of the membrane causes intensity oscillations in the condensate emission. Our results demonstrate spin-phonon coupling in a macroscopically coherent condensate.

Spectrum Gaps of Spin Waves Generated by Interference in a Uniform Nanostripe Waveguide

PubMed Central

Wang, Qi; Zhang, Huaiwu; Ma, Guokun; Liao, Yulong; Tang, Xiaoli; Zhong, Zhiyong

2014-01-01

We studied spin waves excited by two or more excitation sources in a uniform nanostripe waveguide without periodic structures. Several distinct spectrum gaps formed by spin waves interference rather than by Bragg reflection were observed. We found the center frequency and the number of spectrum gaps of spin waves can be controlled by modulating the distance, number and width of the excitation sources. The results obtained by micromagnetic simulations agree well with that of analytical calculations. Our work therefore paves a new way to control the spectrum gaps of spin waves, which is promising for future spin wave-based devices. PMID:25082001

Time domain simulation of Gd3+-Gd3+ distance measurements by EPR

NASA Astrophysics Data System (ADS)

Manukovsky, Nurit; Feintuch, Akiva; Kuprov, Ilya; Goldfarb, Daniella

2017-07-01

Gd3+-based spin labels are useful as an alternative to nitroxides for intramolecular distance measurements at high fields in biological systems. However, double electron-electron resonance (DEER) measurements using model Gd3+ complexes featured a low modulation depth and an unexpected broadening of the distance distribution for short Gd3+-Gd3+ distances, when analysed using the software designed for S = 1/2 pairs. It appears that these effects result from the different spectroscopic characteristics of Gd3+—the high spin, the zero field splitting (ZFS), and the flip-flop terms in the dipolar Hamiltonian that are often ignored for spin-1/2 systems. An understanding of the factors affecting the modulation frequency and amplitude is essential for the correct analysis of Gd3+-Gd3+ DEER data and for the educated choice of experimental settings, such as Gd3+ spin label type and the pulse parameters. This work uses time-domain simulations of Gd3+-Gd3+ DEER by explicit density matrix propagation to elucidate the factors shaping Gd3+ DEER traces. The simulations show that mixing between the |+½, -½> and |-½, +½> states of the two spins, caused by the flip-flop term in the dipolar Hamiltonian, leads to dampening of the dipolar modulation. This effect may be mitigated by a large ZFS or by pulse frequency settings allowing for a decreased contribution of the central transition and the one adjacent to it. The simulations reproduce both the experimental line shapes of the Fourier-transforms of the DEER time domain traces and the trends in the behaviour of the modulation depth, thus enabling a more systematic design and analysis of Gd3+ DEER experiments.

Lock-in detection for pulsed electrically detected magnetic resonance

NASA Astrophysics Data System (ADS)

Hoehne, Felix; Dreher, Lukas; Behrends, Jan; Fehr, Matthias; Huebl, Hans; Lips, Klaus; Schnegg, Alexander; Suckert, Max; Stutzmann, Martin; Brandt, Martin S.

2012-04-01

We show that in pulsed electrically detected magnetic resonance (pEDMR) signal modulation in combination with a lock-in detection scheme can reduce the low-frequency noise level by one order of magnitude and in addition removes the microwave-induced non-resonant background. This is exemplarily demonstrated for spin-echo measurements in phosphorus-doped silicon. The modulation of the signal is achieved by cycling the phase of the projection pulse used in pEDMR for the readout of the spin state.

Nonadiabatic Berry phase in nanocrystalline magnets

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

Skomski, R.; Sellmyer, D. J.

2016-12-20

In this study, it is investigated how a Berry phase is created in polycrystalline nanomagnets and how the phase translates into an emergent magnetic field and into a topological Hall-effect contribution. The analysis starts directly from the spin of the conduction electrons and does not involve any adiabatic Hamiltonian. Completely random spin alignment in the nanocrystallites does not lead to a nonzero emergent field, but a modulation of the local magnetization does. As an explicit example, we consider a wire with a modulated cone angle.

Spatially distributed multipartite entanglement enables EPR steering of atomic clouds.

PubMed

Kunkel, Philipp; Prüfer, Maximilian; Strobel, Helmut; Linnemann, Daniel; Frölian, Anika; Gasenzer, Thomas; Gärttner, Martin; Oberthaler, Markus K

2018-04-27

A key resource for distributed quantum-enhanced protocols is entanglement between spatially separated modes. However, the robust generation and detection of entanglement between spatially separated regions of an ultracold atomic system remain a challenge. We used spin mixing in a tightly confined Bose-Einstein condensate to generate an entangled state of indistinguishable particles in a single spatial mode. We show experimentally that this entanglement can be spatially distributed by self-similar expansion of the atomic cloud. We used spatially resolved spin read-out to reveal a particularly strong form of quantum correlations known as Einstein-Podolsky-Rosen (EPR) steering between distinct parts of the expanded cloud. Based on the strength of EPR steering, we constructed a witness, which confirmed genuine 5-partite entanglement. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

A scenario for magnonic spin-wave traps

PubMed Central

Busse, Frederik; Mansurova, Maria; Lenk, Benjamin; von der Ehe, Marvin; Münzenberg, Markus

2015-01-01

Spatially resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center. This can be attributed to a laser generated temperature profile. We determine a shift of 0.5 GHz in the spin-wave frequency due to the spatial thermal profile induced by the femtosecond pump pulse that persists for up to one nanosecond. Similar experiments are presented for a magnonic crystal composed of a CoFeB-film based antidot lattice with a Damon Eshbach mode at the Brillouin zone boundary and its consequences are discussed. PMID:26279466

Sensitivity enhancements in MQ-MAS NMR of spin-5/2 nuclei using modulated rf mixing pulses

NASA Astrophysics Data System (ADS)

Vosegaard, Thomas; Massiot, Dominique; Grandinetti, Philip J.

2000-08-01

An X- overlineX pulse train with stepped modulation frequency was employed to enhance the multiple-quantum to single-quantum coherence transfer in the mixing period of the multiple-quantum magic-angle spinning (MQ-MAS) experiment for spin I=5/2 nuclei. Two MQ-MAS pulse sequences employing this mixing scheme for the triple-to-single and quintuple-to-single quantum coherence transfers have been designed and their performance is demonstrated for 27Al on samples of NaSi 3AlO 8 and 9Al 2O 3·2B 2O 3 . Compared to the standard single-pulse mixing sequences, the sensitivity is approximately doubled in the present experiments.

Optical solitons and modulation instability analysis of an integrable model of (2+1)-Dimensional Heisenberg ferromagnetic spin chain equation

NASA Astrophysics Data System (ADS)

Inc, Mustafa; Aliyu, Aliyu Isa; Yusuf, Abdullahi; Baleanu, Dumitru

2017-12-01

This paper addresses the nonlinear Schrödinger type equation (NLSE) in (2+1)-dimensions which describes the nonlinear spin dynamics of Heisenberg ferromagnetic spin chains (HFSC) with anisotropic and bilinear interactions in the semiclassical limit. Two integration schemes are employed to study the equation. These are the complex envelope function ansatz and the generalized tanh methods. Dark, dark-bright or combined optical and singular soliton solutions of the equation are derived. Furthermore, the modulational instability (MI) is studied based on the standard linear-stability analysis and the MI gain is got. Numerical simulation of the obtained results are analyzed with interesting figures showing the physical meaning of the solutions.

Optimised frequency modulation for continuous-wave optical magnetic resonance sensing using nitrogen-vacancy ensembles.

PubMed

El-Ella, Haitham A R; Ahmadi, Sepehr; Wojciechowski, Adam M; Huck, Alexander; Andersen, Ulrik L

2017-06-26

Magnetometers based on ensembles of nitrogen-vacancy centres are a promising platform for continuously sensing static and low-frequency magnetic fields. Their combination with phase-sensitive (lock-in) detection creates a highly versatile sensor with a sensitivity that is proportional to the derivative of the optical magnetic resonance lock-in spectrum, which is in turn dependant on the lock-in modulation parameters. Here we study the dependence of the lock-in spectral slope on the modulation of the spin-driving microwave field. Given the presence of the intrinsic nitrogen hyperfine spin transitions, we experimentally show that when the ratio between the hyperfine linewidth and their separation is ≳ 1/4, square-wave based frequency modulation generates the steepest slope at modulation depths exceeding the separation of the hyperfine lines, compared to sine-wave based modulation. We formulate a model for calculating lock-in spectra which shows excellent agreement with our experiments, and which shows that an optimum slope is achieved when the linewidth/separation ratio is ≲ 1/4 and the modulation depth is less then the resonance linewidth, irrespective of the modulation function used.

Spatial Light Modulator Would Serve As Electronic Iris

NASA Technical Reports Server (NTRS)

Gutow, David A.

1991-01-01

In proposed technique for controlling brightness of image formed by lens, spatial light modulator serves as segmented, electronically variable aperture. Offers several advantages: spatial light modulator controlled remotely and responds faster than motorized iris or other remotely controlled mechanical iris. Unlike iris, modulator also configured so as not to vary depth of field appreciably. Unlike lead lanthanum zirconate titanate crystal, spatial light modulator does not require high voltage.

Theory of high-resolution tunneling spin transport on a magnetic skyrmion

NASA Astrophysics Data System (ADS)

Palotás, Krisztián; Rózsa, Levente; Szunyogh, László

2018-05-01

Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque, are calculated in high spatial resolution within the same theoretical framework. A connection between the conventional charge current SP-STM image contrasts and the magnitudes of the spin transport vectors is demonstrated that enables the estimation of tunneling spin transport properties based on experimentally measured SP-STM images. A considerable tunability of the spin transport vectors by the involved spin polarizations is also highlighted. These possibilities and the combined theory of tunneling charge and vector spin transport pave the way for gaining deep insight into electric-current-induced tunneling spin transport properties in SP-STM and to the related dynamics of complex magnetic textures at surfaces.

High-efficiency control of spin-wave propagation in ultra-thin yttrium iron garnet by the spin-orbit torque

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

Evelt, M.; Demidov, V. E., E-mail: demidov@uni-muenster.de; Bessonov, V.

2016-04-25

We study experimentally with submicrometer spatial resolution the propagation of spin waves in microscopic waveguides based on the nanometer-thick yttrium iron garnet and Pt layers. We demonstrate that by using the spin-orbit torque, the propagation length of the spin waves in such systems can be increased by nearly a factor of 10, which corresponds to the increase in the spin-wave intensity at the output of a 10 μm long transmission line by three orders of magnitude. We also show that, in the regime, where the magnetic damping is completely compensated by the spin-orbit torque, the spin-wave amplification is suppressed by themore » nonlinear scattering of the coherent spin waves from current-induced excitations.« less

The classical and quantum dynamics of molecular spins on graphene

PubMed Central

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2015-01-01

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic1 and quantum computing2 devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics3,4, and electrical spin-manipulation4-11. However, the influence of the graphene environment on the spin systems has yet to be unraveled12. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets13 on graphene. While the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly-developed model. Coupling to Dirac electrons introduces a dominant quantum-relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully-coherent, resonant spin tunneling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin-manipulation in graphene nanodevices. PMID:26641019

Realization of spin wave switch for data processing

NASA Astrophysics Data System (ADS)

Balinskiy, M.; Chiang, H.; Khitun, A.

2018-05-01

In this work, experimental data on a spin wave switch based on spin wave interference is reported. The switch is a three terminal device where spin wave propagation between the source and the drain is modulated by the control spin wave signal. The prototype is a micrometer scale device based on Y3Fe2(FeO4)3 film. The output characteristics show the oscillation of the output spin wave signal as a function of the phase difference between the source and the drain spin wave signals. The On/Off ratio of the prototype exceeds 20 dB at room temperature. The utilization of phase in addition to amplitude for information encoding offers an innovative route towards multi-state logic circuits. The advantages and shortcomings of spin wave switches are also discussed.

Stern-Gerlach dynamics with quantum propagators

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

Hsu, Bailey C.; Berrondo, Manuel; Van Huele, Jean-Francois S.

2011-01-15

We study the quantum dynamics of a nonrelativistic neutral particle with spin in inhomogeneous external magnetic fields. We first consider fields with one-dimensional inhomogeneities, both unphysical and physical, and construct the corresponding analytic propagators. We then consider fields with two-dimensional inhomogeneities and develop an appropriate numerical propagation method. We propagate initial states exhibiting different degrees of space localization and various initial spin configurations, including both pure and mixed spin states. We study the evolution of their spin densities and identify characteristic features of spin density dynamics, such as the spatial separation of spin components, and spin localization or accumulation. Wemore » compare our approach and our results with the coverage of the Stern-Gerlach effect in the literature, and we focus on nonstandard Stern-Gerlach outcomes, such as radial separation, spin focusing, spin oscillation, and spin flipping.« less

Influence of DC-biasing on the performance of graphene spin valve

NASA Astrophysics Data System (ADS)

Iqbal, Muhammad Zahir; Hussain, Ghulam; Siddique, Salma; Hussain, Tassadaq; Iqbal, Muhammad Javaid

2018-04-01

Generating and controlling the spin valve signal are key factors in 'spintronics', which aims to utilize the spin degree of electrons. For this purpose, spintronic devices are constructed that can detect the spin signal. Here we investigate the effect of direct current (DC) on the magnetoresistance (MR) of graphene spin valve. The DC input not only decreases the magnitude of MR but also distorts the spin valve signal at higher DC inputs. Also, low temperature measurements revealed higher MR for the device, while the magnitude is noticed to decrease at higher temperatures. Furthermore, the spin polarization associated with NiFe electrodes is continuously increased at low DC bias and low temperatures. We also demonstrate the ohmic behavior of graphene spin valve by showing linear current-voltage (I-V) characteristics of the junction. Our findings may contribute significantly in modulating and controlling the spin transport properties of vertical spin valve structures.

Charge-induced spin torque in Weyl semimetals

NASA Astrophysics Data System (ADS)

Kurebayashi, Daichi; Nomura, Kentaro

In this work, we present phenomenological and microscopic derivations of spin torques in magnetically doped Weyl semimetals. As a result, we obtain the analytical expression of the spin torque generated, without a flowing current, when the chemical potential is modulated. We also find that this spin torque is a direct consequence of the chiral anomaly. Therefore, observing this spin torque in magnetic Weyl semimetals might be an experimental evidence of the chiral anomaly. This spin torque has also a great advantage in application. In contrast to conventional current-induced spin torques such as the spin-transfer torques, this spin torque does not accompany a constant current flow. Thus, devices using this operating principle is free from the Joule heating and possibly have higher efficiency than devices using conventional current-induced spin torques. This work was supported by JSPS KAKENHI Grant Number JP15H05854 and JP26400308.

Control of Spin Wave Dynamics in Spatially Twisted Magnetic Structures

DTIC Science & Technology

2017-06-27

realize high-performance spintronic and magnetic storage devices. 15. SUBJECT TERMS nano- electronics , spin, wave, magnetic, multi-functional, device 16... electronics has required us to develop high-performance and multi-functional electronic devices driven with extremely low power consumption...Spintronics”, simultaneously utilizing the charge and the spin of electrons , provides us with solutions to essential problems for semiconductor-based

Field-controllable Spin-Hall Effect of Light in Optical Crystals: A Conoscopic Mueller Matrix Analysis.

PubMed

Samlan, C T; Viswanathan, Nirmal K

2018-01-31

Electric-field applied perpendicular to the direction of propagation of paraxial beam through an optical crystal dynamically modifies the spin-orbit interaction (SOI), leading to the demonstration of controllable spin-Hall effect of light (SHEL). The electro- and piezo-optic effects of the crystal modifies the radially symmetric spatial variation in the fast-axis orientation of the crystal, resulting in a complex pattern with different topologies due to the symmetry-breaking effect of the applied field. This introduces spatially-varying Pancharatnam-Berry type geometric phase on to the paraxial beam of light, leading to the observation of SHEL in addition to the spin-to-vortex conversion. A wave-vector resolved conoscopic Mueller matrix measurement and analysis provides a first glimpse of the SHEL in the biaxial crystal, identified via the appearance of weak circular birefringence. The emergence of field-controllable fast-axis orientation of the crystal and the resulting SHEL provides a new degree of freedom for affecting and controlling the spin and orbital angular momentum of photons to unravel the rich underlying physics of optical crystals and aid in the development of active photonic spin-Hall devices.

Frequency Dependence of Electron Spin-lattice Relaxation for Semiquinones in Alcohol Solutions

PubMed Central

Elajaili, Hanan B.; Biller, Joshua R.; Eaton, Sandra S.; Eaton, Gareth R.

2014-01-01

The spin-lattice relaxation rates at 293 K for three anionic semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, and 2,3,5,6-tetramethoxy-1,4-benzosemiquinone) were studied at up to 8 frequencies between 250 MHz and 34 GHz in ethanol or methanol solution containing high concentrations of OH-. The relaxation rates are about a factor of 2 faster at lower frequencies than at 9 or 34 GHz. However, in perdeuterated alcohols the relaxation rates exhibit little frequency dependence, which demonstrates that the dominant frequency-dependent contribution to relaxation is modulation of dipolar interactions with solvent nuclei. The relaxation rates were modeled as the sum of two frequency-independent contributions (spin rotation and a local mode) and two frequency-dependent contributions (modulation of dipolar interaction with solvent nuclei and a much smaller contribution from modulation of g anisotropy). The correlation time for modulation of the interaction with solvent nuclei is longer than the tumbling correlation time of the semiquinone and is consistent with hydrogen bonding of the alcohol to the oxygen atoms of the semiquinones. PMID:25261741

Method and Apparatus for Improved Spatial Light Modulation

NASA Technical Reports Server (NTRS)

Soutar, Colin (Inventor); Juday, Richard D. (Inventor)

2000-01-01

A method and apparatus for modulating a light beam in an optical processing system is described. Preferably, an electrically-controlled polarizer unit and/or an analyzer unit are utilized in combination with a spatial light modulator and a controller. Preferably, the spatial light modulator comprises a pixelated birefringent medium such as a liquid crystal video display. The combination of the electrically controlled polarizer unit and analyzer unit make it simple and fast to reconfigure the modulation described by the Jones matrix of the spatial light modulator. A particular optical processing objective is provided to the controller. The controller performs calculations and supplies control signals to the polarizer unit, the analyzer unit, and the spatial light modulator in order to obtain the optical processing objective.

Method and Apparatus for Improved Spatial Light Modulation

NASA Technical Reports Server (NTRS)

Colin, Soutar (Inventor); Juday, Richard D. (Inventor)

1999-01-01

A method and apparatus for modulating a light beam in an optical processing system is described. Preferably, an electrically-controlled polarizer unit and/or an analyzer unit are utilized in combination with a spatial light modulator and a controller. Preferably, the spatial light modulator comprises a pixelated birefringent medium such as a liquid crystal video display. The combination of the electrically controlled polarizer unit and analyzer unit make it simple and fast to reconfigure the modulation described by the Jones matrix of the spatial light modulator. A particular optical processing objective is provided to the controller. The controller performs calculations and supplies control signals to the polarizer unit, the analyzer unit, and the spatial light modulator in order to obtain die optical processing objective.

Multilevel discretized random field models with 'spin' correlations for the simulation of environmental spatial data

NASA Astrophysics Data System (ADS)

Žukovič, Milan; Hristopulos, Dionissios T.

2009-02-01

A current problem of practical significance is how to analyze large, spatially distributed, environmental data sets. The problem is more challenging for variables that follow non-Gaussian distributions. We show by means of numerical simulations that the spatial correlations between variables can be captured by interactions between 'spins'. The spins represent multilevel discretizations of environmental variables with respect to a number of pre-defined thresholds. The spatial dependence between the 'spins' is imposed by means of short-range interactions. We present two approaches, inspired by the Ising and Potts models, that generate conditional simulations of spatially distributed variables from samples with missing data. Currently, the sampling and simulation points are assumed to be at the nodes of a regular grid. The conditional simulations of the 'spin system' are forced to respect locally the sample values and the system statistics globally. The second constraint is enforced by minimizing a cost function representing the deviation between normalized correlation energies of the simulated and the sample distributions. In the approach based on the Nc-state Potts model, each point is assigned to one of Nc classes. The interactions involve all the points simultaneously. In the Ising model approach, a sequential simulation scheme is used: the discretization at each simulation level is binomial (i.e., ± 1). Information propagates from lower to higher levels as the simulation proceeds. We compare the two approaches in terms of their ability to reproduce the target statistics (e.g., the histogram and the variogram of the sample distribution), to predict data at unsampled locations, as well as in terms of their computational complexity. The comparison is based on a non-Gaussian data set (derived from a digital elevation model of the Walker Lake area, Nevada, USA). We discuss the impact of relevant simulation parameters, such as the domain size, the number of discretization levels, and the initial conditions.

Nanoscale magnetic imaging with a single nitrogen-vacancy center in diamond

NASA Astrophysics Data System (ADS)

Hong, Sungkun

Magnetic imaging has been playing central roles not only in fundamental sciences but also in engineering and industry. Their numerous applications can be found in various areas, ranging from chemical analysis and biomedical imaging to magnetic data storage technology. An outstanding problem is to develop new magnetic imaging techniques with improved spatial resolutions down to nanoscale, while maintaining their magnetic sensitivities. For instance, if detecting individual electron or nuclear spins with nanomter spatial resolution is possible, it would allow for direct imaging of chemical structures of complex molecules, which then could bring termendous impacts on biological sciences. While realization of such nanoscale magnetic imaging still remains challenging, nitrogen-vacancy (NV) defects in diamond have recently considered as promising magnetic field sensors, as their electron spins show exceptionally long coherence even at room temperature. This thesis presents experimental progress in realizing a nanoscale magnetic imaging apparatus with a single nitrogen-vacancy (NV) color center diamond. We first fabricated diamond nanopillar devices hosting single NV centers at their ends, and incorporated them to a custom-built atomic force microscope (AFM). Our devices showed unprecedented combination of magnetic field sensitivity and spatial resolution for scanning NV systems. We then used these devices to magnetically image a single isolated electronic spin with nanometer resolution, for the first time under ambient condition. We also extended our study to improve and generalize the application of the scanning NV magnetometer we developed. We first introduced magnetic field gradients from a strongly magnetized tip, and demonstrated that the spatial resolution can be further improved by spectrally distinguishing identical spins at different locations. In addition, we developed a method to synchronize the periodic motion of an AFM tip and pulsed microwave sequences controlling an NV spin. This scheme enabled employment of 'AC magnetic field sensing scheme' in imaging samples with static and spatially varying magnetizations.

Dynamics of 4-oxo-TEMPO-d16-15N nitroxide-propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10-295 K

NASA Astrophysics Data System (ADS)

Goslar, Janina; Hoffmann, Stanislaw K.; Lijewski, Stefan

2016-08-01

ESR spectra and electron spin relaxation of nitroxide radical in 4-oxo-TEMPO-d16-15N in propylene glycol were studied at X-band in the temperature range 10-295 K. The spin-lattice relaxation in the liquid viscous state determined from the resonance line shape is governed by three mechanisms occurring during isotropic molecular reorientations. In the glassy state below 200 K the spin-lattice relaxation, phase relaxation and electron spin echo envelope modulations (ESEEM) were studied by pulse spin echo technique using 2-pulse and 3-pulse induced signals. Electron spin-lattice relaxation is governed by a single non-phonon relaxation process produced by localized oscillators of energy 76 cm-1. Electron spin dephasing is dominated by a molecular motion producing a resonance-type peak in the temperature dependence of the dephasing rate around 120 K. The origin of the peak is discussed and a simple method for the peak shape analysis is proposed, which gives the activation energy of a thermally activated motion Ea = 7.8 kJ/mol and correlation time τ0 = 10-8 s. The spin echo amplitude is strongly modulated and FT spectrum contains a doublet of lines centered around the 2D nuclei Zeeman frequency. The splitting into the doublet is discussed as due to a weak hyperfine coupling of nitroxide unpaired electron with deuterium of reorienting CD3 groups.

Mapping the magnonic landscape in patterned magnetic structures

NASA Astrophysics Data System (ADS)

Davies, C. S.; Poimanov, V. D.; Kruglyak, V. V.

2017-09-01

We report the development of a hybrid numerical/analytical model capable of mapping the spatially varying distributions of the local ferromagnetic resonance (FMR) frequency and dynamic magnetic susceptibility in a wide class of patterned and compositionally modulated magnetic structures. Starting from the numerically simulated static micromagnetic state, the magnetization is deliberately deflected orthogonally to its equilibrium orientation, and the magnetic fields generated in response to this deflection are evaluated using micromagnetic software. This allows us to calculate the elements of the effective demagnetizing tensor, which are then used within a linear analytical formalism to map the local FMR frequency and dynamic magnetic susceptibility. To illustrate the typical results that one can obtain using this model, we analyze three micromagnetic systems boasting nonuniformity in either one or two dimensions, and successfully explain the spin-wave emission observed in each case, demonstrating the ubiquitous nature of the Schlömann excitation mechanism underpinning the observations. Finally, the developed model of local FMR frequency can be used to explain how spin waves could be confined and steered using magnetic nonuniformities of various origins, rendering it a powerful tool for the mapping of the graded magnonic index in magnonics.

Broadband Transmission EPR Spectroscopy

PubMed Central

Hagen, Wilfred R.

2013-01-01

EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9–10 GHz range. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin – nuclear spin interactions and electron spin – electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8–2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed. PMID:23555819

Low-temperature dynamic nuclear polarization at 9.4 T with a 30 mW microwave source.

PubMed

Thurber, Kent R; Yau, Wai-Ming; Tycko, Robert

2010-06-01

Dynamic nuclear polarization (DNP) can provide large signal enhancements in nuclear magnetic resonance (NMR) by transfer of polarization from electron spins to nuclear spins. We discuss several aspects of DNP experiments at 9.4 T (400 MHz resonant frequency for (1)H, 264 GHz for electron spins in organic radicals) in the 7-80K temperature range, using a 30 mW, frequency-tunable microwave source and a quasi-optical microwave bridge for polarization control and low-loss microwave transmission. In experiments on frozen glycerol/water doped with nitroxide radicals, DNP signal enhancements up to a factor of 80 are observed (relative to (1)H NMR signals with thermal equilibrium spin polarization). The largest sensitivity enhancements are observed with a new triradical dopant, DOTOPA-TEMPO. Field modulation with a 10 G root-mean-squared amplitude during DNP increases the nuclear spin polarizations by up to 135%. Dependencies of (1)H NMR signal amplitudes, nuclear spin relaxation times, and DNP build-up times on the dopant and its concentration, temperature, microwave power, and modulation frequency are reported and discussed. The benefits of low-temperature DNP can be dramatic: the (1)H spin polarization is increased approximately 1000-fold at 7 K with DNP, relative to thermal polarization at 80K. (c) 2010 Elsevier Inc. All rights reserved.

Moderate MAS enhances local (1)H spin exchange and spin diffusion.

PubMed

Roos, Matthias; Micke, Peter; Saalwächter, Kay; Hempel, Günter

2015-11-01

Proton NMR spin-diffusion experiments are often combined with magic-angle spinning (MAS) to achieve higher spectral resolution of solid samples. Here we show that local proton spin diffusion can indeed become faster at low (<10 kHz) spinning rates as compared to static conditions. Spin diffusion under static conditions can thus be slower than the often referred value of 0.8 nm(2)/ms, which was determined using slow MAS (Clauss et al., 1993). The enhancement of spin diffusion by slow MAS relies on the modulation of the orientation-dependent dipolar couplings during sample rotation and goes along with transient level crossings in combination with dipolar truncation. The experimental finding and its explanation is supported by density matrix simulations, and also emphasizes the sensitivity of spin diffusion to the local coupling topology. The amplification of spin diffusion by slow MAS cannot be explained by any model based on independent spin pairs; at least three spins have to be considered. Copyright © 2015 Elsevier Inc. All rights reserved.

Spin Biochemistry Modulates Reactive Oxygen Species (ROS) Production by Radio Frequency Magnetic Fields

PubMed Central

Usselman, Robert J.; Hill, Iain; Singel, David J.; Martino, Carlos F.

2014-01-01

The effects of weak magnetic fields on the biological production of reactive oxygen species (ROS) from intracellular superoxide (O2 •−) and extracellular hydrogen peroxide (H2O2) were investigated in vitro with rat pulmonary arterial smooth muscle cells (rPASMC). A decrease in O2 •− and an increase in H2O2 concentrations were observed in the presence of a 7 MHz radio frequency (RF) at 10 μTRMS and static 45 μT magnetic fields. We propose that O2 •− and H2O2 production in some metabolic processes occur through singlet-triplet modulation of semiquinone flavin (FADH•) enzymes and O2 •− spin-correlated radical pairs. Spin-radical pair products are modulated by the 7 MHz RF magnetic fields that presumably decouple flavin hyperfine interactions during spin coherence. RF flavin hyperfine decoupling results in an increase of H2O2 singlet state products, which creates cellular oxidative stress and acts as a secondary messenger that affects cellular proliferation. This study demonstrates the interplay between O2 •− and H2O2 production when influenced by RF magnetic fields and underscores the subtle effects of low-frequency magnetic fields on oxidative metabolism, ROS signaling, and cellular growth. PMID:24681944

Liquid crystal television spatial light modulators

NASA Technical Reports Server (NTRS)

Liu, Hua-Kuang; Chao, Tien-Hsin

1989-01-01

The spatial light modulation characteristics and capabilities of the liquid crystal television (LCTV) spatial light modulators (SLMs) are discussed. A comparison of Radio Shack, Epson, and Citizen LCTV SLMs is made.

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

PubMed Central

Hoff, Daniel E.M.; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Choi, Eric J.; Mardini, Michael; Barnes, Alexander B.

2015-01-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198 GHz MAS DNP probe. Our calculations show that a microwave power input of 17 W is required to generate an average EPR nutation frequency of 0.84 MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5 kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. PMID:26482131

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization.

PubMed

Hoff, Daniel E M; Albert, Brice J; Saliba, Edward P; Scott, Faith J; Choi, Eric J; Mardini, Michael; Barnes, Alexander B

2015-11-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. Copyright © 2015 Elsevier Inc. All rights reserved.

The spatial effect of protein deuteration on nitroxide spin-label relaxation: Implications for EPR distance measurement

PubMed Central

El Mkami, Hassane; Ward, Richard; Bowman, Andrew; Owen-Hughes, Tom; Norman, David G.

2014-01-01

Pulsed electron–electron double resonance (PELDOR) coupled with site-directed spin labeling is a powerful technique for the elucidation of protein or nucleic acid, macromolecular structure and interactions. The intrinsic high sensitivity of electron paramagnetic resonance enables measurement on small quantities of bio-macromolecules, however short relaxation times impose a limit on the sensitivity and size of distances that can be measured using this technique. The persistence of the electron spin-echo, in the PELDOR experiment, is one of the most crucial limitations to distance measurement. At a temperature of around 50 K one of the predominant factors affecting persistence of an echo, and as such, the sensitivity and measurable distance between spin labels, is the electron spin echo dephasing time (Tm). It has become normal practice to use deuterated solvents to extend Tm and recently it has been demonstrated that deuteration of the underlying protein significantly extends Tm. Here we examine the spatial effect of segmental deuteration of the underlying protein, and also explore the concentration and temperature dependence of highly deuterated systems. PMID:25310878

Spectral linewidth of spin-current nano-oscillators driven by nonlocal spin injection

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

Demidov, V. E., E-mail: demidov@uni-muenster.de; Divinskiy, B.; Urazhdin, S.

2015-11-16

We study experimentally the auto-oscillation characteristics of magnetic nano-oscillators driven by pure spin currents generated by nonlocal spin injection. By combining micro-focus Brillouin light scattering spectroscopy with electronic microwave spectroscopy, we are able to simultaneously perform both the spatial and the high-resolution spectral analyses of auto-oscillations induced by spin current. We find that the devices exhibit a highly coherent dynamics with the spectral linewidth of a few megahertz at room temperature. This narrow linewidth can be achieved over a wide range of operational frequencies, demonstrating a significant potential of nonlocal oscillators for applications.

Homogeneous Atomic Fermi Gases

NASA Astrophysics Data System (ADS)

Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

2017-03-01

We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

All-electrical production of spin-polarized currents in carbon nanotubes: Rashba spin-orbit interaction

NASA Astrophysics Data System (ADS)

Santos, Hernán; Latgé, A.; Alvarellos, J. E.; Chico, Leonor

2016-04-01

We study the effect of the Rashba spin-orbit interaction in the quantum transport of carbon nanotubes with arbitrary chiralities. For certain spin directions, we find a strong spin-polarized electrical current that depends on the diameter of the tube, the length of the Rashba region, and on the tube chirality. Predictions for the spin-dependent conductances are presented for different families of achiral and chiral tubes. We have found that different symmetries acting on spatial and spin variables have to be considered in order to explain the relations between spin-resolved conductances in carbon nanotubes. These symmetries are more general than those employed in planar graphene systems. Our results indicate the possibility of having stable spin-polarized electrical currents in absence of external magnetic fields or magnetic impurities in carbon nanotubes.

Spin diffusion and torques in disordered antiferromagnets

NASA Astrophysics Data System (ADS)

Manchon, Aurelien

2017-03-01

We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

On testing for spatial correspondence between maps of human brain structure and function.

PubMed

Alexander-Bloch, Aaron F; Shou, Haochang; Liu, Siyuan; Satterthwaite, Theodore D; Glahn, David C; Shinohara, Russell T; Vandekar, Simon N; Raznahan, Armin

2018-06-01

A critical issue in many neuroimaging studies is the comparison between brain maps. Nonetheless, it remains unclear how one should test hypotheses focused on the overlap or spatial correspondence between two or more brain maps. This "correspondence problem" affects, for example, the interpretation of comparisons between task-based patterns of functional activation, resting-state networks or modules, and neuroanatomical landmarks. To date, this problem has been addressed with remarkable variability in terms of methodological approaches and statistical rigor. In this paper, we address the correspondence problem using a spatial permutation framework to generate null models of overlap by applying random rotations to spherical representations of the cortical surface, an approach for which we also provide a theoretical statistical foundation. We use this method to derive clusters of cognitive functions that are correlated in terms of their functional neuroatomical substrates. In addition, using publicly available data, we formally demonstrate the correspondence between maps of task-based functional activity, resting-state fMRI networks and gyral-based anatomical landmarks. We provide open-access code to implement the methods presented for two commonly-used tools for surface based cortical analysis (https://www.github.com/spin-test). This spatial permutation approach constitutes a useful advance over widely-used methods for the comparison of cortical maps, thereby opening new possibilities for the integration of diverse neuroimaging data. Copyright © 2018 Elsevier Inc. All rights reserved.

The use of precession modulation for nutation control in spin-stabilized spacecraft

NASA Technical Reports Server (NTRS)

Taylor, J. M.; Donner, R. J.; Tasar, V.

1974-01-01

The relations which determine the nutation effects induced in a spinning spacecraft by periodic precession thrust pulses are derived analytically. By utilizing the idea that nutation need only be observed just before each precession thrust pulse, a difficult continuous-time derivation is replaced by a simple discrete-time derivation using z-transforms. The analytic results obtained are used to develop two types of modulated precession control laws which use the precession maneuver to concurrently control nutation. Results are illustrated by digital simulation of an actual spacecraft configuration.

Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR

NASA Astrophysics Data System (ADS)

Takeda, Kazuyuki; Wakisaka, Asato; Takegoshi, K.

2014-12-01

The effect of 1H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951-6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structure of recoupling bands caused by interference of the 1H spin nutation with sample spinning is studied by both experiments and numerical simulations.

Asymmetry in the clockwise and counterclockwise rotation of the bacterial flagellar motor

PubMed Central

Yuan, Junhua; Fahrner, Karen A.; Turner, Linda; Berg, Howard C.

2010-01-01

Cells of Escherichia coli are able to swim up gradients of chemical attractants by modulating the direction of rotation of their flagellar motors, which spin alternately clockwise (CW) and counterclockwise (CCW). Rotation in either direction has been thought to be symmetric and exhibit the same torques and speeds. The relationship between torque and speed is one of the most important measurable characteristics of the motor, used to distinguish specific mechanisms of motor rotation. Previous measurements of the torque–speed relationship have been made with cells lacking the response regulator CheY that spin their motors exclusively CCW. In this case, the torque declines slightly up to an intermediate speed called the “knee speed” after which it falls rapidly to zero. This result is consistent with a “power-stroke” mechanism for torque generation. Here, we measure the torque–speed relationship for cells that express large amounts of CheY and only spin their motors CW. We find that the torque decreases linearly with speed, a result remarkably different from that for CCW rotation. We obtain similar results for wild-type cells by reexamining data collected in previous work. We speculate that CCW rotation might be optimized for runs, with higher speeds increasing the ability of cells to sense spatial gradients, whereas CW rotation might be optimized for tumbles, where the object is to change cell trajectories. But why a linear torque–speed relationship might be optimum for the latter purpose we do not know. PMID:20615986

Magneto-Seebeck effect in spin valves

NASA Astrophysics Data System (ADS)

Zhang, X. M.; Wan, C. H.; Wu, H.; Tang, P.; Yuan, Z. H.; Zhang, Q. T.; Zhang, X.; Tao, B. S.; Fang, C.; Han, X. F.

2017-10-01

The magneto-Seebeck (MS) effect, which is also called magneto-thermo-power, was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in the parallel state were larger than those in the antiparallel state, and the MS ratio defined as (SAP -SP)/SP could reach -9% in our case. The MS effect originated not only from trivial giant magnetoresistance but also from spin current generated due to spin-polarized thermoelectric conductivity of ferromagnetic materials and subsequent modulation of the spin current by different spin configurations in spin valves. A simple Mott two-channel model reproduced a -11% MS effect for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The MS effect could be applied for simultaneously sensing the temperature gradient and the magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and the Seebeck coefficient of ferromagnetic thin films.

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.

Development of a MPPC-based prototype gantry for future MRI-PET scanners

NASA Astrophysics Data System (ADS)

Kurei, Y.; Kataoka, J.; Kato, T.; Fujita, T.; Ohshima, T.; Taya, T.; Yamamoto, S.

2014-12-01

We have developed a high spatial resolution, compact Positron Emission Tomography (PET) module designed for small animals and intended for use in magnetic resonance imaging (MRI) systems. This module consists of large-area, 4 × 4 ch MPPC arrays (S11830-3344MF; Hamamatsu Photonics K.K.) optically coupled with Ce-doped (Lu,Y)2(SiO4)O (Ce:LYSO) scintillators fabricated into 16 × 16 matrices of 0.5 × 0.5 mm2 pixels. We set the temperature sensor (LM73CIMK-0; National Semiconductor Corp.) at the rear of the MPPC acceptance surface, and apply optimum voltage to maintain the gain. The eight MPPC-based PET modules and coincidence circuits were assembled into a gantry arranged in a ring 90 mm in diameter to form the MPPC-based PET system. We have developed two types PET gantry: one made of non-magnetic metal and the other made of acrylonitrile butadiene styrene (ABS) resins. The PET gantry was positioned around the RF coil of the 4.7 T MRI system. We took an image of a point }22Na source under fast spin echo (FSE) and gradient echo (GE), in order to measure the interference between the MPPC-based PET and MRI. The spatial resolution of PET imaging in a transaxial plane of about 1 mm (FWHM) was achieved in all cases. Operating with PET made of ABS has no effect on MR images, while operating with PET made of non-magnetic metal has a significant detrimental effect on MR images. This paper describes our quantitative evaluations of PET images and MR images, and presents a more advanced version of the gantry for future MRI/DOI-PET systems.

Theory of nonreciprocal spin-wave excitations in spin Hall oscillators with Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Zivieri, R.; Giordano, A.; Verba, R.; Azzerboni, B.; Carpentieri, M.; Slavin, A. N.; Finocchio, G.

2018-04-01

A two-dimensional analytical model for the description of the excitation of nonreciprocal spin waves by spin current in spin Hall oscillators in the presence of the interfacial Dzyaloshinskii-Moriya interaction (i -DMI) is developed. The theory allows one to calculate the threshold current for the excitation of spin waves, as well as the frequencies and spatial profiles of the excited spin-wave modes. It is found that the frequency of the excited spin waves exhibits a quadratic redshift with the i -DMI strength. At the same time, in the range of small and moderate values of the i -DMI constant, the averaged wave number of the excited spin waves is almost independent of the i -DMI, which results in a rather weak dependence on the i -DMI of the threshold current of the spin-wave excitation. The obtained analytical results are confirmed by the results of micromagnetic simulations.

K-band single-chip electron spin resonance detector.

PubMed

Anders, Jens; Angerhofer, Alexander; Boero, Giovanni

2012-04-01

We report on the design, fabrication, and characterization of an integrated detector for electron spin resonance spectroscopy operating at 27 GHz. The microsystem, consisting of an LC-oscillator and a frequency division module, is integrated onto a single silicon chip using a conventional complementary metal-oxide-semiconductor technology. The achieved room temperature spin sensitivity is about 10(8)spins/G Hz(1/2), with a sensitive volume of about (100 μm)(3). Operation at 77K is also demonstrated. Copyright © 2012 Elsevier Inc. All rights reserved.

Bioresearch module design definition and space shuttle vehicle integration study. Volume 2: Appendices

NASA Technical Reports Server (NTRS)

Lang, A. L., Jr.

1971-01-01

Data presented in the appendices covers: (1) summary description of baseline power system; (2) revised thermal profile analysis; (3) design analysis of television monitor; (4) bioresearch module ground station support evaluation; (5) variable spin control analysis; and (6) bioresearch modules and work flow.

Nutation control during precession of a spin-stabilized spacecraft

NASA Technical Reports Server (NTRS)

1974-01-01

Precession maneuver control laws for single-spin spacecraft are investigated so that nutation is concurrently controlled. Analysis has led to the development of two types of control laws employing precession modulation for concurrent nutation control. Results were verified through digital simulation of a Synchronous Meteorological Satellite (SMS) configuration. An addition research effort was undertaken to investigate the cause and elimination of nutation anomalies in dual-spin spacecraft. A literature search was conducted and a dual-spin configuration was simulated to verify that nutational anomalies are not predicted by the existing nonlinear model. No conclusions were drawn as to the cause of the observed nutational anomalies in dual-spin spacecraft.

Room-temperature coupling between electrical current and nuclear spins in OLEDs

NASA Astrophysics Data System (ADS)

Malissa, H.; Kavand, M.; Waters, D. P.; van Schooten, K. J.; Burn, P. L.; Vardeny, Z. V.; Saam, B.; Lupton, J. M.; Boehme, C.

2014-09-01

The effects of external magnetic fields on the electrical conductivity of organic semiconductors have been attributed to hyperfine coupling of the spins of the charge carriers and hydrogen nuclei. We studied this coupling directly by implementation of pulsed electrically detected nuclear magnetic resonance spectroscopy in organic light-emitting diodes (OLEDs). The data revealed a fingerprint of the isotope (protium or deuterium) involved in the coherent spin precession observed in spin-echo envelope modulation. Furthermore, resonant control of the electric current by nuclear spin orientation was achieved with radiofrequency pulses in a double-resonance scheme, implying current control on energy scales one-millionth the magnitude of the thermal energy.

Resonant obliquity of Mars?. [climate driven by spin axis and orbit plane precession caused oscillations

NASA Technical Reports Server (NTRS)

Ward, William R.; Rudy, Donald J.

1991-01-01

The large-scale oscillations generated by the obliquity of Mars through spin-axis and orbit-plane precessions constitute basic climate system drivers with periodicities of 100,000 yrs in differential spin axis-orbit precession rates and of over 1 million yrs in amplitude modulations due to orbital-inclination changes. Attention is presently given to a third time-scale for climate change, which involves a possible spin-spin resonance and whose mechanism operates on a 10-million-yr time-scale: this effect implies an average obliquity increase for Mars of 15 deg only 5 million yrs ago, with important climatic consequences.

A two-dimensional spin field-effect switch

NASA Astrophysics Data System (ADS)

Yan, Wenjing; Txoperena, Oihana; Llopis, Roger; Dery, Hanan; Hueso, Luis E.; Casanova, Fèlix

2016-11-01

Future development in spintronic devices will require an advanced control of spin currents, for example by an electric field. Here we demonstrate an approach that differs from previous proposals such as the Datta and Das modulator, and that is based on a van de Waals heterostructure of atomically thin graphene and semiconducting MoS2. Our device combines the superior spin transport properties of graphene with the strong spin-orbit coupling of MoS2 and allows switching of the spin current in the graphene channel between ON and OFF states by tuning the spin absorption into the MoS2 with a gate electrode. Our proposal holds potential for technologically relevant applications such as search engines or pattern recognition circuits, and opens possibilities towards electrical injection of spins into transition metal dichalcogenides and alike materials.

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.

Nanofocusing of structured light for quadrupolar light-matter interactions.

PubMed

Sakai, Kyosuke; Yamamoto, Takeaki; Sasaki, Keiji

2018-05-17

The spatial structure of an electromagnetic field can determine the characteristics of light-matter interactions. A strong gradient of light in the near field can excite dipole-forbidden atomic transitions, e.g., electric quadrupole transitions, which are rarely observed under plane-wave far-field illumination. Structured light with a higher-order orbital angular momentum state may also modulate the selection rules in which an atom can absorb two quanta of angular momentum: one from the spin and another from the spatial structure of the beam. Here, we numerically demonstrate a strong focusing of structured light with a higher-order orbital angular momentum state in the near field. A quadrupole field was confined within a gap region of several tens of nanometres in a plasmonic tetramer structure. A plasmonic crystal surrounding the tetramer structure provides a robust antenna effect, where the incident structured light can be strongly coupled to the quadrupole field in the gap region with a larger alignment tolerance. The proposed system is expected to provide a platform for light-matter interactions with strong multipolar effects.

Optimal configurations of spatial scale for grid cell firing under noise and uncertainty

PubMed Central

Towse, Benjamin W.; Barry, Caswell; Bush, Daniel; Burgess, Neil

2014-01-01

We examined the accuracy with which the location of an agent moving within an environment could be decoded from the simulated firing of systems of grid cells. Grid cells were modelled with Poisson spiking dynamics and organized into multiple ‘modules’ of cells, with firing patterns of similar spatial scale within modules and a wide range of spatial scales across modules. The number of grid cells per module, the spatial scaling factor between modules and the size of the environment were varied. Errors in decoded location can take two forms: small errors of precision and larger errors resulting from ambiguity in decoding periodic firing patterns. With enough cells per module (e.g. eight modules of 100 cells each) grid systems are highly robust to ambiguity errors, even over ranges much larger than the largest grid scale (e.g. over a 500 m range when the maximum grid scale is 264 cm). Results did not depend strongly on the precise organization of scales across modules (geometric, co-prime or random). However, independent spatial noise across modules, which would occur if modules receive independent spatial inputs and might increase with spatial uncertainty, dramatically degrades the performance of the grid system. This effect of spatial uncertainty can be mitigated by uniform expansion of grid scales. Thus, in the realistic regimes simulated here, the optimal overall scale for a grid system represents a trade-off between minimizing spatial uncertainty (requiring large scales) and maximizing precision (requiring small scales). Within this view, the temporary expansion of grid scales observed in novel environments may be an optimal response to increased spatial uncertainty induced by the unfamiliarity of the available spatial cues. PMID:24366144

Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide

NASA Astrophysics Data System (ADS)

Javadi, Alisa; Ding, Dapeng; Appel, Martin Hayhurst; Mahmoodian, Sahand; Löbl, Matthias Christian; Söllner, Immo; Schott, Rüdiger; Papon, Camille; Pregnolato, Tommaso; Stobbe, Søren; Midolo, Leonardo; Schröder, Tim; Wieck, Andreas Dirk; Ludwig, Arne; Warburton, Richard John; Lodahl, Peter

2018-05-01

The spin of an electron is a promising memory state and qubit. Connecting spin states that are spatially far apart will enable quantum nodes and quantum networks based on the electron spin. Towards this goal, an integrated spin-photon interface would be a major leap forward as it combines the memory capability of a single spin with the efficient transfer of information by photons. Here, we demonstrate such an efficient and optically programmable interface between the spin of an electron in a quantum dot and photons in a nanophotonic waveguide. The spin can be deterministically prepared in the ground state with a fidelity of up to 96%. Subsequently, the system is used to implement a single-spin photonic switch, in which the spin state of the electron directs the flow of photons through the waveguide. The spin-photon interface may enable on-chip photon-photon gates, single-photon transistors and the efficient generation of a photonic cluster state.

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

Mauche, C W; Brickhouse, N S; Hoogerwerf, R

Recent satellite observations demonstrate that the phase of maximum flux of the 67 min spin modulation of the white dwarf in the cataclysmic variable EX Hya is drifting away from the optical quadratic ephemeris of Hellier & Sproats (1992, hereafter HS92). Relative to that ephemeris, the peak of the spin-phase extreme ultraviolet (EUV) flux modulation measured with the Extreme Ultraviolet Explorer (EUVE) was {phi}{sub 67} = 0.040 {+-} 0.002 in 1994 May (Mauche 1999) and {phi}{sub 67} = 0.115 {+-} 0.001 in 2000 May (Belle et al. 2002). Similarly, the peak of the spin-phase X-ray flux modulation measured with themore » Chandra X-ray Observatory was {phi}{sub 67} {approx} 0.1 in 2000 May (Hoogerwerf, Brickhouse, & Mauche 2004) and {phi}{sub 67} {approx} 0.2 in 2007 May (Luna, Brickhouse, & Mauche 2008). Because the discrepancy between the observed O and calculated C phases of the spin-phase flux modulation of EX Hya is now approaching a significant fraction of a spin cycle, we have undertaken the task of updating the ephemeris. Toward that end, we have combined the optical data of Vogt, Krzeminski, & Sterken (1980, hereafter VKS80), Gilliland (1982), Sterken et al. (1983), Hill & Watson (1984), Jablonski & Busko (1985), Bond & Freeth (1988), HS92, Walker & Allen (2000), and Belle et al. (2005) with the optical, EUV, and X-ray data listed in Table 1. The optical data were obtained by CS at ESO La Silla using the Danish 1.5-m telescope and the DFOSC CCD camera. Differential V-band magnitudes were obtained by aperture photometry extracted from flat-fielded and bias-corrected CCD frames. Other than the EXOSAT and Ginga data, which have been taken from the given references, all other times of spin maximum in the table have been derived by us from the various datasets. In the processes, we have corrected an error in the (spin and orbit) phases of the ASCA data published by Ishida, Mukai, & Osborne (1994) and the RXTE data published by Mukai et al. (1998). We note that our result for the second EUVE observation agrees within the errors with the result derived independently by Belle et al. (2002). Table 1 lists the observed times of spin maximum in Barycentric Julian Date, the corresponding cycle number derived from the HS92 quadratic ephemeris, and the O-C residuals relative to the VKS80 linear ephemeris, the HS92 quadratic ephemeris, and our cubic ephemeris (eqn. 1).« less

Self-assisted complete hyperentangled Bell state analysis using quantum-dot spins in optical microcavities

NASA Astrophysics Data System (ADS)

Zeng, Zhi

2018-05-01

An efficient scheme for the discrimination of 16 hyperentangled Bell states of a two-photon system that is entangled in both polarization and spatial-mode degrees of freedom is presented in this paper. Using the interaction between the photons and quantum-dot spins in cavities, the spatial-mode Bell states can be distinguished completely and nondestructively in the first step. Subsequently, the preserved spatial-mode entanglement is utilized as an auxiliary to analyze the polarization Bell states. Compared with a previous scheme (Ren et al 2012 Opt. Express 20 24664-77), our scheme reduces the requirement for nonlinear interaction substantially by utilizing the intrinsic degrees of freedom in hyperentanglement.

Spin-valleytronics of silicene based nanodevices (SBNs)

NASA Astrophysics Data System (ADS)

Ahmed, Ibrahim Sayed; Asham, Mina Danial; Phillips, Adel Helmy

2018-06-01

The quantum spin and valley characteristics in normal silicene/ferromagnetic silicene/normal silicene junction are investigated under the effects of both electric field and the exchange field of the ferromagnetic silicene. The spin resolved conductance and valley resolved conductance are deduced by solving the Dirac equation. Results show resonant oscillations of both spin and valley conductance. These oscillations might be due to confined states of ferromagnetic silicene. The spin and valley polarizations are also computed. Their trends of figures show that they might be tuned and modulated by the electric field and the exchange field of the ferromagnetic silicene. The present investigated silicene nanodevice might be good for spin-valleytronics applications which are needed for quantum information processing and quantum logic circuits.

Magnetoresistance effect of heat generation in a single-molecular spin-valve

NASA Astrophysics Data System (ADS)

Jiang, Feng; Yan, Yonghong; Wang, Shikuan; Yan, Yijing

2016-02-01

Based on non-equilibrium Green's functions' theory and small polaron transformation's technology, we study the heat generation by current through a single-molecular spin-valve. Numerical results indicate that the variation of spin polarization degree can change heat generation effectively, the spin-valve effect happens not only in electrical current but also in heat generation when Coulomb repulsion in quantum dot is smaller than phonon frequency and interestingly, when Coulomb repulsion is larger than phonon frequency, the inverse spin-valve effect appears by sweeping gate voltage and is enlarged with bias increasing. The inverse spin-valve effect will induce the unique heat magnetoresistance effect, which can be modulated from heat-resistance to heat-gain by gate voltage easily.

Electron spin resonance and electron spin echo modulation of n-doxylstearic acid and N,N,N',N'-tetramethylbenzidine photoionization in sodium versus lithium dodecyl sulfate micellar solutions: effect of 15-crown-5 and 18-crown-6 ether addition

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

Baglioni, P.; Rivara-Minten, E.; Kevan, L.

1988-08-11

Electron spin echo modulation and electron spin resonance spectra of photogenerated N,N,N',N'-tetramethylbenzidine (TMB) cation radical and n-doxylstearic acids (n-DSA) in frozen micellar solutions of sodium and lithium dodecyl sulfate containing 15-crown-5 and 18-crown-6 ethers in D/sub 2/O have been studied as a function of crown ether concentration. Modulation effects due to N-DSA with water deuteriums give direct evidence that both crown ethers are mainly located at the micellar interface and that this causes a decrease of the hydration of the micellar interface. Crown ether complexation constants for sodium and lithium micellar counterions are reported and show that 18-crown-6 > 15-crown-5more » for sodium counterion and 15-crown-5 > 18-crown-6 for lithium counterion. Modulation effects from TMB/sup +/ interaction with water deuteriums indicate that the TMB molecule moves toward the micelle interfacial region when sodium or lithium cations are complexed by crown ethers. The TMB/sup +/ yield upon TMB photoionization increases by about 10% with crown ether addition for SDS and LDS micellar systems, but it is greater if the absolute values for the LDS system are compared to those for the SDS micellar system. This behavior correlates with the strength of TMB/sup +/-water interactions and suggests that the main factor in the photoionization efficiency is the photocation-water interaction.« less

Spin Structures and Phase Diagrams of Extended Spatially Completely Anisotropic Triangular Lattice Antiferromagnets

NASA Astrophysics Data System (ADS)

Sakakida, Keishiro; Shimahara, Hiroshi

2017-12-01

Motivated by recently discovered organic antiferromagnets, we examine an extended triangular lattice that consists of two types of triangles of bonds with exchange coupling constants Jℓ and J'ℓ (ℓ= 1, 2, and 3), respectively. The simplified system with Jℓ = J'ℓ > 0 is the spatially completely anisotropic triangular lattice (SCATL) antiferromagnet examined previously. The extended system, which we call an extended SCATL (ESCATL), has two different spatial anisotropy parameters J3/J2 and J'3/J'2 when J1 = J'1 is assumed. We derive classical phase diagrams and spin structures. It is found that the ESCATL antiferromagnet exhibits two up-up-down-down (uudd) phases when the imbalance of the anisotropy parameters is significant, in addition to the three Néel phases that occur in the SCATL. When the model parameters vary, these collinear phases are continuously connected by the spiral-spin phase. Using the available model parameters for the organic compounds λ-(BETS)2XCl4 (X = Fe and Ga), we examine the stabilities of the spin structures of the independent π-electron system, which is considered to primarily sustain the magnetic order, where BETS represents bis(ethylenedithio)tetraselenafulvalene. It is found that one of the uudd phases has an energy close to the ground-state energy for λ-(BETS)2FeCl4. We discuss the relevance of the magnetic anion FeCl4 and the quantum fluctuation to the magnetism of these compounds. When J'3 = 0, the system is reduced to a trellis lattice antiferromagnet. The system exhibits a stripe spiral-spin phase, which comprises one-dimensional spiral-spin states stacked alternately.

Rashba-Zeeman-effect-induced spin filtering energy windows in a quantum wire

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

Xiao, Xianbo, E-mail: xxb-11@hotmail.com; Nie, Wenjie; Chen, Zhaoxia

2014-06-14

We perform a numerical study on the spin-resolved transport in a quantum wire (QW) under the modulation of both Rashba spin-orbit coupling (SOC) and a perpendicular magnetic field by using the developed Usuki transfer-matrix method in combination with the Landauer-Büttiker formalism. Wide spin filtering energy windows can be achieved in this system for unpolarized spin injection. In addition, both the width of energy window and the magnitude of spin conductance within these energy windows can be tuned by varying Rashba SOC strength, which can be apprehended by analyzing the energy dispersions and spin-polarized density distributions inside the QW, respectively. Furthermore » study also demonstrates that these Rashba-SOC-controlled spin filtering energy windows show a strong robustness against disorders. These findings may not only benefit to further understand the spin-dependent transport properties of a QW in the presence of external fields but also provide a theoretical instruction to design a spin filter device.« less

Magneto-optical imaging of thin magnetic films using spins in diamond

NASA Astrophysics Data System (ADS)

Simpson, David A.; Tetienne, Jean-Philippe; McCoey, Julia M.; Ganesan, Kumaravelu; Hall, Liam T.; Petrou, Steven; Scholten, Robert E.; Hollenberg, Lloyd C. L.

2016-03-01

Imaging the fields of magnetic materials provides crucial insight into the physical and chemical processes surrounding magnetism, and has been a key ingredient in the spectacular development of magnetic data storage. Existing approaches using the magneto-optic Kerr effect, x-ray and electron microscopy have limitations that constrain further development, and there is increasing demand for imaging and characterisation of magnetic phenomena in real time with high spatial resolution. Here we show how the magneto-optical response of an array of negatively-charged nitrogen-vacancy spins in diamond can be used to image and map the sub-micron stray magnetic field patterns from thin ferromagnetic films. Using optically detected magnetic resonance, we demonstrate wide-field magnetic imaging over 100 × 100 μm2 with sub-micron spatial resolution at video frame rates, under ambient conditions. We demonstrate an all-optical spin relaxation contrast imaging approach which can image magnetic structures in the absence of an applied microwave field. Straightforward extensions promise imaging with sub-μT sensitivity and sub-optical spatial and millisecond temporal resolution. This work establishes practical diamond-based wide-field microscopy for rapid high-sensitivity characterisation and imaging of magnetic samples, with the capability for investigating magnetic phenomena such as domain wall and skyrmion dynamics and the spin Hall effect in metals.

Heralded entanglement between solid-state qubits separated by three metres.

PubMed

Bernien, H; Hensen, B; Pfaff, W; Koolstra, G; Blok, M S; Robledo, L; Taminiau, T H; Markham, M; Twitchen, D J; Childress, L; Hanson, R

2013-05-02

Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin-photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks.

Reporting of quantitative oxygen mapping in EPR imaging

NASA Astrophysics Data System (ADS)

Subramanian, Sankaran; Devasahayam, Nallathamby; McMillan, Alan; Matsumoto, Shingo; Munasinghe, Jeeva P.; Saito, Keita; Mitchell, James B.; Chandramouli, Gadisetti V. R.; Krishna, Murali C.

2012-01-01

Oxygen maps derived from electron paramagnetic resonance spectral-spatial imaging (EPRI) are based upon the relaxivity of molecular oxygen with paramagnetic spin probes. This technique can be combined with MRI to facilitate mapping of pO 2 values in specific anatomic locations with high precision. The co-registration procedure, which matches the physical and digital dimensions of EPR and MR images, may present the pO 2 map at the higher MRI resolution, exaggerating the spatial resolution of oxygen, making it difficult to precisely distinguish hypoxic regions from normoxic regions. The latter distinction is critical in monitoring the treatment of cancer by radiation and chemotherapy, since it is well-established that hypoxic regions are three or four times more resistant to treatment compared to normoxic regions. The aim of this article is to describe pO 2 maps based on the intrinsic resolution of EPRI. A spectral parameter that affects the intrinsic spatial resolution of EPRI is the full width at half maximum (FWHM) height of the gradient-free EPR absorption line in frequency-encoded imaging. In single point imaging too, the transverse relaxation times (T2∗) limit the resolution since the signal decays by exp(-tp/T2∗) where the delay time after excitation pulse, t p, is related to the resolution. Although the spin densities of two point objects may be resolved at this separation, it is inadequate to evaluate quantitative changes of pO 2 levels since the linewidths are proportionately affected by pO 2. A spatial separation of at least twice this resolution is necessary to correctly identify a change in pO 2 level. In addition, the pO 2 values are blurred by uncertainties arising from spectral dimensions. Blurring due to noise and low resolution modulates the pO 2 levels at the boundaries of hypoxic and normoxic regions resulting in higher apparent pO 2 levels in hypoxic regions. Therefore, specification of intrinsic resolution and pO 2 uncertainties are necessary to interpret digitally processed pO 2 illustrations.

Unusual negative permeability of single magnetic nanowire excited by the spin transfer torque effect

NASA Astrophysics Data System (ADS)

Han, Mangui; Zhou, Wu

2018-07-01

Due to the effect of spin transfer torque, negative imaginary parts of permeability (μ″ < 0) are reported in a ferromagnetic nanowire. It is found that negative μ″ values are resulted from the interaction of spin polarized conduction electrons with the spatially non-uniform distributed magnetic moments at both ends of nanowires. The results are well explained from the effect of spin transfer torque on the precession of magnetization under the excitation of both the pulsed magnetic field and static electric field.

Spin Order and Phase Transitions in Chains of Polariton Condensates.

PubMed

Ohadi, H; Ramsay, A J; Sigurdsson, H; Del Valle-Inclan Redondo, Y; Tsintzos, S I; Hatzopoulos, Z; Liew, T C H; Shelykh, I A; Rubo, Y G; Savvidis, P G; Baumberg, J J

2017-08-11

We demonstrate that multiply coupled spinor polariton condensates can be optically tuned through a sequence of spin-ordered phases by changing the coupling strength between nearest neighbors. For closed four-condensate chains these phases span from ferromagnetic (FM) to antiferromagnetic (AFM), separated by an unexpected crossover phase. This crossover phase is composed of alternating FM-AFM bonds. For larger eight-condensate chains, we show the critical role of spatial inhomogeneities and demonstrate a scheme to overcome them and prepare any desired spin state. Our observations thus demonstrate a fully controllable nonequilibrium spin lattice.

Parametric Amplification Protocol for Frequency-Modulated Magnetic Resonance Force Microscopy Signals

NASA Astrophysics Data System (ADS)

Harrell, Lee; Moore, Eric; Lee, Sanggap; Hickman, Steven; Marohn, John

2011-03-01

We present data and theoretical signal and noise calculations for a protocol using parametric amplification to evade the inherent tradeoff between signal and detector frequency noise in force-gradient magnetic resonance force microscopy signals, which are manifested as a modulated frequency shift of a high- Q microcantilever. Substrate-induced frequency noise has a 1 / f frequency dependence, while detector noise exhibits an f2 dependence on modulation frequency f . Modulation of sample spins at a frequency that minimizes these two contributions typically results in a surface frequency noise power an order of magnitude or more above the thermal limit and may prove incompatible with sample spin relaxation times as well. We show that the frequency modulated force-gradient signal can be used to excite the fundamental resonant mode of the cantilever, resulting in an audio frequency amplitude signal that is readily detected with a low-noise fiber optic interferometer. This technique allows us to modulate the force-gradient signal at a sufficiently high frequency so that substrate-induced frequency noise is evaded without subjecting the signal to the normal f2 detector noise of conventional demodulation.

Dual-channel current valve in a three terminal zigzag graphene nanoribbon junction

NASA Astrophysics Data System (ADS)

Zhang, L.

2017-02-01

We theoretically propose a dual-channel current valve based on a three terminal zigzag graphene nanoribbon (ZGNR) junction driven by three asymmetric time-dependent pumping potentials. By means of the Keldysh Green’s function method, we show that two asymmetric charge currents can be pumped in the different left-right terminals of the device at a zero bias, which mainly stems from the single photon-assisted pumping approximation and the valley valve effect in a ZGNR p-n junction. The ON and OFF states of pumped charge currents are crucially dependent on the even-odd chain widths of the three electrodes, the pumping frequency, the lattice potential and the Fermi level. Two-tunneling spin valves are also considered to spatially separate and detect 100% polarized spin currents owing to the combined spin pump effect and the valley selective transport in a three terminal ZGNR ferromagnetic junction. Our investigations might be helpful to control the spatial and spin degrees of freedom of electrons in graphene pumping devices.

Dissipative structures induced by spin-transfer torques in nanopillars

NASA Astrophysics Data System (ADS)

León, Alejandro O.; Clerc, Marcel G.; Coulibaly, Saliya

2014-02-01

Macroscopic magnetic systems subjected to external forcing exhibit complex spatiotemporal behaviors as result of dissipative self-organization. Pattern formation from a uniform magnetization state, induced by the combination of a spin-polarized current and an external magnetic field, is studied for spin-transfer nano-oscillator devices. The system is described in the continuous limit by the Landau-Lifshitz-Gilbert equation. The bifurcation diagram of the quintessence parallel state, as a function of the external field and current, is elucidated. We have shown analytically that this state exhibits a spatial supercritical quintic bifurcation, which generates in two spatial dimensions a family of stationary stripes, squares, and superlattice states. Analytically, we have characterized their respective stabilities and bifurcations, which are controlled by a single dimensionless parameter. This scenario is confirmed numerically.

Dissipative structure in the photo-induced phase under steady light irradiation in the spin crossover complex.

PubMed

Nishihara, Taishi; Bousseksou, Azzdine; Tanaka, Koichiro

2013-12-16

We report the spatial and temporal dynamics of the photo-induced phase in the iron (II) spin crossover complex Fe(ptz)(6)(BF(4))(2) studied by image measurement under steady light irradiation and transient absorption measurement. The dynamic factors are derived from the spatial and temporal fluctuation of the image in the steady state under light irradiation between 65 and 100 K. The dynamic factors clearly indicate that the fluctuation has a resonant frequency that strongly depends on the temperature, and is proportional to the relaxation rate of the photo-induced phase. This oscillation of the speckle pattern under steady light irradiation is ascribed to the nonlinear interaction between the spin state and the lattice volume at the surface.

Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR

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

Takeda, Kazuyuki, E-mail: takezo@kuchem.kyoto-u.ac.jp; Wakisaka, Asato; Takegoshi, K.

The effect of {sup 1}H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951–6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structuremore » of recoupling bands caused by interference of the {sup 1}H spin nutation with sample spinning is studied by both experiments and numerical simulations.« less

Ferroelectricity and competing interactions in Ho-deficient non-stoichiometric orthorhombic HoMnO{sub 3}

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

Wang, J. X.; Yan, Z. B.; Xie, Y. L.

2015-05-07

We investigate the consequences of the Ho-deficient non-stoichiometry in orthorhombic HoMnO{sub 3} in terms of microscopic mechanisms for ferroelectricity modulation. It is suggested that the Ho-deficiency (then Mn excess) results in Ho-vacancies and then Mn occupation of the Ho-site with increasing non-stoichiometry. The Ho-deficiency enhances the Mn-Mn symmetric exchange striction by suppressing the independent Ho-Ho interaction, and thus benefits to the induced Ho spin ordering against the independent Ho spin ordering. The symmetric Ho-Mn exchange striction is thus enhanced by this induced Ho spin ordering, leading to remarkably enhanced ferroelectric polarization as observed. This work presents an alternative scheme tomore » modulate the multiferroicity in rare-earth manganites of strong 4f-3d coupling.« less

Non-exponential decoherence of radio-frequency resonance rotation of spin in storage rings

NASA Astrophysics Data System (ADS)

Saleev, A.; Nikolaev, N. N.; Rathmann, F.; Hinder, F.; Pretz, J.; Rosenthal, M.

2017-08-01

Precision experiments, such as the search for electric dipole moments of charged particles using radio-frequency spin rotators in storage rings, demand for maintaining the exact spin resonance condition for several thousand seconds. Synchrotron oscillations in the stored beam modulate the spin tune of off-central particles, moving it off the perfect resonance condition set for central particles on the reference orbit. Here, we report an analytic description of how synchrotron oscillations lead to non-exponential decoherence of the radio-frequency resonance driven up-down spin rotations. This non-exponential decoherence is shown to be accompanied by a nontrivial walk of the spin phase. We also comment on sensitivity of the decoherence rate to the harmonics of the radio-frequency spin rotator and a possibility to check predictions of decoherence-free magic energies.

Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

PubMed

Rout, Saroj; Sonkusale, Sameer

2016-06-27

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

Bilayer avalanche spin-diode logic

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

Friedman, Joseph S., E-mail: joseph.friedman@u-psud.fr; Querlioz, Damien; Fadel, Eric R.

2015-11-15

A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

Analytic gravitational waveforms for generic precessing compact binaries

NASA Astrophysics Data System (ADS)

Chatziioannou, Katerina; Klein, Antoine; Cornish, Neil; Yunes, Nicolas

2017-01-01

Gravitational waves from compact binaries are subject to amplitude and phase modulations arising from interactions between the angular momenta of the system. Failure to account for such spin-precession effects in gravitational wave data analysis could hinder detection and completely ruin parameter estimation. In this talk I will describe the construction of closed-form, frequency-domain waveforms for fully-precessing, quasi-circular binary inspirals. The resulting waveforms can model spinning binaries of arbitrary spin magnitudes, spin orientations, and masses during the inspiral phase. I will also describe ongoing efforts to extend these inspiral waveforms to the merger and ringdown phases.

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses

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

Yoshimine, Isao; Iida, Ryugo; Shimura, Tsutomu

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed formore » excitation fluences higher than 100 mJ/cm{sup 2}.« less

Theory of ground state factorization in quantum cooperative systems.

PubMed

Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio

2008-05-16

We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows us to determine rigorously the existence, location, and exact form of separable ground states in a large variety of, generally nonexactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range.

Direct observation of spin-layer locking by local Rashba effect in monolayer semiconducting PtSe2 film.

PubMed

Yao, Wei; Wang, Eryin; Huang, Huaqing; Deng, Ke; Yan, Mingzhe; Zhang, Kenan; Miyamoto, Koji; Okuda, Taichi; Li, Linfei; Wang, Yeliang; Gao, Hongjun; Liu, Chaoxing; Duan, Wenhui; Zhou, Shuyun

2017-01-31

The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials. In recent times it has been suggested that spin polarization originates fundamentally from local atomic site asymmetries and therefore centrosymmetric materials may exhibit previously overlooked spin polarizations. Here, by using spin- and angle-resolved photoemission spectroscopy, we report the observation of helical spin texture in monolayer, centrosymmetric and semiconducting PtSe 2 film without the characteristic spin splitting in conventional Rashba effect (R-1). First-principles calculations and effective analytical model analysis suggest local dipole induced Rashba effect (R-2) with spin-layer locking: opposite spins are degenerate in energy, while spatially separated in the top and bottom Se layers. These results not only enrich our understanding of the spin polarization physics but also may find applications in electrically tunable spintronics.

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

Tuning spin-spin interactions in radical dendrimers.

PubMed

Vidal-Gancedo, José; Lloveras, Vega; Liko, Flonja; Pinto, Luiz F; Muñoz-Gómez, Jose L

2018-05-10

Two generations of phosphorous dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in Gn-imino-TEMPO dendrimers presented a strong spin-spin interaction, in the Gn-acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal spin filtering effect and giant magnetoresistance of half-metallic graphene nanoribbon co-doped with non-metallic Nitrogen and Boron

NASA Astrophysics Data System (ADS)

Huang, Hai; Zheng, Anmin; Gao, Guoying; Yao, Kailun

2018-03-01

Ab initio calculations based on density functional theory and non-equilibrium Green's function are performed to investigate the thermal spin transport properties of single-hydrogen-saturated zigzag graphene nanoribbon co-doped with non-metallic Nitrogen and Boron in parallel and anti-parallel spin configurations. The results show that the doped graphene nanoribbon is a full half-metal. The two-probe system based on the doped graphene nanoribbon exhibits various excellent spin transport properties, including the spin-filtering effect, the spin Seebeck effect, the single-spin negative differential thermal resistance effect and the sign-reversible giant magnetoresistance feature. Excellently, the spin-filtering efficiency can reach nearly 100% in the parallel configuration and the magnetoresistance ratio can be up to -1.5 × 1010% by modulating the electrode temperature and temperature gradient. Our findings indicate that the metal-free doped graphene nanoribbon would be a promising candidate for spin caloritronic applications.

Electrical controllable spin pump based on a zigzag silicene nanoribbon junction.

PubMed

Zhang, Lin; Tong, Peiqing

2017-12-13

We propose a possible electrical controllable spin pump based on a zigzag silicene nanoribbon ferromagnetic junction by applying two time-dependent perpendicular electric fields. By using the Keldysh Green's function method, we derive the analytic expression of the spin-resolved current at the adiabatic approximation and demonstrate that two asymmetric spin up and spin down currents can be pumped out in the device without an external bias. The pumped currents mainly come from the interplay between the photon-assisted spin pump effect and the electrically-modulated energy band structure of the tunneling junction. The spin valve phenomena are not only related to the energy gap opened by two perpendicular staggered potentials, but also dependent on the system parameters such as the pumping frequency, the pumping phase difference, the spin-orbit coupling and the Fermi level, which can be tuned by the electrical methods. The proposed device can also be used to produce a pure spin current and a 100% polarized spin current through the photon-assisted pumping process. Our investigations may provide an electrical manipulation of spin-polarized electrons in graphene-like pumping devices.

Spin current and spin transfer torque in ferromagnet/superconductor spin valves

NASA Astrophysics Data System (ADS)

Moen, Evan; Valls, Oriol T.

2018-05-01

Using fully self-consistent methods, we study spin transport in fabricable spin valve systems consisting of two magnetic layers, a superconducting layer, and a spacer normal layer between the ferromagnets. Our methods ensure that the proper relations between spin current gradients and spin transfer torques are satisfied. We present results as a function of geometrical parameters, interfacial barrier values, misalignment angle between the ferromagnets, and bias voltage. Our main results are for the spin current and spin accumulation as functions of position within the spin valve structure. We see precession of the spin current about the exchange fields within the ferromagnets, and penetration of the spin current into the superconductor for biases greater than the critical bias, defined in the text. The spin accumulation exhibits oscillating behavior in the normal metal, with a strong dependence on the physical parameters both as to the structure and formation of the peaks. We also study the bias dependence of the spatially averaged spin transfer torque and spin accumulation. We examine the critical-bias effect of these quantities, and their dependence on the physical parameters. Our results are predictive of the outcome of future experiments, as they take into account imperfect interfaces and a realistic geometry.

Study on real-time images compounded using spatial light modulator

NASA Astrophysics Data System (ADS)

Xu, Jin; Chen, Zhebo; Ni, Xuxiang; Lu, Zukang

2007-01-01

Image compounded technology is often used on film and its facture. In common, image compounded use image processing arithmetic, get useful object, details, background or some other things from the images firstly, then compounding all these information into one image. When using this method, the film system needs a powerful processor, for the process function is very complex, we get the compounded image for a few time delay. In this paper, we introduce a new method of image real-time compounded, use this method, we can do image composite at the same time with movie shot. The whole system is made up of two camera-lens, spatial light modulator array and image sensor. In system, the spatial light modulator could be liquid crystal display (LCD), liquid crystal on silicon (LCoS), thin film transistor liquid crystal display (TFTLCD), Deformable Micro-mirror Device (DMD), and so on. Firstly, one camera-lens images the object on the spatial light modulator's panel, we call this camera-lens as first image lens. Secondly, we output an image to the panel of spatial light modulator. Then, the image of the object and image that output by spatial light modulator will be spatial compounded on the panel of spatial light modulator. Thirdly, the other camera-lens images the compounded image to the image sensor, and we call this camera-lens as second image lens. After these three steps, we will gain the compound images by image sensor. For the spatial light modulator could output the image continuously, then the image will be compounding continuously too, and the compounding procedure is completed in real-time. When using this method to compounding image, if we will put real object into invented background, we can output the invented background scene on the spatial light modulator, and the real object will be imaged by first image lens. Then, we get the compounded images by image sensor in real time. The same way, if we will put real background to an invented object, we can output the invented object on the spatial light modulator and the real background will be imaged by first image lens. Then, we can also get the compounded images by image sensor real time. Commonly, most spatial light modulator only can do modulate light intensity, so we can only do compounding BW images if use only one panel which without color filter. If we will get colorful compounded image, we need use the system like three spatial light modulator panel projection. In the paper, the system's optical system framework we will give out. In all experiment, the spatial light modulator used liquid crystal on silicon (LCoS). At the end of the paper, some original pictures and compounded pictures will be given on it. Although the system has a few shortcomings, we can conclude that, using this system to compounding images has no delay to do mathematic compounding process, it is a really real time images compounding system.

Direct evidence of hidden local spin polarization in a centrosymmetric superconductor LaO0.55 F0.45BiS2.

PubMed

Wu, Shi-Long; Sumida, Kazuki; Miyamoto, Koji; Taguchi, Kazuaki; Yoshikawa, Tomoki; Kimura, Akio; Ueda, Yoshifumi; Arita, Masashi; Nagao, Masanori; Watauchi, Satoshi; Tanaka, Isao; Okuda, Taichi

2017-12-04

Conventional Rashba spin polarization is caused by the combination of strong spin-orbit interaction and spatial inversion asymmetry. However, Rashba-Dresselhaus-type spin-split states are predicted in the centrosymmetric LaOBiS 2 system by recent theory, which stem from the local inversion asymmetry of active BiS 2 layer. By performing high-resolution spin- and angle-resolved photoemission spectroscopy, we have investigated the electronic band structure and spin texture of superconductor LaO 0.55 F 0.45 BiS 2 . Here we present direct spectroscopic evidence for the local spin polarization of both the valence band and the conduction band. In particular, the coexistence of Rashba-like and Dresselhaus-like spin textures has been observed in the conduction band. The finding is of key importance for fabrication of proposed dual-gated spin-field effect transistor. Moreover, the spin-split band leads to a spin-momentum locking Fermi surface from which superconductivity emerges. Our demonstration not only expands the scope of spintronic materials but also enhances the understanding of spin-orbit interaction-related superconductivity.

Orbit-induced localized spin angular momentum in strong focusing of optical vectorial vortex beams

NASA Astrophysics Data System (ADS)

Li, Manman; Cai, Yanan; Yan, Shaohui; Liang, Yansheng; Zhang, Peng; Yao, Baoli

2018-05-01

Light beams may carry optical spin or orbital angular momentum, or both. The spin and orbital parts manifest themselves by the ellipticity of the state of polarization and the vortex structure of phase of light beams, separately. Optical spin and orbit interaction, arising from the interaction between the polarization and the spatial structure of light beams, has attracted enormous interest recently. The optical spin-to-orbital angular momentum conversion under strong focusing is well known, while the converse process, orbital-to-spin conversion, has not been reported so far. In this paper, we predict in theory that the orbital angular momentum can induce a localized spin angular momentum in strong focusing of a spin-free azimuthal polarization vortex beam. This localized longitudinal spin of the focused field can drive the trapped particle to spin around its own axis. This investigation provides a new degree of freedom for spinning particles by using a vortex phase, which may have considerable potentials in optical spin and orbit interaction, light-beam shaping, or optical manipulation.

Scanned Image Projection System Employing Intermediate Image Plane

NASA Technical Reports Server (NTRS)

DeJong, Christian Dean (Inventor); Hudman, Joshua M. (Inventor)

2014-01-01

In imaging system, a spatial light modulator is configured to produce images by scanning a plurality light beams. A first optical element is configured to cause the plurality of light beams to converge along an optical path defined between the first optical element and the spatial light modulator. A second optical element is disposed between the spatial light modulator and a waveguide. The first optical element and the spatial light modulator are arranged such that an image plane is created between the spatial light modulator and the second optical element. The second optical element is configured to collect the diverging light from the image plane and collimate it. The second optical element then delivers the collimated light to a pupil at an input of the waveguide.

Two-dimensional magneto-optical light modulation in EuTiO3

NASA Astrophysics Data System (ADS)

Bussmann-Holder, Annette; Roleder, Krystian; Stuhlhofer, Benjamin; Logvenov, Gennady; Simon, Arndt; KöHler, Jürgen

EuTiO3 is antiferromagnetic at low temperature, namely below TN = 5.7K. In the high temperature paramagnetic phase the strongly nonlinear coupling between the lattice and the nomnially silent Eu 4f7 spins induces magnetic correlations which become apparent in muon spin rotation experiments and more recently in birefringence measurments in an external magnetic field. It is shown here, that high quality films of insulating EuTiO3 deposited on a thin SrTiO3 substrate are versatile tools for light modulation. The operating temperature is close to room temperature and admits multiple device engineering. By using small magnetic fields the birefringence of the samples can be switched off and on. Similarly, rotation of the sample in the field can modify its birefringence Δn. In addition, Δn can be increased by a factor of 4 in very modest fields with simultaneously enhancing the operating temperature by almost 100K. The results can be understood in terms of paramagnon phonon interaction where spin activity is achieved via the local spin-phonon double-well potential.

Electron spin resonance and electron spin echo modulation studies of N,N,N prime ,N prime -tetramethylbenzidine photoionization adsorbed at the interface of polymeric latices

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

Baglioni, P.; Rivara-Minten, E.; Kevan, L.

1989-02-23

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) of photoionized N,N,N{prime},N{prime}-tetramethylbenzidine (TMB) cation adsorbed at the interface of butadiene-acrylonitrile-methacrylic acid and butadiene-styrene-acrylic acid polymeric latices have been studied as a function of sodium dodecyl sulfate (SDS) concentration adsorbed at the latex interface. The photoionization yield of TMB in frozen latices mainly depends on the strength of TMB{sup +}-water interactions, which are enhanced by added SDS as measured by ESEM. An increase in the negative surface potential of the latex particles, due to the adsorption of SDS at the latex surface, does not affect the photoionization yield, showing thatmore » the particle surface potential has, for negatively charged systems, a secondary role in promoting the photoionization yield. Differences in the TMB{sup +} yield are found for the two polymeric latices and are attributed to the different latex compositions and/or different interfacial structures.« less

Photoionization of N,N,N',N'-tetramethylbenzidine in anionic-cationic mixed micelles of sodium dodecyl sulfate-dodecyltrimethylammonium chloride: electron spin resonance and electron spin echo modulation studies

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

Rivara-Minten, E.; Baglioni, P.; Kevan, L.

1988-05-05

Electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N',N'-tetramethylbenzidine cation radical (TMB/sup +/) in frozen mixed micelles of dodecyltrimethylammonium chloride (DTAC) and sodium dodecyl sulfate (SDS) have been studied as a function of the mixed micelle composition. ESEM effects due to TMB/sup +/ interactions with deuterium in D/sub 2/O show a decrease of the TMB/sup +/-water interaction that depends on the SDS-DTAC mixed micelle composition and reaches a minimum for the equimolar mixed micelle. The efficiency of charge separation upon photoionization of TMB to produce TMB/sup +/ measured by ESR correlates with the degreemore » of water penetration into the micelle. ESEM effects due to interaction of x-doxylstearic acid nitroxide probes with deuterium in D/sub 2/O show that the decrease of water penetration is due to higher surface packing due to electrostatic attraction among the polar headgroups of the two surfactants.« less

Discovery of Enhanced Magnetoelectric Coupling through Electric Field Control of Two-Magnon Scattering within Distorted Nanostructures.

PubMed

Xue, Xu; Zhou, Ziyao; Dong, Guohua; Feng, Mengmeng; Zhang, Yijun; Zhao, Shishun; Hu, Zhongqiang; Ren, Wei; Ye, Zuo-Guang; Liu, Yaohua; Liu, Ming

2017-09-26

Electric field control of dynamic spin interactions is promising to break through the limitation of the magnetostatic interaction based magnetoelectric (ME) effect. In this work, electric field control of the two-magnon scattering (TMS) effect excited by in-plane lattice rotation has been demonstrated in a La 0.7 Sr 0.3 MnO 3 (LSMO)/Pb(Mn 2/3 Nb 1/3 )-PbTiO 3 (PMN-PT) (011) multiferroic heterostructure. Compared with the conventional strain-mediated ME effect, a giant enhancement of ME effect up to 950% at the TMS critical angle is precisely determined by angular resolution of the ferromagnetic resonance (FMR) measurement. Particularly, a large electric field modulation of magnetic anisotropy (464 Oe) and FMR line width (401 Oe) is achieved at 173 K. The electric-field-controllable TMS effect and its correlated ME effect have been explained by electric field modulation of the planar spin interactions triggered by spin-lattice coupling. The enhancement of the ME effect at various temperatures and spin dynamics control are promising paradigms for next-generation voltage-tunable spintronic devices.

Visual sensitivity to spatially sampled modulation in human observers

NASA Technical Reports Server (NTRS)

Mulligan, Jeffrey B.; Macleod, Donald I. A.

1991-01-01

Thresholds were measured for detecting spatial luminance modulation in regular lattices of visually discrete dots. Thresholds for modulation of a lattice are generally higher than the corresponding threshold for modulation of a continuous field, and the size of the threshold elevation, which depends on the spacing of the lattice elements, can be as large as a one log unit. The largest threshold elevations are seen when the sample spacing is 12 min arc or greater. Theories based on response compression cannot explain the further observation that the threshold elevations due to spatial sampling are also dependent on modulation frequency: the greatest elevations occur with higher modulation frequencies. The idea that this is due to masking of the modulation frequency by the spatial frequencies in the sampling lattice is considered.

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

Suppression of the impurity-induced local magnetism by the opening of a spin pseudogap in Ni-doped Sr2CuO3

NASA Astrophysics Data System (ADS)

Utz, Yannic; Hammerath, Franziska; Nishimoto, Satoshi; Hess, Christian; Beesetty, Neela Sekhar; Saint-Martin, Romuald; Revcolevschi, Alexandre; Büchner, Bernd; Grafe, Hans-Joachim

2015-08-01

The S =1 /2 antiferromagnetic Heisenberg spin chain compound Sr2CuO3 doped with 1 % and 2 % of Ni impurities has been studied by means of 63Cu nuclear magnetic resonance. A strong decrease of the spin-lattice relaxation rate T1-1 at low temperatures points toward a spin gap, while a stretching exponent λ <1 and a frequency dependence of T1-1 indicate that this spin gap varies spatially and should rather be characterized as a spin pseudogap. The magnitude of the spin pseudogap scales with doping level. Our results therefore evidence the finite-size character of this phenomenon. Moreover, an unusual narrowing of the low-temperature NMR lines reveals the suppression of the impurity-induced staggered paramagnetic response with increasing doping level.

Measuring coalescing massive binary black holes with gravitational waves: The impact of spin-induced precession

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

Lang, Ryan N.; Hughes, Scott A.

The coalescence of massive black holes generates gravitational waves (GWs) that will be measurable by space-based detectors such as LISA to large redshifts. The spins of a binary's black holes have an important impact on its waveform. Specifically, geodetic and gravitomagnetic effects cause the spins to precess; this precession then modulates the waveform, adding periodic structure which encodes useful information about the binary's members. Following pioneering work by Vecchio, we examine the impact upon GW measurements of including these precession-induced modulations in the waveform model. We find that the additional periodicity due to spin precession breaks degeneracies among certain parameters,more » greatly improving the accuracy with which they may be measured. In particular, mass measurements are improved tremendously, by one to several orders of magnitude. Localization of the source on the sky is also improved, though not as much--low redshift systems can be localized to an ellipse which is roughly 10-a fewx10 arcminutes in the long direction and a factor of 2 smaller in the short direction. Though not a drastic improvement relative to analyses which neglect spin precession, even modest gains in source localization will greatly facilitate searches for electromagnetic counterparts to GW events. Determination of distance to the source is likewise improved: We find that relative error in measured luminosity distance is commonly {approx}0.1%-0.4% at z{approx}1. Finally, with the inclusion of precession, we find that the magnitude of the spins themselves can typically be determined for low redshift systems with an accuracy of about 0.1%-10%, depending on the spin value, allowing accurate surveys of mass and spin evolution over cosmic time.« less

Modeling spin magnetization transport in a spatially varying magnetic field

NASA Astrophysics Data System (ADS)

Picone, Rico A. R.; Garbini, Joseph L.; Sidles, John A.

2015-01-01

We present a framework for modeling the transport of any number of globally conserved quantities in any spatial configuration and apply it to obtain a model of magnetization transport for spin-systems that is valid in new regimes (including high-polarization). The framework allows an entropy function to define a model that explicitly respects the laws of thermodynamics. Three facets of the model are explored. First, it is expressed as nonlinear partial differential equations that are valid for the new regime of high dipole-energy and polarization. Second, the nonlinear model is explored in the limit of low dipole-energy (semi-linear), from which is derived a physical parameter characterizing separative magnetization transport (SMT). It is shown that the necessary and sufficient condition for SMT to occur is that the parameter is spatially inhomogeneous. Third, the high spin-temperature (linear) limit is shown to be equivalent to the model of nuclear spin transport of Genack and Redfield (1975) [1]. Differences among the three forms of the model are illustrated by numerical solution with parameters corresponding to a magnetic resonance force microscopy (MRFM) experiment (Degen et al., 2009 [2]; Kuehn et al., 2008 [3]; Sidles et al., 2003 [4]; Dougherty et al., 2000 [5]). A family of analytic, steady-state solutions to the nonlinear equation is derived and shown to be the spin-temperature analog of the Langevin paramagnetic equation and Curie's law. Finally, we analyze the separative quality of magnetization transport, and a steady-state solution for the magnetization is shown to be compatible with Fenske's separative mass transport equation (Fenske, 1932 [6]).

Spin interactions in Graphene-Single Molecule Magnets Hybrids

NASA Astrophysics Data System (ADS)

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Aña; Luis, Fernando; Rauschenbach, Stephan; Dressel, Martin; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2014-03-01

Graphene is a potential component of novel spintronics devices owing to its long spin diffusion length. Besides its use as spin-transport channel, graphene can be employed for the detection and manipulation of molecular spins. This requires an appropriate coupling between the sheets and the single molecular magnets (SMM). Here, we present a comprehensive characterization of graphene-Fe4 SMM hybrids. The Fe4 clusters are anchored non-covalently to the graphene following a diffusion-limited assembly and can reorganize into random networks when subjected to slightly elevated temperature. Molecules anchored on graphene sheets show unaltered static magnetic properties, whilst the quantum dynamics is profoundly modulated. Interaction with Dirac fermions becomes the dominant spin-relaxation channel, with observable effects produced by graphene phonons and reduced dipolar interactions. Coupling to graphene drives the spins over Villain's threshold, allowing the first observation of strongly-perturbative tunneling processes. Preliminary spin-transport experiments at low-temperature are further presented.

Spin-orbit signatures in the dynamics of singlet-triplet qubits in double quantum dots

NASA Astrophysics Data System (ADS)

Rolon, Juan E.; Cota, Ernesto; Ulloa, Sergio E.

2017-05-01

We characterize numerically and analytically the signatures of the spin-orbit interaction in a two-electron GaAs double quantum dot in the presence of an external magnetic field. In particular, we obtain the return probability of the singlet state by simulating Landau-Zener voltage detuning sweeps which traverse the singlet-triplet (S -T+ ) resonance. Our results indicate that non-spin-conserving interdot tunneling processes arising from the spin-orbit interaction have well defined signatures. These allow direct access to the spin-orbit interaction scales and are characterized by a frequency shift and Fourier amplitude modulation of the Rabi flopping dynamics of the singlet-triplet qubits S -T0 and S -T+ . By applying the Bloch-Feshbach projection formalism, we demonstrate analytically that the aforementioned effects originate from the interplay between spin-orbit interaction and processes driven by the hyperfine interaction between the electron spins and those of the GaAs nuclei.

Spin-filtering and giant magnetoresistance effects in polyacetylene-based molecular devices

NASA Astrophysics Data System (ADS)

Chen, Tong; Yan, Shenlang; Xu, Liang; Liu, Desheng; Li, Quan; Wang, Lingling; Long, Mengqiu

2017-07-01

Using the non-equilibrium Green's function formalism in combination with density functional theory, we performed ab initio calculations of spin-dependent electron transport in molecular devices consisting of a polyacetylene (CnHn+1) chain vertically attached to a carbon chain sandwiched between two semi-infinite zigzag-edged graphene nanoribbon electrodes. Spin-charge transport in the device could be modulated to different magnetic configurations by an external magnetic field. The results showed that single spin conduction could be obtained. Specifically, the proposed CnHn+1 devices exhibited several interesting effects, including (dual) spin filtering, spin negative differential resistance, odd-even oscillation, and magnetoresistance (MR). Marked spin polarization with a filtering efficiency of up to 100% over a large bias range was found, and the highest MR ratio for the CnHn+1 junctions reached 4.6 × 104. In addition, the physical mechanisms for these phenomena were also revealed.

Surprises from the spins: astrophysics and relativity with detections of spinning black-hole mergers

NASA Astrophysics Data System (ADS)

Gerosa, Davide

2018-03-01

Measurements of black-hole spins are of crucial importance to fulfill the promise of gravitational-wave astronomy. On the astrophysics side, spins are perhaps the cleanest indicator of black-hole evolutionary processes, thus providing a preferred way to discriminate how LIGO's black holes form. On the relativity side, spins are responsible for peculiar dynamical phenomena (from precessional modulations in the long inspiral to gravitational-wave recoils at merger) which encode precious information on the underlying astrophysical processes. I present some examples to explore this deep and fascinating interplay between spin dynamics (relativity) and environmental effects (astrophysics). Black-hole spins indeed hide remarkable surprises on both fronts: morphologies, resonances, constraints on supernova kicks, multiple merger generations and more... These findings were presented at 12th Edoardo Amaldi Conference on Gravitational Waves, held on July 9-14, 2017 in Pasadena, CA, USA.

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

PubMed Central

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-01-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution. PMID:28338011

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

NASA Astrophysics Data System (ADS)

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-03-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

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.

The time-dependence of exchange-induced relaxation during modulated radio frequency pulses.

PubMed

Sorce, Dennis J; Michaeli, Shalom; Garwood, Michael

2006-03-01

The problem of the relaxation of identical spins 1/2 induced by chemical exchange between spins with different chemical shifts in the presence of time-dependent RF irradiation (in the first rotating frame) is considered for the fast exchange regime. The solution for the time evolution under the chemical exchange Hamiltonian in the tilted doubly rotating frame (TDRF) is presented. Detailed derivation is specified to the case of a two-site chemical exchange system with complete randomization between jumps of the exchanging spins. The derived theory can be applied to describe the modulation of the chemical exchange relaxation rate constants when using a train of adiabatic pulses, such as the hyperbolic secant pulse. Theory presented is valid for quantification of the exchange-induced time-dependent rotating frame longitudinal T1rho,ex and transverse T2rho,ex relaxations in the fast chemical exchange regime.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

NASA Astrophysics Data System (ADS)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

2015-05-01

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

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

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy

2015-05-07

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this usingmore » inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.« less

Photo-induced spatial modulation of THz waves: opportunities and limitations.

PubMed

Kannegulla, Akash; Shams, Md Itrat Bin; Liu, Lei; Cheng, Li-Jing

2015-12-14

Programmable conductive patterns created by photoexcitation of semiconductor substrates using digital light processing (DLP) provides a versatile approach for spatial and temporal modulation of THz waves. The reconfigurable nature of the technology has great potential in implementing several promising THz applications, such as THz beam steering, THz imaging or THz remote sensing, in a simple, cost-effective manner. In this paper, we provide physical insight about how the semiconducting materials, substrate dimension, optical illumination wavelength and illumination size impact the performance of THz modulation, including modulation depth, modulation speed and spatial resolution. The analysis establishes design guidelines for the development of photo-induced THz modulation technology. Evolved from the theoretical analysis, a new mesa array technology composed by a matrix of sub-THz wavelength structures is introduced to maximize both spatial resolution and modulation depth for THz modulation with low-power photoexcitation by prohibiting the lateral diffusion of photogenerated carriers.

Transient radical pairs studied by time-resolved EPR.

PubMed

Bittl, Robert; Weber, Stefan

2005-02-25

Photogenerated short-lived radical pairs (RP) are common in biological photoprocesses such as photosynthesis and enzymatic DNA repair. They can be favorably probed by time-resolved electron paramagnetic resonance (EPR) methods with adequate time resolution. Two EPR techniques have proven to be particularly useful to extract information on the working states of photoinduced biological processes that is only difficult or sometimes even impossible to obtain by other types of spectroscopy. Firstly, transient EPR yields crucial information on the chemical nature and the geometry of the individual RP halves in a doublet-spin pair generated by a short laser pulse. This time-resolved method is applicable in all magnetic field/microwave frequency regimes that are used for continuous-wave EPR, and is nowadays routinely utilized with a time resolution reaching about 10 ns. Secondly, a pulsed EPR method named out-of-phase electron spin echo envelope modulation (OOP-ESEEM) is increasingly becoming popular. By this pulsed technique, the mutual spin-spin interaction between the RP halves in a doublet-spin pair manifests itself as an echo modulation detected as a function of the microwave-pulse spacing of a two-pulse echo sequence subsequent to a laser pulse. From the dipolar coupling, the distance between the radicals is readily derived. Since the spin-spin interaction parameters are typically not observable by transient EPR, the two techniques complement each other favorably. Both EPR methods have recently been applied to a variety of light-induced RPs in photobiology. This review summarizes the results obtained from such studies in the fields of plant and bacterial photosynthesis and DNA repair mediated by the enzyme DNA photolyase.

Spin Forming Aluminum Crew Module (CM) Metallic Aft Pressure Vessel Bulkhead (APVBH) - Phase II

NASA Technical Reports Server (NTRS)

Hoffman, Eric K.; Domack, Marcia S.; Torres, Pablo D.; McGill, Preston B.; Tayon, Wesley A.; Bennett, Jay E.; Murphy, Joseph T.

2015-01-01

The principal focus of this project was to assist the Multi-Purpose Crew Vehicle (MPCV) Program in developing a spin forming fabrication process for manufacture of the Orion crew module (CM) aft pressure vessel bulkhead. The spin forming process will enable a single piece aluminum (Al) alloy 2219 aft bulkhead resulting in the elimination of the current multiple piece welded construction, simplify CM fabrication, and lead to an enhanced design. Phase I (NASA TM-2014-218163 (1)) of this assessment explored spin forming the single-piece CM forward pressure vessel bulkhead. The Orion MPCV Program and Lockheed Martin (LM) recently made two critical decisions relative to the NESC Phase I work scope: (1) LM selected the spin forming process to manufacture a single-piece aft bulkhead for the Orion CM, and (2) the aft bulkhead will be manufactured from Al 2219. Based on the Program's new emphasis related to the spin forming process, the NESC was asked to conduct a Phase II assessment to assist in the LM manufacture of the aft bulkhead and to conduct a feasibility study into spin forming the Orion CM cone. This activity was approved on June 19, 2013. Dr. Robert Piascik, NASA Technical Fellow for Materials at the Langley Research Center (LaRC), was selected to lead this assessment. The project plan was approved by the NASA Engineering and Safety Center (NESC) Review Board (NRB) on July 18, 2013. The primary stakeholders for this assessment were the NASA and LM MPCV Program offices. Additional benefactors are commercial launch providers developing CM concepts.

Spin Forming Aluminum Crew Module (CM) Metallic Aft Pressure Vessel Bulkhead (APVBH) - Phase II

NASA Technical Reports Server (NTRS)

Hoffman, Eric K.; Domack, Marcia S.; Torres, Pablo D.; McGill, Preston B.; Tayon, Wesley A.; Bennett, Jay E.; Murphy, Joseph T.

2015-01-01

The principal focus of this project was to assist the Multi-Purpose Crew Vehicle (MPCV) program in developing a spin forming fabrication process for manufacture of the Orion crew module (CM) aft pressure vessel bulkhead. The spin forming process will enable a single piece aluminum (Al) alloy 2219 aft bulkhead resulting in the elimination of the current multiple piece welded construction, simplify CM fabrication, and lead to an enhanced design. Phase I (NASA TM-2014-218163, (1)) of this assessment explored spin forming the single-piece CM forward pressure vessel bulkhead. The MPCV Program and Lockheed Martin (LM) recently made two critical decisions relative to the NESC Phase I work scope: (1) LM selected the spin forming process to manufacture a singlepiece aft bulkhead for the Orion CM, and (2) the aft bulkhead will be manufactured from Al 2219. Based on the Program's new emphasis related to the spin forming process, the NESC was asked to conduct a Phase II assessment to assist in the LM manufacture of the aft bulkhead and to conduct a feasibility study into spin forming the Orion CM cone. This activity was approved on June 19, 2013. Dr. Robert Piascik, NASA Technical Fellow for Materials at the Langley Research Center (LaRC), was selected to lead this assessment. The project plan was approved by the NASA Engineering and Safety Center (NESC) Review Board (NRB) on July 18, 2013. The primary stakeholders for this assessment are the NASA and LM MPCV Program offices. Additional benefactors are commercial launch providers developing CM concepts.

The Effects of Acutely Administered 3,4-Methylenedioxymethamphetamine on Spontaneous Brain Function in Healthy Volunteers Measured with Arterial Spin Labeling and Blood Oxygen Level–Dependent Resting State Functional Connectivity

PubMed Central

Carhart-Harris, Robin L.; Murphy, Kevin; Leech, Robert; Erritzoe, David; Wall, Matthew B.; Ferguson, Bart; Williams, Luke T.J.; Roseman, Leor; Brugger, Stefan; De Meer, Ineke; Tanner, Mark; Tyacke, Robin; Wolff, Kim; Sethi, Ajun; Bloomfield, Michael A.P.; Williams, Tim M.; Bolstridge, Mark; Stewart, Lorna; Morgan, Celia; Newbould, Rexford D.; Feilding, Amanda; Curran, H. Val; Nutt, David J.

2015-01-01

Background The compound 3,4-methylenedioxymethamphetamine (MDMA) is a potent monoamine releaser that produces an acute euphoria in most individuals. Methods In a double-blind, placebo-controlled, balanced-order study, MDMA was orally administered to 25 physically and mentally healthy individuals. Arterial spin labeling and seed-based resting state functional connectivity (RSFC) were used to produce spatial maps displaying changes in cerebral blood flow (CBF) and RSFC after MDMA administration. Participants underwent two arterial spin labeling and two blood oxygen level–dependent scans in a 90-minute scan session; MDMA and placebo study days were separated by 1 week. Results Marked increases in positive mood were produced by MDMA. Decreased CBF only was observed after MDMA, and this was localized to the right medial temporal lobe (MTL), thalamus, inferior visual cortex, and the somatosensory cortex. Decreased CBF in the right amygdala and hippocampus correlated with ratings of the intensity of global subjective effects of MDMA. The RSFC results complemented the CBF results, with decreases in RSFC between midline cortical regions, the medial prefrontal cortex, and MTL regions, and increases between the amygdala and hippocampus. There were trend-level correlations between these effects and ratings of intense and positive subjective effects. Conclusions The MTLs appear to be specifically implicated in the mechanism of action of MDMA, but further work is required to elucidate how the drug’s characteristic subjective effects arise from its modulation of spontaneous brain activity. PMID:24495461

Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

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

Chaghazardi, Zahra; Faez, Rahim; Touski, Shoeib Babaee

2016-08-07

In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping ratemore » and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene.« less

Enhanced spatial near-infrared modulation of graphene-loaded perfect absorbers using plasmonic nanoslits.

PubMed

Cai, Yijun; Zhu, Jinfeng; Liu, Qing Huo; Lin, Timothy; Zhou, Jianyang; Ye, Longfang; Cai, Zhiping

2015-12-14

Modulating spatial near-infrared light for ultra-compact electro-optic devices is a critical issue in optical communication and imaging applications. To date, spatial near-infrared modulators based on graphene have been reported, but they showed limited modulation effects due to the relatively weak light-graphene interaction. In combination with graphene and metallic nanoslits, we design a kind of ultrathin near-infrared perfect absorber with enhanced spatial modulation effects and independence on a wide range of incident angles. The modulated spectral shift of central wavelength is up to 258.2 nm in the near-infrared range, which is more promising in applications than state-of-the-art devices. The modulation enhancement is attributed to the plasmonic nanoslit mode, in which the optical electric field is highly concentrated in the deep subwavelength scale and the light-graphene interaction is significantly strengthened. The physical insight is deeply revealed by a combination of equivalent circuit and electromagnetic field analysis. The design principles are not only crucial for spatial near-infrared modulators, but also provide a key guide for developing active near-infrared patch nanoantennas based on graphene.

Toward nonlinear magnonics: Intensity-dependent spin-wave switching in insulating side-coupled magnetic stripes

NASA Astrophysics Data System (ADS)

Sadovnikov, A. V.; Odintsov, S. A.; Beginin, E. N.; Sheshukova, S. E.; Sharaevskii, Yu. P.; Nikitov, S. A.

2017-10-01

We demonstrate that the nonlinear spin-wave transport in two laterally parallel magnetic stripes exhibit the intensity-dependent power exchange between the adjacent spin-wave channels. By the means of Brillouin light scattering technique, we investigate collective nonlinear spin-wave dynamics in the presence of magnetodipolar coupling. The nonlinear intensity-dependent effect reveals itself in the spin-wave mode transformation and differential nonlinear spin-wave phase shift in each adjacent magnetic stripe. The proposed analytical theory, based on the coupled Ginzburg-Landau equations, predicts the geometry design involving the reduction of power requirement to the all-magnonic switching. A very good agreement between calculation and experiment was found. In addition, a micromagnetic and finite-element approach has been independently used to study the nonlinear behavior of spin waves in adjacent stripes and the nonlinear transformation of spatial profiles of spin-wave modes. Our results show that the proposed spin-wave coupling mechanism provides the basis for nonlinear magnonic circuits and opens the perspectives for all-magnonic computing architecture.

Demonstration of a robust magnonic spin wave interferometer.

PubMed

Kanazawa, Naoki; Goto, Taichi; Sekiguchi, Koji; Granovsky, Alexander B; Ross, Caroline A; Takagi, Hiroyuki; Nakamura, Yuichi; Inoue, Mitsuteru

2016-07-22

Magnonics is an emerging field dealing with ultralow power consumption logic circuits, in which the flow of spin waves, rather than electric charges, transmits and processes information. Waves, including spin waves, excel at encoding information via their phase using interference. This enables a number of inputs to be processed in one device, which offers the promise of multi-input multi-output logic gates. To realize such an integrated device, it is essential to demonstrate spin wave interferometers using spatially isotropic spin waves with high operational stability. However, spin wave reflection at the waveguide edge has previously limited the stability of interfering waves, precluding the use of isotropic spin waves, i.e., forward volume waves. Here, a spin wave absorber is demonstrated comprising a yttrium iron garnet waveguide partially covered by gold. This device is shown experimentally to be a robust spin wave interferometer using the forward volume mode, with a large ON/OFF isolation value of 13.7 dB even in magnetic fields over 30 Oe.

Demonstration of a robust magnonic spin wave interferometer

PubMed Central

Kanazawa, Naoki; Goto, Taichi; Sekiguchi, Koji; Granovsky, Alexander B.; Ross, Caroline A.; Takagi, Hiroyuki; Nakamura, Yuichi; Inoue, Mitsuteru

2016-01-01

Magnonics is an emerging field dealing with ultralow power consumption logic circuits, in which the flow of spin waves, rather than electric charges, transmits and processes information. Waves, including spin waves, excel at encoding information via their phase using interference. This enables a number of inputs to be processed in one device, which offers the promise of multi-input multi-output logic gates. To realize such an integrated device, it is essential to demonstrate spin wave interferometers using spatially isotropic spin waves with high operational stability. However, spin wave reflection at the waveguide edge has previously limited the stability of interfering waves, precluding the use of isotropic spin waves, i.e., forward volume waves. Here, a spin wave absorber is demonstrated comprising a yttrium iron garnet waveguide partially covered by gold. This device is shown experimentally to be a robust spin wave interferometer using the forward volume mode, with a large ON/OFF isolation value of 13.7 dB even in magnetic fields over 30 Oe. PMID:27443989

Critical behavior of a quantum chain with four-spin interactions in the presence of longitudinal and transverse magnetic fields.

PubMed

Boechat, B; Florencio, J; Saguia, A; de Alcantara Bonfim, O F

2014-03-01

We study the ground-state properties of a spin-1/2 model on a chain containing four-spin Ising-like interactions in the presence of both transverse and longitudinal magnetic fields. We use entanglement entropy and finite-size scaling methods to obtain the phase diagrams of the model. Our numerical calculations reveal a rich variety of phases and the existence of multicritical points in the system. We identify phases with both ferromagnetic and antiferromagnetic orderings. We also find periodically modulated orderings formed by a cluster of like spins followed by another cluster of opposite like spins. The quantum phases in the model are found to be separated by either first- or second-order transition lines.

Antiferromagnetic Spin Wave Field-Effect Transistor

DOE PAGES

Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; ...

2016-04-06

In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. In conclusion, our findings open up the exciting possibilitymore » of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.« less

The current-induced heat generation in a spin-flip quantum dot sandwiched between a ferromagnetic and a superconducting electrode

NASA Astrophysics Data System (ADS)

Jiang, Feng; Yan, Yonghong; Wang, Shikuan; Yan, Yijing

2017-12-01

Using non-equilibrium Green's functions' theory based on extended Nambu representation and small polaron transformation, we studied the current-induced heat generation in a spin-flip quantum dot sandwiched between a ferromagnetic and a superconducting electrode. We focused on moderate dot-leads coupling and relative small phonon energy, and derived the detailed expression of heat generation. The numerical results show (i) the heat generation decreases with polarization degree increasing, (ii) the intradot spin-flip can have a great effect on the heat generation at both zero temperature and finite temperature and (iii) at finite temperature an optimal workspace of keeping spin current and tuning heat generation by modulating the spin-flip intensity can be found.

Sensitivity optimization of Bell-Bloom magnetometers by manipulation of atomic spin synchronization

NASA Astrophysics Data System (ADS)

Ranjbaran, M.; Tehranchi, M. M.; Hamidi, S. M.; Khalkhali, S. M. H.

2018-05-01

Many efforts have been devoted to the developments of atomic magnetometers for achieving the high sensitivity required in biomagnetic applications. To reach the high sensitivity, many types of atomic magnetometers have been introduced for optimization of the creation and relaxation rates of atomic spin polarization. In this paper, regards to sensitivity optimization techniques in the Mx configuration, we have proposed a novelty approach for synchronization of the spin precession in the Bell-Bloom magnetometers. We have utilized the phenomenological Bloch equations to simulate the spin dynamics when modulation of pumping light and radio frequency magnetic field were both used for atomic spin synchronization. Our results showed that the synchronization process, improved the magnetometer sensitivity respect to the classical configurations.

Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton.

PubMed

Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

2015-05-22

Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology.

Tailoring Spin Textures in Complex Oxide Micromagnets

DOE PAGES

Lee, Michael S.; Wynn, Thomas A.; Folven, Erik; ...

2016-09-12

Engineered topological spin textures with submicron dimensions in magnetic materials have emerged in recent years as the building blocks for various spin-based memory devices. Examples of these magnetic configurations include magnetic skyrmions, vortices, and domain walls. Here in this paper, we show the ability to control and characterize the evolution of spin textures in complex oxide micromagnets as a function of temperature through the delicate balance of fundamental materials parameters, micromagnet geometries, and epitaxial strain. These results demonstrate that in order to fully describe the observed spin textures, it is necessary to account for the spatial variation of the magneticmore » parameters within the micromagnet. This study provides the framework to accurately characterize such structures, leading to efficient design of spin-based memory devices based on complex oxide thin films.« less

Detecting Kondo Entanglement by Electron Conductance

NASA Astrophysics Data System (ADS)

Yoo, Gwangsu; Lee, S.-S. B.; Sim, H.-S.

2018-04-01

Quantum entanglement between an impurity spin and electrons nearby is a key property of the single-channel Kondo effects. We show that the entanglement can be detected by measuring electron conductance through a double quantum dot in an orbital Kondo regime. We derive a relation between the entanglement and the conductance, when the SU(2) spin symmetry of the regime is weakly broken. The relation reflects the universal form of many-body states near the Kondo fixed point. Using it, the spatial distribution of the entanglement—hence, the Kondo cloud—can be detected, with breaking of the symmetry spatially nonuniformly by electrical means.

Spatially periodic patterns in rotating fluids: a new spin on the old "soup-can race"

NASA Astrophysics Data System (ADS)

Carnevali, Antonino; Carnevali, Dora; Christ, Jessica

2000-11-01

A student's investigation of the old "soup-can race" experiment revealed spatially periodic structures at the surface of the rotating fluid. To better observe this effect, the experiment was transferred to a test bench, where an electric motor was used to spin a cylindrical bottle, partially filled with fluids of varied densities, about its longitudinal axis. A photogate and event-counter software provided real-time measurements of the rotational frequency. Various cell-formation patterns were observed. Experimental results will be presented, and connections with the theory will be explored.

Polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a flat-bottomed optical trap with a weak magnetic field

NASA Astrophysics Data System (ADS)

Zheng, Gong-Ping; Li, Pin; Li, Ting; Xue, Ya-Jie

2018-02-01

Motivated by the recent experiments realized in a flat-bottomed optical trap (Navon et al., 2015; Chomaz et al., 2015), we study the ground state of polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a finite-size homogeneous trap with a weak magnetic field. The exact spatial distribution of local spin is obtained with a variational method. Unlike the fully-magnetized planar spin texture with a zero-spin core, which was schematically demonstrated in previous studies for the ideal polar-core spin vortex in a homogeneous trap with infinitely large boundary, some plateaus and two-cores structure emerge in the distribution curves of spin magnitude in the polar-core spin vortex we obtained for the larger effective spin-dependent interaction. More importantly, the spin values of the plateaus are not 1 as expected in the fully-magnetized spin texture, except for the sufficiently large spin-dependent interaction and the weak-magnetic-field limit. We attribute the decrease of spin value to the effect of finite size of the system. The spin values of the plateaus can be controlled by the quadratic Zeeman energy q of the weak magnetic field, which decreases with the increase of q.

A two-dimensional spin field-effect switch

DOE PAGES

Yan, Wenjing; Txoperena, Oihana; Llopis, Roger; ...

2016-11-11

Future development in spintronic devices will require an advanced control of spin currents, for example by an electric field. Here we demonstrate an approach that differs from previous proposals such as the Datta and Das modulator, and that is based on a van de Waals heterostructure of atomically thin graphene and semiconducting MoS 2. Our device combines the superior spin transport properties of graphene with the strong spin–orbit coupling of MoS 2 and allows switching of the spin current in the graphene channel between ON and OFF states by tuning the spin absorption into the MoS 2 with a gatemore » electrode. Lastly, our proposal holds potential for technologically relevant applications such as search engines or pattern recognition circuits, and opens possibilities towards electrical injection of spins into transition metal dichalcogenides and alike materials.« less

Detecting topological phases in silicene by anomalous Nernst effect

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

Xu, Yafang; Zhou, Xingfei; Jin, Guojun, E-mail: gjin@nju.edu.cn

2016-05-16

Silicene undergoes various topological phases under the interplay of intrinsic spin-orbit coupling, perpendicular electric field, and off-resonant light. We propose that the abundant topological phases can be distinguished by measuring the Nernst conductivity even at room temperature, and their phase boundaries can be determined by differentiating the charge and spin Nernst conductivities. By modulating the electric and light fields, pure spin polarized, valley polarized, and even spin-valley polarized Nernst currents can be generated. As Nernst conductivity is zero for linear polarized light, silicene can act as an optically controlled spin and valley field-effect transistor. Similar investigations can be extended frommore » silicene to germanene and stanene, and a comparison is made for the anomalous thermomagnetic figure of merits between them. These results will facilitate potential applications in spin and valley caloritronics.« less

Time-domain detection of current controlled magnetization damping in Pt/Ni{sub 81}Fe{sub 19} bilayer and determination of Pt spin Hall angle

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

Ganguly, A.; Haldar, A.; Sinha, J.

2014-09-15

The effect of spin torque from the spin Hall effect in Pt/Ni{sub 81}Fe{sub 19} rectangular bilayer film was investigated using time-resolved magneto-optical Kerr microscopy. Current flow through the stack resulted in a linear variation of effective damping up to ±7%, attributed to spin current injection from the Pt into the Ni{sub 81}Fe{sub 19}. The spin Hall angle of Pt was estimated as 0.11 ± 0.03. The modulation of the damping depended on the angle between the current and the bias magnetic field. These results demonstrate the importance of optical detection of precessional magnetization dynamics for studying spin transfer torque due to spinmore » Hall effect.« less

A reevaluation of the proposed spin-down of the white dwarf pulsar in AR Scorpii.

NASA Astrophysics Data System (ADS)

Potter, Stephen B.; Buckley, David A. H.

2018-05-01

We present high-speed optical photometric observations, spanning ˜2 years, of the recently-discovered white dwarf pulsar AR Scorpii. The amplitudes of the orbital, spin and beat modulations appear to be remarkably stable and repeatable over the time span of our observations. It has been suggested that the polarized and non-polarized emission from AR Scorpii is powered by the spin-down of the white dwarf. However, we find that our new data is inconsistent with the published spin-down ephemeris. Whilst our data is consistent with a constant spin period further observations over an extended time-base are required in order to ascertain the true spin-evolution of the white dwarf. This may have implications for the various models put forward to explain the energetics and evolution of AR Scorpii.

Soliton solution for the spin current in a ferromagnetic nanowire.

PubMed

Li, Zai-Dong; Li, Qiu-Yan; Li, Lu; Liu, W M

2007-08-01

We investigate the interaction of a periodic solution and a one-soliton solution for the spin-polarized current in a uniaxial ferromagnetic nanowire. The amplitude and wave number of the periodic solution for the spin current give different contributions to the width, velocity, and amplitude of the soliton. Moreover, we found that the soliton can be trapped only in space with proper conditions. Finally, we analyze the modulation instability and discuss dark solitary wave propagation for a spin current on the background of a periodic solution. In some special cases, the solution can be expressed as the linear combination of the periodic and soliton solutions.

Modification of the magnetization dynamics of a NiFe nanodot due to thermal spin injection

NASA Astrophysics Data System (ADS)

Asam, Nagarjuna; Yamanoi, Kazuto; Kimura, Takashi

2018-06-01

An array of NiFe nanodots has been prepared on a Cu/CoFeAl film. Since a thermal spin current is expected to be excited owing to a large spin-dependent Seebeck coefficient for the CoFeAl, we investigate the magnetization dynamics of the NiFe dots under the temperature gradient along the vertical direction. By using vector network analyzer measurements, we have demonstrated that the temperature gradient produces modulations of the frequency of ferromagnetic resonance and the linewidth of the resonance spectra. The observed parabolic dependences are well explained by the damping-like and field-like components of spin transfer torque.

Highly Efficient Spin-Current Operation in a Cu Nano-Ring

NASA Astrophysics Data System (ADS)

Murphy, Benedict A.; Vick, Andrew J.; Samiepour, Marjan; Hirohata, Atsufumi

2016-11-01

An all-metal lateral spin-valve structure has been fabricated with a medial Copper nano-ring to split the diffusive spin-current path. We have demonstrated significant modulation of the non-local signal by the application of a magnetic field gradient across the nano-ring, which is up to 30% more efficient than the conventional Hanle configuration at room temperature. This was achieved by passing a dc current through a current-carrying bar to provide a locally induced Ampère field. We have shown that in this manner a lateral spin-valve gains an additional functionality in the form of three-terminal gate operation for future spintronic logic.

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.

Room temperature ferromagnetism in BiFe1-xMnxO3 thin film induced by spin-structure manipulation

NASA Astrophysics Data System (ADS)

Shigematsu, Kei; Asakura, Takeshi; Yamamoto, Hajime; Shimizu, Keisuke; Katsumata, Marin; Shimizu, Haruki; Sakai, Yuki; Hojo, Hajime; Mibu, Ko; Azuma, Masaki

2018-05-01

The evolution of crystal structure, spin structure, and macroscopic magnetization of manganese-substituted BiFeO3 (BiFe1-xMnxO3), a candidate for multiferroic materials, were investigated on bulk and epitaxial thin-film. Mn substitution for Fe induced collinear antiferromagnetic spin structure around room temperature by destabilizing the cycloidal spin modulation which prohibited the appearance of net magnetization generated by Dzyaloshinskii-Moriya interaction. For the bulk samples, however, no significant signal of ferromagnetism was observed because the direction of the ordered spins was close to parallel to the electric polarization so that spin-canting did not occur. On the contrary, BiFe1-xMnxO3 thin film on SrTiO3 (001) had a collinear spin structure with the spin direction perpendicular to the electric polarization at room temperature, where the appearance of spontaneous magnetization was expected. Indeed, ferromagnetic hysteresis behavior was observed for BiFe0.9Mn0.1O3 thin film.

Cu nuclear magnetic resonance study of charge and spin stripe order in La 1.875 Ba 0.125 CuO 4

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

Pelc, D.; Grafe, H. -J.; Gu, G. D.

In this paper, we present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide informationmore » on the nature and suppression of spin fluctuations associated with charge order. Lastly, we find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.« less

Neutron Spin Resonance in the 112-Type Iron-Based Superconductor

NASA Astrophysics Data System (ADS)

Xie, Tao; Gong, Dongliang; Ghosh, Haranath; Ghosh, Abyay; Soda, Minoru; Masuda, Takatsugu; Itoh, Shinichi; Bourdarot, Frédéric; Regnault, Louis-Pierre; Danilkin, Sergey; Li, Shiliang; Luo, Huiqian

2018-03-01

We use inelastic neutron scattering to study the low-energy spin excitations of the 112-type iron pnictide Ca0.82La0.18Fe0.96Ni0.04As2 with bulk superconductivity below Tc=22 K . A two-dimensional spin resonance mode is found around E =11 meV , where the resonance energy is almost temperature independent and linearly scales with Tc along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Because of the unique monoclinic structure with additional zigzag arsenic chains, the As 4 p orbitals contribute to a three-dimensional hole pocket around the Γ point and an extra electron pocket at the X point. Our results suggest that the energy and momentum distribution of the spin resonance does not directly respond to the kz dependence of the fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.

Cu nuclear magnetic resonance study of charge and spin stripe order in La 1.875 Ba 0.125 CuO 4

DOE PAGES

Pelc, D.; Grafe, H. -J.; Gu, G. D.; ...

2017-02-15

In this paper, we present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide informationmore » on the nature and suppression of spin fluctuations associated with charge order. Lastly, we find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.« less

Modulation bandwidth of spin torque oscillators under current modulation

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

Quinsat, M.; CEA, INAC-SPINTEC, F-38054 Grenoble; CNRS, SPINTEC, F-38054 Grenoble

2014-10-13

For practical applications of spin torque nano-oscillators (STNO), one of the most critical characteristics is the speed at which an STNO responds to variations of external control parameters, such as current or/and field. Theory predicts that this speed is limited by the amplitude relaxation rate Γ{sub p} that determines the timescale over which the amplitude fluctuations are damped out. In this study, this limit is verified experimentally by analyzing the amplitude and frequency noise spectra of the output voltage signal when modulating an STNO by a microwave current. In particular, it is shown that due to the non-isochronous nature ofmore » the STNO the amplitude relaxation rate Γ{sub p} determines not only the bandwidth of an amplitude modulation, but also the bandwidth of a frequency modulation. The presented experimental technique will be important for the optimisation of the STNO characteristics for applications in telecommunications or/and data storage and is applicable even in the case when the STNO output signal is only several times higher than noise.« less

Electromagnetic behavior of spatial terahertz wave modulators based on reconfigurable micromirror gratings in Littrow configuration.

PubMed

Kappa, Jan; Schmitt, Klemens M; Rahm, Marco

2017-08-21

Efficient, high speed spatial modulators with predictable performance are a key element in any coded aperture terahertz imaging system. For spectroscopy, the modulators must also provide a broad modulation frequency range. In this study, we numerically analyze the electromagnetic behavior of a dynamically reconfigurable spatial terahertz wave modulator based on a micromirror grating in Littrow configuration. We show that such a modulator can modulate terahertz radiation over a wide frequency range from 1.7 THz to beyond 3 THz at a modulation depth of more than 0.6. As a specific example, we numerically simulated coded aperture imaging of an object with binary transmissive properties and successfully reconstructed the image.

Spin-dependent quantum transport in nanoscaled geometries

NASA Astrophysics Data System (ADS)

Heremans, Jean J.

2011-10-01

We discuss experiments where the spin degree of freedom leads to quantum interference phenomena in the solid-state. Under spin-orbit interactions (SOI), spin rotation modifies weak-localization to weak anti-localization (WAL). WAL's sensitivity to spin- and phase coherence leads to its use in determining the spin coherence lengths Ls in materials, of importance moreover in spintronics. Using WAL we measure the dependence of Ls on the wire width w in narrow nanolithographic ballistic InSb wires, ballistic InAs wires, and diffusive Bi wires with surface states with Rashba-like SOI. In all three systems we find that Ls increases with decreasing w. While theory predicts the increase for diffusive wires with linear (Rashba) SOI, we experimentally conclude that the increase in Ls under dimensional confinement may be more universal, with consequences for various applications. Further, in mesoscopic ring geometries on an InAs/AlGaSb 2D electron system (2DES) we observe both Aharonov-Bohm oscillations due to spatial quantum interference, and Altshuler-Aronov-Spivak oscillations due to time-reversed paths. A transport formalism describing quantum coherent networks including ballistic transport and SOI allows a comparison of spin- and phase coherence lengths extracted for such spatial- and temporal-loop quantum interference phenomena. We further applied WAL to study the magnetic interactions between a 2DES at the surface of InAs and local magnetic moments on the surface from rare earth (RE) ions (Gd3+, Ho3+, and Sm3+). The magnetic spin-flip rate carries information about magnetic interactions. Results indicate that the heavy RE ions increase the SOI scattering rate and the spin-flip rate, the latter indicating magnetic interactions. Moreover Ho3+ on InAs yields a spin-flip rate with an unusual power 1/2 temperature dependence, possibly characteristic of a Kondo system. We acknowledge funding from DOE (DE-FG02-08ER46532).

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy.

PubMed

Segawa, Takuya F; Doll, Andrin; Pribitzer, Stephan; Jeschke, Gunnar

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclear modulation spectrum.

Investigation of Abnormal Grain Growth in a Friction Stir Welded and Spin-Formed Al-Li Alloy 2195 Crew Module

NASA Technical Reports Server (NTRS)

Tayon, Wesley A.; Domack, Marcia S.; Hoffman, Eric K.; Hales, Stephen J.

2013-01-01

In order to improve manufacturing efficiency and reduce structural mass and costs in the production of launch vehicle structures, NASA is pursuing a wide-range of innovative, near-net shape manufacturing technologies. A technology that combines friction stir welding (FSW) and spin-forming has been applied to manufacture a single-piece crew module using Aluminum-Lithium (AL-Li) Alloy 2195. Plate size limitations for Al-Li alloy 2195 require that two plates be FSW together to produce a spin-forming blank of sufficient size to form the crew module. Subsequent forming of the FSW results in abnormal grain growth (AGG) within the weld region upon solution heat treatment (SHT), which detrimentally impacts strength, ductility, and fracture toughness. The current study seeks to identify microstructural factors that contribute to the development of AGG. Electron backscatter diffraction (EBSD) was used to correlate driving forces for AGG, such as stored energy, texture, and grain size distributions, with the propensity for AGG. Additionally, developmental annealing treatments prior to SHT are examined to reduce or eliminate the occurrence of AGG by promoting continuous, or uniform, grain growth

Enhanced modulation rates via field modulation in spin torque nano-oscillators

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

Purbawati, A.; Garcia-Sanchez, F.; Buda-Prejbeanu, L. D.

Spin Transfer Nano-Oscillators (STNOs) are promising candidates for telecommunications applications due to their frequency tuning capabilities via either a dc current or an applied field. This frequency tuning is of interest for Frequency Shift Keying concepts to be used in wireless communication schemes or in read head applications. For these technological applications, one important parameter is the characterization of the maximum achievable rate at which an STNO can respond to a modulating signal, such as current or field. Previous studies of in-plane magnetized STNOs on frequency modulation via an rf current revealed that the maximum achievable rate is limited bymore » the amplitude relaxation rate Γ{sub p}, which gives the time scale over which amplitude fluctuations are damped out. This might be a limitation for applications. Here, we demonstrate via numerical simulation that application of an additional rf field is an alternative way for modulation of the in-plane magnetized STNO configuration, which has the advantage that frequency modulation is not limited by the amplitude relaxation rate, so that higher modulation rates above GHz are achievable. This occurs when the modulating rf field is oriented along the easy axis (longitudinal rf field). Tilting the direction of the modulating rf field in-plane and perpendicularly with respect to the easy axis (transverse rf field), the modulation is again limited by the amplitude relaxation rate similar to the response observed in current modulation.« less

CIDME: Short distances measured with long chirp pulses.

PubMed

Doll, Andrin; Qi, Mian; Godt, Adelheid; Jeschke, Gunnar

2016-12-01

Frequency-swept pulses have recently been introduced as pump pulses into double electron-electron resonance (DEER) experiments. A limitation of this approach is that the pump pulses need to be short in comparison to dipolar evolution periods. The "chirp-induced dipolar modulation enhancement" (CIDME) pulse sequence introduced in this work circumvents this limitation by means of longitudinal storage during the application of one single or two consecutive pump pulses. The resulting six-pulse sequence is closely related to the five-pulse "relaxation-induced dipolar modulation enhancement" (RIDME) pulse sequence: While dipolar modulation in RIDME is due to stochastic spin flips during longitudinal storage, modulation in CIDME is due to the pump pulse during longitudinal storage. Experimentally, CIDME is examined for Gd-Gd and nitroxide-nitroxide distance determination using a high-power Q-band spectrometer. Since longitudinal storage results in a 50% signal loss, comparisons between DEER using short chirp pump pulses of 64ns duration and CIDME using longer pump pulses are in favor of DEER. While the lower sensitivity restrains the applicability of CIDME for routine distance determination on high-power spectrometers, this result is not to be generalized to spectrometers having lower power and to specialized "non-routine" applications or different types of spin labels. In particular, the advantage of prolonged CIDME pump pulses is demonstrated for experiments at large frequency offset between the pumped and observed spins. At a frequency separation of 1GHz, where broadening due to dipolar pseudo-secular contributions becomes largely suppressed, a Gd-Gd modulation depth larger than 10% is achieved. Moreover, a CIDME experiment at deliberately reduced power underlines the potential of the new technique for spectrometers with lower power, as often encountered at higher microwave frequencies. With longitudinal storage times T below 10μs, however, CIDME appears rather susceptible to artifacts. For nitroxide-nitroxide experiments, these currently inhibit a faithful data analysis. To facilitate further developments, the artifacts are characterized experimentally. In addition, effects that are specific to the high spin of S=7/2 Gd-centers are examined. Herein, population transfer within the observer spin's multiplet due to the pump pulse as well as excitation of dipolar harmonics are discussed. Copyright © 2016 Elsevier Inc. All rights reserved.

Universality of modulation length and time exponents.

PubMed

Chakrabarty, Saurish; Dobrosavljević, Vladimir; Seidel, Alexander; Nussinov, Zohar

2012-10-01

We study systems with a crossover parameter λ, such as the temperature T, which has a threshold value λ(*) across which the correlation function changes from exhibiting fixed wavelength (or time period) modulations to continuously varying modulation lengths (or times). We introduce a hitherto unknown exponent ν(L) characterizing the universal nature of this crossover and compute its value in general instances. This exponent, similar to standard correlation length exponents, is obtained from motion of the poles of the momentum (or frequency) space correlation functions in the complex k-plane (or ω-plane) as the parameter λ is varied. Near the crossover (i.e., for λ→λ(*)), the characteristic modulation wave vector K(R) in the variable modulation length "phase" is related to that in the fixed modulation length "phase" q via |K(R)-q|[proportionality]|T-T(*)|(νL). We find, in general, that ν(L)=1/2. In some special instances, ν(L) may attain other rational values. We extend this result to general problems in which the eigenvalue of an operator or a pole characterizing general response functions may attain a constant real (or imaginary) part beyond a particular threshold value λ(*). We discuss extensions of this result to multiple other arenas. These include the axial next-nearest-neighbor Ising (ANNNI) model. By extending our considerations, we comment on relations pertaining not only to the modulation lengths (or times), but also to the standard correlation lengths (or times). We introduce the notion of a Josephson time scale. We comment on the presence of aperiodic "chaotic" modulations in "soft-spin" and other systems. These relate to glass-type features. We discuss applications to Fermi systems, with particular application to metal to band insulator transitions, change of Fermi surface topology, divergent effective masses, Dirac systems, and topological insulators. Both regular periodic and glassy (and spatially chaotic behavior) may be found in strongly correlated electronic systems.

Zeeman perturbed nuclear quadrupole spin echo envelope modulations for spin 3/2 nuclei in polycrystalline specimens

NASA Astrophysics Data System (ADS)

Ramachandran, R.; Narasimhan, P. T.

The results of theoretical and experimental studies of Zeeman-perturbed nuclear quadrupole spin echo envelope modulations (ZSEEM) for spin 3/2 nuclei in polycrystalline specimens are presented. The response of the Zeeman-perturbed spin ensemble to resonant two pulse excitations has been calculated using the density matrix formalism. The theoretical calculation assumes a parallel orientation of the external r.f. and static Zeeman fields and an arbitrary orientation of these fields to the principal axes system of the electric field gradient. A numerical powder averaging procedure has been adopted to simulate the response of the polycrystalline specimens. Using a coherent pulsed nuclear quadrupole resonance spectrometer the ZSEEM patterns of the 35Cl nuclei have been recorded in polycrystalline specimens of potassium chlorate, barium chlorate, mercuric chloride (two sites) and antimony trichloride (two sites) using the π/2-τ-π/2 sequence. The theoretical and experimental ZSEEM patterns have been compared. In the case of mercuric chloride, the experimental 35Cl ZSEEM patterns are found to be nearly identical for the two sites and correspond to a near-zero value of the asymmetry parameter, η, of the electric field gradient tensor. The difference in the η values for the two 35Cl sites (η ˜0·06 and η˜0·16) in antimony trichloride is clearly reflected in the experimental and theoretical ZSEEM patterns. The present study indicates the feasibility of evaluating η for spin 3/2 nuclei in polycrystalline specimens from ZSEEM investigations.

Negativity as the entanglement measure to probe the Kondo regime in the spin-chain Kondo model

NASA Astrophysics Data System (ADS)

Bayat, Abolfazl; Sodano, Pasquale; Bose, Sougato

2010-02-01

We study the entanglement of an impurity at one end of a spin chain with a block of spins using negativity as a true measure of entanglement to characterize the unique features of the gapless Kondo regime in the spin-chain Kondo model. For this spin chain in the Kondo regime we determine—with a true entanglement measure—the spatial extent of the Kondo screening cloud, we propose an ansatz for its ground state and demonstrate that the impurity spin is indeed maximally entangled with the cloud. To better evidence the peculiarities of the Kondo regime, we carry a parallel analysis of the entanglement properties of the Kondo spin-chain model in the gapped dimerized regime. Our study shows how a genuine entanglement measure stemming from quantum information theory can fully characterize also nonperturbative regimes accessible to certain condensed matter systems.

Systematic study of the spin stiffness dependence on phosphorus alloying in the ferromagnetic semiconductor (Ga,Mn)As

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

Shihab, S.; Thevenard, L.; Bardeleben, H. J. von

2015-04-06

We study the dependence of the spin stiffness constant on the phosphorus concentration in the ferromagnetic semiconductor (Ga,Mn)(As,P) with the aim of determining whether alloying with phosphorus is detrimental, neutral, or advantageous to the spin stiffness. Time-resolved magneto-optical experiments are carried out in thin epilayers. Laser pulses excite two perpendicular standing spin wave modes, which are exchange related. We show that the first mode is spatially uniform across the layer corresponding to a k≈0 wavevector. From the two frequencies and k-vector spacings we obtain the spin stiffness constant for different phosphorus concentrations using weak surface pinning conditions. The mode assessmentmore » is checked by comparison to the spin stiffness obtained from domain pattern analysis for samples with out-of-plane magnetization. The spin stiffness is found to exhibit little variation with phosphorus concentration in contradiction with ab-initio predictions.« less

Designing magnetic droplet soliton nucleation employing spin polarizer

NASA Astrophysics Data System (ADS)

Mohseni, Morteza; Mohseni, Majid

2018-04-01

We show by means of micromagnetic simulations that spin polarizer in nano-contact (NC) spin torque oscillators as the representative of the fixed layer in an orthogonal pseudo-spin valve can be employed to design and to control magnetic droplet soliton nucleation and dynamics. We found that using a tilted spin polarizer layer decreases the droplet nucleation time which is more suitable for high speed applications. However, a tilted spin polarizer increases the nucleation current and decreases the frequency stability of the droplet. Additionally, by driving the magnetization inhomogenously at the NC region, it is found that a tilted spin polarizer reduces the precession angle of the droplet and through an interplay with the Oersted field of the DC current, it breaks the spatial symmetry of the droplet profile. Our findings explore fundamental insight into nano-scale magnetic droplet soliton dynamics with potential tunability parameters for future microwave electronics.

Spin diffusion from an inhomogeneous quench in an integrable system.

PubMed

Ljubotina, Marko; Žnidarič, Marko; Prosen, Tomaž

2017-07-13

Generalized hydrodynamics predicts universal ballistic transport in integrable lattice systems when prepared in generic inhomogeneous initial states. However, the ballistic contribution to transport can vanish in systems with additional discrete symmetries. Here we perform large scale numerical simulations of spin dynamics in the anisotropic Heisenberg XXZ spin 1/2 chain starting from an inhomogeneous mixed initial state which is symmetric with respect to a combination of spin reversal and spatial reflection. In the isotropic and easy-axis regimes we find non-ballistic spin transport which we analyse in detail in terms of scaling exponents of the transported magnetization and scaling profiles of the spin density. While in the easy-axis regime we find accurate evidence of normal diffusion, the spin transport in the isotropic case is clearly super-diffusive, with the scaling exponent very close to 2/3, but with universal scaling dynamics which obeys the diffusion equation in nonlinearly scaled time.

Using neuronal populations to study the mechanisms underlying spatial and feature attention

PubMed Central

Cohen, Marlene R.; Maunsell, John H.R.

2012-01-01

Summary Visual attention affects both perception and neuronal responses. Whether the same neuronal mechanisms mediate spatial attention, which improves perception of attended locations, and non-spatial forms of attention has been a subject of considerable debate. Spatial and feature attention have similar effects on individual neurons. Because visual cortex is retinotopically organized, however, spatial attention can co-modulate local neuronal populations, while feature attention generally requires more selective modulation. We compared the effects of feature and spatial attention on local and spatially separated populations by recording simultaneously from dozens of neurons in both hemispheres of V4. Feature and spatial attention affect the activity of local populations similarly, modulating both firing rates and correlations between pairs of nearby neurons. However, while spatial attention appears to act on local populations, feature attention is coordinated across hemispheres. Our results are consistent with a unified attentional mechanism that can modulate the responses of arbitrary subgroups of neurons. PMID:21689604

Spatially and time-resolved magnetization dynamics driven by spin-orbit torques

NASA Astrophysics Data System (ADS)

Baumgartner, Manuel; Garello, Kevin; Mendil, Johannes; Avci, Can Onur; Grimaldi, Eva; Murer, Christoph; Feng, Junxiao; Gabureac, Mihai; Stamm, Christian; Acremann, Yves; Finizio, Simone; Wintz, Sebastian; Raabe, Jörg; Gambardella, Pietro

2017-10-01

Current-induced spin-orbit torques are one of the most effective ways to manipulate the magnetization in spintronic devices, and hold promise for fast switching applications in non-volatile memory and logic units. Here, we report the direct observation of spin-orbit-torque-driven magnetization dynamics in Pt/Co/AlOx dots during current pulse injection. Time-resolved X-ray images with 25 nm spatial and 100 ps temporal resolution reveal that switching is achieved within the duration of a subnanosecond current pulse by the fast nucleation of an inverted domain at the edge of the dot and propagation of a tilted domain wall across the dot. The nucleation point is deterministic and alternates between the four dot quadrants depending on the sign of the magnetization, current and external field. Our measurements reveal how the magnetic symmetry is broken by the concerted action of the damping-like and field-like spin-orbit torques and the Dzyaloshinskii-Moriya interaction, and show that reproducible switching events can be obtained for over 1012 reversal cycles.

Spin filtering in a double quantum dot device: Numerical renormalization group study of the internal structure of the Kondo state

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

Vernek, E.; Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos-SP 13560-970; Büsser, C. A.

2014-03-31

A double quantum dot device, connected to two channels that only interact through interdot Coulomb repulsion, is analyzed using the numerical renormalization group technique. Using a two-impurity Anderson model, and realistic parameter values [S. Amasha, A. J. Keller, I. G. Rau, A. Carmi, J. A. Katine, H. Shtrikman, Y. Oreg, and D. Goldhaber-Gordon, Phys. Rev. Lett. 110, 046604 (2013)], it is shown that, by applying a moderate magnetic field and independently adjusting the gate potential of each quantum dot at half-filling, a spin-orbital SU(2) Kondo state can be achieved where the Kondo resonance originates from spatially separated parts of themore » device. Our results clearly link this spatial separation effect to currents with opposing spin polarizations in each channel, i.e., the device acts as a spin filter. In addition, an experimental probe of this polarization effect is suggested, pointing to the exciting possibility of experimentally probing the internal structure of an SU(2) Kondo state.« less

Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels

PubMed Central

Tan, Chao; Wu, Xinghua; Wang, Qinkai; Tang, Pinghua; Shi, Xiaohui; Zhan, Shiping; Xi, Zaifang; Fu, Xiquan

2017-01-01

The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration. PMID:28772712

ESR lineshape and {sup 1}H spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals – Joint analysis

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

Kruk, D., E-mail: danuta.kruk@matman.uwm.edu.pl; Hoffmann, S. K.; Goslar, J.

2013-12-28

Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d{sub 16} containing {sup 15}N and {sup 14}N isotopes. The NMRD experiments refer to {sup 1}H spin-lattice relaxation measurements in a broad frequency range (10 kHz–20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recentlymore » presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the {sup 1}H relaxation of the solvent. The {sup 1}H relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin–nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.« less

All-optical quantum fluid spin beam splitter

NASA Astrophysics Data System (ADS)

Askitopoulos, A.; Nalitov, A. V.; Sedov, E. S.; Pickup, L.; Cherotchenko, E. D.; Hatzopoulos, Z.; Savvidis, P. G.; Kavokin, A. V.; Lagoudakis, P. G.

2018-06-01

We investigate the spin behavior of the first excited state of a polariton condensate in an optical trap by means of polarization resolved spectroscopy. The interplay between the repulsive polariton interactions and the gain saturation results in a nontrivial spontaneous switching between the two quasidegenerate spatial modes of the polariton condensate. As a result, the polarization pattern of the emitted light dramatically changes. Successful harnessing of this effect can lead to a spin-demultiplexing device for polariton-based optical integrated circuits.

Distinction of nuclear spin states with the scanning tunneling microscope.

PubMed

Natterer, Fabian Donat; Patthey, François; Brune, Harald

2013-10-25

We demonstrate rotational excitation spectroscopy with the scanning tunneling microscope for physisorbed H(2) and its isotopes HD and D(2). The observed excitation energies are very close to the gas phase values and show the expected scaling with the moment of inertia. Since these energies are characteristic for the molecular nuclear spin states we are able to identify the para and ortho species of hydrogen and deuterium, respectively. We thereby demonstrate nuclear spin sensitivity with unprecedented spatial resolution.

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.

Half-metallic superconducting triplet spin multivalves

NASA Astrophysics Data System (ADS)

Alidoust, Mohammad; Halterman, Klaus

2018-02-01

We study spin switching effects in finite-size superconducting multivalve structures. We examine F1F2SF3 and F1F2SF3F4 hybrids where a singlet superconductor (S) layer is sandwiched among ferromagnet (F) layers with differing thicknesses and magnetization orientations. Our results reveal a considerable number of experimentally viable spin-valve configurations that lead to on-off switching of the superconducting state. For S widths on the order of the superconducting coherence length ξ0, noncollinear magnetization orientations in adjacent F layers with multiple spin axes leads to a rich variety of triplet spin-valve effects. Motivated by recent experiments, we focus on samples where the magnetizations in the F1 and F4 layers exist in a fully spin-polarized half-metallic phase, and calculate the superconducting transition temperature, spatially and energy resolved density of states, and the spin-singlet and spin-triplet superconducting correlations. Our findings demonstrate that superconductivity in these devices can be completely switched on or off over a wide range of magnetization misalignment angles due to the generation of equal-spin and opposite-spin triplet pairings.

Reduced field-of-view imaging for single-shot MRI with an amplitude-modulated chirp pulse excitation and Fourier transform reconstruction.

PubMed

Li, Jing; Zhang, Miao; Chen, Lin; Cai, Congbo; Sun, Huijun; Cai, Shuhui

2015-06-01

We employ an amplitude-modulated chirp pulse to selectively excite spins in one or more regions of interest (ROIs) to realize reduced field-of-view (rFOV) imaging based on single-shot spatiotemporally encoded (SPEN) sequence and Fourier transform reconstruction. The proposed rFOV imaging method was theoretically analyzed and illustrated with numerical simulation and tested with phantom experiments and in vivo rat experiments. In addition, point spread function was applied to demonstrate the feasibility of the proposed method. To evaluate the proposed method, the rFOV results were compared with those obtained using the EPI method with orthogonal RF excitation. The simulation and experimental results show that the proposed method can image one or two separated ROIs along the SPEN dimension in a single shot with higher spatial resolution, less sensitive to field inhomogeneity, and practically no aliasing artifacts. In addition, the proposed method may produce rFOV images with comparable signal-to-noise ratio to the rFOV EPI images. The proposed method is promising for the applications under severe susceptibility heterogeneities and for imaging separate ROIs simultaneously. Copyright © 2015 Elsevier Inc. All rights reserved.

Electrochemical capacitance modulation in an interacting mesoscopic capacitor induced by internal charge transfer

NASA Astrophysics Data System (ADS)

Liu, Wei; He, Jianhong; Guo, Huazhong; Gao, Jie

2018-04-01

We report experiments on the dynamic response of an interacting mesoscopic capacitor consisting of a quantum dot with two confined spin-split levels of the lowest Landau level. In high magnetic fields, states inside the dot are regulated by a mixture of Coulomb interaction and Landau-level quantization, and electrons distribute on two spatially separated regions. Quantum point contact voltage and magnetic field are employed to manipulate the number and distribution of electrons inside the quantum dot. We find that the periodicity of the electrochemical capacitance oscillations is dominated by the charging energy, and their amplitudes, due to internal charge transfer and strong internal capacitive coupling, show rich variations of modulations. Magnetocapacitance displays a sawtoothlike manner and may differ in tooth directions for different voltages, which, we demonstrate, result from a sawtoothlike electrochemical potential change induced by internal charge transfer and field-sensitive electrostatic potential. We further build a charge stability diagram, which, together with all other capacitance properties, is consistently interpreted in terms of a double-dot model. The demonstrated technique is of interest as a tool for fast and sensitive charge state readout of a double-quantum-dot qubit in the gigahertz frequency quantum electronics.

Thermally induced spin-dependent current based on Zigzag Germanene Nanoribbons

NASA Astrophysics Data System (ADS)

Majidi, Danial; Faez, Rahim

2017-02-01

In this paper, using first principle calculation and non-equilibrium Green's function, the thermally induced spin current in Hydrogen terminated Zigzag-edge Germanene Nanoribbon (ZGeNR-H) is investigated. In this model, because of the difference between the source and the drain temperature of ZGeNR device, the spin up and spin down currents flow in the opposite direction with two different threshold temperatures (Tth). Hence, a pure spin polarized current which belongs to spin down is obtained. It is shown that, for temperatures above the threshold temperature spin down current increases with the increasing temperature up to 75 K and then decreases. But spin up current rises steadily and in the high temperature we can obtain polarized spin up current. In addition, we show an acceptable spin current around the room temperature for ZGeNR. The transmission peaks in ZGeNR which are closer to the Fermi level rather than Zigzag Graphene Nanoribbon (ZGNRS) which causes ZGeNR to have spin current at higher temperatures. Finally, it is indicated that by tuning the back gate voltage, the spin current can be completely modulated and polarized. Simulation results verify the Zigzag Germanene Nanoribbon as a promising candidate for spin caloritronics devices, which can be applied in future low power consumption technology.

Reexamination of Spin Transport Through a DOUBLE-δ Magnetic Barrier with Spin-Orbit Interactions

NASA Astrophysics Data System (ADS)

Bi, Caihua; Zhai, Feng

We revisit the properties of spin transport through a semiconductor 2DEG system subjected to the modulation of both a ferromagnetic metal (FM) stripe on top and the Rashba and Dresselhaus spin-orbit interactions (SOIs). The FM stripe has a magnetization along the transporting direction and generates an inhomogeneous magnetic field in the 2DEG plane which is taken as a double-δ shape. It is found that the spin polarization of this system generated from a spin-unpolarized injection can be remarkable only within a low Fermi energy region and is not more than 30% for the parameters available in current experiments. In this energy region, both the magnitude and the orientation of the spin polarization can be tuned by the Rashba strength, the Dresselhaus strength, and the magnetic field strength. The magnetization reversal of the FM stripe cannot result in a change of the conductance, but can rotate the orientation of the spin polarization. The results are in contrast to those in [ J. Phys.: Condens. Matter 15 (2003) L31] where a pure spin state for incident electrons is artificially assumed.

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

Self-sustaining dynamical nuclear polarization oscillations in quantum dots.

PubMed

Rudner, M S; Levitov, L S

2013-02-22

Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports self-sustained oscillations. Our mechanism relies on a nuclear spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods.

Large Spin-Wave Bullet in a Ferrimagnetic Insulator Driven by the Spin Hall Effect

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

Jungfleisch, M. B.; Zhang, W.; Sklenar, J.

2016-02-01

Due to its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y 3Fe 5O 12 based on the excitation and detection by SHEs. The driven spin dynamics in Y 3Fe 5O 12 is directly imaged by spatially-resolved microfocused Brillouin light scattering (BLS) spectroscopy.more » Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. A strong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave `bullet'.« less

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.

Thermoelectric efficiency enhanced in a quantum dot with polarization leads, spin-flip and external magnetic field

NASA Astrophysics Data System (ADS)

Yao, Hui; Niu, Peng-Bin; Zhang, Chao; Xu, Wei-Ping; Li, Zhi-Jian; Nie, Yi-Hang

2018-03-01

We theoretically study the thermoelectric transport properties in a quantum dot system with two ferromagnetic leads, the spin-flip scattering and the external magnetic field. The results show that the spin polarization of the leads strongly influences thermoelectric coefficients of the device. For the parallel configuration the peak of figure of merit increases with the increase of polarization strength and non-collinear configuration trends to destroy the improvement of figure of merit induced by lead polarization. While the modulation of the spin-flip scattering on the figure of merit is effective only in the absence of external magnetic field or small magnetic field. In terms of improving the thermoelectric efficiency, the external magnetic field plays a more important role than spin-flip scattering. The thermoelectric efficiency can be significantly enhanced by the magnetic field for a given spin-flip scattering strength.

Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

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

Mitamura, H.; Watanuki, R.; Kaneko, Koji

Magnetic field (B) variation of the electrical polarization P c ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO 4) 2 is examined up to the saturation point of the magnetization for B⊥c. P c is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P c at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation ofmore » which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less

Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

DOE PAGES

Mitamura, H.; Watanuki, R.; Kaneko, Koji; ...

2014-10-01

Magnetic field (B) variation of the electrical polarization P c ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO 4) 2 is examined up to the saturation point of the magnetization for B⊥c. P c is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P c at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation ofmore » which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less

Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

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

Matsuyama, H., E-mail: matsu@phys.sci.hokudai.ac.jp; Nara, D.; Kageyama, R.

We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM) in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin imagemore » of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.« less

Exchange-mediated spin-lattice relaxation of Fe3+ ions in borate glasses.

PubMed

Misra, Sushil K; Pilbrow, John R

2007-03-01

Spin-lattice relaxation times (T1) of two borate glasses doped with different concentrations of Fe2O3 were measured using the Electron Spin-Echo (ESE) technique at X-band (9.630 GHz) in the temperature range 2-6K. In comparison with a previous investigation of Fe3+-doped silicate glasses, the relaxation rates were comparable and differed by no more than a factor of two. The data presented here extend those previously reported for borate glasses in the 10-250K range but measured using the amplitude-modulation technique. The T1 values were found to depend on temperature (T) as T(n) with n approximately 1 for the 1% and 0.1% Fe2O3-doped glass samples. These results are consistent with spin-lattice relaxation as effected by exchange interaction of a Fe3+ spin exchange-coupled to another Fe3+ spin in an amorphous material.

Burst Oscillations: Watching Neutron Stars Spin

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2010-01-01

It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

Spacer type mediated tunable spin crossover (SCO) characteristics of pyrene decorated 2,6-bis(pyrazol-1-yl)pyridine (bpp) based Fe(ii) molecular spintronic modules.

PubMed

Kumar, Kuppusamy Senthil; Šalitroš, Ivan; Moreno-Pineda, Eufemio; Ruben, Mario

2017-08-14

A simple "isomer-like" variation of the spacer group in a set of Fe(ii) spin crossover (SCO) complexes designed to probe spin state dependence of electrical conductivity in graphene-based molecular spintronic junctions led to the observation of remarkable variations in the thermal- and light-induced magnetic characteristics, paving a simple route for the design of functional SCO complexes with different temperature switching regimes based on a 2,6-bis(pyrazol-1-yl)pyridine ligand skeleton.

Optimal strategy for polarization modulation in the LSPE-SWIPE experiment

NASA Astrophysics Data System (ADS)

Buzzelli, A.; de Bernardis, P.; Masi, S.; Vittorio, N.; de Gasperis, G.

2018-01-01

Context. Cosmic microwave background (CMB) B-mode experiments are required to control systematic effects with an unprecedented level of accuracy. Polarization modulation by a half wave plate (HWP) is a powerful technique able to mitigate a large number of the instrumental systematics. Aims: Our goal is to optimize the polarization modulation strategy of the upcoming LSPE-SWIPE balloon-borne experiment, devoted to the accurate measurement of CMB polarization at large angular scales. Methods: We departed from the nominal LSPE-SWIPE modulation strategy (HWP stepped every 60 s with a telescope scanning at around 12 deg/s) and performed a thorough investigation of a wide range of possible HWP schemes (either in stepped or continuously spinning mode and at different azimuth telescope scan-speeds) in the frequency, map and angular power spectrum domain. In addition, we probed the effect of high-pass and band-pass filters of the data stream and explored the HWP response in the minimal case of one detector for one operation day (critical for the single-detector calibration process). We finally tested the modulation performance against typical HWP-induced systematics. Results: Our analysis shows that some stepped HWP schemes, either slowly rotating or combined with slow telescope modulations, represent poor choices. Moreover, our results point out that the nominal configuration may not be the most convenient choice. While a large class of spinning designs provides comparable results in terms of pixel angle coverage, map-making residuals and BB power spectrum standard deviations with respect to the nominal strategy, we find that some specific configurations (e.g., a rapidly spinning HWP with a slow gondola modulation) allow a more efficient polarization recovery in more general real-case situations. Conclusions: Although our simulations are specific to the LSPE-SWIPE mission, the general outcomes of our analysis can be easily generalized to other CMB polarization experiments.

Padalka spins a box of chocolates as Kaleri looks on in the SM during EXP 9 / EXP 8

NASA Image and Video Library

2004-04-22

ISS008-E-22002 (22 April 2004) --- Cosmonaut Gennady I. Padalka, Expedition 9 commander, spins a box of chocolates as cosmonaut Alexander Y. Kaleri, Expedition 8 flight engineer, looks on in the Zvezda Service Module on the International Space Station (ISS). Padalka and Kaleri represent Russia’s Federal Space Agency.

Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves

PubMed Central

Giordano, A.; Verba, R.; Zivieri, R.; Laudani, A.; Puliafito, V.; Gubbiotti, G.; Tomasello, R.; Siracusano, G.; Azzerboni, B.; Carpentieri, M.; Slavin, A.; Finocchio, G.

2016-01-01

Spin-Hall oscillators (SHO) are promising sources of spin-wave signals for magnonics applications, and can serve as building blocks for magnonic logic in ultralow power computation devices. Thin magnetic layers used as “free” layers in SHO are in contact with heavy metals having large spin-orbital interaction, and, therefore, could be subject to the spin-Hall effect (SHE) and the interfacial Dzyaloshinskii-Moriya interaction (i-DMI), which may lead to the nonreciprocity of the excited spin waves and other unusual effects. Here, we analytically and micromagnetically study magnetization dynamics excited in an SHO with oblique magnetization when the SHE and i-DMI act simultaneously. Our key results are: (i) excitation of nonreciprocal spin-waves propagating perpendicularly to the in-plane projection of the static magnetization; (ii) skyrmions generation by pure spin-current; (iii) excitation of a new spin-wave mode with a spiral spatial profile originating from a gyrotropic rotation of a dynamical skyrmion. These results demonstrate that SHOs can be used as generators of magnetic skyrmions and different types of propagating spin-waves for magnetic data storage and signal processing applications. PMID:27786261

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

Electrical detection of spin transport in Si two-dimensional electron gas systems

NASA Astrophysics Data System (ADS)

Chang, Li-Te; Fischer, Inga Anita; Tang, Jianshi; Wang, Chiu-Yen; Yu, Guoqiang; Fan, Yabin; Murata, Koichi; Nie, Tianxiao; Oehme, Michael; Schulze, Jörg; Wang, Kang L.

2016-09-01

Spin transport in a semiconductor-based two-dimensional electron gas (2DEG) system has been attractive in spintronics for more than ten years. The inherent advantages of high-mobility channel and enhanced spin-orbital interaction promise a long spin diffusion length and efficient spin manipulation, which are essential for the application of spintronics devices. However, the difficulty of making high-quality ferromagnetic (FM) contacts to the buried 2DEG channel in the heterostructure systems limits the potential developments in functional devices. In this paper, we experimentally demonstrate electrical detection of spin transport in a high-mobility 2DEG system using FM Mn-germanosilicide (Mn(Si0.7Ge0.3)x) end contacts, which is the first report of spin injection and detection in a 2DEG confined in a Si/SiGe modulation doped quantum well structure (MODQW). The extracted spin diffusion length and lifetime are l sf = 4.5 μm and {τ }{{s}}=16 {{ns}} at 1.9 K respectively. Our results provide a promising approach for spin injection into 2DEG system in the Si-based MODQW, which may lead to innovative spintronic applications such as spin-based transistor, logic, and memory devices.

Chaotic behavior of a spin-glass model on a Cayley tree

NASA Astrophysics Data System (ADS)

da Costa, F. A.; de Araújo, J. M.; Salinas, S. R.

2015-06-01

We investigate the phase diagram of a spin-1 Ising spin-glass model on a Cayley tree. According to early work of Thompson and collaborators, this problem can be formulated in terms of a set of nonlinear discrete recursion relations along the branches of the tree. Physically relevant solutions correspond to the attractors of these mapping equations. In the limit of infinite coordination of the tree, and for some choices of the model parameters, we make contact with findings for the phase diagram of more recently investigated versions of the Blume-Emery-Griffiths spin-glass model. In addition to the anticipated phases, we numerically characterize the existence of modulated and chaotic structures.

Magnetic-field-modulated resonant tunneling in ferromagnetic-insulator-nonmagnetic junctions.

PubMed

Song, Yang; Dery, Hanan

2014-07-25

We present a theory for resonance-tunneling magnetoresistance (MR) in ferromagnetic-insulator-nonmagnetic junctions. The theory sheds light on many of the recent electrical spin injection experiments, suggesting that this MR effect rather than spin accumulation in the nonmagnetic channel corresponds to the electrically detected signal. We quantify the dependence of the tunnel current on the magnetic field by quantum rate equations derived from the Anderson impurity model, with the important addition of impurity spin interactions. Considering the on-site Coulomb correlation, the MR effect is caused by competition between the field, spin interactions, and coupling to the magnetic lead. By extending the theory, we present a basis for operation of novel nanometer-size memories.

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.

Four-state non-volatile memory in a multiferroic spin filter tunnel junction

NASA Astrophysics Data System (ADS)

Ruan, Jieji; Li, Chen; Yuan, Zhoushen; Wang, Peng; Li, Aidong; Wu, Di

2016-12-01

We report a spin filter type multiferroic tunnel junction with a ferromagnetic/ferroelectric bilayer barrier. Memory functions of a spin filter magnetic tunnel junction and a ferroelectric tunnel junction are combined in this single device, producing four non-volatile resistive states that can be read out in a non-destructive manner. This concept is demonstrated in a LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 all-oxide tunnel junction. The ferromagnetic insulator Pr0.8Ca0.2MnO3 serves as the spin filter and the ferromagnetic metal La0.7Sr0.3MnO3 is the spin analyzer. The ferroelectric polarization reversal in the BaTiO3 barrier switches the tunneling barrier height to produce a tunneling electroresistance. The ferroelectric switching also modulates the spin polarization and the spin filtering efficiency in Pr0.8Ca0.2MnO3.

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.

Degeneracy of vector-channel spatial correlators in high temperature QCD

NASA Astrophysics Data System (ADS)

Rohrhofer, Christian; Aoki, Yasumichi; Cossu, Guido; Fukaya, Hidenori; Glozman, Leonid; Hashimoto, Shoji; Lang, Christian B.; Prelovsek, Sasa

2018-03-01

We study spatial isovector meson correlators in Nf = 2 QCD with dynamical domain-wall fermions on 323 × 8 lattices at temperatures up to 380 MeV with various quark masses. We measure the correlators of spin-one isovector operators including vector, axial-vector, tensor and axial-tensor. At temperatures above Tc we observe an approximate degeneracy of the correlators in these channels, which is unexpected because some of them are not related under SU(2)L×SU(2)R nor U(1)A symmetries. The observed approximate degeneracy suggests emergent SU(2)CS (chiral-spin) and SU(4) symmetries at high T.

A Highly Sensitive Biocompatible Spin Probe for Imaging of Oxygen Concentration in Tissues

PubMed Central

Bratasz, Anna; Kulkarni, Aditi C.; Kuppusamy, Periannan

2007-01-01

The development of an injectable probe formulation, consisting of perchlorotriphenylmethyl triester radical dissolved in hexafluorobenzene, for in vivo oximetry and imaging of oxygen concentration in tissues using electron paramagnetic resonance (EPR) imaging is reported. The probe was evaluated for its oxygen sensitivity, biostability, and distribution in a radiation-induced fibrosarcoma tumor transplanted into C3H mice. Some of the favorable features of the probe are: a single narrow EPR peak (anoxic linewidth, 41 μT), high solubility in hexafluorobenzene (>12 mM), large linewidth sensitivity to molecular oxygen (∼1.8 μT/mmHg), good stability in tumor tissue (half-life: 3.3 h), absence of spin-spin broadening (up to 12 mM), and lack of power saturation effects (up to 200 mW). Three-dimensional spatial and spectral-spatial (spectroscopic) EPR imaging measurements were used to visualize the distribution of the probe, as well as to obtain spatially resolved pO2 information in the mice tumor subjected to normoxic and hyperoxic treatments. The new probe should enable unique opportunities for measurement of the oxygen concentration in tumors using EPR methods. PMID:17259268

Micromagnetic modal analysis of spin-transfer-driven ferromagnetic resonance of individual nanomagnets

NASA Astrophysics Data System (ADS)

Torres, L.; Finocchio, G.; Lopez-Diaz, L.; Martinez, E.; Carpentieri, M.; Consolo, G.; Azzerboni, B.

2007-05-01

In a recent investigation Sankey et al. [Phys. Rev. Lett. 96, 227601 (2006)] demonstrated a technique for measuring spin-transfer-driven ferromagnetic resonance in individual ellipsoidal PyCu nanomagnets as small as 30×90×5.5nm3. In the present work, these experiments are analyzed by means of full micromagnetic modeling finding quantitative agreement and enlightening the spatial distribution of the normal modes found in the experiment. The magnetic parameter set used in the computations is obtained by fitting static magnetoresistance measurements. The temperature effect is also included together with all the nonuniform contributions to the effective field as the magnetostatic coupling and the Ampere field. The polarization function of Slonczewski [J. Magn. Magn. Mater. 159, L1 (1996)] is used including its spatial and angular dependences. Experimental spin-transfer-driven ferromagnetic resonance spectra are reproduced using the same currents as in the experiment. The use of full micromagnetic modeling allows us to further investigate the spatial dependence of the modes. The dependence of the normal mode frequency on the dc and the external field together with a comparison to the normal modes induced by a microwave current is also addressed.

Tuning the electrical and optical anisotropy of a monolayer black phosphorus magnetic superlattice

NASA Astrophysics Data System (ADS)

Li, X. J.; Yu, J. H.; Luo, K.; Wu, Z. H.; Yang, W.

2018-04-01

We investigate theoretically the effects of modulated periodic perpendicular magnetic fields on the electronic states and optical absorption spectrum in monolayer black phosphorus (phosphorene). We demonstrate that different phosphorene magnetic superlattice (PMS) orientations can give rise to distinct energy spectra, i.e. tuning the intrinsic electronic anisotropy. Rashba spin-orbit coupling (RSOC) develops a spin-splitting energy dispersion in this phosphorene magnetic superlattice. Anisotropic momentum-dependent carrier distributions along/perpendicular to the magnetic strips are demonstrated. The manipulations of these exotic electronic properties by tuning superlattice geometry, magnetic field and the RSOC term are addressed systematically. Accordingly, we find bright-to-dark transitions in the ground-state electron-hole pair transition rate spectrum and the PMS orientation-dependent anisotropic optical absorption spectrum. This feature offers us a practical way of modulating the electronic anisotropy in phosphorene by magnetic superlattice configurations and detecting this modulation capability by using an optical technique.

Improved heteronuclear dipolar decoupling sequences for liquid-crystal NMR

NASA Astrophysics Data System (ADS)

Thakur, Rajendra Singh; Kurur, Narayanan D.; Madhu, P. K.

2007-04-01

Recently we introduced a radiofrequency pulse scheme for heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance under magic-angle spinning [R.S. Thakur, N.D. Kurur, P.K. Madhu, Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR, Chem. Phys. Lett. 426 (2006) 459-463]. Variants of this sequence, swept-frequency TPPM, employing frequency modulation of different types have been further tested to improve the efficiency of heteronuclear dipolar decoupling. Among these, certain sequences that were found to perform well at lower spinning speeds are demonstrated here on a liquid-crystal sample of MBBA for application in static samples. The new sequences are compared with the standard TPPM and SPINAL schemes and are shown to perform better than them. These modulated schemes perform well at low decoupler radiofrequency power levels and are easy to implement on standard spectrometers.

Spatial entanglement patterns and Einstein-Podolsky-Rosen steering in Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Fadel, Matteo; Zibold, Tilman; Décamps, Boris; Treutlein, Philipp

2018-04-01

Many-particle entanglement is a fundamental concept of quantum physics that still presents conceptual challenges. Although nonclassical states of atomic ensembles were used to enhance measurement precision in quantum metrology, the notion of entanglement in these systems was debated because the correlations among the indistinguishable atoms were witnessed by collective measurements only. Here, we use high-resolution imaging to directly measure the spin correlations between spatially separated parts of a spin-squeezed Bose-Einstein condensate. We observe entanglement that is strong enough for Einstein-Podolsky-Rosen steering: We can predict measurement outcomes for noncommuting observables in one spatial region on the basis of corresponding measurements in another region with an inferred uncertainty product below the Heisenberg uncertainty bound. This method could be exploited for entanglement-enhanced imaging of electromagnetic field distributions and quantum information tasks.

Spatial Lattice Modulation for MIMO Systems

NASA Astrophysics Data System (ADS)

Choi, Jiwook; Nam, Yunseo; Lee, Namyoon

2018-06-01

This paper proposes spatial lattice modulation (SLM), a spatial modulation method for multipleinput-multiple-output (MIMO) systems. The key idea of SLM is to jointly exploit spatial, in-phase, and quadrature dimensions to modulate information bits into a multi-dimensional signal set that consists oflattice points. One major finding is that SLM achieves a higher spectral efficiency than the existing spatial modulation and spatial multiplexing methods for the MIMO channel under the constraint ofM-ary pulseamplitude-modulation (PAM) input signaling per dimension. In particular, it is shown that when the SLM signal set is constructed by using dense lattices, a significant signal-to-noise-ratio (SNR) gain, i.e., a nominal coding gain, is attainable compared to the existing methods. In addition, closed-form expressions for both the average mutual information and average symbol-vector-error-probability (ASVEP) of generic SLM are derived under Rayleigh-fading environments. To reduce detection complexity, a low-complexity detection method for SLM, which is referred to as lattice sphere decoding, is developed by exploiting lattice theory. Simulation results verify the accuracy of the conducted analysis and demonstrate that the proposed SLM techniques achieve higher average mutual information and lower ASVEP than do existing methods.

EPR and Ferromagnetism in Diluted Magnetic Semiconductor Quantum Wells

NASA Astrophysics Data System (ADS)

König, Jürgen; MacDonald, Allan H.

2003-08-01

Motivated by recent measurements of electron paramagnetic resonance spectra in modulation-doped CdMnTe quantum wells [

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy

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

Segawa, Takuya F.; Doll, Andrin; Pribitzer, Stephan

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclearmore » modulation spectrum.« less

Universal holonomic single quantum gates over a geometric spin with phase-modulated polarized light.

PubMed

Ishida, Naoki; Nakamura, Takaaki; Tanaka, Touta; Mishima, Shota; Kano, Hiroki; Kuroiwa, Ryota; Sekiguchi, Yuhei; Kosaka, Hideo

2018-05-15

We demonstrate universal non-adiabatic non-abelian holonomic single quantum gates over a geometric electron spin with phase-modulated polarized light and 93% average fidelity. This allows purely geometric rotation around an arbitrary axis by any angle defined by light polarization and phase using a degenerate three-level Λ-type system in a negatively charged nitrogen-vacancy center in diamond. Since the control light is completely resonant to the ancillary excited state, the demonstrated holonomic gate not only is fast with low power, but also is precise without the dynamical phase being subject to control error and environmental noise. It thus allows pulse shaping for further fidelity.

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

Ma, Q. L., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp

The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting methodmore » for magnetization dynamics modulation.« less

Comparison of Arterial Spin-labeling Perfusion Images at Different Spatial Normalization Methods Based on Voxel-based Statistical Analysis.

PubMed

Tani, Kazuki; Mio, Motohira; Toyofuku, Tatsuo; Kato, Shinichi; Masumoto, Tomoya; Ijichi, Tetsuya; Matsushima, Masatoshi; Morimoto, Shoichi; Hirata, Takumi

2017-01-01

Spatial normalization is a significant image pre-processing operation in statistical parametric mapping (SPM) analysis. The purpose of this study was to clarify the optimal method of spatial normalization for improving diagnostic accuracy in SPM analysis of arterial spin-labeling (ASL) perfusion images. We evaluated the SPM results of five spatial normalization methods obtained by comparing patients with Alzheimer's disease or normal pressure hydrocephalus complicated with dementia and cognitively healthy subjects. We used the following methods: 3DT1-conventional based on spatial normalization using anatomical images; 3DT1-DARTEL based on spatial normalization with DARTEL using anatomical images; 3DT1-conventional template and 3DT1-DARTEL template, created by averaging cognitively healthy subjects spatially normalized using the above methods; and ASL-DARTEL template created by averaging cognitively healthy subjects spatially normalized with DARTEL using ASL images only. Our results showed that ASL-DARTEL template was small compared with the other two templates. Our SPM results obtained with ASL-DARTEL template method were inaccurate. Also, there were no significant differences between 3DT1-conventional and 3DT1-DARTEL template methods. In contrast, the 3DT1-DARTEL method showed higher detection sensitivity, and precise anatomical location. Our SPM results suggest that we should perform spatial normalization with DARTEL using anatomical images.

Multi-photon transitions and Rabi resonance in continuous wave EPR.

PubMed

Saiko, Alexander P; Fedaruk, Ryhor; Markevich, Siarhei A

2015-10-01

The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. Copyright © 2015 Elsevier Inc. All rights reserved.

Neutron Spin Resonance in the 112-Type Iron-Based Superconductor.

PubMed

Xie, Tao; Gong, Dongliang; Ghosh, Haranath; Ghosh, Abyay; Soda, Minoru; Masuda, Takatsugu; Itoh, Shinichi; Bourdarot, Frédéric; Regnault, Louis-Pierre; Danilkin, Sergey; Li, Shiliang; Luo, Huiqian

2018-03-30

We use inelastic neutron scattering to study the low-energy spin excitations of the 112-type iron pnictide Ca_{0.82}La_{0.18}Fe_{0.96}Ni_{0.04}As_{2} with bulk superconductivity below T_{c}=22  K. A two-dimensional spin resonance mode is found around E=11  meV, where the resonance energy is almost temperature independent and linearly scales with T_{c} along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Because of the unique monoclinic structure with additional zigzag arsenic chains, the As 4p orbitals contribute to a three-dimensional hole pocket around the Γ point and an extra electron pocket at the X point. Our results suggest that the energy and momentum distribution of the spin resonance does not directly respond to the k_{z} dependence of the fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.

Spin coherent states phenomena probed by quantum state tomography in Zeeman perturbed nuclear quadrupole resonance

NASA Astrophysics Data System (ADS)

Teles, João; Auccaise, Ruben; Rivera-Ascona, Christian; Araujo-Ferreira, Arthur G.; Andreeta, José P.; Bonagamba, Tito J.

2018-07-01

Recently, we reported an experimental implementation of quantum information processing (QIP) by nuclear quadrupole resonance (NQR). In this work, we present the first quantum state tomography (QST) experimental implementation in the NQR QIP context. Two approaches are proposed, employing coherence selection by temporal and spatial averaging. Conditions for reduction in the number of cycling steps are analyzed, which can be helpful for larger spin systems. The QST method was applied to the study of spin coherent states, where the alignment-to-orientation phenomenon and the evolution of squeezed spin states show the effect of the nonlinear quadrupole interaction intrinsic to the NQR system. The quantum operations were implemented using a single-crystal sample of KClO3 and observing ^{35}Cl nuclei, which posses spin 3/2.

Electron spin echo envelope modulation studies of the Cu(II)-substituted derivative of isopenicillin N synthase: A structural and spectroscopic model

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

Feng Jiang; Peisach, J.; Lijune Ming

Electron spin echo envelope modulation spectroscopy (ESEEM) was used to study the active site structure of isopenicillin N synthase (IPNS) from Cephalosporium acremonium with Cu(II) as a spectroscopic probe. Fourier transform of the simulated electron spin-echo envelope for the Cu(II)-substituted enzyme, Cu(II)IPNS, revealed two nearly magnetically equivalent, equatorially coordinated His imidazoles. The superhyperfine coupling constant, A{sub iso}, for the remote {sup 14}N of each imidazole was 1.65 MHz. The binding of substrate to the enzyme altered the magnetic coupling so that A{sub iso} is 1.30 MHz for one nitrogen and 2.16 MHz for the other. From a comparison of themore » ESSEM of Cu(II)IPNS in D{sub 2}O and H{sub 2}O, it is suggested that water is a ligand of Cu(II) and this is displaced upon the addition of substrate.« less

Technique to determine location of radio sources from measurements taken on spinning spacecraft

NASA Technical Reports Server (NTRS)

Fainberg, J.

1979-01-01

The procedure developed to extract average source direction and average source size from spin-modulated radio astronomy data measured on the IMP-6 spacecraft is described. Because all measurements are used, rather than just finding maxima or minima in the data, the method is very sensitive, even in the presence of large amounts of noise. The technique is applicable to all experiments with directivity characteristics. It is suitable for onboard processing on satellites to reduce the data flow to Earth. The application to spin-modulated nonpolarized radio astronomy data is made and includes the effects of noise, background, and second source interference. The analysis was tested with computer simulated data and the results agree with analytic predictions. Applications of this method with IMP-6 radio data have led to: (1) determination of source positions of traveling solar radio bursts at large distances from the Sun; (2) mapping of magnetospheric radio emissions by radio triangulation; and (3) detection of low frequency radio emissions from Jupiter and Saturn.

Spin-density fluctuations and the fluctuation-dissipation theorem in 3 d ferromagnetic metals

DOE PAGES

Wysocki, Alex L.; Valmispild, V. N.; Kutepov, A.; ...

2017-11-15

Spatial and time scales of spin-density fluctuations (SDFs) were analyzed in 3d ferromagnets using ab initio linear-response calculations of complete wave-vector and energy dependence of the dynamic spin susceptibility tensor. We demonstrate that SDFs are spread continuously over the entire Brillouin zone and while the majority of them reside within the 3d bandwidth, a significant amount comes from much higher energies. A validity of the adiabatic approximation in spin dynamics is discussed. The SDF spectrum is shown to have two main constituents: a minor low-energy spin-wave contribution and a much larger high-energy component from more localized excitations. Furthermore, using themore » fluctuation-dissipation theorem, the on-site spin correlator and the related effective fluctuating moment were properly evaluated and their universal dependence on the 3d band population is further discussed.« less

Scanning nuclear resonance imaging of a hyperfine-coupled quantum Hall system.

PubMed

Hashimoto, Katsushi; Tomimatsu, Toru; Sato, Ken; Hirayama, Yoshiro

2018-06-07

Nuclear resonance (NR) is widely used to detect and characterise nuclear spin polarisation and conduction electron spin polarisation coupled by a hyperfine interaction. While the macroscopic aspects of such hyperfine-coupled systems have been addressed in most relevant studies, the essential role of local variation in both types of spin polarisation has been indicated in 2D semiconductor systems. In this study, we apply a recently developed local and highly sensitive NR based on a scanning probe to a hyperfine-coupled quantum Hall (QH) system in a 2D electron gas subject to a strong magnetic field. We succeed in imaging the NR intensity and Knight shift, uncovering the spatial distribution of both the nuclear and electron spin polarisation. The results reveal the microscopic origin of the nonequilibrium QH phenomena, and highlight the potential use of our technique in microscopic studies on various electron spin systems as well as their correlations with nuclear spins.

Spin-density fluctuations and the fluctuation-dissipation theorem in 3 d ferromagnetic metals

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

Wysocki, Alex L.; Valmispild, V. N.; Kutepov, A.

Spatial and time scales of spin-density fluctuations (SDFs) were analyzed in 3d ferromagnets using ab initio linear-response calculations of complete wave-vector and energy dependence of the dynamic spin susceptibility tensor. We demonstrate that SDFs are spread continuously over the entire Brillouin zone and while the majority of them reside within the 3d bandwidth, a significant amount comes from much higher energies. A validity of the adiabatic approximation in spin dynamics is discussed. The SDF spectrum is shown to have two main constituents: a minor low-energy spin-wave contribution and a much larger high-energy component from more localized excitations. Furthermore, using themore » fluctuation-dissipation theorem, the on-site spin correlator and the related effective fluctuating moment were properly evaluated and their universal dependence on the 3d band population is further discussed.« less

Selective spatial attention modulates bottom-up informational masking of speech

PubMed Central

Carlile, Simon; Corkhill, Caitlin

2015-01-01

To hear out a conversation against other talkers listeners overcome energetic and informational masking. Largely attributed to top-down processes, information masking has also been demonstrated using unintelligible speech and amplitude-modulated maskers suggesting bottom-up processes. We examined the role of speech-like amplitude modulations in information masking using a spatial masking release paradigm. Separating a target talker from two masker talkers produced a 20 dB improvement in speech reception threshold; 40% of which was attributed to a release from informational masking. When across frequency temporal modulations in the masker talkers are decorrelated the speech is unintelligible, although the within frequency modulation characteristics remains identical. Used as a masker as above, the information masking accounted for 37% of the spatial unmasking seen with this masker. This unintelligible and highly differentiable masker is unlikely to involve top-down processes. These data provides strong evidence of bottom-up masking involving speech-like, within-frequency modulations and that this, presumably low level process, can be modulated by selective spatial attention. PMID:25727100

Selective spatial attention modulates bottom-up informational masking of speech.

PubMed

Carlile, Simon; Corkhill, Caitlin

2015-03-02

To hear out a conversation against other talkers listeners overcome energetic and informational masking. Largely attributed to top-down processes, information masking has also been demonstrated using unintelligible speech and amplitude-modulated maskers suggesting bottom-up processes. We examined the role of speech-like amplitude modulations in information masking using a spatial masking release paradigm. Separating a target talker from two masker talkers produced a 20 dB improvement in speech reception threshold; 40% of which was attributed to a release from informational masking. When across frequency temporal modulations in the masker talkers are decorrelated the speech is unintelligible, although the within frequency modulation characteristics remains identical. Used as a masker as above, the information masking accounted for 37% of the spatial unmasking seen with this masker. This unintelligible and highly differentiable masker is unlikely to involve top-down processes. These data provides strong evidence of bottom-up masking involving speech-like, within-frequency modulations and that this, presumably low level process, can be modulated by selective spatial attention.

Role of density modulation in the spatially resolved dynamics of strongly confined liquids

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

Saw, Shibu, E-mail: shibu.saw@sydney.edu.au; Dasgupta, Chandan, E-mail: cdgupta@physics.iisc.ernet.in

Confinement by walls usually produces a strong modulation in the density of dense liquids near the walls. Using molecular dynamics simulations, we examine the effects of the density modulation on the spatially resolved dynamics of a liquid confined between two parallel walls, using a resolution of a fraction of the interparticle distance in the liquid. The local dynamics is quantified by the relaxation time associated with the temporal autocorrelation function of the local density. We find that this local relaxation time varies in phase with the density modulation. The amplitude of the spatial modulation of the relaxation time can bemore » quite large, depending on the characteristics of the wall and thermodynamic parameters of the liquid. To disentangle the effects of confinement and density modulation on the spatially resolved dynamics, we compare the dynamics of a confined liquid with that of an unconfined one in which a similar density modulation is induced by an external potential. We find several differences indicating that density modulation alone cannot account for all the features seen in the spatially resolved dynamics of confined liquids. We also examine how the dynamics near a wall depends on the separation between the two walls and show that the features seen in our simulations persist in the limit of large wall separation.« less

FMR-driven spin pumping in Y3Fe5O12-based structures

NASA Astrophysics Data System (ADS)

Yang, Fengyuan; Hammel, P. Chris

2018-06-01

Ferromagnetic resonance driven spin pumping, a topic of steadily increasing interest since its emergence over two decades ago, remains one of the most exciting research fields in condensed matter physics. Among the many materials that have been explored for spin pumping, yttrium iron garnet (YIG) is one of the most extensively studied because of its exceptionally low magnetic damping and insulating nature. There is a great amount of literature in the spin pumping and related research fields, too broad for this review to cover. In this Topical Review, we focus on the YIG-based spin pumping results carried out by our groups, including: the mechanism and technical details of our off-axis sputtering technique for the growth of single-crystalline YIG epitaxial films with a high degree ordering, experimental evidence for the high quality of the YIG films, spin pumping results from YIG into various transition metals and their heterostructures, dynamic spin transport in YIG/antiferromagnet hybrid structures, intralayer spin pumping by localized spin wave modes confined by a micromagnetic probe, dynamic spin coupling between YIG and nitrogen-vacancy centers in diamond, parametric spin pumping from high-wavevector spin waves in YIG, and localized spin wave mode behavior in broadly tunable spatially complex magnetic configurations. These results build on the power and versatility of YIG spin pumping to improve our understanding of spin dynamics, spin currents, spin Hall physics, spin–orbit coupling, dynamic magnetic coupling, and the relationship between these phenomena in a broad range of materials, geometries, and settings.

Programmable Illumination and High-Speed, Multi-Wavelength, Confocal Microscopy Using a Digital Micromirror

PubMed Central

Martial, Franck P.; Hartell, Nicholas A.

2012-01-01

Confocal microscopy is routinely used for high-resolution fluorescence imaging of biological specimens. Most standard confocal systems scan a laser across a specimen and collect emitted light passing through a single pinhole to produce an optical section of the sample. Sequential scanning on a point-by-point basis limits the speed of image acquisition and even the fastest commercial instruments struggle to resolve the temporal dynamics of rapid cellular events such as calcium signals. Various approaches have been introduced that increase the speed of confocal imaging. Nipkov disk microscopes, for example, use arrays of pinholes or slits on a spinning disk to achieve parallel scanning which significantly increases the speed of acquisition. Here we report the development of a microscope module that utilises a digital micromirror device as a spatial light modulator to provide programmable confocal optical sectioning with a single camera, at high spatial and axial resolution at speeds limited by the frame rate of the camera. The digital micromirror acts as a solid state Nipkov disk but with the added ability to change the pinholes size and separation and to control the light intensity on a mirror-by-mirror basis. The use of an arrangement of concave and convex mirrors in the emission pathway instead of lenses overcomes the astigmatism inherent with DMD devices, increases light collection efficiency and ensures image collection is achromatic so that images are perfectly aligned at different wavelengths. Combined with non-laser light sources, this allows low cost, high-speed, multi-wavelength image acquisition without the need for complex wavelength-dependent image alignment. The micromirror can also be used for programmable illumination allowing spatially defined photoactivation of fluorescent proteins. We demonstrate the use of this system for high-speed calcium imaging using both a single wavelength calcium indicator and a genetically encoded, ratiometric, calcium sensor. PMID:22937130

Programmable illumination and high-speed, multi-wavelength, confocal microscopy using a digital micromirror.

PubMed

Martial, Franck P; Hartell, Nicholas A

2012-01-01

Confocal microscopy is routinely used for high-resolution fluorescence imaging of biological specimens. Most standard confocal systems scan a laser across a specimen and collect emitted light passing through a single pinhole to produce an optical section of the sample. Sequential scanning on a point-by-point basis limits the speed of image acquisition and even the fastest commercial instruments struggle to resolve the temporal dynamics of rapid cellular events such as calcium signals. Various approaches have been introduced that increase the speed of confocal imaging. Nipkov disk microscopes, for example, use arrays of pinholes or slits on a spinning disk to achieve parallel scanning which significantly increases the speed of acquisition. Here we report the development of a microscope module that utilises a digital micromirror device as a spatial light modulator to provide programmable confocal optical sectioning with a single camera, at high spatial and axial resolution at speeds limited by the frame rate of the camera. The digital micromirror acts as a solid state Nipkov disk but with the added ability to change the pinholes size and separation and to control the light intensity on a mirror-by-mirror basis. The use of an arrangement of concave and convex mirrors in the emission pathway instead of lenses overcomes the astigmatism inherent with DMD devices, increases light collection efficiency and ensures image collection is achromatic so that images are perfectly aligned at different wavelengths. Combined with non-laser light sources, this allows low cost, high-speed, multi-wavelength image acquisition without the need for complex wavelength-dependent image alignment. The micromirror can also be used for programmable illumination allowing spatially defined photoactivation of fluorescent proteins. We demonstrate the use of this system for high-speed calcium imaging using both a single wavelength calcium indicator and a genetically encoded, ratiometric, calcium sensor.

Photoionization of N,N,N[prime],N[prime]-tetramethylbenzidine in a mixed micelle of ionic and nonionic surfactants: Electron spin-echo modulation and electron spin resonance studies

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

Baglioni, P.; Rivara-Minten, E.; Stenland, C.

1991-11-28

Electron spin-echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N[prime],N[prime]-tetramethylbenzidine (TMB) cation radical in frozen mixed micelles of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTAC) and hexakis(ethylene glycol) monododecyl ether (C[sub 12]E[sub 6]), selectively deuterated along the poly(ethylene glycol) group (C[sub 12]D[sub 6]) or along the alkyl chain ((CD)[sub 12]E[sub 6]), have been studied as a function of the mixed-micelle composition in H[sub 2]O and D[sub 2]O. ESEM effects due to TMB[sup +] interactions with deuterium in D[sub 2]O show a decrease of the TMB[sup +]-water interactions for the system DTAC/C[sub 12]E[sub 6] and anmore » increase for the system SDS/C[sub 12]E[sub 6] that depend on the composition of the mixed micelle. The location of TMB[sup +] in the mixed micelles, deduced by comparing the modulation effects due to interactions of the photocation with water deuteriums or deuteriums of deuterated surfactants, is reported for the SDS/C[sub 12]E[sub 6] and DTAC/C[sub 12]E[sub 6] mixed micelles. The efficiency of charge separation upon the photoionization of TMB to produce TMB[sup +] measured by ESR correlates with the surface charge and with the degree of water penetration into the mixed micelle.« less

Immense Magnetic Response of Exciplex Light Emission due to Correlated Spin-Charge Dynamics

NASA Astrophysics Data System (ADS)

Wang, Yifei; Sahin-Tiras, Kevser; Harmon, Nicholas J.; Wohlgenannt, Markus; Flatté, Michael E.

2016-01-01

As carriers slowly move through a disordered energy landscape in organic semiconductors, tiny spatial variations in spin dynamics relieve spin blocking at transport bottlenecks or in the electron-hole recombination process that produces light. Large room-temperature magnetic-field effects (MFEs) ensue in the conductivity and luminescence. Sources of variable spin dynamics generate much larger MFEs if their spatial structure is correlated on the nanoscale with the energetic sites governing conductivity or luminescence such as in coevaporated organic blends within which the electron resides on one molecule and the hole on the other (an exciplex). Here, we show that exciplex recombination in blends exhibiting thermally activated delayed fluorescence produces MFEs in excess of 60% at room temperature. In addition, effects greater than 4000% can be achieved by tuning the device's current-voltage response curve by device conditioning. Both of these immense MFEs are the largest reported values for their device type at room temperature. Our theory traces this MFE and its unusual temperature dependence to changes in spin mixing between triplet exciplexes and light-emitting singlet exciplexes. In contrast, spin mixing of excitons is energetically suppressed, and thus spin mixing produces comparatively weaker MFEs in materials emitting light from excitons by affecting the precursor pairs. Demonstration of immense MFEs in common organic blends provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices without patterning the constituent materials on the nanoscale. Magnetic fields increase the power efficiency of unconditioned devices by 30% at room temperature, also showing that magnetic fields may increase the efficiency of the thermally activated delayed fluorescence process.

Immense Magnetic Response of Exciplex Light Emission due to Correlated Spin-Charge Dynamics

DOE PAGES

Wang, Yifei; Sahin-Tiras, Kevser; Harmon, Nicholas J.; ...

2016-02-05

As carriers slowly move through a disordered energy landscape in organic semiconductors, tiny spatial variations in spin dynamics relieve spin blocking at transport bottlenecks or in the electron-hole recombination process that produces light. Large room-temperature magnetic-field effects (MFEs) ensue in the conductivity and luminescence. Sources of variable spin dynamics generate much larger MFEs if their spatial structure is correlated on the nanoscale with the energetic sites governing conductivity or luminescence such as in coevaporated organic blends within which the electron resides on one molecule and the hole on the other (an exciplex). Here, we show that exciplex recombination in blendsmore » exhibiting thermally activated delayed fluorescence produces MFEs in excess of 60% at room temperature. In addition, effects greater than 4000% can be achieved by tuning the device’s current-voltage response curve by device conditioning. Both of these immense MFEs are the largest reported values for their device type at room temperature. Our theory traces this MFE and its unusual temperature dependence to changes in spin mixing between triplet exciplexes and light-emitting singlet exciplexes. In contrast, spin mixing of excitons is energetically suppressed, and thus spin mixing produces comparatively weaker MFEs in materials emitting light from excitons by affecting the precursor pairs. Demonstration of immense MFEs in common organic blends provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices without patterning the constituent materials on the nanoscale. In conclusion, magnetic fields increase the power efficiency of unconditioned devices by 30% at room temperature, also showing that magnetic fields may increase the efficiency of the thermally activated delayed fluorescence process.« less

A long serendipitous XMM-Newton observation of the intermediate polar XY Ari1

NASA Astrophysics Data System (ADS)

Zengin Ćamurdan, D.; Balman, Ş.; Burwitz, V.

2018-07-01

XY Ari is one of the few known eclipsing intermediate polars. We present results from a detailed analysis of an unpublished archival observation using XMM-Newton EPIC pn and MOS data in a quiescent state of XY Ari. The X-ray orbital modulation and spin-pulse variations were investigated for energy-dependent modulations in different energy bands. The broad orbital modulation observed with various observations was confirmed with XMM-Newton in the hard X-ray (>1.6 keV). The EPIC light curves folded at the spin phases show a double-peak profile, as expected from two-pole accretion. The pulse profile is found to be energy-dependent. Hardness-ratio variations and energy modulation depth during spin modulation can be explained by photoelectric absorption. The simultaneously fitted EPIC spectra with a multi-temperature plasma emission model (CEVMKL) model yield a maximum plasma temperature of 28^{+3.1}_{-2.9} keV with an iron abundance Fe/Fe_{⊙}=0.37^{+0.06}_{-0.05}. We find two intrinsic partial covering absorption columns of 6.2^{+1.0}_{-0.9} × 10^{22} and 105.3^{+35.4}_{-30.4} × 10^{22} cm^{-2} with covering fractions of 0.53^{+0.05}_{-0.04}, 0.41^{+0.14}_{-0.13}, respectively. In addition, a Gaussian emission line at 6.43^{+0.01}_{-0.02} keV with an equivalent width of 51^{+12}_{-10} eV is required to account for fluorescent emission from neutral iron. The X-ray luminosity of the source is 4.2 × 1032 erg s-1 in the 0.2-10.0 keV energy band.

Magnetic and Electric Transverse Spin Density of Spatially Confined Light

NASA Astrophysics Data System (ADS)

Neugebauer, Martin; Eismann, Jörg S.; Bauer, Thomas; Banzer, Peter

2018-04-01

When a beam of light is laterally confined, its field distribution can exhibit points where the local magnetic and electric field vectors spin in a plane containing the propagation direction of the electromagnetic wave. The phenomenon indicates the presence of a nonzero transverse spin density. Here, we experimentally investigate this transverse spin density of both magnetic and electric fields, occurring in highly confined structured fields of light. Our scheme relies on the utilization of a high-refractive-index nanoparticle as a local field probe, exhibiting magnetic and electric dipole resonances in the visible spectral range. Because of the directional emission of dipole moments that spin around an axis parallel to a nearby dielectric interface, such a probe particle is capable of locally sensing the magnetic and electric transverse spin density of a tightly focused beam impinging under normal incidence with respect to said interface. We exploit the achieved experimental results to emphasize the difference between magnetic and electric transverse spin densities.

Developing Accurate Spatial Maps of Cotton Fiber Quality Parameters

USDA-ARS?s Scientific Manuscript database

Awareness of the importance of cotton fiber quality (Gossypium, L. sps.) has increased as advances in spinning technology require better quality cotton fiber. Recent advances in geospatial information sciences allow an improved ability to study the extent and causes of spatial variability in fiber p...

Theory of Tunneling Spectroscopy in a Mn12 Single-Electron Transistor by Density-Functional Theory Methods

NASA Astrophysics Data System (ADS)

Michalak, Ł.; Canali, C. M.; Pederson, M. R.; Paulsson, M.; Benza, V. G.

2010-01-01

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Theory of tunneling spectroscopy in a Mn12 single-electron transistor by density-functional theory methods.

PubMed

Michalak, Ł; Canali, C M; Pederson, M R; Paulsson, M; Benza, V G

2010-01-08

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Active processes in one dimension

NASA Astrophysics Data System (ADS)

Demaerel, Thibaut; Maes, Christian

2018-03-01

We consider the thermal and athermal overdamped motion of particles in one-dimensional geometries where discrete internal degrees of freedom (spin) are coupled with the translational motion. Adding a driving velocity that depends on the time-dependent spin constitutes the simplest model of active particles (run-and-tumble processes) where the violation of the equipartition principle and of the Sutherland-Einstein relation can be studied in detail even when there is generalized reversibility. We give an example (with four spin values) where the irreversibility of the translational motion manifests itself only in higher-order (than two) time correlations. We derive a generalized telegraph equation as the Smoluchowski equation for the spatial density for an arbitrary number of spin values. We also investigate the Arrhenius exponential law for run-and-tumble particles; due to their activity the slope of the potential becomes important in contrast to the passive diffusion case and activity enhances the escape from a potential well (if that slope is high enough). Finally, in the absence of a driving velocity, the presence of internal currents such as in the chemistry of molecular motors may be transmitted to the translational motion and the internal activity is crucial for the direction of the emerging spatial current.

Engineering frequency-dependent superfluidity in Bose-Fermi mixtures

NASA Astrophysics Data System (ADS)

Arzamasovs, Maksims; Liu, Bo

2018-04-01

Unconventional superconductivity and superfluidity are among the most exciting and fascinating quantum phenomena in condensed-matter physics. Usually such states are characterized by nontrivial spin or spatial symmetry of the pairing order parameter, such as "spin triplet" or "p wave." However, besides spin and spatial dependence the order parameter may have unconventional frequency dependence which is also permitted by Fermi-Dirac statistics. Odd-frequency fermionic pairing is an exciting paradigm when discussing exotic superfluidity or superconductivity and is yet to be realized in experiments. In this paper we propose a symmetry-based method of controlling frequency dependence of the pairing order parameter via manipulating the inversion symmetry of the system. First, a toy model is introduced to illustrate that frequency dependence of the order parameter can be achieved through our proposed approach. Second, by taking advantage of recent rapid developments in producing spin-orbit-coupled dispersions in ultracold gases, we propose a Bose-Fermi mixture to realize such frequency-dependent superfluid. The key idea is introducing the frequency-dependent attraction between fermions mediated by Bogoliubov phonons with asymmetric dispersion. Our proposal should pave an alternative way for exploring frequency-dependent superfluids with cold atoms.

Throughput increase by adjustment of the BARC drying time with coat track process

NASA Astrophysics Data System (ADS)

Brakensiek, Nickolas L.; Long, Ryan

2005-05-01

Throughput of a coater module within the coater track is related to the solvent evaporation rate from the material that is being coated. Evaporation rate is controlled by the spin dynamics of the wafer and airflow dynamics over the wafer. Balancing these effects is the key to achieving very uniform coatings across a flat unpatterned wafer. As today"s coat tracks are being pushed to higher throughputs to match the scanner, the coat module throughput must be increased as well. For chemical manufacturers the evaporation rate of the material depends on the solvent used. One measure of relative evaporation rates is to compare flash points of a solvent. The lower the flash point, the quicker the solvent will evaporate. It is possible to formulate products with these volatile solvents although at a price. Shipping and manufacturing a more flammable product increase chances of fire, thereby increasing insurance premiums. Also, the end user of these chemicals will have to take extra precautions in the fab and in storage of these more flammable chemicals. An alternative coat process is possible which would allow higher throughput in a distinct coat module without sacrificing safety. A tradeoff is required for this process, that being a more complicated coat process and a higher viscosity chemical. The coat process uses the fact that evaporation rate depends on the spin dynamics of the wafer by utilizing a series of spin speeds that first would set the thickness of the material followed by a high spin speed to remove the residual solvent. This new process can yield a throughput of over 150 wafers per hour (wph) given two coat modules. The thickness uniformity of less than 2 nm (3 sigma) is still excellent, while drying times are shorter than 10 seconds to achieve the 150 wph throughput targets.

X-ray Spectra and Pulse Frequency Changes in SAX J2103.5+4545

NASA Technical Reports Server (NTRS)

Baykal, A.; Stark, M. J.; Swank, J. H.; White, Nicholas E. (Technical Monitor)

2002-01-01

The November 1999 outburst of the transient pulsar SAX J2103.5+4545 was monitored with the large area detectors of the Rossi X-Ray Timing Explorer until the pulsar faded after a year. The 358 s pulsar was spun up for 150 days, at which point the flux dropped quickly by a factor of approximately 7, the frequency saturated and, as the flux continued to decline, a weak spin-down began. The pulses remained strong during the decay and the spin-up/flux correlation can be fit to the Ghosh and Lamb derivations for the spin-up caused by accretion from a thin, pressure-dominated disk, for a distance approximately 3.2 kpc and a surface magnetic field approximately 1.2 x 10(exp 13) Gauss. During the bright spin-up part of the outburst, the flux was subject to strong orbital modulation, peaking approximately 3 days after periastron of the eccentric 12.68 day orbit, while during the faint part, there was little orbital modulation. The X-ray spectra were typical of accreting pulsars, describable by a cut-off power-law, with an emission line near the 6.4 keV of Kappa(sub alpha) fluorescence from cool iron. The equivalent width of this emission did not share the orbital modulation, but nearly doubled during the faint phase, despite little change in the column density. The outburst could have been caused by an episode of increased wind from a Be star, such that a small accretion disk is formed during each periastron passage. A change in the wind and disk structure apparently occurred after 5 months such that the accretion rate was no longer modulated or the diffusion time was longer. The distance estimate implies the X-ray luminosity observed was between 1 X 10(exp 36) ergs s(exp -1) and 6 x 10(exp 34) ergs s(exp -1), with a small but definite correlation of the intrinsic power-law spectral index.

Dynamical characteristics of an electromagnetic field under conditions of total reflection

NASA Astrophysics Data System (ADS)

Bekshaev, Aleksandr Ya

2018-04-01

The dynamical characteristics of electromagnetic fields include energy, momentum, angular momentum (spin) and helicity. We analyze their spatial distributions near the planar interface between two transparent and non-dispersive media, when the incident monochromatic plane wave with arbitrary polarization is totally reflected, and an evanescent wave is formed in the medium with lower optical density. Based on the recent arguments in favor of the Minkowski definition of the electromagnetic momentum in a material medium (Philbin 2011 Phys. Rev. A 83 013823; Philbin and Allanson 2012 86 055802; Bliokh et al 2017 Phys. Rev. Lett. 119 073901), we derive the explicit expressions for the dynamical characteristics in both media, with special attention to their behavior at the interface. In particular, the ‘extraordinary’ spin and momentum components orthogonal to the plane of incidence are described, and a canonical (spin-orbital) momentum decomposition is performed that contains no singular terms. The field energy, helicity, the spin momentum and orbital momentum components are everywhere regular but experience discontinuities at the interface; the spin components parallel to the interface appear to be continuous, which testifies to the consistency of the adopted Minkowski picture. The results supply a meaningful example of the electromagnetic momentum decomposition, with separation of spatial and polarization degrees of freedom, in inhomogeneous media, and can be used in engineering the structured fields designed for optical sorting, dispatching and micromanipulation.

Basic Fishing. Aquatic Skills Series. Instructor Manual.

ERIC Educational Resources Information Center

Staton, Robert D., Jr.

Part of a series of self-contained instructional units to teach Missourians how to use outdoor resources wisely and skillfully, this module of the Aquatic Skills Series introduces the basics of sport fishing using spin-casting equipment. The instructor may modify the module to meet the individual needs of class members based on age, experience…

A unified heteronuclear decoupling strategy for magic-angle-spinning solid-state NMR spectroscopy

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

Equbal, Asif; Bjerring, Morten; Nielsen, Niels Chr., E-mail: madhu@tifr.res.in, E-mail: ncn@inano.au.dk

2015-05-14

A unified strategy of two-pulse based heteronuclear decoupling for solid-state magic-angle spinning nuclear magnetic resonance is presented. The analysis presented here shows that different decoupling sequences like two-pulse phase-modulation (TPPM), X-inverse-X (XiX), and finite pulse refocused continuous wave (rCW{sup A}) are basically specific solutions of a more generalized decoupling scheme which incorporates the concept of time-modulation along with phase-modulation. A plethora of other good decoupling conditions apart from the standard, TPPM, XiX, and rCW{sup A} decoupling conditions are available from the unified decoupling approach. The importance of combined time- and phase-modulation in order to achieve the best decoupling conditions ismore » delineated. The consequences of different indirect dipolar interactions arising from cross terms comprising of heteronuclear and homonuclear dipolar coupling terms and also those between heteronuclear dipolar coupling and chemical-shift anisotropy terms are presented in order to unfold the effects of anisotropic interactions under different decoupling conditions. Extensive numerical simulation results are corroborated with experiments on standard amino acids.« less

Burst Oscillations: A New Spin on Neutron Stars

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2007-01-01

Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have shown that the X-ray flux during thermonuclear X-ray bursts fr-om accreting neutron stars is often strongly pulsed at frequencies as high as 620 Hz. We now know that these oscillations are produced by spin modulation of the thermonuclear flux from the neutron star surface. In addition to revealing the spin frequency, they provide new ways to probe the properties and physics of accreting neutron stars. I will briefly review our current observational and theoretical understanding of these oscillations and discuss what they are telling us about neutron stars.

Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

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

Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi

2014-05-28

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

A Ramsey’s Method With Pulsed Neutrons for a T-Violation Experiment

PubMed Central

Masuda, Y.; Ino, T.; Muto, S.; Skoy, V.

2005-01-01

A Ramsey’s method with pulsed neutrons is discussed for neutron spin manipulation in a time reversal (T) symmetry violation experiment. The neutron spin (sn) is aligned to the direction of a vector product of the nuclear spin (I) and the neutron momentum (kn) for the measurement of a T-odd correlation term, which is represented as sn · (kn × I), during propagation through a polarized nuclear target. The phase control and amplitude modulation of separated oscillatory fields are discussed for the measurement of the T-odd correlation term. PMID:27308171

A Ramsey's Method With Pulsed Neutrons for a T-Violation Experiment.

PubMed

Masuda, Y; Ino, T; Muto, S; Skoy, V

2005-01-01

A Ramsey's method with pulsed neutrons is discussed for neutron spin manipulation in a time reversal (T) symmetry violation experiment. The neutron spin (s n) is aligned to the direction of a vector product of the nuclear spin ( I ) and the neutron momentum ( k n) for the measurement of a T-odd correlation term, which is represented as s n · ( k n × I ), during propagation through a polarized nuclear target. The phase control and amplitude modulation of separated oscillatory fields are discussed for the measurement of the T-odd correlation term.

Large current modulation and spin-dependent tunneling of vertical graphene/MoS2 heterostructures.

PubMed

Myoung, Nojoon; Seo, Kyungchul; Lee, Seung Joo; Ihm, G

2013-08-27

Vertical graphene heterostructures have been introduced as an alternative architecture for electronic devices by using quantum tunneling. Here, we present that the current on/off ratio of vertical graphene field-effect transistors is enhanced by using an armchair graphene nanoribbon as an electrode. Moreover, we report spin-dependent tunneling current of the graphene/MoS2 heterostructures. When an atomically thin MoS2 layer sandwiched between graphene electrodes becomes magnetic, Dirac fermions with different spins feel different heights of the tunnel barrier, leading to spin-dependent tunneling. Our finding will develop the present graphene heterostructures for electronic devices by improving the device performance and by adding the possibility of spintronics based on graphene.

Nonlinear convective flows in a two-layer system under the action of spatial temperature modulation of heat release/consumption at the interface

NASA Astrophysics Data System (ADS)

Simanovskii, Ilya B.; Viviani, Antonio; Dubois, Frank

2018-06-01

An influence of a spatial temperature modulation of the interfacial heat release/consumption on nonlinear convective flows in the 47v2 silicone oil - water system, is studied. Rigid heat-insulated lateral walls, corresponding to the case of closed cavities, have been considered. Transitions between the flows with different spatial structures, have been investigated. It is shown that the spatial modulation can change the sequence of bifurcations and lead to the appearance of specific steady and oscillatory flows in the system.

Perturbing laser field dependent high harmonic phase modulations

NASA Astrophysics Data System (ADS)

Li, Zhengyan; Kong, Fanqi; Brown, Graham; Hammond, TJ; Ko, Dong-Hyuk; Zhang, Chunmei; Corkum, P. B.

2018-06-01

A perturbing laser pulse modulates and controls the phase of the high harmonic radiation driven by an intense fundamental pulse. Thus, a structured wave front can impress a specific spatial phase onto the generated high harmonic wave front. This modulation procedure leads to all-optical spatial light modulators for VUV or XUV radiation created by high harmonic generation. Here, through theoretical analysis and experiment, we study the correlation between the high harmonic phase modulations and the perturbing laser field amplitude and phase, providing guidelines for practical high harmonic spatial light modulators. In addition, we show that the petahertz optical oscilloscope for measuring electric fields of a perturbing beam is most robust using low order harmonics, far from the cut-off.

Optimal control of universal quantum gates in a double quantum dot

NASA Astrophysics Data System (ADS)

Castelano, Leonardo K.; de Lima, Emanuel F.; Madureira, Justino R.; Degani, Marcos H.; Maialle, Marcelo Z.

2018-06-01

We theoretically investigate electron spin operations driven by applied electric fields in a semiconductor double quantum dot (DQD) formed in a nanowire with longitudinal potential modulated by local gating. We develop a model that describes the process of loading and unloading the DQD taking into account the overlap between the electron wave function and the leads. Such a model considers the spatial occupation and the spin Pauli blockade in a time-dependent fashion due to the highly mixed states driven by the external electric field. Moreover, we present a road map based on the quantum optimal control theory (QOCT) to find a specific electric field that performs two-qubit quantum gates on a faster timescale and with higher possible fidelity. By employing the QOCT, we demonstrate the possibility of performing within high efficiency a universal set of quantum gates {cnot, H, and T } , where cnot is the controlled-not gate, H is the Hadamard gate, and T is the π /8 gate, even in the presence of the loading/unloading process and charge noise effects. Furthermore, by varying the intensity of the applied magnetic field B , the optimized fidelity of the gates oscillates with a period inversely proportional to the gate operation time tf. This behavior can be useful to attain higher fidelity for fast gate operations (>1 GHz) by appropriately choosing B and tf to produce a maximum of the oscillation.

Charge and spin diffusion on the metallic side of the metal-insulator transition: A self-consistent approach

NASA Astrophysics Data System (ADS)

Wellens, Thomas; Jalabert, Rodolfo A.

2016-10-01

We develop a self-consistent theory describing the spin and spatial electron diffusion in the impurity band of doped semiconductors under the effect of a weak spin-orbit coupling. The resulting low-temperature spin-relaxation time and diffusion coefficient are calculated within different schemes of the self-consistent framework. The simplest of these schemes qualitatively reproduces previous phenomenological developments, while more elaborate calculations provide corrections that approach the values obtained in numerical simulations. The results are universal for zinc-blende semiconductors with electron conductance in the impurity band, and thus they are able to account for the measured spin-relaxation times of materials with very different physical parameters. From a general point of view, our theory opens a new perspective for describing the hopping dynamics in random quantum networks.

Bose-Fermi mapping and a multibranch spin-chain model for strongly interacting quantum gases in one dimension: Dynamics and collective excitations

NASA Astrophysics Data System (ADS)

Yang, Li; Pu, Han

2016-09-01

We show that the wave function in one spatial sector x1

Direct observation and imaging of a spin-wave soliton with p-like symmetry

NASA Astrophysics Data System (ADS)

Bonetti, S.; Kukreja, R.; Chen, Z.; Macià, F.; Hernàndez, J. M.; Eklund, A.; Backes, D.; Frisch, J.; Katine, J.; Malm, G.; Urazhdin, S.; Kent, A. D.; Stöhr, J.; Ohldag, H.; Dürr, H. A.

2015-11-01

Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

PubMed

Wang, Zechao; Tavabi, Amir H; Jin, Lei; Rusz, Ján; Tyutyunnikov, Dmitry; Jiang, Hanbo; Moritomo, Yutaka; Mayer, Joachim; Dunin-Borkowski, Rafal E; Yu, Rong; Zhu, Jing; Zhong, Xiaoyan

2018-03-01

In order to obtain a fundamental understanding of the interplay between charge, spin, orbital and lattice degrees of freedom in magnetic materials and to predict and control their physical properties 1-3 , experimental techniques are required that are capable of accessing local magnetic information with atomic-scale spatial resolution. Here, we show that a combination of electron energy-loss magnetic chiral dichroism 4 and chromatic-aberration-corrected transmission electron microscopy, which reduces the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone, can achieve atomic-scale imaging of magnetic circular dichroism and provide element-selective orbital and spin magnetic moments atomic plane by atomic plane. This unique capability, which we demonstrate for Sr 2 FeMoO 6 , opens the door to local atomic-level studies of spin configurations in a multitude of materials that exhibit different types of magnetic coupling, thereby contributing to a detailed understanding of the physical origins of magnetic properties of materials at the highest spatial resolution.

Steady motion of skyrmions and domains walls under diffusive spin torques

NASA Astrophysics Data System (ADS)

Elías, Ricardo Gabriel; Vidal-Silva, Nicolas; Manchon, Aurélien

2017-03-01

We explore the role of the spin diffusion of conducting electrons in two-dimensional magnetic textures (domain walls and skyrmions) with spatial variation of the order of the spin precession length λex. The effect of diffusion reflects in four additional torques that are third order in spatial derivatives of magnetization and bilinear in λex and in the nonadiabatic parameter β'. In order to study the dynamics of the solitons when these diffusive torques are present, we derive the Thiele equation in the limit of steady motion and we compare the results with the nondiffusive limit. When considering a homogenous current these torques increase the longitudinal velocity of transverse domain walls of width Δ by a factor (λex/Δ)2(α/3), α being the magnetic damping constant. In the case of single skyrmions with core radius r0these new contributions tend to increase the Magnus effect in an amount proportional to (λex/r0) 2(1 +2 α β') .

Pairing Instability and Quasiparticle Properties of an Unconventional Superconductor with a Skyrmion Texture of Localized Spins

NASA Astrophysics Data System (ADS)

Zhu, Jian-Xin; Tai, Yuan-Yen

Majorana fermions are believed to perform better than regular fermions in keeping quantum coherence, which is an important factor for quantum computation. Recently there has been intensive interest in their realization in solid-state systems. Zero-energy quasiparticle modes in a superconductor serve as a promising candidate. We present a theoretical study on the influence of a two-dimensional (2D) skyrmion texture of localized spins on the pairing instability and quasiparticle properties in an unconventional superconductor. By solving the Bogoliubov-de Gennes equations for an effective BCS model Hamiltonian with nearest-neighbor pairing interaction on a 2D square lattice, we analyze the spatial dependence of superconducting order parameter for varying strength of spin-exchange interaction. The quasiparticle properties are studied by calculating local density of states and its spatial dependence. This work was supported by U.S. DOE NNSA through the LANL LDRD Program, and by Center for Integrated Nanotechnologies, a U.S. DOE BES user facility.

Photo-induced spin and valley-dependent Seebeck effect in the low-buckled Dirac materials

NASA Astrophysics Data System (ADS)

Mohammadi, Yawar

2018-04-01

Employing the Landauer-Buttiker formula we investigate the spin and valley dependence of Seebeck effect in low-buckled Dirac materials (LBDMs), whose band structure are modulated by local application of a gate voltage and off-resonant circularly polarized light. We calculate the charge, spin and valley Seebeck coefficients of an irradiated LBDM as functions of electronic doping, light intensity and the amount of the electric field in the linear regime. Our calculation reveal that all Seebeck coefficients always shows an odd features with respect to the chemical potential. Moreover, we show that, due to the strong spin-orbit coupling in the LBDMs, the induced thermovoltage in the irradiated LBDMs is spin polarized, and can also become valley polarized if the gate voltage is applied too. It is also found that the valley (spin) polarization of the induced thermovoltage could be inverted by reversing the circular polarization of light or reversing the direction the electric field (only by reversing the circular polarization of light).

Signature of enhanced spin-orbit interaction in the magnetoresistance of LaTiO3/SrTiO3 interfaces on δ doping

NASA Astrophysics Data System (ADS)

Das, Shubhankar; Hossain, Z.; Budhani, R. C.

2016-09-01

We present a study of modulation of spin-orbit interaction (SOI) at the interface of LaTiO3/SrTiO3 by δ doping with an isostructural ferromagnetic perovskite LaCoO3. The sheet carrier density at the interface decreases exponentially with δ -doping thickness. We have explored that the spin-orbit scattering time (τs o) can be decreased by nearly three orders of magnitude, whereas the inelastic scattering time (τi) remains almost constant with δ -doping thickness. We have also observed that the τi varies almost inversely proportional to temperature and τs o remains insensitive to temperature, which suggest that the spin relaxation in these interfaces follows D'yakonov-Perel mechanism. The observed in-plane anisotropic magnetoresistance is attributed to the mixing of the spin-up and spin-down states of the d band at the Fermi level due to SOI.

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

A spin current rectifier

NASA Astrophysics Data System (ADS)

Eyni, Zahra; Mohammadpour, Hakimeh

2017-12-01

Current modulation and rectification is an important subject of electronics as well as spintronics. In this paper, an efficient rectifying mesoscopic device is introduced. The device is a two terminal device on the 2D plane of electron gas. The lateral contacts are half-metal ferromagnetic with antiparallel magnetizations and the central channel region is taken as ferromagnetic or normal in the presence of an applied magnetic field. The device functionality is based on the modification of spin-current by tuning the strength of the magnetic field or equivalently by the exchange coupling of the channel to the substrate. The result is that the (spin-) current depends on the polarity of the bias voltage. Converting an alternating bias voltage to direct current is the main achievement of this model device with an additional profit of rectified spin-current. We analyze the results in terms of the spin-dependent barrier in the channel. Detecting the strength of the magnetic field by spin polarization is also suggested.

Controlling superconducting spin flow with a single homogeneous ferromagnet: interference, torque and spin-flip immunity

NASA Astrophysics Data System (ADS)

Jacobsen, Sol; Kulagina, Iryna; Linder, Jacob

Superconducting spintronics has the potential to overcome the Joule heating and short decay lengths of electron transport by harnessing the dissipationless spin currents of superconductors in thin-film devices. Using conventional singlet superconductive sources, such dissipationless currents have only been demonstrated experimentally using intricate magnetically inhomogeneous multilayers, which can be difficult to construct, control and measure. Here we present analytic and numerical results proving the possibility of both generating and controlling a long-ranged spin supercurrent using only one single homogeneous magnetic element (arXiv:1510.02488). The spin supercurrent generated in this way does not decay spatially, in stark contrast to normal spin currents that remain polarized only up to the spin relaxation length. Through a novel interference term between long-ranged and short-ranged Cooper pairs, we expose the existence of a superconductivity-mediated torque even without magnetic inhomogeneities, showing that the different components of the spin supercurrent polarization respond fundamentally differently to a change in the superconducting phase difference. This establishes a mechanism for tuning dissipationless spin and charge flow separately via superconductors. Supported by COST Action MP-1201 and RCN Grant Numbers 205591, 216700 and 24806.

Atomic-scale sensing of the magnetic dipolar field from single atoms

NASA Astrophysics Data System (ADS)

Choi, Taeyoung; Paul, William; Rolf-Pissarczyk, Steffen; MacDonald, Andrew J.; Natterer, Fabian D.; Yang, Kai; Willke, Philip; Lutz, Christopher P.; Heinrich, Andreas J.

2017-05-01

Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions. In recent years, there have been notable achievements in detecting and coherently controlling individual atomic-scale spin centres for sensitive local magnetometry. However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges. Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r-3.01±0.04). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.

Spin-dependent tunneling recombination in heterostructures with a magnetic layer

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

Denisov, K. S., E-mail: denisokonstantin@gmail.com; Rozhansky, I. V.; Averkiev, N. S.

We propose a mechanism for the generation of spin polarization in semiconductor heterostructures with a quantum well and a magnetic impurity layer spatially separated from it. The spin polarization of carriers in a quantum well originates from spin-dependent tunneling recombination at impurity states in the magnetic layer, which is accompanied by a fast linear increase in the degree of circular polarization of photoluminescence from the quantum well. Two situations are theoretically considered. In the first case, resonant tunneling to the spin-split sublevels of the impurity center occurs and spin polarization is caused by different populations of resonance levels in themore » quantum well for opposite spin projections. In the second, nonresonant case, the spin-split impurity level lies above the occupied states of electrons in the quantum well and plays the role of an intermediate state in the two-stage coherent spin-dependent recombination of an electron from the quantum well and a hole in the impurity layer. The developed theory allows us to explain both qualitatively and quantitatively the kinetics of photoexcited electrons in experiments with photoluminescence with time resolution in Mn-doped InGaAs heterostructures.« less

Current-Tunable NbTiN Coplanar Photonic Bandgap Resonators

NASA Astrophysics Data System (ADS)

Asfaw, A.; Sigillito, A. J.; Tyryshkin, A. M.; Lyon, S. A.

Coplanar waveguide resonators have been used in several experimental settings, from superconducting qubits to electron spin resonance. In our particular application of electron spin resonance, these resonators provide increased sensitivity to electron spins due to the small mode volume. Experiments have shown that these resonators can be used to readout as few as 300 spins per shot. Recently, photonic bandgap resonators have been shown to extend the advantages of traditional CPW resonators by allowing spin manipulation both at microwave and radio frequencies, thereby enabling both electron and nuclear spin resonance within the same resonator. We present measurements made using photonic bandgap resonators fabricated with thin NbTiN films which demonstrate microwave tunability of the resonator by modulating the kinetic inductance of the superconductor. Driving a small direct current through the center pin of the resonator allows us to tune the resonant frequency by over 30 MHz around 6.4 GHz while maintaining a quality factor over 8000 at 4.8K. This provides fast and simple tunability of coplanar waveguide resonators and opens new possibilities for multiple frequency electron spin resonance experiments.

Spin-phonon coupling in BaFe{sub 12}O{sub 19} M-type hexaferrite

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

Silva Júnior, Flávio M.; Paschoal, Carlos W. A., E-mail: paschoal.william@gmail.com

2014-12-28

The spin-phonon coupling in magnetic materials is due to the modulation of the exchange integral by lattice vibrations. BaFe{sub 12}O{sub 19} M-type hexaferrite, which is the most used magnetic material as permanent magnet, transforms into ferrimagnet at high temperatures, but no spin-phonon coupling was previously observed at this transition. In this letter, we investigated the temperature-dependent Raman spectra of polycrystalline BaFe{sub 12}O{sub 19} M-type hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at the ferrimagnetic transition. An anomaly was observed in the position of the phonon attributed to the Fe{sup (4)}O{sub 6}, Fe{sup (5)}O{sub 6}, and Fe{supmore » (1)}O{sub 6} octahedra, evidencing the presence of a spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The results also confirmed the spin-phonon coupling is different for each phonon even when they couple with the same spin configuration.« less

A dressed spin qubit in silicon

DOE PAGES

Laucht, Arne; Kalra, Rachpon; Simmons, Stephanie; ...

2016-10-17

Coherent dressing of a quantum two-level system provides access to a new quantum system with improved properties—a different and easily tunable level splitting, faster control and longer coherence times. In our work we investigate the properties of the dressed, donor-bound electron spin in silicon, and assess its potential as a quantum bit in scalable architectures. The two dressed spin-polariton levels constitute a quantum bit that can be coherently driven with an oscillating magnetic field, an oscillating electric field, frequency modulation of the driving field or a simple detuning pulse. We measure coherence times of T* 2p = 2.4 ms andmore » T Hahn 2p = 9 ms, one order of magnitude longer than those of the undressed spin. Moreover, the use of the dressed states enables coherent coupling of the solid-state spins to electric fields and mechanical oscillations.« less

Electrical detection of nuclear spins in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Malissa, H.; Kavand, M.; Waters, D. P.; Lupton, J. M.; Vardeny, Z. V.; Saam, B.; Boehme, C.

2014-03-01

We present pulsed combined electrically detected electron paramagnetic and nuclear magnetic resonance experiments on MEH-PPV OLEDs. Spin dynamics in these structures are governed by hyperfine interactions between charge carriers and the surrounding hydrogen nuclei, which are abundant in these materials. Hyperfine coupling has been observed by monitoring the device current during coherent spin excitation. Electron spin echoes (ESEs) are detected by applying one additional readout pulse at the time of echo formation. This allows for the application of high-resolution spectroscopy based on ESE detection, such as electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance (ENDOR) available for electrical detection schemes. We conduct electrically detected ESEEM and ENDOR experiments and show how hyperfine interactions in MEH-PPV with and without deuterated polymer side groups can be observed by device current measurements. We acknowledge support by the Department of Energy, Office of Basic Energy Sciences under Award #DE-SC0000909.

Landau-Zener-Stückelberg-Majorana Interferometry of a Single Hole

NASA Astrophysics Data System (ADS)

Bogan, Alex; Studenikin, Sergei; Korkusinski, Marek; Gaudreau, Louis; Zawadzki, Piotr; Sachrajda, Andy S.; Tracy, Lisa; Reno, John; Hargett, Terry

2018-05-01

We perform Landau-Zener-Stückelberg-Majorana (LZSM) spectroscopy on a system with strong spin-orbit interaction (SOI), realized as a single hole confined in a gated double quantum dot. Analogous to electron systems, at a magnetic field B =0 and high modulation frequencies, we observe photon-assisted tunneling between dots, which smoothly evolves into the typical LZSM funnel-shaped interference pattern as the frequency is decreased. In contrast to electrons, the SOI enables an additional, efficient spin-flip interdot tunneling channel, introducing a distinct interference pattern at finite B . Magnetotransport spectra at low-frequency LZSM driving show the two channels to be equally coherent. High-frequency LZSM driving reveals complex photon-assisted tunneling pathways, both spin conserving and spin flip, which form closed loops at critical magnetic fields. In one such loop, an arbitrary hole spin state is inverted, opening the way toward its all-electrical manipulation.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia; Park, Jungsik; Pearson, John E.; Novosad, Valentine; Schiffer, Peter; Hoffmann, Axel

2017-12-01

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magnetotransport measurements. The experimental findings are described using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.

High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

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

Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia

Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magneto-transport measurements. The experimental findings are describedmore » using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.« less

High resolution multiplexed functional imaging in live embryos (Conference Presentation)

NASA Astrophysics Data System (ADS)

Xu, Dongli; Zhou, Weibin; Peng, Leilei

2017-02-01

Fourier multiplexed fluorescence lifetime imaging (FmFLIM) scanning laser optical tomography (FmFLIM-SLOT) combines FmFLIM and Scanning laser optical tomography (SLOT) to perform multiplexed 3D FLIM imaging of live embryos. The system had demonstrate multiplexed functional imaging of zebrafish embryos genetically express Foster Resonant Energy Transfer (FRET) sensors. However, previous system has a 20 micron resolution because the focused Gaussian beam diverges quickly from the focused plane, makes it difficult to achieve high resolution imaging over a long projection depth. Here, we present a high-resolution FmFLIM-SLOT system with achromatic Bessel beam, which achieves 3 micron resolution in 3D deep tissue imaging. In Bessel-FmFLIM-SLOT, multiple laser excitation lines are firstly intensity modulated by a Michelson interferometer with a spinning polygon mirror optical delay line, which enables Fourier multiplexed multi-channel lifetime measurements. Then, a spatial light modulator and a prism are used to transform the modulated Gaussian laser beam to an achromatic Bessel beam. The achromatic Bessel beam scans across the whole specimen with equal angular intervals as sample rotated. After tomography reconstruction and the frequency domain lifetime analysis method, both the 3D intensity and lifetime image of multiple excitation-emission can be obtained. Using Bessel-FmFLIM-SLOT system, we performed cellular-resolution FLIM tomography imaging of live zebrafish embryo. Genetically expressed FRET sensors in these embryo will allow non-invasive observation of multiple biochemical processes in vivo.

cluster trials v. 1.0

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

Mitchell, John; Castillo, Andrew

2016-09-21

This software contains a set of python modules – input, search, cluster, analysis; these modules read input files containing spatial coordinates and associated attributes which can be used to perform nearest neighbor search (spatial indexing via kdtree), cluster analysis/identification, and calculation of spatial statistics for analysis.

Aerial projection of three-dimensional motion pictures by electro-holography and parabolic mirrors.

PubMed

Kakue, Takashi; Nishitsuji, Takashi; Kawashima, Tetsuya; Suzuki, Keisuke; Shimobaba, Tomoyoshi; Ito, Tomoyoshi

2015-07-08

We demonstrate an aerial projection system for reconstructing 3D motion pictures based on holography. The system consists of an optical source, a spatial light modulator corresponding to a display and two parabolic mirrors. The spatial light modulator displays holograms calculated by computer and can reconstruct holographic motion pictures near the surface of the modulator. The two parabolic mirrors can project floating 3D images of the motion pictures formed by the spatial light modulator without mechanical scanning or rotating. In this demonstration, we used a phase-modulation-type spatial light modulator. The number of pixels and the pixel pitch of the modulator were 1,080 × 1,920 and 8.0 μm × 8.0 μm, respectively. The diameter, the height and the focal length of each parabolic mirror were 288 mm, 55 mm and 100 mm, respectively. We succeeded in aerially projecting 3D motion pictures of size ~2.5 mm(3) by this system constructed by the modulator and mirrors. In addition, by applying a fast computational algorithm for holograms, we achieved hologram calculations at ~12 ms per hologram with 4 CPU cores.

Aerial projection of three-dimensional motion pictures by electro-holography and parabolic mirrors

PubMed Central

Kakue, Takashi; Nishitsuji, Takashi; Kawashima, Tetsuya; Suzuki, Keisuke; Shimobaba, Tomoyoshi; Ito, Tomoyoshi

2015-01-01

We demonstrate an aerial projection system for reconstructing 3D motion pictures based on holography. The system consists of an optical source, a spatial light modulator corresponding to a display and two parabolic mirrors. The spatial light modulator displays holograms calculated by computer and can reconstruct holographic motion pictures near the surface of the modulator. The two parabolic mirrors can project floating 3D images of the motion pictures formed by the spatial light modulator without mechanical scanning or rotating. In this demonstration, we used a phase-modulation-type spatial light modulator. The number of pixels and the pixel pitch of the modulator were 1,080 × 1,920 and 8.0 μm × 8.0 μm, respectively. The diameter, the height and the focal length of each parabolic mirror were 288 mm, 55 mm and 100 mm, respectively. We succeeded in aerially projecting 3D motion pictures of size ~2.5 mm3 by this system constructed by the modulator and mirrors. In addition, by applying a fast computational algorithm for holograms, we achieved hologram calculations at ~12 ms per hologram with 4 CPU cores. PMID:26152453

Creation of diffraction-limited non-Airy multifocal arrays using a spatially shifted vortex beam

NASA Astrophysics Data System (ADS)

Lin, Han; Gu, Min

2013-02-01

Diffraction-limited non-Airy multifocal arrays are created by focusing a phase-modulated vortex beam through a high numerical-aperture objective. The modulated phase at the back aperture of the objective resulting from the superposition of two concentric phase-modulated vortex beams allows for the generation of a multifocal array of cylindrically polarized non-Airy patterns. Furthermore, we shift the spatial positions of the phase vortices to manipulate the intensity distribution at each focal spot, leading to the creation of a multifocal array of split-ring patterns. Our method is experimentally validated by generating the predicted phase modulation through a spatial light modulator. Consequently, the spatially shifted circularly polarized vortex beam adopted in a dynamic laser direct writing system facilitates the fabrication of a split-ring microstructure array in a polymer material by a single exposure of a femtosecond laser beam.

Attention operates uniformly throughout the classical receptive field and the surround.

PubMed

Verhoef, Bram-Ernst; Maunsell, John Hr

2016-08-22

Shifting attention among visual stimuli at different locations modulates neuronal responses in heterogeneous ways, depending on where those stimuli lie within the receptive fields of neurons. Yet how attention interacts with the receptive-field structure of cortical neurons remains unclear. We measured neuronal responses in area V4 while monkeys shifted their attention among stimuli placed in different locations within and around neuronal receptive fields. We found that attention interacts uniformly with the spatially-varying excitation and suppression associated with the receptive field. This interaction explained the large variability in attention modulation across neurons, and a non-additive relationship among stimulus selectivity, stimulus-induced suppression and attention modulation that has not been previously described. A spatially-tuned normalization model precisely accounted for all observed attention modulations and for the spatial summation properties of neurons. These results provide a unified account of spatial summation and attention-related modulation across both the classical receptive field and the surround.

Improving spectral resolution in spatial encoding dimension of single-scan nuclear magnetic resonance 2D spin echo correlated spectroscopy

NASA Astrophysics Data System (ADS)

Lin, Liangjie; Wei, Zhiliang; Yang, Jian; Lin, Yanqin; Chen, Zhong

2014-11-01

The spatial encoding technique can be used to accelerate the acquisition of multi-dimensional nuclear magnetic resonance spectra. However, with this technique, we have to make trade-offs between the spectral width and the resolution in the spatial encoding dimension (F1 dimension), resulting in the difficulty of covering large spectral widths while preserving acceptable resolutions for spatial encoding spectra. In this study, a selective shifting method is proposed to overcome the aforementioned drawback. This method is capable of narrowing spectral widths and improving spectral resolutions in spatial encoding dimensions by selectively shifting certain peaks in spectra of the ultrafast version of spin echo correlated spectroscopy (UFSECSY). This method can also serve as a powerful tool to obtain high-resolution correlated spectra in inhomogeneous magnetic fields for its resistance to any inhomogeneity in the F1 dimension inherited from UFSECSY. Theoretical derivations and experiments have been carried out to demonstrate performances of the proposed method. Results show that the spectral width in spatial encoding dimension can be reduced by shortening distances between cross peaks and axial peaks with the proposed method and the expected resolution improvement can be achieved. Finally, the shifting-absent spectrum can be recovered readily by post-processing.

High Speed Computational Ghost Imaging via Spatial Sweeping

NASA Astrophysics Data System (ADS)

Wang, Yuwang; Liu, Yang; Suo, Jinli; Situ, Guohai; Qiao, Chang; Dai, Qionghai

2017-03-01

Computational ghost imaging (CGI) achieves single-pixel imaging by using a Spatial Light Modulator (SLM) to generate structured illuminations for spatially resolved information encoding. The imaging speed of CGI is limited by the modulation frequency of available SLMs, and sets back its practical applications. This paper proposes to bypass this limitation by trading off SLM’s redundant spatial resolution for multiplication of the modulation frequency. Specifically, a pair of galvanic mirrors sweeping across the high resolution SLM multiply the modulation frequency within the spatial resolution gap between SLM and the final reconstruction. A proof-of-principle setup with two middle end galvanic mirrors achieves ghost imaging as fast as 42 Hz at 80 × 80-pixel resolution, 5 times faster than state-of-the-arts, and holds potential for one magnitude further multiplication by hardware upgrading. Our approach brings a significant improvement in the imaging speed of ghost imaging and pushes ghost imaging towards practical applications.

Off-forward gluonic structure of vector mesons

NASA Astrophysics Data System (ADS)

Detmold, W.; Pefkou, D.; Shanahan, P. E.

2017-06-01

The spin-independent and transversity generalized form factors (GFFs) of the ϕ meson are studied using lattice QCD calculations with light quark masses corresponding to a pion mass mπ˜450 (5 ) MeV . One transversity and three spin-independent GFFs related to the lowest moments of leading-twist spin-independent and transversity gluon distributions are obtained at six nonzero values of the momentum transfer up to 1.2 GeV 2 . These quantities are compared with the analogous spin-independent quark GFFs and the electromagnetic form factors determined on the same lattice ensemble. The results show quantitative distinction between the spatial distribution of transversely polarized gluons, unpolarized gluons, and quarks and point the way towards further investigations of the gluon structure of nucleons and nuclei.

Three-dimensional spin mapping of antiferromagnetic nanopyramids having spatially alternating surface anisotropy at room temperature.

PubMed

Wang, Kangkang; Smith, Arthur R

2012-11-14

Antiferromagnets play a key role in modern spintronic devices owing to their ability to modify the switching behavior of adjacent ferromagnets via the exchange bias effect. Consequently, detailed measurements of the spin structure at antiferromagnetic interfaces and surfaces are highly desirable, not only for advancing technologies but also for enabling new insights into the underlying physics. Here using spin-polarized scanning tunneling microscopy at room-temperature, we reveal in three-dimensions an orthogonal spin structure on antiferromagnetic compound nanopyramids. Contrary to expected uniaxial anisotropy based on bulk properties, the atomic terraces are found to have alternating in-plane and out-of-plane magnetic anisotropies. The observed layer-wise alternation in anisotropy could have strong influences on future nanoscale spintronic applications.

Measurement-Based Entanglement of Noninteracting Bosonic Atoms

NASA Astrophysics Data System (ADS)

Lester, Brian J.; Lin, Yiheng; Brown, Mark O.; Kaufman, Adam M.; Ball, Randall J.; Knill, Emanuel; Rey, Ana M.; Regal, Cindy A.

2018-05-01

We demonstrate the ability to extract a spin-entangled state of two neutral atoms via postselection based on a measurement of their spatial configuration. Typically, entangled states of neutral atoms are engineered via atom-atom interactions. In contrast, in our Letter, we use Hong-Ou-Mandel interference to postselect a spin-singlet state after overlapping two atoms in distinct spin states on an effective beam splitter. We verify the presence of entanglement and determine a bound on the postselected fidelity of a spin-singlet state of (0.62 ±0.03 ). The experiment has direct analogy to creating polarization entanglement with single photons and hence demonstrates the potential to use protocols developed for photons to create complex quantum states with noninteracting atoms.

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

Cable, J.W.

The diffuse scattering of neutrons from magnetic materials provides unique and important information regarding the spatial correlations of the atoms and the spins. Such measurements have been extensively applied to magnetically ordered systems, such as the ferromagnetic binary alloys, for which the observed correlations describe the magnetic moment fluctuations associated with local environment effects. With the advent of polarization analysis, these techniques are increasingly being applied to study disordered paramagnetic systems such as the spin-glasses and the diluted magnetic semiconductors. The spin-pair correlations obtained are essential in understanding the exchange interactions of such systems. In this paper, we describe recentmore » neutron diffuse scattering results on the atom-pair and spin-pair correlations in some of these disordered magnetic systems. 56 refs.« less

Measurement-Based Entanglement of Noninteracting Bosonic Atoms.

PubMed

Lester, Brian J; Lin, Yiheng; Brown, Mark O; Kaufman, Adam M; Ball, Randall J; Knill, Emanuel; Rey, Ana M; Regal, Cindy A

2018-05-11

We demonstrate the ability to extract a spin-entangled state of two neutral atoms via postselection based on a measurement of their spatial configuration. Typically, entangled states of neutral atoms are engineered via atom-atom interactions. In contrast, in our Letter, we use Hong-Ou-Mandel interference to postselect a spin-singlet state after overlapping two atoms in distinct spin states on an effective beam splitter. We verify the presence of entanglement and determine a bound on the postselected fidelity of a spin-singlet state of (0.62±0.03). The experiment has direct analogy to creating polarization entanglement with single photons and hence demonstrates the potential to use protocols developed for photons to create complex quantum states with noninteracting atoms.

Quantum gyroscope based on Berry phase of spins in diamond

NASA Astrophysics Data System (ADS)

Song, Xuerui; Wang, Liujun; Diao, Wenting; Duan, Chongdi

2018-02-01

Gyroscope is the crucial sensor of the inertial navigation system, there is always high demand to improve the sensitivity and reduce the size of the gyroscopes. Using the NV center electronic spin and nuclear spin qubits in diamond, we introduce the research of new types of quantum gyroscopes based on the Berry phase shifts of the spin states during the rotation of the sensor systems. Compared with the performance of the traditional MEMS gyroscope, the sensitivity of the new types of quantum gyroscopes was highly improved and the spatial resolution was reduced to nano-scale. With the help of micro-manufacturing technology in the semiconductor industry, the quantum gyroscopes introduced here can be further integrated into chip-scale sensors.

Circuit quantum electrodynamics with a spin qubit.

PubMed

Petersson, K D; McFaul, L W; Schroer, M D; Jung, M; Taylor, J M; Houck, A A; Petta, J R

2012-10-18

Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.

Spatial resolution limitation of liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Wang, Xinghua; Wang, Bin; McManamon, Paul F., III; Pouch, John J.; Miranda, Felix A.; Anderson, James E.; Bos, Philip J.

2004-10-01

The effect of fringing electric fields in a liquid crystal (LC) Optical Phased Array (OPA), also referred to as a spatial light modulator (SLM), is a governing factor that determines the diffraction efficiency (DE) of the LC OPA for high resolution spatial phase modulation. In this article, the fringing field effect in a high resolution LC OPA is studied by accurate modeling the DE of the LC blazed gratings by LC director simulation and Finite Difference Time Domain (FDTD) simulation. Influence factors that contribute significantly to the DE are discussed. Such results provide fundamental understanding for high resolution LC devices.

Spinning particles in vacuum spacetimes of different curvature types

NASA Astrophysics Data System (ADS)

Semerák, O.; Šrámek, M.

2015-09-01

We consider the motion of spinning test particles with nonzero rest mass in the "pole-dipole" approximation, as described by the Mathisson-Papapetrou-Dixon (MPD) equations, and examine its properties in dependence on the spin supplementary condition added to close the system. In order to better understand the spin-curvature interaction, the MPD equation of motion is decomposed in the orthonormal tetrad whose time vector is given by the four-velocity Vμ chosen to fix the spin condition (the "reference observer") and the first spatial vector by the corresponding spin sμ; such projections do not contain the Weyl scalars Ψ0 and Ψ4 obtained in the associated Newman-Penrose (NP) null tetrad. One natural option of how to choose the remaining two spatial basis vectors is shown to follow "intrinsically" whenever Vμ has been chosen; it is realizable if the particle's four-velocity and four-momentum are not parallel. In order to see how the problem depends on the algebraic type of curvature, one first identifies the first vector of the NP tetrad kμ with the highest-multiplicity principal null direction of the Weyl tensor, and then sets Vμ so that kμ belong to the spin-bivector eigenplane. In spacetimes of any algebraic type but III, it is known to be possible to rotate the tetrads so as to become "transverse," namely so that Ψ1 and Ψ3 vanish. If the spin-bivector eigenplane could be made to coincide with the real-vector plane of any of such transverse frames, the spinning particle motion would consequently be fully determined by Ψ2 and the cosmological constant; however, this can be managed in exceptional cases only. Besides focusing on specific Petrov types, we derive several sets of useful relations that are valid generally and check whether/how the exercise simplifies for some specific types of motion. The particular option of having four-velocity parallel to four-momentum is advocated, and a natural resolution of nonuniqueness of the corresponding reference observer Vμ is suggested.

Spatially Modulated Gain Waveguide Electro-Optic Laser

DTIC Science & Technology

2013-08-09

1997, pp 1223-1226. 5. Y. Li, S. M. Goldwasser, P. Herczfeld, L.M. Narducci, "Dynamics of an electro-optically tunable microchip laser ", IEEE...TYPE Final 3. DATES COVERED (From 7/2/2010-5-10-2013 To) 4. TITLE AND SUBTITLE Spatially modulated gain waveguide electro-optic laser 5a...optical waveguides laser on LiNb03 substrate. The main goal of this work is to implement an active LiNb03 waveguide with the desired spatially modulated

Observation of a Discrete Time Crystal

NASA Astrophysics Data System (ADS)

Kyprianidis, A.; Zhang, J.; Hess, P.; Becker, P.; Lee, A.; Smith, J.; Pagano, G.; Potter, A.; Vishwanath, A.; Potirniche, I.-D.; Yao, N.; Monroe, C.

2017-04-01

Spontaneous symmetry breaking is a key concept in the understanding of many physical phenomena, such as the formation of spatial crystals and the phase transition from paramagnetism to magnetic order. While the breaking of time translation symmetry is forbidden in equilibrium systems, it is possible for non-equilibrium Floquet driven systems to break a discrete time translation symmetry, and we present clear signatures of the formation of such a discrete time crystal. We apply a time periodic Hamiltonian to a chain of interacting spins under many-body localization conditions and observe the system's sub-harmonic response at twice that period. This spontaneous doubling of the periodicity is robust to external perturbations. We represent the spins with a linear chain of trapped 171Yb+ ions in an rf Paul trap, generate spin-spin interactions through spin-dependent optical dipole forces, and measure each spin using state-dependent fluorescence. This work is supported by the ARO Atomic Physics Program, the AFOSR MURI on Quantum Measurement and Verification, and the NSF Physics Frontier Center at JQI.

Suppression of electron spin decoherence in Rabi oscillations induced by an inhomogeneous microwave field

NASA Astrophysics Data System (ADS)

Saiko, A. P.; Fedaruk, R.; Markevich, S. A.

2018-05-01

The decay of Rabi oscillations provides direct information about coherence of electron spins. When observed in EPR experiments, it is often shortened by spatial inhomogeneity of the microwave field amplitude in a bulk sample. In order to suppress this undesired loss of coherence, we propose an additional dressing of spin states by a weak longitudinal continuous radiofrequency field. The Gaussian, cosine and linear distributions of the microwave amplitude is analyzed. Our calculations of the Rabi oscillations between the doubly dressed spin states show that for all these distributions the maximum suppression of the inhomogeneity-induced decoherence is achieved at the so-called Rabi resonance when the radio-field frequency is in resonance with the Rabi frequency of spins in the microwave field. The manifestations of such suppression in the published EPR experiments with the bichromatic driving are discussed. The realization of the Rabi resonance using the radiofrequency field could open new possibilities for separating the contributions of relaxation mechanisms from those due to the inhomogeneous driving in spin decoherence.

Optical charge state control of spin defects in 4H-SiC

DOE PAGES

Wolfowicz, Gary; Anderson, Christopher P.; Yeats, Andrew L.; ...

2017-11-30

Defects in silicon carbide (SiC) have emerged as a favorable platform for optically active spin-based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ability to control these states can provide enhanced spin-dependent readout and long-term charge stability. We investigate this charge state control for two major spin qubits in 4H-SiC, the divacancy and silicon vacancy, obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from divacancy ensembles by up to three orders of magnitude using near-ultraviolet excitation, depending on the substrate, and without degrading themore » electron spin coherence time. This charge conversion remains stable for hours at cryogenic temperatures, allowing spatial and persistent patterning of the charge state populations. As a result, we develop a comprehensive model of the defects and optical processes involved, offering a strong basis to improve material design and to develop quantum applications in SiC.« less

Optical charge state control of spin defects in 4H-SiC

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

Wolfowicz, Gary; Anderson, Christopher P.; Yeats, Andrew L.

Defects in silicon carbide (SiC) have emerged as a favorable platform for optically active spin-based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ability to control these states can provide enhanced spin-dependent readout and long-term charge stability. We investigate this charge state control for two major spin qubits in 4H-SiC, the divacancy and silicon vacancy, obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from divacancy ensembles by up to three orders of magnitude using near-ultraviolet excitation, depending on the substrate, and without degrading themore » electron spin coherence time. This charge conversion remains stable for hours at cryogenic temperatures, allowing spatial and persistent patterning of the charge state populations. As a result, we develop a comprehensive model of the defects and optical processes involved, offering a strong basis to improve material design and to develop quantum applications in SiC.« less

Single-spin stochastic optical reconstruction microscopy

PubMed Central

Pfender, Matthias; Aslam, Nabeel; Waldherr, Gerald; Neumann, Philipp; Wrachtrup, Jörg

2014-01-01

We experimentally demonstrate precision addressing of single-quantum emitters by combined optical microscopy and spin resonance techniques. To this end, we use nitrogen vacancy (NV) color centers in diamond confined within a few ten nanometers as individually resolvable quantum systems. By developing a stochastic optical reconstruction microscopy (STORM) technique for NV centers, we are able to simultaneously perform sub–diffraction-limit imaging and optically detected spin resonance (ODMR) measurements on NV spins. This allows the assignment of spin resonance spectra to individual NV center locations with nanometer-scale resolution and thus further improves spatial discrimination. For example, we resolved formerly indistinguishable emitters by their spectra. Furthermore, ODMR spectra contain metrology information allowing for sub–diffraction-limit sensing of, for instance, magnetic or electric fields with inherently parallel data acquisition. As an example, we have detected nuclear spins with nanometer-scale precision. Finally, we give prospects of how this technique can evolve into a fully parallel quantum sensor for nanometer resolution imaging of delocalized quantum correlations. PMID:25267655

Modulation of spatial Stroop by object-based attention but not by space-based attention.

PubMed

Luo, Chunming; Lupiáñez, Juan; Funes, María Jesús; Fu, Xiaolan

2010-03-01

Earlier studies have shown that the spatial Stroop effect systematically decreases when a peripheral precue is presented at the same location as the target, compared to an uncued location condition. In this study, two experiments were conducted to explore whether the cueing modulation of spatial Stroop is object based and/or space based. In Experiment 1, we found evidence favouring the view that the cueing modulation of the spatial Stroop effect is entirely object based, as no differences were found in conflict reduction for the same-location and same-object conditions. In Experiment 2, the cue was predictive, and a similar object-based modulation of spatial Stroop was still observed. However, the direction of such modulation was affected by the rectangles' orientation. Overall, the pattern of results obtained favours the object-integration (Lupiáñez & Milliken, 1999; Lupiáñez, Milliken, Solano, Weaver, & Tipper, 2001) and referential-coding accounts (Danziger, Kingstone, & Ward, 2001) and seems to provide evidence against the attention-shift account (Rubichi, Nicoletti, Iani, & Umilta, 1997; Stoffer, 1991).

Nitrogen-vacancy-assisted magnetometry of paramagnetic centers in an individual diamond nanocrystal.

PubMed

Laraoui, Abdelghani; Hodges, Jonathan S; Meriles, Carlos A

2012-07-11

Semiconductor nanoparticles host a number of paramagnetic point defects and impurities, many of them adjacent to the surface, whose response to external stimuli could help probe the complex dynamics of the particle and its local, nanoscale environment. Here, we use optically detected magnetic resonance in a nitrogen-vacancy (NV) center within an individual diamond nanocrystal to investigate the composition and spin dynamics of the particle-hosted spin bath. For the present sample, a ∼45 nm diamond crystal, NV-assisted dark-spin spectroscopy reveals the presence of nitrogen donors and a second, yet-unidentified class of paramagnetic centers. Both groups share a common spin lifetime considerably shorter than that observed for the NV spin, suggesting some form of spatial clustering, possibly on the nanoparticle surface. Using double spin resonance and dynamical decoupling, we also demonstrate control of the combined NV center-spin bath dynamics and attain NV coherence lifetimes comparable to those reported for bulk, Type Ib samples. Extensions based on the experiments presented herein hold promise for applications in nanoscale magnetic sensing, biomedical labeling, and imaging.

Rashba quantum wire: exact solution and ballistic transport.

PubMed

Perroni, C A; Bercioux, D; Ramaglia, V Marigliano; Cataudella, V

2007-05-08

The effect of Rashba spin-orbit interaction in quantum wires with hard-wall boundaries is discussed. The exact wavefunction and eigenvalue equation are worked out, pointing out the mixing between the spin and spatial parts. The spectral properties are also studied within perturbation theory with respect to the strength of the spin-orbit interaction and diagonalization procedure. A comparison is made with the results of a simple model, the two-band model, that takes account only of the first two sub-bands of the wire. Finally, the transport properties within the ballistic regime are analytically calculated for the two-band model and through a tight-binding Green function for the entire system. Single and double interfaces separating regions with different strengths of spin-orbit interaction are analysed by injecting carriers into the first and the second sub-band. It is shown that in the case of a single interface the spin polarization in the Rashba region is different from zero, and in the case of two interfaces the spin polarization shows oscillations due to spin-selective bound states.

Spin precession in spin-orbit coupled weak links: Coulomb repulsion and Pauli quenching

NASA Astrophysics Data System (ADS)

Shekhter, R. I.; Entin-Wohlman, O.; Jonson, M.; Aharony, A.

2017-12-01

A simple model for the transmission of pairs of electrons through a weak electric link in the form of a nanowire made of a material with strong electron spin-orbit interaction (SOI) is presented, with emphasis on the effects of Coulomb interactions and the Pauli exclusion principle. The constraints due to the Pauli principle are shown to "quench" the coherent SOI-induced precession of the spins when the spatial wave packets of the two electrons overlap significantly. The quenching, which results from the projection of the pair's spin states onto spin-up and spin-down states on the link, breaks up the coherent propagation in the link into a sequence of coherent hops that add incoherently. Applying the model to the transmission of Cooper pairs between two superconductors, we find that in spite of Pauli quenching, the Josephson current oscillates with the strength of the SOI, but may even change its sign (compared to the limit of the Coulomb blockade, when the quenching is absent). Conditions for an experimental detection of these features are discussed.

Towards Lagrangian formulations of mixed-symmetry higher spin fields on AdS-space within BFV-BRST formalism

NASA Astrophysics Data System (ADS)

Reshetnyak, A. A.

2010-11-01

The spectrum of superstring theory on the AdS 5 × S 5 Ramond-Ramond background in tensionless limit contains integer and half-integer higher-spin fields subject at most to two-rows Young tableaux Y( s 1, s 2). We review the details of a gauge-invariant Lagrangian description of such massive and massless higher-spin fields in anti-de-Sitter spaces with arbitrary dimensions. The procedure is based on the construction of Verma modules, its oscillator realizations and of a BFV-BRST operator for non-linear algebras encoding unitary irreducible representations of AdS group.

New nitrosoureas and their spin-labeled derivatives influence dopa-oxidase activity of tyrosinase.

PubMed

Rachkova, M; Raikova, E; Raikov, Z

1991-06-01

Tyrosinase is a key enzyme in melanine biosynthesis. The modulating effect of cytostatic agents on DOPA-oxidase activity of tyrosinase could be linked with the drug treatment of melanoma tumors. Two groups of nitrosoureas which influence DOPA-oxidase activity of tyrosinase were studied: new nitrosoureas and their spin-labeled derivatives synthesized in our laboratory. Using Burnett's spectrophotometric method (Burnett et al., 1967) the following effects were established: inhibition by CCNU, inhibition and the activating effects of the other investigated nitrosoureas depend on their physicochemical half-life. The predominant activating effect of the spin-labeled derivatives is due to the nitroxyl radical present in these compounds.

Electrical Control of g-Factor in a Few-Hole Silicon Nanowire MOSFET.

PubMed

Voisin, B; Maurand, R; Barraud, S; Vinet, M; Jehl, X; Sanquer, M; Renard, J; De Franceschi, S

2016-01-13

Hole spins in silicon represent a promising yet barely explored direction for solid-state quantum computation, possibly combining long spin coherence, resulting from a reduced hyperfine interaction, and fast electrically driven qubit manipulation. Here we show that a silicon-nanowire field-effect transistor based on state-of-the-art silicon-on-insulator technology can be operated as a few-hole quantum dot. A detailed magnetotransport study of the first accessible hole reveals a g-factor with unexpectedly strong anisotropy and gate dependence. We infer that these two characteristics could enable an electrically driven g-tensor-modulation spin resonance with Rabi frequencies exceeding several hundred mega-Hertz.

Reevaluation of spin-dependent WIMP-proton interactions as an explanation of the DAMA data

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

Nobile, Eugenio Del; Gelmini, Graciela B.; Georgescu, Andreea

2015-08-25

We reexamine the interpretation of the annual modulation signal observed by the DAMA experiment as due to WIMPs with a spin-dependent coupling mostly to protons. We consider both axial-vector and pseudo-scalar couplings, and elastic as well as endothermic and exothermic inelastic scattering. We conclude that the DAMA signal is in strong tension with null results of other direct detection experiments, particularly PICASSO and KIMS.

Direct observation and imaging of a spin-wave soliton with p-like symmetry

DOE PAGES

Bonetti, S.; Kukreja, R.; Chen, Z.; ...

2015-11-16

Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Moreover, micromagnetic simulations explain the measurements and reveal that the symmetrymore » of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.« less

Nanopatterned reconfigurable spin-textures for magnonics

NASA Astrophysics Data System (ADS)

Albisetti, E.; Petti, D.; Pancaldi, M.; Madami, M.; Tacchi, S.; Curtis, J.; King, W. P.; Papp, A.; Csaba, G.; Porod, W.; Vavassori, P.; Riedo, E.; Bertacco, R.

The control of spin-waves holds the promise to enable energy-efficient information transport and wave-based computing. Conventionally, the engineering of spin-waves is achieved via physically patterning magnetic structures such as magnonic crystals and micro-nanowires. We demonstrate a new concept for creating reconfigurable magnonic nanostructures, by crafting at the nanoscale the magnetic anisotropy landscape of a ferromagnet exchange-coupled to an antiferromagnet. By performing a highly localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are patterned without modifying the film chemistry and topography. We demonstrate that, in such structures, the spin-wave excitation and propagation can be spatially controlled at remanence, and can be tuned by external magnetic fields. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits. Partially funded by the EC through project SWING (no. 705326).

Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases

NASA Astrophysics Data System (ADS)

Ong, W.; Cheng, Chingyun; Arakelyan, I.; Thomas, J. E.

2015-03-01

We measure the density profiles for a Fermi gas of Li 6 containing N1 spin-up atoms and N2 spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N2/N1 and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N2/N1. Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases.

Direct measurement of nonlocal entanglement of two-qubit spin quantum states.

PubMed

Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou

2016-01-18

We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation.

Electron spin-echo envelope modulation (ESEEM) reveals water and phosphate interactions with the KcsA potassium channel.

PubMed

Cieslak, John A; Focia, Pamela J; Gross, Adrian

2010-02-23

Electron spin-echo envelope modulation (ESEEM) spectroscopy is a well-established technique for the study of naturally occurring paramagnetic metal centers. The technique has been used to study copper complexes, hemes, enzyme mechanisms, micellar water content, and water permeation profiles in membranes, among other applications. In the present study, we combine ESEEM spectroscopy with site-directed spin labeling (SDSL) and X-ray crystallography in order to evaluate the technique's potential as a structural tool to describe the native environment of membrane proteins. Using the KcsA potassium channel as a model system, we demonstrate that deuterium ESEEM can detect water permeation along the lipid-exposed surface of the KcsA outer helix. We further demonstrate that (31)P ESEEM is able to identify channel residues that interact with the phosphate headgroup of the lipid bilayer. In combination with X-ray crystallography, the (31)P data may be used to define the phosphate interaction surface of the protein. The results presented here establish ESEEM as a highly informative technique for SDSL studies of membrane proteins.

Panoramic attitude sensor for Radio Astronomy Explorer B

NASA Technical Reports Server (NTRS)

Thomsen, R.

1973-01-01

An instrument system to acquire attitude determination data for the RAE-B spacecraft was designed and built. The system consists of an electronics module and two optical scanner heads. Each scanner head has an optical scanner with a field of view of 0.7 degrees diameter which scans the sky and measures the position of the moon, earth and sun relative to the spacecraft. This scanning is accomplished in either of two modes. When the spacecraft is spinning, the scanner operates in spherical mode, with the spacecraft spin providing the slow sweep of lattitude to scan the entire sky. After the spacecraft is placed in lunar orbit and despun, the scanner will operate in planar mode, advancing at a rate of 5.12 seconds per revolution in a fixed plane parallel to the spacecraft Z axis. This scan will cross and measure the moon horizons with every revolution. Each scanner head also has a sun slit which is aligned parallel to the spin axis of the spacecraft and which provides a sun pulse each revolution of the spacecraft. The electronics module provides the command and control, data processing and housekeeping functions.

Spatial and spectral imaging of point-spread functions using a spatial light modulator

NASA Astrophysics Data System (ADS)

Munagavalasa, Sravan; Schroeder, Bryce; Hua, Xuanwen; Jia, Shu

2017-12-01

We develop a point-spread function (PSF) engineering approach to imaging the spatial and spectral information of molecular emissions using a spatial light modulator (SLM). We show that a dispersive grating pattern imposed upon the emission reveals spectral information. We also propose a deconvolution model that allows the decoupling of the spectral and 3D spatial information in engineered PSFs. The work is readily applicable to single-molecule measurements and fluorescent microscopy.

Atom Interferometry on Atom Chips - A Novel Approach Towards Precision Inertial Navigation System - PINS

DTIC Science & Technology

2010-06-01

Demonstration of an area-enclosing guided-atom interferometer for rotation sensing, Phys. Rev. Lett. 99, 173201 (2007). 4. Heralded Single- Magnon Quantum...excitations are quantized spin waves ( magnons ), such that transitions between its energy levels ( magnon number states) correspond to highly directional...polarization storage in the form of a single collective-spin excitation ( magnon ) that is shared between two spatially overlapped atomic ensembles

Differences in Visual-Spatial Input May Underlie Different Compression Properties of Firing Fields for Grid Cell Modules in Medial Entorhinal Cortex

PubMed Central

Raudies, Florian; Hasselmo, Michael E.

2015-01-01

Firing fields of grid cells in medial entorhinal cortex show compression or expansion after manipulations of the location of environmental barriers. This compression or expansion could be selective for individual grid cell modules with particular properties of spatial scaling. We present a model for differences in the response of modules to barrier location that arise from different mechanisms for the influence of visual features on the computation of location that drives grid cell firing patterns. These differences could arise from differences in the position of visual features within the visual field. When location was computed from the movement of visual features on the ground plane (optic flow) in the ventral visual field, this resulted in grid cell spatial firing that was not sensitive to barrier location in modules modeled with small spacing between grid cell firing fields. In contrast, when location was computed from static visual features on walls of barriers, i.e. in the more dorsal visual field, this resulted in grid cell spatial firing that compressed or expanded based on the barrier locations in modules modeled with large spacing between grid cell firing fields. This indicates that different grid cell modules might have differential properties for computing location based on visual cues, or the spatial radius of sensitivity to visual cues might differ between modules. PMID:26584432

Intrinsic errors in transporting a single-spin qubit through a double quantum dot

NASA Astrophysics Data System (ADS)

Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.

2017-07-01

Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.

Single voxel localization for dynamic hyperpolarized 13C MR spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Albert P.; Cunningham, Charles H.

2015-09-01

The PRESS technique has been widely used to achieve voxel localization for in vivo1H MRS acquisitions. However, for dynamic hyperpolarized 13C MRS experiments, the transition bands of the refocusing pulses may saturate the pre-polarized substrate spins flowing into the voxel. This limitation may be overcome by designing refocusing pulses that do not perturb the resonance of the hyperpolarized substrate, but selectively refocuses the spins of the metabolic products. In this study, a PRESS pulse sequence incorporating spectral-spatial refocusing pulses that have a stop band ('notch') at the substrate resonance is tested in vivo using hyperpolarized [1-13C]pyruvate. Higher metabolite SNR was observed in experiments using the spectral-spatial refocusing pulses as compared to conventional refocusing pulses.

Phase-space analysis of the Schwinger effect in inhomogeneous electromagnetic fields

NASA Astrophysics Data System (ADS)

Kohlfürst, Christian

2018-05-01

Schwinger pair production in spatially and temporally inhomogeneous electric and magnetic fields is studied. The focus is on the particle phase-space distribution within a high-intensity few-cycle pulse. Accurate numerical solutions of a quantum kinetic theory (DHW formalism) are presented in momentum space and, with the aid of coarse-graining techniques, in a mixed spatial-momentum representation. Additionally, signatures of the carrier-envelope phase as well as spin-field interactions are discussed on the basis of a trajectory-based model taking into account instantaneous pair production and relativistic single-particle dynamics. Although our simple semi-classical single-particle model cannot describe every aspect of the particle production process (quantum interferences), essential features such as spin-field interactions are captured.

Nanoscale magnetic imaging using picosecond thermal gradients

NASA Astrophysics Data System (ADS)

Fuchs, Gregory

Research and development in spintronics is challenged by the lack of table-top magnetic imaging technologies that posses the simultaneous temporal resolution and spatial resolution to characterize magnetization dynamics in emerging spintronic devices. In addition, many of the most exciting magnetic material systems for spintronics are difficult to image with any method. To address this challenge, we developed a spatiotemporal magnetic microscope based on picosecond heat pulses that stroboscopically transduces an in-plane magnetization into a voltage signal. When the magnetic device contains a magnetic metal like FeCoB or NiFe, we use the time-resolved anomalous Nernst effect. When it contains a magnetic insulator/normal metal bilayer like yttrium iron garnet/platinum, we use the combination of the time-resolved longitudinal spin Seebeck effect and the inverse spin Hall effect. We demonstrate that these imaging modalities have time resolutions in the range of 10-100 ps and sensitivities in the range of 0.1 - 0.3° /√{Hz} , which enables not only static magnetic imaging, but also phase-sensitive ferromagnetic resonance imaging. One application of this technology is for magnetic torque vector imaging, which we apply to a spin Hall device. We find an unexpected variation in the spin torque vector that suggests conventional, all-electrical FMR measurements of spin torque vectors can produce a systematic error as large as 30% when quantifying the spin Hall efficiency. Finally, I will describe how time-resolved magnetic imaging can greatly exceed the spatial resolution of optical diffraction. We demonstrate scanning a sharp gold tip to create near-field thermal transfer from a picosecond laser pulse to a magnetic sample as the basis of a nanoscale spatiotemporal microscope. We gratefully acknowledge support from the AFOSR (FA9550-14-1-0243) and the NSF through the Cornell Center for Materials Research (DMR-1120296).

Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers.

PubMed

Kumar, Krishan; Moudgil, R K

2012-10-17

We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.

Modulating complex beams in amplitude and phase using fast tilt-micromirror arrays and phase masks.

PubMed

Roth, Matthias; Heber, Jörg; Janschek, Klaus

2018-06-15

The Letter proposes a system for the spatial modulation of light in amplitude and phase at kilohertz frame rates and high spatial resolution. The focus is fast spatial light modulators (SLMs) consisting of continuously tiltable micromirrors. We investigate the utilization of such SLMs in combination with a static phase mask in a 4f setup. The phase mask enables the complex beam modulation in a linear optical arrangement. Furthermore, adding so-called phase steps to the phase mask increases both the number of image pixels at constant SLM resolution and the optical efficiency. We illustrate our concept based on numerical simulations.

Optically addressed and submillisecond response phase only liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Zhao, Xiangjie; Duan, Jiazhu; Zhang, Dayong; Luo, Yongquan

2014-10-01

Liquid crystal based phase only spatial light modulator has attracted many research interests since last decades because of its superior advantage. Until now the liquid crystal spatial light modulator has been applied in many fields, but the response speed of nematic LC limited its further application. In this paper, an optically addressed phase only LC spatial light modulator was proposed based on polymer network liquid crystal. Morphology effect on the light scattering of PNLC was studied, which was mainly consisted of fiber and fiber bundles. The morphology nearly determined the light scattering and electro-optical property. Due to the high threshold voltage, to address the PNLC phase modulator was also concerned. Optical addressing method was proposed, in which BSO crystal was selected to replace one of the glass substrate. The response speed of PNLC was so fast that the reorientation of liquid crystal director will follow the change of effective voltage applied on LC layer, which was related with the voltage signal and especially with electron transport of photo-induced carriers due to diffusion and drift. The on state dynamic response of phase change was investigated. Based on this device, beam steering was also achieved by loading 488nm laser strip on the optical addressed phase only spatial light modulator.

Whole-brain intracranial vessel wall imaging at 3 Tesla using cerebrospinal fluid-attenuated T1-weighted 3D turbo spin echo.

PubMed

Fan, Zhaoyang; Yang, Qi; Deng, Zixin; Li, Yuxia; Bi, Xiaoming; Song, Shlee; Li, Debiao

2017-03-01

Although three-dimensional (3D) turbo spin echo (TSE) with variable flip angles has proven to be useful for intracranial vessel wall imaging, it is associated with inadequate suppression of cerebrospinal fluid (CSF) signals and limited spatial coverage at 3 Tesla (T). This work aimed to modify the sequence and develop a protocol to achieve whole-brain, CSF-attenuated T 1 -weighted vessel wall imaging. Nonselective excitation and a flip-down radiofrequency pulse module were incorporated into a commercial 3D TSE sequence. A protocol based on the sequence was designed to achieve T 1 -weighted vessel wall imaging with whole-brain spatial coverage, enhanced CSF-signal suppression, and isotropic 0.5-mm resolution. Human volunteer and pilot patient studies were performed to qualitatively and quantitatively demonstrate the advantages of the sequence. Compared with the original sequence, the modified sequence significantly improved the T 1 -weighted image contrast score (2.07 ± 0.19 versus 3.00 ± 0.00, P = 0.011), vessel wall-to-CSF contrast ratio (0.14 ± 0.16 versus 0.52 ± 0.30, P = 0.007) and contrast-to-noise ratio (1.69 ± 2.18 versus 4.26 ± 2.30, P = 0.022). Significant improvement in vessel wall outer boundary sharpness was observed in several major arterial segments. The new 3D TSE sequence allows for high-quality T 1 -weighted intracranial vessel wall imaging at 3 T. It may potentially aid in depicting small arteries and revealing T 1 -mediated high-signal wall abnormalities. Magn Reson Med 77:1142-1150, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings

NASA Astrophysics Data System (ADS)

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-01

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter rS is increased, we observe—at a fixed spin magnetic moment—the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing rS. We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical rSc at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing rS the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings.

PubMed

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-24

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid. © 2011 IOP Publishing Ltd

A web-based spatial decision support system for spatial planning and governance in the Guangdong Province

NASA Astrophysics Data System (ADS)

Wu, Qitao; Zhang, Hong-ou; Chen, Fengui; Dou, Jie

2008-10-01

After three decades' rapid economic development, Guangdong province faces to thorny problems related to pollution, resource shortage and environmental deterioration. What is worse, the future accelerated development, urbanization and industrialization also comes at the cost of regional imbalance with economic gaps growing and the quality of life in different regions degrading. Development and Reform Commission of Guangdong Province (GDDRC) started a spatial planning project under the national frame in 2007. The prospective project is expected to enhance the equality of different regions and balance the economic development with environmental protection and improved sustainability. This manuscript presents the results of scientific research aiming to develop a Spatial Decision Support System (SDSS) for this spatial planning project. The system composes four modules include the User interface module (UIM), Spatial Analyze module (SAM), Database management module (DMM) and Help module (HM) base on ArcInfo, JSP/Servlet, JavaScript, MapServer, Visual C++ and Visual Basic technologies. The web-based SDSS provides a user-friendly tool for local decision makers, regional planners and other stakeholders in understanding and visualizing the different territorial dimensions of economic development against sustainable environmental and exhausted resources, and in defining, comparing and prioritizing specific territorially-based actions in order to prevent non-sustainable development and implement relevant politics.

Polaron Thermodynamics of Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases

NASA Astrophysics Data System (ADS)

Ong, Willie; Cheng, Chingyun; Arakelyan, Ilya; Thomas, John

2015-05-01

We present the first spatial profile measurements for spin-imbalanced mixtures of atomic 6Li fermions in a quasi-2D geometry with tunable strong interactions. The observed minority and majority profiles are not correctly predicted by BCS theory for a true 2D system, but are reasonably well fit by a 2D-polaron model of the free energy. Density difference profiles reveal a flat center with two peaks at the edges, consistent with a fully paired core of the corresponding 2D density profiles. These features are more prominent for higher interaction strengths. Not predicted by the polaron model is an observed transition from a spin-imbalanced normal fluid phase to a spin-balanced central core above a critical imbalance. Supported by ARO, DOE, AFOSR, NSF.

Multivariate quantum memory as controllable delayed multi-port beamsplitter

NASA Astrophysics Data System (ADS)

Vetlugin, A. N.; Sokolov, I. V.

2016-03-01

The addressability of parallel spatially multimode quantum memory for light allows one to control independent collective spin waves within the same cold atomic ensemble. Generally speaking, there are transverse and longitudinal degrees of freedom of the memory that one can address by a proper choice of the pump (control) field spatial pattern. Here we concentrate on the mutual evolution and transformation of quantum states of the longitudinal modes of collective spin coherence in the cavity-based memory scheme. We assume that these modes are coherently controlled by the pump waves of the on-demand transverse profile, that is, by the superpositions of waves propagating in the directions close to orthogonal to the cavity axis. By the write-in, this allows one to couple a time sequence of the incoming quantized signals to a given set of superpositions of orthogonal spin waves. By the readout, one can retrieve quantum states of the collective spin waves that are controllable superpositions of the initial ones and are coupled on demand to the output signal sequence. In a general case, the memory is able to operate as a controllable delayed multi-port beamsplitter, capable of transformation of the delays, the durations and time shapes of signals in the sequence. We elaborate the theory of such light-matter interface for the spatially multivariate cavity-based off-resonant Raman-type quantum memory. Since, in order to speed up the manipulation of complex signals in multivariate memories, it might be of interest to store relatively short light pulses of a given time shape, we also address some issues of the cavity-based memory operation beyond the bad cavity limit.

Attention operates uniformly throughout the classical receptive field and the surround

PubMed Central

Verhoef, Bram-Ernst; Maunsell, John HR

2016-01-01

Shifting attention among visual stimuli at different locations modulates neuronal responses in heterogeneous ways, depending on where those stimuli lie within the receptive fields of neurons. Yet how attention interacts with the receptive-field structure of cortical neurons remains unclear. We measured neuronal responses in area V4 while monkeys shifted their attention among stimuli placed in different locations within and around neuronal receptive fields. We found that attention interacts uniformly with the spatially-varying excitation and suppression associated with the receptive field. This interaction explained the large variability in attention modulation across neurons, and a non-additive relationship among stimulus selectivity, stimulus-induced suppression and attention modulation that has not been previously described. A spatially-tuned normalization model precisely accounted for all observed attention modulations and for the spatial summation properties of neurons. These results provide a unified account of spatial summation and attention-related modulation across both the classical receptive field and the surround. DOI: http://dx.doi.org/10.7554/eLife.17256.001 PMID:27547989

Spin-polarized current injection induced magnetic reconstruction at oxide interface

DOE PAGES

Fang, F.; Yin, Y. W.; Li, Qi; ...

2017-01-04

Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO 3/La 0.5Ca 0.5MnO 3/La 0.7Sr 0.3MnO 3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition ofmore » the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. As a result, the effect is robust and may serve as a viable route for electronic and spintronic applications.« less