Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes
NASA Astrophysics Data System (ADS)
Hamaya, K.; Kitabatake, M.; Shibata, K.; Jung, M.; Kawamura, M.; Hirakawa, K.; Machida, T.; Taniyama, T.; Ishida, S.; Arakawa, Y.
2007-12-01
Using a laterally fabricated quantum-dot (QD) spin-valve device, we experimentally study the Kondo effect in the electron transport through a semiconductor QD with an odd number of electrons (N). In a parallel magnetic configuration of the ferromagnetic electrodes, the Kondo resonance at N =3 splits clearly without external magnetic fields. With applying magnetic fields (B), the splitting is gradually reduced, and then the Kondo effect is almost restored at B =1.2T. This means that, in the Kondo regime, an inverse effective magnetic field of B ˜1.2T can be applied to the QD in the parallel magnetic configuration of the ferromagnetic electrodes.
Effect of Si Substitution on the Antiferromagnetic Ordering in the Kondo Semiconductor CeRu2Al10
NASA Astrophysics Data System (ADS)
Hayashi, Kyosuke; Muro, Yuji; Fukuhara, Tadashi; Kawabata, Jo; Kuwai, Tomohiko; Takabatake, Toshiro
2016-03-01
We have studied the effect of 3p electron doping on the unusual antiferromagnetic (AFM) order in the Kondo semiconductor CeRu2Al10 with TN = 27 K by measuring the magnetic susceptibility χ, specific heat C, and electrical resistivity ρ for polycrystalline samples of CeRu2Al10-ySiy. The large decrease in the absolute value of paramagnetic Curie temperature |θP| with increasing y indicates the suppression of c-f hybridization. The thermal activation behavior in ρ(T) above TN disappears for y ≥ 0.3 and TN decreases to 12 K for y = 0.38. These systematic changes in |θP|, ρ(T), and TN coincide with those reported in the 4d-electron doped system Ce(Ru1-xRhx)2Al10 with respect to the number of doped electrons per formula unit. This coincidence indicates that the Al 3p- and Ru 4d-electrons in CeRu2Al10 play the equivalent role in both the formation of hybridization gap and the unusual AFM ordering.
NASA Astrophysics Data System (ADS)
Tanida, H.; Nakamura, M.; Sera, M.; Nishioka, T.; Matsumura, M.
2015-12-01
We examined the chemical doping effect on the Kondo semiconductor CeFe2Al10 with a nonmagnetic ground state by means of the magnetic susceptibility, specific heat, electrical resistivity, and thermopower. The effect of Ru doping on the ground state is small. On the other hand, by a small amount of Rh doping, the magnetic susceptibility is strongly enhanced along the orthorhombic a axis, and a Curie-Weiss behavior is observed in a wide temperature range. The low-temperature specific heat is also strongly enhanced by the doping, and a metallic ground state is realized at low temperatures. These results suggest the collapse of the spin and charge gap due to the suppression of the c -f hybridization effect. From the results of a crystalline electric field analysis on the magnetic susceptibility of Ce (Fe1 -xRhx )2Al10 , it was revealed that the Rh-doping effect on the c -f hybridization effect is anisotropic, especially for the a axis. Similar doping effects are seen in the Rh-doped CeRu2Al10 , Ir-doped CeOs2Al10 , and Si-doped CeRu2Al10 . From these results, we conclude that the collapse of the spin and charge gap by such an excess electron doping is one of the universal features of the Kondo semiconductor Ce T2Al10 (T = Fe, Ru, and Os).
Fisk, Z.; Sarrao, J.L.; Thompson, J.D.
1994-10-01
The Kondo insulating materials present a particularly simple limiting case of the strongly correlated electron lattice problem: one occupied f-state interacting with a single half-filled conduction band. Experiment shows that the solution to this problem has some remarkably simple aspects. Optical conductivity data display the strong coupling nature of this physics.
NASA Astrophysics Data System (ADS)
Yoshida, K.; Okubo, R.; Tanida, H.; Matsumura, T.; Sera, M.; Nishioka, T.; Matsumura, M.; Moriyoshi, C.; Kuroiwa, Y.
2015-06-01
We have studied the Pr- and La-doping effects on the magnetic anisotropy in the antiferro-magnetic (AFM) phase of CeRu2Al10 . The crystalline electric field (CEF) splitting in PrRu2Al10 was found to be as large as ˜800 K with a singlet ground state. In Ce1 -xPrxRu2Al10 , the CEF level scheme of the Pr ion is not changed with x . The AFM moment (mAF) is rotated from c to b axis in both systems at xcsr˜0.03 and ˜0.07 for Ln=Pr and La, respectively. As the ionic radius of La and Pr is larger and smaller than that of Ce, respectively, these results indicate that the chemical pressure effect is not associated with the rotation of mAF, but is caused by the suppression of the c -f hybridization originating from the decrease of 4 f electrons of Ce ions by Ce-site substitution. Since a small amount of Pr or La doping changes easily the magnetization easy axis of all the moments on Ce sites, the origin of the magnetic anisotropy is not the local single ion effect but the bandlike effect through the anisotropic c -f hybridization. The magnetic phase diagrams of Ce1 -xLnxRu2Al10 indicate that above xcsr, the AFM order with mAF∥b continues to exist up to xc, which is ˜0.4 and ˜0.6 in Ln=Pr and Ln=La, respectively. This indicates that even in the sample with an AFM transition temperature (T0) near xc, the anisotropic c -f hybridization dominates the AFM order. A large positive transverse magnetoresistance is seen below T0, but a very small one above T0. Together with the results of Hall resistivity and the observation of Shubnikov-de Haas oscillation, we propose that there exist large Fermi surfaces above T0 and small ones below T0. A gap is opened by the AFM order on almost the area of the large Fermi surface, and small Fermi surfaces are constructed below T0, although we do not know the mechanism, which might be specific to the AFM order in Kondo semiconductors. The largest suppression of the magnetic scattering below T0 is observed for the current I ∥a and the
Photoinduced Kondo effect in CeZn3P3
NASA Astrophysics Data System (ADS)
Kitagawa, J.; Kitajima, D.; Shimokawa, K.; Takaki, H.
2016-01-01
The Kondo effect, which originates from the screening of a localized magnetic moment by a spin-spin interaction, is widely observed in nonartificial magnetic materials, artificial quantum dots, and carbon nanotubes. In devices based on quantum dots or carbon nanotubes that target quantum information applications, the Kondo effect can be tuned by a gate voltage, a magnetic field, or light. However, the manipulation of the Kondo effect in nonartificial materials has not been thoroughly studied; in particular, the artificial creation of the Kondo effect remains unexplored. Per this subject study, however, a route for the optical creation of the Kondo effect in the nonartificial material p -type semiconductor CeZn3P3 is presented. The Kondo effect emerges under visible-light illumination of the material by a continuous-wave laser diode and is ultimately revealed by photoinduced electrical resistivity, which clearly exhibits a logarithmic temperature dependency. By contrast, a La-based compound (LaZn3P3 ) displays only normal metallic behavior under similar illumination. The photoinduced Kondo effect, which occurs at higher temperatures when compared with the Kondo effect in artificial systems, provides a potential range of operation for not only quantum information/computation devices but also for operation of magneto-optic devices, thereby expanding the range of device applications based on the Kondo effect.
Spin Relaxation in Kondo Lattice Systems with Anisotropic Kondo Interaction
NASA Astrophysics Data System (ADS)
Belov, S. I.; Kutuzov, A. S.
2016-04-01
We study the influence of the Kondo effect on the spin relaxation in systems with anisotropic Kondo interaction at temperatures both high and low as compared with the static magnetic field. In the absence of the Kondo effect, the electron spin resonance linewidth is not narrowed in the whole temperature range due to the high anisotropy of the Kondo interaction. The Kondo effect leads to the universal energy scale, which regulates the temperature and magnetic field dependence of different kinetic coefficients and results in a mutual cancelation of their singular parts in a collective spin mode.
Renormalization group theory for Kondo breakdown in Kondo lattice systems
NASA Astrophysics Data System (ADS)
Ballmann, K.; Nejati, A.; Kroha, J.
2015-03-01
We present a renormalization group (RG) theory for the breakdown of Kondo screening in the Kondo lattice model (KLM) without pre-assumptions about the competition between Kondo effect and magnetic ordering or Fermi surface criticality. We show that the vertex between a single, local Kondo spin and the extended conduction electrons obtains RKKY- induced, non-local contributions in the in-and out-going coordinates of scattering electrons due to scattering at surrounding Kondo sites, but it remains local in the Kondo spin position. This enables the existence of a local Kondo screening scale TK(y) in the KLM, controlled by the effective RKKY coupling parameter y. TK(y) is determined by the RG flow of the local spin exchange coupling in the presence of the self-consistent spin response on surrounding Kondo sites. We show that TK(y) exhibits universal behavior and is suppressed by the antiferromagnetic RKKY coupling. Beyond a maximal RKKY parameter value ymax Kondo screening ceases to exist even without magnetic ordering. The theory opens up the possibility of describing quantum critical scenarios involving spin wave instabilities or local Kondo breakdown on the same footing.
How does a Kondo impurity respond to its local environment?
NASA Astrophysics Data System (ADS)
Heinrich, Andreas
2008-03-01
The interplay between localized electrons on a magnetic atom and the conducting electrons in a metal can lead to intriguing many-body ground states such as the Kondo effect. When a spin is Kondo screened by conduction electrons the entire spin system performs a complicated dance that results in the formation of a spin singlet at sufficiently low temperature. For simplicity, most theoretical considerations of Kondo screening focus on magnetic impurities with the lowest possible spin S = 1/2. Such systems can be studied experimentally in exquisite detail and with great control using quantum dots in semiconductor heterostructures or carbon nanotubes. However, in Kondo systems consisting of localized magnetic atoms, the spin is often larger, making the Kondo effect richer and more complex. Here we use the imaging and spectroscopy capabilities of a scanning tunnelling microscope to study how the Kondo screening of a known high-spin atom is determined by its local environment. Co and Ti atoms were deposited on a thin insulating layer (Cu2N) on a copper substrate. We study the influence of external magnetic fields, crystalline magnetic anisotropy, as well as spin-coupling to surrounding atomic spins on the Kondo effect that forms on the Co or Ti atoms. We find that the anisotropy of the crystalline field quenches the high-spin system of Co (S = 3/2) into an effective S = 1/2 Kramers doublet. Surprisingly, much of the impact of these environmental factors on the complex many-body ground state can be understood simply through their effects on the energy levels of the unscreened spin.
NASA Astrophysics Data System (ADS)
Dzero, Maxim; Xia, Jing; Galitski, Victor; Coleman, Piers
2016-03-01
This article reviews recent theoretical and experimental work on a new class of topological material -- topological Kondo insulators, which develop through the interplay of strong correlations and spin-orbit interactions. The history of Kondo insulators is reviewed along with the theoretical models used to describe these heavy fermion compounds. The Fu-Kane method of topological classification of insulators is used to show that hybridization between the conduction electrons and localized f electrons in these systems gives rise to interaction-induced topological insulating behavior. Finally, some recent experimental results are discussed, which appear to confirm the theoretical prediction of the topological insulating behavior in samarium hexaboride, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from robust surface states.
Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system
Ren, Jindong; Wu, Xu; Guo, Haiming Pan, Jinbo; Du, Shixuan; Gao, Hong-Jun; Luo, Hong-Gang
2015-08-17
The atomic-scale spatial relationship of a two-impurity Kondo system has been determined at varying lateral distance by scanning tunneling microscopy (STM) and spectroscopy. The localized spins of two cobalt magnetic adatoms that are placed on different electrodes of an STM form two individual Kondo singlet states, each showing quite different Kondo coupling, i.e., the tip-Kondo with low Kondo temperature and the sample-Kondo with high Kondo temperature. The differential conductance dI/dV spectra show the continuous changes of the resonance peak feature when approaching the Kondo tip laterally to the local sample-Kondo impurity on the surface. The result indicates a notable interplay between these two Kondo systems. We propose a convolution model based on the q factor of the sample-Kondo (q{sub s}) and tip-Kondo (q{sub t}) to interpret the change of various tunneling channels and the evolution of the experimental spectra.
NASA Astrophysics Data System (ADS)
Kettemann, S.; Mucciolo, E. R.; Varga, I.; Slevin, K.
2012-03-01
Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature TK is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.
From Kondo lattices to Kondo superlattices.
Shimozawa, Masaaki; Goh, Swee K; Shibauchi, Takasada; Matsuda, Yuji
2016-07-01
block layer. In addition, recent experiments involving CeCoIn5/YbCoIn5 superlattices have shown that the degree of the inversion symmetry breaking and, in turn, the Rashba splitting are controllable, offering the prospect of achieving even more fascinating superconducting states. Thus, these Kondo superlattices pave the way for the exploration of unconventional metallic and superconducting states. PMID:27275757
From Kondo lattices to Kondo superlattices
NASA Astrophysics Data System (ADS)
Shimozawa, Masaaki; Goh, Swee K.; Shibauchi, Takasada; Matsuda, Yuji
2016-07-01
block layer. In addition, recent experiments involving CeCoIn5/YbCoIn5 superlattices have shown that the degree of the inversion symmetry breaking and, in turn, the Rashba splitting are controllable, offering the prospect of achieving even more fascinating superconducting states. Thus, these Kondo superlattices pave the way for the exploration of unconventional metallic and superconducting states.
Observation of the two-channel Kondo effect
NASA Astrophysics Data System (ADS)
Potok, R. M.; Rau, I. G.; Shtrikman, Hadas; Oreg, Yuval; Goldhaber-Gordon, D.
2007-03-01
Some of the most intriguing problems in solid-state physics arise when the motion of one electron dramatically affects the motion of surrounding electrons. Traditionally, such highly correlated electron systems have been studied mainly in materials with complex transition metal chemistry. Over the past decade, researchers have learned to confine one or a few electrons within a nanometre-scale semiconductor `artificial atom', and to understand and control this simple system in detail3. Here we combine artificial atoms to create a highly correlated electron system within a nano-engineered semiconductor structure. We tune the system in situ through a quantum phase transition between two distinct states, each a version of the Kondo state, in which a bound electron interacts with surrounding mobile electrons. The boundary between these competing Kondo states is a quantum critical point-namely, the exotic and previously elusive two-channel Kondo state, in which electrons in two reservoirs are entangled through their interaction with a single localized spin.
Spin polarization of the split Kondo state.
von Bergmann, Kirsten; Ternes, Markus; Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J
2015-02-20
Spin-resolved scanning tunneling microscopy is employed to quantitatively determine the spin polarization of the magnetic field-split Kondo state. Tunneling conductance spectra of a Kondo-screened magnetic atom are evaluated within a simple model taking into account inelastic tunneling due to spin excitations and two Kondo peaks positioned symmetrically around the Fermi energy. We fit the spin state of the Kondo-screened atom with a spin Hamiltonian independent of the Kondo effect and account for Zeeman splitting of the Kondo peak in the magnetic field. We find that the width and the height of the Kondo peaks scales with the Zeeman energy. Our observations are consistent with full spin polarization of the Kondo peaks, i.e., a majority spin peak below the Fermi energy and a minority spin peak above. PMID:25763966
A Maximally Supersymmetric Kondo Model
Harrison, Sarah; Kachru, Shamit; Torroba, Gonzalo; /Stanford U., Phys. Dept. /SLAC
2012-02-17
We study the maximally supersymmetric Kondo model obtained by adding a fermionic impurity to N = 4 supersymmetric Yang-Mills theory. While the original Kondo problem describes a defect interacting with a free Fermi liquid of itinerant electrons, here the ambient theory is an interacting CFT, and this introduces qualitatively new features into the system. The model arises in string theory by considering the intersection of a stack of M D5-branes with a stack of N D3-branes, at a point in the D3 worldvolume. We analyze the theory holographically, and propose a dictionary between the Kondo problem and antisymmetric Wilson loops in N = 4 SYM. We perform an explicit calculation of the D5 fluctuations in the D3 geometry and determine the spectrum of defect operators. This establishes the stability of the Kondo fixed point together with its basic thermodynamic properties. Known supergravity solutions for Wilson loops allow us to go beyond the probe approximation: the D5s disappear and are replaced by three-form flux piercing a new topologically non-trivial S3 in the corrected geometry. This describes the Kondo model in terms of a geometric transition. A dual matrix model reflects the basic properties of the corrected gravity solution in its eigenvalue distribution.
NASA Astrophysics Data System (ADS)
Yanagisawa, Takashi
2015-07-01
We investigate the Kondo effect in Dirac systems, where Dirac electrons interact with the localized spin via the s-d exchange coupling. The Dirac electron in solid state has the linear dispersion and is described typically by the Hamiltonian such as Hk = vk · σ for the wave number k where σj are Pauli matrices. We derived the formula of the Kondo temperature TK by means of the Green's function theory for small J. The TK is determined from a singularity of Green's functions in the form T{K} ≃ bar{D}exp ( - {const}{.}/ρ |J|) when the exchange coupling |J| is small where bar{D} = D/√{1 + D2/(2μ )2} for a cutoff D and ρ is the density of states at the Fermi surface. When |μ| ≪ D, TK is proportional to |μ|: TK ≃ |μ| exp(-const./ρ|J|). The Kondo screening will, however, disappear when the Fermi surface shrinks to a point called the Dirac point, that is, TK vanishes when the chemical potential μ is just at the Dirac point. The resistivity and the specific heat exhibit a log-T singularity in the range TK < T ≪ |μ|/kB. Instead, for T ˜ O(|μ|) or T > |μ|, they never show log-T.
Probing the Kondo State using Terahertz Radiation
NASA Astrophysics Data System (ADS)
Wetli, Christoph; Kroha, Johann; Krellner, Cornelius; Kliemt, Kristin; Stockert, Oliver; v. Loehneysen, Hilbert; Fiebig, Manfred
The appearance of quantum critical phase transitions is boosting the interest in the field of Kondo-lattice systems. After intense research over the last decades, experimental insights have been mainly gained by measuring the specific heat capacity or the magnetic susceptibility and relating them to the increase of the effective mass. Lately, it has been demonstrated that ARPES experiments allow direct access to the electrons contributing to the Kondo-lattice effect, but with some experimental restrictions. We will show that THz radiation is a powerful and highly accurate alternative for investigating the approach to the coherent Kondo-state of heavy-fermion systems. Photons in the THz range directly couple to the electronic heavy quasiparticles causing the Kondo-singlet behavior. Additionally, this technique allows studying Kondo-state dynamics on the picosecond time scale. We report lifetime measurements of excited Kondo singlets for the two crystalline rare earth heavy-fermion systems CeCu6 and YbRh2Si2, where the lifetimes scale inversely proportional to the Kondo-temperature. THz spectroscopy thus gives a very different perspective towards the Kondo-lattice effect, with the unique ability to combine temporal resolution and possible measurements in magnetic field.
A holographic model of the Kondo effect
NASA Astrophysics Data System (ADS)
Erdmenger, Johanna; Hoyos, Carlos; O'Bannon, Andy; Wu, Jackson
2013-12-01
We propose a model of the Kondo effect based on the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, also known as holography. The Kondo effect is the screening of a magnetic impurity coupled anti-ferromagnetically to a bath of conduction electrons at low temperatures. In a (1+1)-dimensional CFT description, the Kondo effect is a renormalization group flow triggered by a marginally relevant (0+1)-dimensional operator between two fixed points with the same Kac-Moody current algebra. In the large- N limit, with spin SU( N) and charge U(1) symmetries, the Kondo effect appears as a (0+1)-dimensional second-order mean-field transition in which the U(1) charge symmetry is spontaneously broken. Our holographic model, which combines the CFT and large- N descriptions, is a Chern-Simons gauge field in (2+1)-dimensional AdS space, AdS 3, dual to the Kac-Moody current, coupled to a holographic superconductor along an AdS 2 sub-space. Our model exhibits several characteristic features of the Kondo effect, including a dynamically generated scale, a resistivity with power-law behavior in temperature at low temperatures, and a spectral flow producing a phase shift. Our holographic Kondo model may be useful for studying many open problems involving impurities, including for example the Kondo lattice problem.
Mapping itinerant electrons around Kondo impurities.
Prüser, H; Wenderoth, M; Weismann, A; Ulbrich, R G
2012-04-20
We investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic. PMID:22680744
The Kondo Effect and Controlled Spin Entanglement in Coupled Double-Quantum-Dots
NASA Astrophysics Data System (ADS)
Chang, Albert M.
2005-07-01
Semiconductor double-quantum dots represent an ideal system for studying the novel spin physics of localized spins. On each quantum dot when the number of electrons is odd and the net spin is 1/2, a strong coupling of this localized spin to conducting electrons in the leads gives rise to Kondo correlation. On the other hand, in the coupled double-quantum-dot if the inter-dot antiferromagnetic interaction is strong, the two spins can form a correlated spin-singlet state, quenching the Kondo effect. This competition between Kondo and antiferromagnetic correlation is studied in a controlled manner by tuning the inter-dot tunnel coupling. Increasing the inter-dot tunneling, we observe a continuous transition from a single-peaked to a double-peaked Kondo resonance in the differential conductance. On the double-peaked side, the differential conductance becomes suppressed at zero source-drain bias. The observed strong suppression of the differential conductance at zero bias provides direct evidence signaling the formation of an entangled spin-singlet state. This evidence for entanglement and the tunability of our devices bode well for quantum computation applications.
Kondo peak splitting and Kondo dip induced by a local moment.
Niu, Pengbin; Shi, Yun-Long; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang
2015-01-01
Many features like spin-orbit coupling, bias and magnetic fields applied, and so on, can strongly influence the Kondo effect. One of the consequences is Kondo peak splitting. However, Kondo peak splitting led by a local moment has not been investigated systematically. In this research we study theoretically electronic transport through a single-level quantum dot exchange coupled to a local magnetic moment in the Kondo regime. We focus on the Kondo peak splitting induced by an anisotropic exchange coupling between the quantum dot and the local moment, which shows rich splitting behavior. We consider the cases of a local moment with S = 1/2 and S = 1. The longitudinal (z-component) coupling plays a role of multivalued magnetic fields and the transverse (x, y-components) coupling lifts the degeneracy of the quantum dot, both of which account for the fine Kondo peak splitting structures. The inter-level or intra-level transition processes are identified in detail. Moreover, we find a Kondo dip at the Fermi level under the proper parameters. The possible experimental observations of these theoretical results should deepen our understanding of Kondo physics. PMID:26658128
Kondo peak splitting and Kondo dip induced by a local moment
Niu, Pengbin; Shi, Yun-Long; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang
2015-01-01
Many features like spin-orbit coupling, bias and magnetic fields applied, and so on, can strongly influence the Kondo effect. One of the consequences is Kondo peak splitting. However, Kondo peak splitting led by a local moment has not been investigated systematically. In this research we study theoretically electronic transport through a single-level quantum dot exchange coupled to a local magnetic moment in the Kondo regime. We focus on the Kondo peak splitting induced by an anisotropic exchange coupling between the quantum dot and the local moment, which shows rich splitting behavior. We consider the cases of a local moment with S = 1/2 and S = 1. The longitudinal (z-component) coupling plays a role of multivalued magnetic fields and the transverse (x, y-components) coupling lifts the degeneracy of the quantum dot, both of which account for the fine Kondo peak splitting structures. The inter-level or intra-level transition processes are identified in detail. Moreover, we find a Kondo dip at the Fermi level under the proper parameters. The possible experimental observations of these theoretical results should deepen our understanding of Kondo physics. PMID:26658128
NASA Astrophysics Data System (ADS)
Flottat, T.; Hébert, F.; Rousseau, V. G.; Scalettar, R. T.; Batrouni, G. G.
2015-07-01
We study, using quantum Monte Carlo simulations, the bosonic Kondo-Hubbard model in a two-dimensional square lattice. We explore the phase diagram and analyze the mobility of particles and magnetic properties. At unit filling, the transition from a paramagnetic Mott insulator to a ferromagnetic superfluid appears continuous, contrary to what was predicted with mean field. For double occupation per site, both the Mott insulating and superfluid phases are ferromagnetic and the transition is still continuous. Multiband tight-binding Hamiltonians can be realized in optical lattice experiments, which offer not only the possibility of tuning the different energy scales over wide ranges, but also the option of loading the system with either fermionic or bosonic atoms.
Chern Kondo Insulator in an Optical Lattice.
Chen, Hua; Liu, Xiong-Jun; Xie, X C
2016-01-29
We propose to realize and observe Chern Kondo insulators in an optical superlattice with laser-assisted s and p orbital hybridization and a synthetic gauge field, which can be engineered based on the recent cold atom experiments. Considering a double-well square optical lattice, the localized s orbitals are decoupled from itinerant p bands and are driven into a Mott insulator due to the strong Hubbard interaction. Raman laser beams are then applied to induce tunnelings between s and p orbitals, and generate a staggered flux simultaneously. Because of the strong Hubbard interaction of s orbital states, we predict the existence of a critical Raman laser-assisted coupling, beyond which the Kondo screening is achieved, and then a fully gapped Chern Kondo phase emerges, with the topology characterized by integer Chern numbers. Being a strongly correlated topological state, the Chern Kondo phase is different from the single-particle quantum anomalous Hall state, and can be identified by measuring the band topology and double occupancy of s orbitals. The experimental realization and detection of the predicted Chern Kondo insulator are also proposed. PMID:26871345
Colossal magnetoresistance in topological Kondo insulator
NASA Astrophysics Data System (ADS)
Slieptsov, Igor O.; Karnaukhov, Igor N.
2016-04-01
Abnormal electronic properties of complex systems require new ideas concerning explanation of their behavior and possibility of realization. In this acticle we show that a colossal magnetoresistance is realized in the state of the topological Kondo insulator, that is similar to the Kondo insulator state in the Kondo lattice. The mechanism of the phenomenon is the following: in the spin gapless phase an external magnetic field induces the gap in the spectrum of spin excitations, the gap in the spectrum of fermions is opened due to a hybridization between spin and fermion subsystems at half-filling, as the result the magnetic field leads to metal–insulator (or bad metal–insulator) phase transition. A model of the topological Kondo lattice defined on a honeycomb lattice is studied for the case when spinless fermion bands are half-filled. It is shown that the hybridization between local moments and itinerant fermions should be understood as the hybridization between corresponding Majorana fermions of the spin and charge sectors. The system is a topological insulator, single fermion and spin excitations at low energies are massive. We will show that a spin gap induces a gap in the charge channel, it leads to an appearance of a topological insulator state with chiral gapless edge modes and the Chern number one or two depending on the exchange integrals’ values. The relevance of this to the traditional Kondo insulator state is discussed.
The Kondo effect in ferromagnetic atomic contacts.
Calvo, M Reyes; Fernández-Rossier, Joaquín; Palacios, Juan José; Jacob, David; Natelson, Douglas; Untiedt, Carlos
2009-04-30
Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system; this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent log-normal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures. PMID:19407797
Chern Kondo Insulator in an Optical Lattice
NASA Astrophysics Data System (ADS)
Chen, Hua; Liu, Xiong-Jun; Xie, X. C.
2016-01-01
We propose to realize and observe Chern Kondo insulators in an optical superlattice with laser-assisted s and p orbital hybridization and a synthetic gauge field, which can be engineered based on the recent cold atom experiments. Considering a double-well square optical lattice, the localized s orbitals are decoupled from itinerant p bands and are driven into a Mott insulator due to the strong Hubbard interaction. Raman laser beams are then applied to induce tunnelings between s and p orbitals, and generate a staggered flux simultaneously. Because of the strong Hubbard interaction of s orbital states, we predict the existence of a critical Raman laser-assisted coupling, beyond which the Kondo screening is achieved, and then a fully gapped Chern Kondo phase emerges, with the topology characterized by integer Chern numbers. Being a strongly correlated topological state, the Chern Kondo phase is different from the single-particle quantum anomalous Hall state, and can be identified by measuring the band topology and double occupancy of s orbitals. The experimental realization and detection of the predicted Chern Kondo insulator are also proposed.
Kondo effect in charm and bottom nuclei
NASA Astrophysics Data System (ADS)
Yasui, Shigehiro
2016-06-01
The Kondo effect for isospin-exchange interaction between a D ¯, B meson and a valence nucleon in charm and bottom atomic nuclei including the discrete energy levels for valence nucleons is discussed. To investigate the binding energy by the Kondo effect, I introduce the mean-field approach for the bound state of the D ¯, B meson in charm and bottom nuclei. Assuming a simple model, I examine the validity of the mean-field approximation by comparing the results with the exact solutions. The effect of the quantum fluctuation is estimated beyond the mean-field approximation. The competition between the Kondo effect and the other correlations in valence nucleons, the isospin symmetry breaking and the nucleon pairings, are discussed.
Global phase diagram and single particle excitations in Kondo insulators
NASA Astrophysics Data System (ADS)
Si, Qimiao; Pixley, Jedediah; Yu, Rong; Paschen, Silke
Motivated by quantum criticality in Kondo insulators tuned by pressure or doping we study the effects of magnetic frustration and the properties of the single particle excitations in a Kondo lattice model. Focusing on the Kondo insulating limit we study the Shastry-Sutherland Kondo lattice and determine the zero temperature phase diagram, which incorporates a valence bond solid, antiferromagnet, and Kondo insulating ground states, with metal-to-insulator quantum phase transitions. We argue that this phase diagram is generic and represents a ``global'' phase diagram of Kondo insulators in terms of quantum fluctuations and the Kondo interaction. We then focus on the momentum distribution of single particle excitations within the Kondo insulating ground state. We show how features of the Fermi-surface of the underlying conduction electrons appear in the Kondo insulating phase. Lastly, we discuss the implications of our results for quantum criticality in Kondo insulators as well as for the recent de Haas-von Alphen measurements in the Kondo insulator SmB6.
Effect of anisotropy in the S=1 underscreened Kondo lattice
NASA Astrophysics Data System (ADS)
Thomas, Christopher; da Rosa Simões, Acirete S.; Lacroix, Claudine; Iglesias, José Roberto; Coqblin, Bernard
2014-12-01
We study the effect of crystal field anisotropy in the underscreened S=1 Kondo lattice model. Starting from the two orbital Anderson lattice model and including a local anisotropy term, we show, through Schrieffer-Wolff transformation, that local anisotropy is equivalent to an anisotropic Kondo interaction (J∥≠J⊥). The competition and coexistence between ferromagnetism and Kondo effect in this effective model is studied within a generalized mean-field approximation. Several regimes are obtained, depending on the parameters, exhibiting or not coexistence of magnetic order and Kondo effect. Particularly, we show that a re-entrant Kondo phase at low temperature can be obtained. We are also able to describe phases where the Kondo temperature is smaller than the Curie temperature (TK
The physics of Kondo impurities in graphene.
Fritz, Lars; Vojta, Matthias
2013-03-01
This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. PMID:23411583
Voltage Quench Dynamics of a Kondo System.
Antipov, Andrey E; Dong, Qiaoyuan; Gull, Emanuel
2016-01-22
We examine the dynamics of a correlated quantum dot in the mixed valence regime. We perform numerically exact calculations of the current after a quantum quench from equilibrium by rapidly applying a bias voltage in a wide range of initial temperatures. The current exhibits short equilibration times and saturates upon the decrease of temperature at all times, indicating Kondo behavior both in the transient regime and in the steady state. The time-dependent current saturation temperature connects the equilibrium Kondo temperature to a substantially increased value at voltages outside of the linear response. These signatures are directly observable by experiments in the time domain. PMID:26849606
The physics of Kondo impurities in graphene
NASA Astrophysics Data System (ADS)
Fritz, Lars; Vojta, Matthias
2013-03-01
This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids.
Kondo Tunneling through Real and Artificial Molecules
NASA Astrophysics Data System (ADS)
Kikoin, Konstantin; Avishai, Yshai
2001-03-01
When an asymmetric double dot is hybridized with itinerant electrons, its singlet ground state and lowly excited triplet state cross, leading to a competition between the Zhang-Rice mechanism of singlet-triplet splitting in a confined cluster and the Kondo effect (which accompanies the tunneling through quantum dot under a Coulomb blockade restriction). The rich physics of an underscreened S = 1 Kondo impurity in the presence of low-lying triplet-singlet excitations is exposed and estimates of the magnetic susceptibility and the electric conductance are presented, together with applications for molecule chemisorption on metallic substrates.
Transport across two interacting quantum dots: bulk Kondo, Kondo box and molecular regimes
NASA Astrophysics Data System (ADS)
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2014-03-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N non-interacting sites connecting both of them. The inter-dot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of small number of sites, so that Kondo box effects are present. For odd N and small coupling between the inter-dot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dots spins by the spin in the finite chain. As the coupling to the inter-dot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule spin by the leads. For even N the two-Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism. We finally study how the transport properties are affected as N is increased. We used exact multi-configurational Lanczos calculations and finite U slave-boson mean-field theory. The results obtained with both methods describe qualitatively and also quantitatively the same physics.
Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes
NASA Astrophysics Data System (ADS)
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2015-03-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We acknowledge financial support from the Brazilian agencies FAPERJ and CNPq.
Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes
NASA Astrophysics Data System (ADS)
Ribeiro, L. C.; Hamad, I. J.; Chiappe, G.; Anda, E. V.
2014-01-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We finally study how the transport properties are affected as N is increased. For the study we used exact multiconfigurational Lanczos calculations and finite-U slave-boson mean-field theory at T =0. The results obtained with both methods describe qualitatively and also quantitatively the same physics.
Kondo peak splitting and Kondo dip in single molecular magnet junctions
NASA Astrophysics Data System (ADS)
Niu, Pengbin; Shi, Yunlong; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang
2016-01-01
Many factors containing bias, spin-orbit coupling, magnetic fields applied, and so on can strongly influence the Kondo effect, and one of the consequences is Kondo peak splitting (KPS). It is natural that KPS should also appear when another spin degree of freedom is involved. In this work we study the KPS effects of single molecular magnets (SMM) coupled with two metallic leads in low-temperature regime. It is found that the Kondo transport properties are strongly influenced by the exchange coupling and anisotropy of the magnetic core. By employing Green's function method in Hubbard operator representation, we give an analytical expression for local retarded Green's function of SMM and discussed its low-temperature transport properties. We find that the anisotropy term behaves as a magnetic field and the splitting behavior of exchange coupling is quite similar to the spin-orbit coupling. These splitting behaviors are explained by introducing inter-level or intra-level transitions, which account for the seven-peak splitting structure. Moreover, we find a Kondo dip at Fermi level under proper parameters. These Kondo peak splitting behaviors in SMM deepen our understanding to Kondo physics and should be observed in the future experiments.
Kondo physics in a dissipative environment
NASA Astrophysics Data System (ADS)
Ingersent, K.; Glossop, M. T.; Khoshkhou, N.
2007-03-01
In recent years impurity models with quantum critical points have attracted much interest. Well-studied examples include the pseudogap and Bose-Fermi Kondo models. In the former model, the depletion of the host density of states at the Fermi level can destroy the Kondo effect; in the latter case, Kondo screening competes with coupling to a dissipative bosonic bath representing, e.g., collective spin fluctuations of the host. The physics of both models is dominated by an interacting quantum critical point. Here, we focus on the more general case of a magnetic impurity interacting with a pseudogap fermionic density of states ρ(ɛ)|ɛ|^r and with a bosonic bath having a spectral function B(φ)ŝ. Perturbative renormalization-group (RG) studies of the resulting model, discussed in relation to Kondo temperature suppression in underdoped cuprates [1], have established a rich phase diagram with three stable and two critical fixed points. We report nonperturbative results for this model, obtained using a Bose-Fermi numerical RG approach [2]. We discuss the phase diagram for the Ising-anisotropic case, together with quantum critical properties probed via response to a local magnetic field. [1] M. Vojta and M. Kir'can, PRL 90, 157203 (2003). [2] M. T. Glossop and K. Ingersent, PRL 95, 067202 (2005); PRB (2006).
Colossal positive magnetoresistance in a doped nearly magnetic semiconductor
Hu, R.; Thomas, K.; Lee, Y.; Vogt, T.; Choi, E.; Mitrovic, V.; Hermann, R.; Grandjean, F.; Canfield, P.; Kim, J.; Goldman, A.; Petrovic, C.
2008-02-27
We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb{sub 2}, a nearly magnetic or 'Kondo' semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity.
Pressure effects on the optical conductivity of Kondo insulators
Zhang, Sun
2001-06-01
The effects of pressure on the optical conductivity of Kondo insulators are studied in the framework of the slave-boson mean-field theory under the coherent potential approximation. A unified picture is presented for both the hole-type Kondo insulators [H. Okamura , Phys. Rev. B >58, R7496 (1998)] and the electron-type Kondo insulators [B. Bucher , Phys. Rev. Lett. >72, 522 (1994)]. The density of states of f electrons under the applied pressure and its variation with the concentration of the impurity doping are calculated self-consistently. The Kondo temperature and the optical conductivity are obtained, in agreement with the experiments qualitatively. The two contrasting pressure-dependent effects for the hole-type Kondo insulators and the electron-type Kondo insulators are also given as predictions for further observations.
Dynamical symmetries in Kondo tunneling through complex quantum dots.
Kuzmenko, T; Kikoin, K; Avishai, Y
2002-10-01
Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4). PMID:12366008
Charge Kondo effect in a triple quantum dot
NASA Astrophysics Data System (ADS)
Yoo, Gwangsu; Park, Jinhong; Lee, S. S.-B.; Sim, H.-S.
2014-03-01
We predict that the charge Kondo effect appears in a triangular triple quantum dot. The system has two-fold degenerate ground-state charge configurations, interdot Coulomb interactions, lead-dot electron tunnelings, but no interdot electron tunneling. We show, using bosonization and refermionization, that the system is described by the anisotropic Kondo model. The anisotropy can be tuned by changing lead-dot electron tunneling strength, which allows one to experimentally explore the transition between the ferromagnetic non-Fermi liquid and antiferromagnetic Kondo phases in the Kondo phase diagram. Using numerical renormalization group method, we demonstrate that the transition is manifested in electron conductances through the dot.
Antiferromagnetic phases of the Kondo lattice
NASA Astrophysics Data System (ADS)
Eder, R.; Grube, K.; Wróbel, P.
2016-04-01
We discuss the paramagnetic and Néel-ordered phases of the Kondo lattice Hamiltonian on the two-dimensional square lattice by means of bond fermions. In the doped case we find two antiferromagnetic solutions, the first one with small ordered moment, heavy bands, and an antiferromagnetically folded large Fermi surface—i.e., including the localized spins—the second one with large ordered moment, light bands, and an antiferromagnetically folded conduction electron-only Fermi surface. The zero temperature phase diagram as a function of Kondo coupling and conduction electron density shows first- and second-order transition lines between the three different phases and agrees qualitatively with previous numerical studies. We compare to experiments on CeRh1 -xCoxIn5 and find qualitative agreement.
Scattering Theory of Kondo Mirages and Observation of Single Kondo Atom Phase Shift*
NASA Astrophysics Data System (ADS)
Fiete, Gregory A.; Hersch, Jesse S.; Heller, Eric J.; Manoharan, H. C.; Lutz, C. P.; Eigler, D. M.
2001-03-01
We explain the origin of the Kondo mirage seen in recent quantum corral Scanning Tunneling Microscope (STM) experiments with a scattering theory of electrons on the surfaces of metals. Our theory combined with experimental data provides the first direct observation of a single Kondo atom phase shift. The Kondo mirage observed at the empty focus of an elliptical quantum corral is shown to arise from multiple electron bounces off the corral wall adatoms in a manner analagous to the formation of a real image in optics. We demonstrate our theory with direct quantitive comparision to experimental data. *This research was supported by the National Science Foundation under Grant No. CHE9610501 and by ITAMP.
Kondo Force in Shuttling Devices: Dynamical Probe for a Kondo Cloud
NASA Astrophysics Data System (ADS)
Kiselev, M. N.; Kikoin, K. A.; Gorelik, L. Y.; Shekhter, R. I.
2013-02-01
We consider the electromechanical properties of a single-electronic device consisting of a movable quantum dot attached to a vibrating cantilever, forming a tunnel contact with a nonmovable source electrode. We show that the resonance Kondo tunneling of electrons amplifies exponentially the strength of nanoelectromechanical (NEM) coupling in such a device and make the latter insensitive to mesoscopic fluctuations of electronic levels in a nanodot. It is also shown that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a nonmechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.
Nuclear magnetic resonance in Kondo lattice systems
NASA Astrophysics Data System (ADS)
Curro, Nicholas J.
2016-06-01
Nuclear magnetic resonance has emerged as a vital tool to explore the fundamental physics of Kondo lattice systems. Because nuclear spins experience two different hyperfine couplings to the itinerant conduction electrons and to the local f moments, the Knight shift can probe multiple types of spin correlations that are not accessible via other techniques. The Knight shift provides direct information about the onset of heavy electron coherence and the emergence of the heavy electron fluid.
Application of the underscreened Kondo lattice model to neptunium compounds
NASA Astrophysics Data System (ADS)
Thomas, Christopher; da Rosa Simoes, Acirete S.; Iglesias, J. R.; Lacroix, C.; Coqublin, B.
2012-12-01
The coexistence of Kondo effect and ferromagnetic order has been observed in many uranium and neptunium compounds such as UTe or Np2PdGa3. This coexistence can be described within the underscreened Anderson lattice model with two f-electrons and S = 1 spins on each site. After performing the Schrieffer-Wolff transformation on this model, we have obtained an effective Hamiltonian with a f-band term in addition to the Kondo interaction for S = 1 spins. The results indicate a coexistence of Kondo effect and ferromagnetic order, with different relative values of the Kondo TK and Curie TC temperatures. We emphasize here especially the case TK < TC where there is a Kondo behavior below TC and a clear decrease of the magnetization below TK. Such a behavior has been observed in the magnetization curves of NpNiSi2 at low temperatures.
Magnetic frustration in itinerant systems: the Kondo polaron problem
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Batista, Cristian; Vekhter, Ilya
2013-03-01
We study the interplay between magnetic frustration and Kondo screening in Kondo lattices by analyzing the J1-J2 antiferromagnetic chain coupled to a conduction band. The system is tuned to the Majumdar-Ghosh point J2 =J1 / 2 which stabilizes a dimer valence-bond solid at weak Kondo coupling JK. We use an effective low-energy theory to demonstrate that sufficiently large JK results in a proliferation of ``Kondo polarons'', i.e. Kondo-screened domain-wall excitations of the dimer state, and collapse of the dimer order via a 2nd order quantum phase transition. At the quantum critical point, JK =JKc , these polarons become gapless, and we argue that the transition itself belongs to a 2D Ising universality class. For JK >JKc increasing concentration of the polarons leads to a continuous growth of the electron Fermi momentum until all spins are absorbed by the Fermi sea.
Anisotropic charge Kondo effect in a triple quantum dot.
Yoo, Gwangsu; Park, Jinhong; Lee, S-S B; Sim, H-S
2014-12-01
We predict that an anisotropic charge Kondo effect appears in a triple quantum dot, when the system has twofold degenerate ground states of (1,1,0) and (0,0,1) charge configurations. Using bosonization and refermionization methods, we find that at low temperature the system has the two different phases of massive charge fluctuations between the two charge configurations and vanishing fluctuations, which are equivalent with the Kondo-screened and ferromagnetic phases of the anisotropic Kondo model, respectively. The phase transition is identifiable by electron conductance measurement, offering the possibility of experimentally exploring the anisotropic Kondo model. Our charge Kondo effect has a similar origin to that in a negative-U Anderson impurity. PMID:25526143
Anisotropic Charge Kondo Effect in a Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Yoo, Gwangsu; Park, Jinhong; Lee, S.-S. B.; Sim, H.-S.
2014-12-01
We predict that an anisotropic charge Kondo effect appears in a triple quantum dot, when the system has twofold degenerate ground states of (1,1,0) and (0,0,1) charge configurations. Using bosonization and refermionization methods, we find that at low temperature the system has the two different phases of massive charge fluctuations between the two charge configurations and vanishing fluctuations, which are equivalent with the Kondo-screened and ferromagnetic phases of the anisotropic Kondo model, respectively. The phase transition is identifiable by electron conductance measurement, offering the possibility of experimentally exploring the anisotropic Kondo model. Our charge Kondo effect has a similar origin to that in a negative-U Anderson impurity.
Fano-Kondo and the Kondo box regimes crossover in a quantum dot coupled to a quantum box.
Apel, Victor M; Orellana, Pedro A; Pacheco, Monica; Anda, Enrique V
2013-12-18
In this work, we study the Kondo effect of a quantum dot (QD) connected to leads and to a discrete set of one-particle states provided by a quantum box represented by a quantum ring (QR) pierced by a magnetic flux side attached to the QD. The interplay between the bulk Kondo effect and the so-called Kondo box regime is studied. In this system the QR energies can be continuously modified by the application of the magnetic field. The crossover between these two regimes is analyzed by changing the connection of the QD to the QR from the weak to the strong coupling regime. In the weak coupling regime, the differential conductance develops a sequence of Fano-Kondo anti-resonances due to destructive interference between the discrete quantum ring levels and the conducting Kondo channel provided by the leads. In the strong coupling regime the differential conductance has very sharp resonances when one of the Kondo discrete sub-levels characterizing the Kondo box is tuned by the applied potential. The conductance, the current fluctuations and the Fano coefficient result as being the relevant physical magnitudes to be analyzed to reveal the physical properties of these two Kondo regimes and the crossover region between them. The results were obtained by using the slave boson mean field theory (SBMFT). PMID:24275637
Kondo effect in triple quantum dots
NASA Astrophysics Data System (ADS)
Žitko, R.; Bonča, J.; Ramšak, A.; Rejec, T.
2006-04-01
Numerical analysis of the simplest odd-numbered system of coupled quantum dots reveals an interplay between magnetic ordering, charge fluctuations, and the tendency of itinerant electrons in the leads to screen magnetic moments. The transition from local-moment to molecular-orbital behavior is visible in the evolution of correlation functions as the interdot coupling is increased. Resulting Kondo phases are presented in a phase diagram which can be sampled by measuring the zero-bias conductance. We discuss the origin of the even-odd effects by comparing with the double quantum dot.
Integrable Two-Impurity Kondo Model
Schlottmann, P.
1998-06-01
The exact solution by means of Bethe{close_quote}s {ital Ansatz} of a variant of the two-impurity Kondo problem is presented. The occupation of the singlet and triplet states, the expectation value {l_angle}{rvec S}{sub 1}{center_dot} {cflx S}{sub 2}{r_angle} , the homogeneous and staggered magnetic field susceptibilities, and the specific heat {gamma} coefficient are studied for the ground state as a function of the Ruderman-Kittel-Kasuya-Yosida{endash}coupling strength. {copyright} {ital 1998} {ital The American Physical Society}
Numerical analysis of the spatial range of the Kondo effect
Busser, C. A.; Martins, G. B.; Ribeiro, L. Costa; Vernek, E.; Anda, E. V.; Dagotto, Elbio R
2010-01-01
The spatial length of the Kondo screening is still a controversial issue related to Kondo physics. While renormalization-group and Bethe-Ansatz solutions have provided detailed information about the thermodynamics of magnetic impurities, they are insufficient to study the effect on the surrounding electrons, i.e., the spatial range of the correlations created by the Kondo effect between the localized magnetic moment and the conduction electrons. The objective of this work is to present a quantitative way of measuring the extension of these correlations by studying their effect directly on the local density of states (LDOS) at arbitrary distances from the impurity. The numerical techniques used, the embedded cluster approximation, the finite-U slave bosons, and numerical renormalization group, calculate the Green s functions in real space. With this information, one can calculate how the local density of states away from the impurity is modified by its presence, below and above the Kondo temperature, and then estimate the range of the disturbances in the noninteracting Fermi sea due to the Kondo effect, and how it changes with the Kondo temperature TK. The results obtained agree with results obtained through spin-spin correlations, showing that the LDOS captures the phenomenology of the Kondo cloud as well.
Competing Kondo Effects in Non-Kramers Doublet Systems
NASA Astrophysics Data System (ADS)
Kusunose, Hiroaki
2016-06-01
In non-Kramers Kondo systems with quadrupolar degrees of freedom, an ordinary magnetic Kondo effect can compete with the quadrupolar Kondo effect. We discuss such competition keeping PrT2Zn20 (T = Ir, Rh) and PrT2Al20 (T = V, Ti) in mind, where the Γ3 non-Kramers crystalline-electric-field (CEF) doublet ground state is realized in a Pr3+ ion with a (4f)2 configuration under cubic symmetry. The quadrupolar Kondo effect can be described by the two-channel Kondo model, which leads to the local non-Fermi-liquid (NFL) ground state, while the magnetic Kondo effect favors the ordinary local Fermi-liquid (FL) ground state. On the basis of the minimal extended two-channel Kondo model including the magnetic Kondo coupling as well, we investigate the competition and resulting thermodynamics, and orbital/magnetic and single-particle excitation spectra by Wilson's numerical renormalization group (NRG) method. There is a first-order transition between the NFL and FL ground states. In addition to these two states, the alternative FL state accompanied by a free magnetic spin appears in the intermediate temperature range, which eventually reaches the true NFL ground state, as a consequence of the stronger competition between the magnetic and quadrupolar Kondo effects. In this peculiar state, the magnetic susceptibility shows a Curie-like behavior, while the orbital fluctuation exhibits the FL behavior. Moreover, the single-particle spectra yield a more singular behavior. Implications to the Pr 1-2-20 systems are briefly discussed.
Collective Kondo effect in the Anderson-Hubbard lattice
NASA Astrophysics Data System (ADS)
Fazekas, P.; Itai, K.
1997-02-01
The periodic Anderson model is extended by switching on a Hubbard U for the conduction electrons. We use the Gutzwiller variational method to study the nearly integral valent limit. The lattice Kondo energy contains the U-dependent chemical potential of the Hubbard subsystem in the exponent, and the correlation-induced band narrowing in the prefactor. Both effects tend to suppress the Kondo scale, which can be understood to result from the blocking of hybridization. At half-filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator.
Kondo effect and non-Fermi-liquid behavior in Dirac and Weyl semimetals
NASA Astrophysics Data System (ADS)
Principi, Alessandro; Vignale, Giovanni; Rossi, E.
2015-07-01
We study the Kondo effect in three-dimensional (3D) Dirac materials and Weyl semimetals. We find the scaling of the Kondo temperature with respect to the doping n and the coupling J between the moment of the magnetic impurity and the carriers of the semimetal. We consider the interplay of long-range scalar disorder and Kondo screening and find that it causes the Kondo effect to be characterized not by a Kondo temperature, but by a distribution of Kondo temperatures with features that cause the appearance of strong non-Fermi-liquid behavior. We then consider the effect of Kondo screening, and of the interplay of Kondo screening and long-range scalar disorder, on the transport properties of Weyl semimetals. Finally, we compare the properties of the Kondo effect in 3D and 2D Dirac materials such as graphene and topological insulators.
Is the black phase of SmS a topological Kondo insulator?
NASA Astrophysics Data System (ADS)
Bauer, Eric; Ghimire, N. J.; Ronning, F.; Batista, C.; Byler, D.; Thompson, J. D.; Rahmanisisan, A.; Fisk, Z.
2015-03-01
SmS is a prototypical Kondo insulator where electronic correlations drive a system insulating that would otherwise be metallic. Whether or not such a system is also a topological insulator that hosts a protected metallic surface state, depends on the parity of the wavefunction of the occupied states. However, unlike weakly correlated materials, it is unclear whether state-of-the-art electronic structure calculations accurately predict the parity of the occupied wavefunctions of correlated insulators. Nevertheless, Dzero and collaborators suggest that Kondo insulators such as SmB6 can be topological. Like SmB6, Cubic SmS is a non-magnetic semiconductor with an insulating behavior at ambient pressure and low temperatures driven by hybridization with the Sm f-electrons. At 6 kbar, SmS undergoes a phase transition into a valance fluctuating phase accompanied by a visible color change from black to gold. It then undergoes a second phase transition at about 20 kbar to an antiferromagnetic order at low temperatures. We will discuss whether electronic structure calculations indicate a topological state of SmS at P =0. We will also discuss whether or not the magnetic, thermal and transport properties of the black phase of SmS are consistent with the existence of a topological protected surface state.
Coexistence of Kondo effect and ferromagnetism in the Underscreened Kondo Lattice model
NASA Astrophysics Data System (ADS)
Thomas, C.; Simões, A. S. R.; Iglesias, J. R.; Lacroix, C.; Perkins, N. B.; Coqblin, B.
2011-12-01
In this work we use a Schrieffer-Wolff transformation in a two-fold degenerate periodic Anderson lattice to describe the coexistence of Kondo effect and ferromagnetism in some uranium and neptunium compounds. We show that the inclusion of a bandwidth for the f electrons can account for a weak delocalization of 5f electrons. Using a mean field approximation, we show that a maximum of TC versus JK can be found when the bandwidth is proportional to JK.
Competition between Kondo Screening and Quantum Hall Edge Reconstruction.
Heine, A W; Tutuc, D; Zwicknagl, G; Haug, R J
2016-03-01
We report on a Kondo correlated quantum dot connected to two-dimensional leads where we demonstrate the renormalization of the g factor in the pure Zeeman case. i.e., for magnetic fields parallel to the plane of the quantum dot. For the same system, we study the influence of orbital effects by investigating the quantum Hall regime; i.e., a perpendicular magnetic field is applied. In this case an unusual behavior of the suppression of the Kondo effect and of the split zero-bias anomaly is observed. The splitting decreases with magnetic field and shows discontinuous changes that are attributed to the intricate interplay between Kondo screening and the quantum Hall edge structure originating from electrostatic screening. This edge structure, made up of compressible and incompressible stripes, strongly affects the Kondo temperature of the quantum dot and thereby influences the renormalized g factor. PMID:26991192
Competition between Kondo Screening and Quantum Hall Edge Reconstruction
NASA Astrophysics Data System (ADS)
Heine, A. W.; Tutuc, D.; Zwicknagl, G.; Haug, R. J.
2016-03-01
We report on a Kondo correlated quantum dot connected to two-dimensional leads where we demonstrate the renormalization of the g factor in the pure Zeeman case. i.e., for magnetic fields parallel to the plane of the quantum dot. For the same system, we study the influence of orbital effects by investigating the quantum Hall regime; i.e., a perpendicular magnetic field is applied. In this case an unusual behavior of the suppression of the Kondo effect and of the split zero-bias anomaly is observed. The splitting decreases with magnetic field and shows discontinuous changes that are attributed to the intricate interplay between Kondo screening and the quantum Hall edge structure originating from electrostatic screening. This edge structure, made up of compressible and incompressible stripes, strongly affects the Kondo temperature of the quantum dot and thereby influences the renormalized g factor.
Tunable unconventional Kondo effect on topological insulator surfaces
NASA Astrophysics Data System (ADS)
Isaev, L.; Ortiz, G.; Vekhter, I.
2015-11-01
We study Kondo physics of a spin-1/2 impurity in electronic matter with strong spin-orbit interaction, which can be realized by depositing magnetic adatoms on the surface of a three-dimensional topological insulator. We show that magnetic properties of topological surface states and the very existence of Kondo screening strongly depend on details of the bulk material, and specifics of surface preparation encoded in time-reversal preserving boundary conditions for electronic wavefunctions. When this tunable Kondo effect occurs, the impurity spin is screened by purely orbital motion of surface electrons. This mechanism gives rise to a transverse magnetic response of the surface metal, and to spin textures that can be used to experimentally probe signatures of a Kondo resonance. Our predictions are particularly relevant for STM measurements in Pb Te -class crystalline topological insulators, but we also discuss implications for other classes of topological materials.
Spin dynamics in paramagnetic diluted magnetic semiconductors
NASA Astrophysics Data System (ADS)
Phan, Van-Nham; Tran, Minh-Tien
2015-10-01
Microscopic properties of low-energy spin dynamics in diluted magnetic semiconductor are addressed in a framework of the Kondo lattice model including random distribution of magnetic dopants. Based on the fluctuation-dissipation theorem, we derive an explicit dependence of the spin diffusion coefficient on the single-particle Green function which is directly evaluated by dynamical mean-field theory. In the paramagnetic state, the magnetic scattering has been manifested to suppress spin diffusion. In agreement with other ferromagnet systems, we also point out that the spin diffusion in diluted magnetic semiconductors at small carrier concentration displays a monotonic 1 /T -like temperature dependence. By investigating the spin diffusion coefficient on a wide range of the model parameters, the obtained results have provided a significant scenario to understand the spin dynamics in the paramagnetic diluted magnetic semiconductors.
Rakhmilevitch, David
2015-01-01
Summary The vibration-mediated Kondo effect attracted considerable theoretical interest during the last decade. However, due to lack of extensive experimental demonstrations, the fine details of the phenomenon were not addressed. Here, we analyze the evolution of vibration-mediated Kondo effect in molecular junctions during mechanical stretching. The described analysis reveals the different contributions of Kondo and inelastic transport. PMID:26734532
Quantum entanglement in the two-impurity Kondo model
Cho, Sam Young; McKenzie, Ross H.
2006-01-15
In order to quantify quantum entanglement in two-impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, namely the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, I. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two-impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created [and quantum information processing (QIP) will only be possible] if the RKKY interaction exchange energy, I, is at least several times larger than the Kondo temperature, T{sub K}. Quantitative criteria for QIP are given in terms of the impurity spin-spin correlation.
Haldane phase in one-dimensional topological Kondo insulators
NASA Astrophysics Data System (ADS)
Mezio, Alejandro; Lobos, Alejandro M.; Dobry, Ariel O.; Gazza, Claudio J.
2015-11-01
We investigate the ground-state properties of a recently proposed model for a topological Kondo insulator in one dimension (i.e., the p -wave Kondo-Heisenberg lattice model) by means of the density-matrix renormalization-group method. The nonstandard Kondo interaction in this model is different from the usual (i.e., local) Kondo interaction in that the localized spins couple to the "p -wave" spin density of conduction electrons, inducing a topologically nontrivial insulating ground state. Based on the analysis of the charge- and spin-excitation gaps, the string order parameter, and the spin profile in the ground state, we show that, at half filling and low energies, the system is in the Haldane phase and hosts topologically protected spin-1/2 end states. Beyond its intrinsic interest as a useful "toy model" to understand the effects of strong correlations on topological insulators, we show that the p -wave Kondo-Heisenberg model could be experimentally implemented in p -band optical lattices loaded with ultracold Fermi gases.
Quantitative Calculation of the Spatial Extension of the Kondo Cloud
NASA Astrophysics Data System (ADS)
Gerd, Bergmann
2008-03-01
A recently developed compact solution for the singlet state of the Friedel-Anderson and the Kondo impurity is applied to investigate the old question of a Kondo cloud in the Kondo ground state. Wilson's states with an exponentially decreasing frame of energy cells towards the Fermi level are used. The Wilson states are expressed as free electron waves with a linear dispersion and integrated over the width of their energy cells. For the magnetic state of the Friedel-Anderson impurity one finds essentially no spin polarization in the vicinity of the d-impurity. However, for the magnetic component of the singlet state a spin polarization cloud is observed which screens the spin (magnetic moment) of the d-electron. The range ξK of this polarization cloud is investigated in detail for the Kondo impurity. The range is inversely proportional to the Kondo energy δK. The extent of the electron density in real space is a detector for a resonance in energy. The spatial extension ξ and the resonance width δ are reciprocal and given by the relation ξδ vF.
Quantitative calculation of the spatial extension of the Kondo cloud
NASA Astrophysics Data System (ADS)
Bergmann, Gerd
2008-03-01
A recently developed compact solution for the singlet state of the Friedel-Anderson and the Kondo impurity is applied to investigate the old question of a Kondo cloud in the Kondo ground state. Wilson’s states with an exponentially decreasing frame of energy cells toward the Fermi level are used. The Wilson states are expressed as free electron waves with a linear dispersion and integrated over the width of their energy cells. For the magnetic state of the Friedel-Anderson impurity, one finds essentially no spin polarization in the vicinity of the d impurity. However, for the magnetic component of the singlet state, a spin polarization cloud is observed which screens the spin (magnetic moment) of the d electron. The range ξK of this polarization cloud is investigated in detail for the Kondo impurity. The range is inversely proportional to the Kondo energy ΔK . The extent of the electron density in real space is a detector for a resonance in energy. The spatial extension ξ and the resonance width Δ are reciprocal and given by the relation ξΔ≈ℏvF .
Evolution of the Kondo effect in a quantum dot probed by shot noise.
Yamauchi, Yoshiaki; Sekiguchi, Koji; Chida, Kensaku; Arakawa, Tomonori; Nakamura, Shuji; Kobayashi, Kensuke; Ono, Teruo; Fujii, Tatsuya; Sakano, Rui
2011-04-29
We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2. PMID:21635054
Scanning Tunneling Electron Transport into a Kondo Lattice
NASA Astrophysics Data System (ADS)
Yang, Fu-Bin; Wu, Hua
2016-05-01
We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice. We calculate the density of states (DOS) and the tunneling current and differential conductance (DC) under different conduction-fermion band hybridization and temperature in the Kondo lattice. It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy. The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice. Supported by the National Natural Science Foundation of China under Grant No. 11547203, and the Research Project of Education Department in Sichuan Province of China under Grant No. 15ZB0457
Cotunneling into a Kondo lattice with odd hybridization
NASA Astrophysics Data System (ADS)
Baruselli, Pier Paolo; Vojta, Matthias
2016-06-01
Cotunneling into Kondo systems, where an electron enters an f -electron material via a cotunneling process through the local-moment orbital, has been proposed to explain the characteristic line shapes observed in scanning-tunneling-spectroscopy (STS) experiments. Here we extend the theory of electron cotunneling to Kondo-lattice systems in which the bulk hybridization between conduction and f electrons is odd under inversion, being particularly relevant to Kondo insulators. Compared to the case of even hybridization, we show that the interference between normal tunneling and cotunneling processes is fundamentally altered: it is entirely absent for layered, i.e., quasi-two-dimensional materials, while its energy dependence is strongly modified for three-dimensional materials. We discuss implications for STS experiments.
Tunable Kondo effect and spin textures on topological insulators surfaces
NASA Astrophysics Data System (ADS)
Vekhter, Ilya; Ortiz, Gerardo; Isaev, Leonid
We consider screening of a spin- 1 / 2 impurity at the surface of a topological insulator, and show that the very existence of Kondo screening strongly depend on details of the bulk material and surface preparation whose details are encoded in time-reversal preserving boundary conditions for electronic wavefunctions. We investigate in detail the formation of the Kondo resonance by studying the ''orbital-flip'' processes that screen the impurity spin in the resulting strongly spin-orbit coupled system. This mechanism gives rise to spin textures that can be used to experimentally probe signatures of a Kondo resonance in topological insulators, and we give examples relevant to specific materials. L.I. was supported by the NSF (PIF-1211914 and PFC-1125844), AFOSR, AFOSR-MURI, NIST and ARO individual investigator awards, and also in part by ICAM. I.V. acknowledges support from NSF Grant DMR-1105339.
Quadrupolar Kondo effect in uranium heavy-electron materials?
NASA Technical Reports Server (NTRS)
Cox, D. L.
1987-01-01
The possibility of an electric quadrupole Kondo effect for a non-Kramers doublet on a uranium (U) ion is a cubic metallic host is demonstrated by model calculations showing a Kondo upturn in the resistivity, universal quenching of the quadrupolar moment, and a heavy-electron anomaly in the electronic specific heat. With inclusion of excited crystal-field levels, some of the unusual magnetic-response data in the heavy-electron superconductor UBe13 may be understood. Structural phase transitions at unprecedented low temperatures may occur in U-based heavy-electron materials.
The entanglement structure of the Kondo singlet in energy space
NASA Astrophysics Data System (ADS)
Yang, Chun; Feiguin, Adrian
We unveil the entanglement structure of the Kondo singlet in energy space by studying the contribution of each individual free electron eigenstate. This is a problem of two spins coupled to a bath, where the bath is formed by the remaining conduction electrons. Being a mixed state, we resort to the ''concurrence'' as a good measure of entanglement. Using the density matrix renormalization group and analytical variational calculations with the Yoshida wave-function, and slave bosons, we find a distinct transition between weak and strong coupling regimes characterized by very different entanglement distributions. We discuss implications to the theory of the Kondo cloud.
Robust Josephson-Kondo screening cloud in circuit quantum electrodynamics
NASA Astrophysics Data System (ADS)
Snyman, Izak; Florens, Serge
2015-08-01
We investigate the entanglement properties of a standard circuit-QED setup that consists of a Cooper pair box coupled to a long chain of Josephson junctions. We calculate the static charge polarization at finite distances along the device. Our calculations reveal a deep connection to the Kondo screening cloud, together with robust correlations that are difficult to measure in a condensed matter context. We also find weak sensitivity of these Kondo signatures to the actual parameters and design of the device, demonstrating the universality of the Josephson entanglement cloud.
Kondo effect in a topological insulator quantum dot
NASA Astrophysics Data System (ADS)
Xin, Xianhao; Zhou, Di
2015-04-01
We investigate theoretically the nonequilibrium transport properties of a topological insulator quantum dot (TIQD) in the Coulomb blockade and Kondo regime. An Anderson impurity model is applied to a TIQD system coupled to two external leads, and we show that the model realizes the spin-orbital Kondo effect at the Dirac point where the edge states are not split by a finite-size effect, leading to an additional S U (4 ) symmetry because of the presence of strong mixture among four internal degrees of freedom. In a more realistic situation where the degeneracy is lifted due to the finite-size effect, we demonstrate that there is a richer structure in transport measurements. We illustrate a continuous crossover from four (spin and orbital) Coulomb peaks with large interpair spacing and small intrapair spacing to a double-peak structure in the local density of states (LDOS) as increasing the hybridization strength Γ within the Coulomb blockade regime. When temperature falls below the Kondo temperature TK, four Kondo peaks show up in the nonequilibrium LDOS. Two of them are located at the chemical potential of each lead, and the other two are shifted away from the chemical potential by an amount proportional to the TIQD's bare energy level, leading to a triple-peak structure in the differential conductance when a bias voltage is applied.
Antiferromagnetism and Kondo screening on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Lin, Heng-Fu; Hong-Shuai, Tao; Guo, Wen-Xiang; Liu, Wu-Ming
2015-05-01
Magnetic adatoms in the honeycomb lattice have received tremendous attention due to the interplay between Ruderman-Kittel-Kasuya-Yosida interaction and Kondo coupling leading to very rich physics. Here we study the competition between the antiferromagnetism and Kondo screening of local moments by the conduction electrons on the honeycomb lattice using the determinant quantum Monte Carlo method. While changing the interband hybridization V, we systematically investigate the antiferromagnetic-order state and the Kondo singlet state transition, which is characterized by the behavior of the local moment, antiferromagnetic structure factor, and the short range spin-spin correlation. The evolution of the single particle spectrum are also calculated as a function of hybridization V, we find that the system presents a small gap in the antiferromagnetic-order region and a large gap in the Kondo singlet region in the Fermi level. We also find that the localized and itinerant electrons coupling leads to the midgap states in the conduction band in the Fermi level at very small V. Moreover, the formation of antiferromagnetic order and Kondo singlet are studied as on-site interaction U or temperature T increasing, we have derived the phase diagrams at on-site interaction U (or temperature T) and hybridization V plane. Project supported by the National Key Basic Research Special Foundation of China (Grants Nos. 2011CB921502 and 2012CB821305), the National Natural Science Foundation of China (Grants Nos. 61227902, 61378017, and 11434015), the State Key Laboratory for Quantum Optics and Quantum Optical Devices, China (Grant No. KF201403).
Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12.
Hagiwara, Kenta; Ohtsubo, Yoshiyuki; Matsunami, Masaharu; Ideta, Shin-Ichiro; Tanaka, Kiyohisa; Miyazaki, Hidetoshi; Rault, Julien E; Fèvre, Patrick Le; Bertran, François; Taleb-Ibrahimi, Amina; Yukawa, Ryu; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Sumida, Kazuki; Okuda, Taichi; Iga, Fumitoshi; Kimura, Shin-Ichi
2016-01-01
A synergistic effect between strong electron correlation and spin-orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). One TKI candidate has been experimentally observed on the KI SmB6(001), and the origin of the surface states (SS) and the topological order of SmB6 has been actively discussed. Here, we show a metallic SS on the clean surface of another TKI candidate YbB12(001) using angle-resolved photoelectron spectroscopy. The SS shows temperature-dependent reconstruction corresponding to the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c-f hybridization is metallic, forming a closed Fermi contour surrounding on the surface Brillouin zone and agreeing with the theoretically expected behaviour for SS on TKIs. These results demonstrate the temperature-dependent holistic reconstruction of two-dimensional states localized on KIs surface driven by the Kondo effect. PMID:27576449
NASA Astrophysics Data System (ADS)
Si, Qimiao; Goswami, Pallab
2014-03-01
Heavy fermion systems represent a prototypical setting to study magnetic quantum phase transitions. In this context, we study the spin one-half Kondo-Heisenberg model on a honeycomb lattice at half filling. The problem is approached from the Kondo destroyed, antiferromagnetically ordered insulating phase. We describe the local moments in terms of a coarse grained quantum non-linear sigma model, and show that the skyrmion defects of the antiferromagnetic order parameter host a number of competing order parameters. In addition to the spin Peierls, charge and current density wave order parameters, we identify for the first time Kondo singlets as the competing dual orders of the antiferromagnetism, which can be related to each other via generalized chiral transformations of the underlying fermions. We also show that the conduction electrons acquire a Berry phase through their coupling to the hedgehog configurations of the Néel order, which cancels the Berry phase of the local moments. Our results demonstrate the competition between the Kondo-singlet formation and spin-Peierls order when the antiferromagnetic order is suppressed, thereby shedding new light on the global phase diagram of heavy fermion systems at zero temperature. NSF.
NASA Astrophysics Data System (ADS)
Zhong, Yin; Wang, Yu-Feng; Lu, Han-Tao; Luo, Hong-Gang
2014-08-01
We have studied Kondo spin liquid phase of Kondo necklace models from the perspective of quantum O(N) non-linear sigma model (NLSM) field theory, particularly we focus on its possible topologically nontrivial phases. In the one-dimensional case, the Kondo spin liquid phase is a usual quantum disordered phase in contrast to the well-known topologically nontrivial Haldane phase due to destructive interference effect of topological θ term. In the two-dimensional case, the system can be mapped onto an O(4)-like NLSM with some O(3) anisotropy. Interestingly, if hedgehog-like point defects are included together with the restoration of the full O(4) symmetry, our model is identical to a kind of SU(2) symmetry-protected topological (SPT) state, which highlights a possible link between the extended Kondo necklace models and the desirable SPT states. Additionally, if the system has the expanded O(5) symmetry instead, the effective NLSM with the Wess-Zumino-Witten term is just a description of the surface modes of a three-dimensional SPT state. The deviations from fully symmetrical cases are discussed. We expect that the results might provide useful threads to identify certain microscopic bilayer antiferromagnet models (and related materials), which can support the SPT states.
Kondo effect in magnetic tunnel junctions with an AlOx tunnel barrier
NASA Astrophysics Data System (ADS)
Zheng, Chao; Shull, Robert D.; Chen, P. J.; Pong, Philip W. T.
2016-06-01
The influence of the magnetization configuration on the Kondo effect in a magnetic tunnel junction is investigated. In the parallel configuration, an additional resistance contribution (R*) below 40 K exhibits a logarithmic temperature dependence, indicating the presence of the Kondo effect. However, in the anti-parallel configuration, the Kondo-effect-associated spin-flip scattering has a nontrivial contribution to the tunneling current, which compensates the reduction of the current directly caused by Kondo scattering, making R* disappear. These results indicate that suppression and restoration of the Kondo effect can be experimentally achieved by altering the magnetization configuration, enhancing our understanding of the role of the Kondo effect in spin-dependent transport.
Non-Kondo Mechanism for Resistivity Minimum in Spin Ice Conduction Systems
NASA Astrophysics Data System (ADS)
Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi
2012-02-01
We present a mechanism of resistivity minimum in conduction electron systems coupled with localized moments, which is distinguished from the Kondo effect. Instead of the spin-flip process in the Kondo effect, electrons are elastically scattered by local spin correlations which evolve in a particular way under geometrical frustration as decreasing temperature. This is demonstrated by the cellular dynamical mean-field theory for a spin-ice-type Kondo lattice model on a pyrochlore lattice. Peculiar temperature dependences of the resistivity, specific heat, and magnetic susceptibility in the non-Kondo mechanism are compared with the experimental data in metallic Ir pyrochlore oxides.
Influence of organic ligands on the line shape of the Kondo resonance
NASA Astrophysics Data System (ADS)
Meyer, Jörg; Ohmann, Robin; Nickel, Anja; Toher, Cormac; Gresser, Roland; Leo, Karl; Ryndyk, Dmitry A.; Moresco, Francesca; Cuniberti, Gianaurelio
2016-04-01
The Kondo resonance of an organic molecule containing a Co atom is investigated by scanning tunneling spectroscopy and ab initio calculations on a Ag(100) surface. High resolution mapping of the line shape shows evidence of local nonradially symmetric variations of the Fano factor and the Kondo amplitude, revealing a strong influence of the molecular ligand. We show that the decay of the amplitude of the Kondo resonance is determined by the spatial distribution of the ligand's orbital being hybridized with the singly occupied Co dz2 orbital, forming together the singly occupied Kondo-active orbital.
Semiconductor photoelectrochemistry
NASA Technical Reports Server (NTRS)
Buoncristiani, A. M.; Byvik, C. E.
1983-01-01
Semiconductor photoelectrochemical reactions are investigated. A model of the charge transport processes in the semiconductor, based on semiconductor device theory, is presented. It incorporates the nonlinear processes characterizing the diffusion and reaction of charge carriers in the semiconductor. The model is used to study conditions limiting useful energy conversion, specifically the saturation of current flow due to high light intensity. Numerical results describing charge distributions in the semiconductor and its effects on the electrolyte are obtained. Experimental results include: an estimate rate at which a semiconductor photoelectrode is capable of converting electromagnetic energy into chemical energy; the effect of cell temperature on the efficiency; a method for determining the point of zero zeta potential for macroscopic semiconductor samples; a technique using platinized titanium dioxide powders and ultraviolet radiation to produce chlorine, bromine, and iodine from solutions containing their respective ions; the photoelectrochemical properties of a class of layered compounds called transition metal thiophosphates; and a technique used to produce high conversion efficiency from laser radiation to chemical energy.
NASA Technical Reports Server (NTRS)
Gatos, Harry C. (Inventor); Lagowski, Jacek (Inventor)
1977-01-01
A semiconductor sensor adapted to detect with a high degree of sensitivity small magnitudes of a mechanical force, presence of traces of a gas or light. The sensor includes a high energy gap (i.e., .about. 1.0 electron volts) semiconductor wafer. Mechanical force is measured by employing a non-centrosymmetric material for the semiconductor. Distortion of the semiconductor by the force creates a contact potential difference (cpd) at the semiconductor surface, and this cpd is determined to give a measure of the force. When such a semiconductor is subjected to illumination with an energy less than the energy gap of the semiconductors, such illumination also creates a cpd at the surface. Detection of this cpd is employed to sense the illumination itself or, in a variation of the system, to detect a gas. When either a gas or light is to be detected and a crystal of a non-centrosymmetric material is employed, the presence of gas or light, in appropriate circumstances, results in a strain within the crystal which distorts the same and the distortion provides a mechanism for qualitative and quantitative evaluation of the gas or the light, as the case may be.
NASA Technical Reports Server (NTRS)
1982-01-01
The primary thrust of the semiconductor processing is outlined. The purpose is to (1) advance the theoretical basis for bulk growth of elemental and compound semiconductors in single crystal form, and (2) to develop a new experimental approaches by which semiconductor matrices with significantly improved crystalline and chemical perfection can be obtained. The most advanced approaches to silicon crystal growth is studied. The projected research expansion, directed toward the capability of growth of 4 inch diameter silicon crystals was implemented. Both intra and interdepartmental programs are established in the areas of process metallurgy, heat transfer, mass transfer, and systems control. Solutal convection in melt growth systems is also studied.
Quantum spins on star graphs and the Kondo model
NASA Astrophysics Data System (ADS)
Crampé, N.; Trombettoni, A.
2013-06-01
We study the XX model for quantum spins on the star graph with three legs (i.e., on a Y-junction). By performing a Jordan-Wigner transformation supplemented by the introduction of an auxiliary space we find a Kondo Hamiltonian of fermions, in the spin 1 representation of su(2), locally coupled with a magnetic impurity. In the continuum limit our model is shown to be equivalent to the 4-channel Kondo model coupling spin-1/2 fermions with a spin-1/2 impurity and exhibiting a non-Fermi liquid behavior. We also show that it is possible to find an XY model such that - after the Jordan-Wigner transformation - one obtains a quadratic fermionic Hamiltonian directly diagonalizable.
Kondo effect goes anisotropic in vanadate oxide superlattices
NASA Astrophysics Data System (ADS)
Rotella, H.; Pautrat, A.; Copie, O.; Boullay, P.; David, A.; Mercey, B.; Morales, M.; Prellier, W.
2015-11-01
We study the transport properties in SrVO3/LaVO3 (SVO/LVO) superlattices deposited on SrTiO3 (STO) substrates. We show that the electronic conduction occurs in the metallic LVO layers with a galvanomagnetism typical of a 2D Fermi surface. In addition, a Kondo-like component appears in both the thermal variation of resistivity and the magnetoresistance. Surprisingly, in this system where the STO interface does not contribute to the measured conduction, the Kondo correction is strongly anisotropic. We show that the growth temperature allows a direct control of this contribution. Finally, the key role of vanadium mixed valency stabilized by oxygen vacancies is enlightened.
Kondo and Majorana doublet interactions in quantum dots
NASA Astrophysics Data System (ADS)
Kim, Younghyun; Liu, Dong E.; Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten; Lutchyn, Roman
We study the properties of a quantum dot coupled to a normal lead and a time-reversal topological superconductor with Majorana Kramers pair at the end. We explore the phase diagram of the system as a function of Kondo and Majorana-induced coupling strengths using perturbative renormalization group study and slave-boson mean-field theory. We find that, in the presence of coupling between a quantum dot and a Majorana doublet, the system flows to a new fixed point controlled by the Majorana doublet, rather than the Kondo coupling, which is characterized by correlations between a localized spin and the fermion parity of each spin sector of the topological superconductor. We find that this fixed point is stable with respect to Gaussian fluctuations. We also investigate the effect of spin-spin interaction between a quantum dot and Majorana doublet and compare the result with a case where a normal lead is directly coupled to Majorana doublet.
Observation of the underscreened Kondo effect in a molecular transistor.
Roch, Nicolas; Florens, Serge; Costi, Theo A; Wernsdorfer, Wolfgang; Balestro, Franck
2009-11-01
We present the first quantitative experimental evidence for the underscreened Kondo effect, an incomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozières and Blandin. The device consists of an even charge spin S=1 molecular quantum dot, obtained by electromigration of C60 molecules into gold nanogaps and operated in a dilution fridge. The persistence of logarithmic singularities in the low temperature conductance is demonstrated by a comparison to the fully screened configuration obtained in odd charge spin S=1/2 Coulomb diamonds. We also discover an extreme sensitivity of the underscreened Kondo resonance to the magnetic field that we confirm on the basis of numerical renormalization group calculations. PMID:20365950
Observation of the Underscreened Kondo Effect in a Molecular Transistor
NASA Astrophysics Data System (ADS)
Roch, Nicolas; Florens, Serge; Costi, Theo A.; Wernsdorfer, Wolfgang; Balestro, Franck
2009-11-01
We present the first quantitative experimental evidence for the underscreened Kondo effect, an incomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozières and Blandin. The device consists of an even charge spin S=1 molecular quantum dot, obtained by electromigration of C60 molecules into gold nanogaps and operated in a dilution fridge. The persistence of logarithmic singularities in the low temperature conductance is demonstrated by a comparison to the fully screened configuration obtained in odd charge spin S=1/2 Coulomb diamonds. We also discover an extreme sensitivity of the underscreened Kondo resonance to the magnetic field that we confirm on the basis of numerical renormalization group calculations.
Characterization of a correlated topological Kondo insulator in one dimension
NASA Astrophysics Data System (ADS)
Hagymási, I.; Legeza, Ö.
2016-04-01
We investigate the ground state of a p -wave Kondo-Heisenberg model introduced by Alexandrov and Coleman with an Ising-type anisotropy in the Kondo interaction and correlated conduction electrons. Our aim is to understand how they affect the stability of the Haldane state obtained in the SU(2)-symmetric case without the Hubbard interaction. By applying the density-matrix renormalization group algorithm and calculating the entanglement entropy we show that in the anisotropic case a phase transition occurs and a Néel state emerges above a critical value of the Coulomb interaction. These findings are also corroborated by the examination of the entanglement spectrum and the spin profile of the system which clarify the structure of each phase.
First principles electron transport simulations in the Kondo regime
NASA Astrophysics Data System (ADS)
Rungger, Ivan; Radonjic, Milos; Appelt, Wilhelm; Chioncel, Liviu; Droghetti, Andrea
When magnetic atoms, molecules or thin films are brought into contact with metals the electron-electron interaction leads to the appearance of the correlated Kondo state at low temperatures. In this talk we will present results for the electronic structure and conductance in the Kondo regime of recent STM and break junction experiments for stable radical molecules, which correspond to spin half molecular magnets. We will outline the methodological approach to evaluate the conductance of such systems from first principles, as implemented in the Smeagol electron transport code. The method combines the density functional theory (DFT) with Anderson impurity solvers within the continuum time quantum Monte Carlo (CTQMC) and numerical renormalization group (NRG) approaches.
Ferromagnetic Kondo Effect in a Triple Quantum Dot System
NASA Astrophysics Data System (ADS)
Baruselli, P. P.; Requist, R.; Fabrizio, M.; Tosatti, E.
2013-07-01
A simple device of three laterally coupled quantum dots, the central one contacted by metal leads, provides a realization of the ferromagnetic Kondo model, which is characterized by interesting properties like a nonanalytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Tuning the gate voltages of the lateral dots allows us to study the transition from a ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field.
Ferromagnetic Kondo effect in a triple quantum dot system.
Baruselli, P P; Requist, R; Fabrizio, M; Tosatti, E
2013-07-26
A simple device of three laterally coupled quantum dots, the central one contacted by metal leads, provides a realization of the ferromagnetic Kondo model, which is characterized by interesting properties like a nonanalytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Tuning the gate voltages of the lateral dots allows us to study the transition from a ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field. PMID:23931401
Kondo physics from quasiparticle poisoning in Majorana devices
NASA Astrophysics Data System (ADS)
Plugge, S.; Zazunov, A.; Eriksson, E.; Tsvelik, A. M.; Egger, R.
2016-03-01
We present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M =2 attached leads, such "dangerous" quasiparticle poisoning processes cause a spin S =1 /2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effect of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M >3 , the topological Kondo fixed point re-emerges, though now it involves only M -1 leads. As a consequence, for M =3 , the low-energy fixed point becomes trivial corresponding to decoupled leads.
Neutron scattering from the Kondo Insulator SmB6
NASA Astrophysics Data System (ADS)
Broholm, Collin
A review of neutron scattering work probing the Kondo insulator SmB6 is presented with special emphasis on assessing the topology of the underlying strongly renormalized band structure. A 14 meV excition dominates the spectrum and is evidence of strong electron correlations [1]. Though the data generally supports the proposal that SmB6 is a topological Kondo insulator, specific heat and high-resolution neutron scattering data show a continuum of states well below the bulk transport gap, which enrich the problem and may connect to the recent surprising de Haas van Alpen results. ``Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6,'' W. T. Fuhrman, J. Leiner, P. Nikolic, G. E. Granroth, M. B. Stone, M. D. Lumsden, L. DeBeer-Schmitt, P. A. Alekseev, J.-M. Mignot, S. M. Koohpayeh, P. Cottingham, W. Adam Phelan, L. Schoop, T. M. McQueen, and C. Broholm, Phys. Rev. Lett. 114, 036401 (2015). Supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Grant No. DEFG02-08ER46544 and the Gordon and Betty Moore Foundation.
Kondo physics from quasiparticle poisoning in Majorana devices
Plugge, S.; Tsvelik, A. M.; Zazunov, A.; Eriksson, E.; Egger, R.
2016-03-24
Here, we present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M = 2 attached leads, such “dangerous” quasiparticle poisoning processes cause a spin S = 1/2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effectmore » of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M > 3, the topological Kondo fixed point re-emerges, though now it involves only M–1 leads. As a consequence, for M = 3, the low-energy fixed point becomes trivial corresponding to decoupled leads.« less
Conductance fingerprint of Majorana fermions in the topological Kondo effect
NASA Astrophysics Data System (ADS)
Galpin, Martin R.; Mitchell, Andrew K.; Temaismithi, Jesada; Logan, David E.; Béri, Benjamin; Cooper, Nigel R.
2014-01-01
We consider an interacting nanowire/superconductor heterostructure attached to metallic leads. The device is described by an unusual low-energy model involving spin-1 conduction electrons coupled to a nonlocal spin-1/2 Kondo impurity built from Majorana fermions. The topological origin of the resulting Kondo effect is manifest in distinctive non-Fermi-liquid (NFL) behavior, and the existence of Majorana fermions in the device is demonstrated unambiguously by distinctive conductance line shapes. We study the physics of the model in detail, using the numerical renormalization group, perturbative scaling, and Abelian bosonization. In particular, we calculate the full scaling curves for the differential conductance in ac and dc fields, onto which experimental data should collapse. Scattering t matrices and thermodynamic quantities are also calculated, recovering asymptotes from conformal field theory. We show that the NFL physics is robust to asymmetric Majorana-lead couplings, and here we uncover a duality between strong and weak coupling. The NFL behavior is understood physically in terms of competing Kondo effects. The resulting frustration is relieved by inter-Majorana coupling which generates a second crossover to a regular Fermi liquid.
NASA Astrophysics Data System (ADS)
Takada, Yasutami; Maezono, Ryo; Yoshizawa, Kanako
2015-10-01
Hydrogen in metals has attracted much attention for a long time from both basic scientific and technological points of view. Its electronic state has been investigated in terms of a proton embedded in the electron gas mostly by the local density approximation (LDA) to the density functional theory. At high electronic densities, it is well described by a bare proton H+ screened by metallic electrons (charge resonance), while at low densities two electrons are localized at the proton site to form a closed-shell negative ion H- protected from surrounding metallic electrons by the Pauli exclusion principle. However, no details are known about the transition from H+ to H- in the intermediate-density region. Here, by accurately determining the ground-state electron distribution n (r ) by the use of LDA and diffusion Monte Carlo simulations with the total electron number up to 170, we obtain a complete picture of the transition, in particular, a sharp transition from short-range H+ screening charge resonance to long-range Kondo-type spin-singlet resonance, the emergence of which is confirmed by the presence of an anomalous Friedel oscillation characteristic to the Kondo singlet state with the Kondo temperature TK well beyond 1000 K. This study not only reveals interesting competition between charge and spin resonances, enriching the century-old paradigm of metallic screening to a point charge, but also discovers a high-TK system long sought in relation to the development of exotic superconductivity in the quantum critical regime.
Quantum phase transitions and anomalous Hall effect in a pyrochlore Kondo lattice
NASA Astrophysics Data System (ADS)
Grefe, Sarah; Ding, Wenxin; Si, Qimiao
The metallic variant of the pyrochlore iridates Pr2Ir2O7 has shown characteristics of a possible chiral spin liquid state [PRL 96 087204 (2006), PRL 98, 057203 (2007), Nature 463, 210 (2010)] and quantum criticality [Nat. Mater. 13, 356 (2014)]. An important question surrounding the significant anomalous Hall response observed in Pr2Ir2O7 is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on the pyrochlore lattice. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations and determine the zero-temperature phase diagram. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr2Ir2O7 and related frustrated Kondo-lattice systems.
Optical Study of Interactions in a d-Electron Kondo Lattice with Ferromagnetism
Burch, K. S.; Schafgans, A.; Butch, N. P.; Sayles, T. A.; Maple, M. B.; Sales, Brian C; Mandrus, David; Basov, D. N.
2005-01-01
We report on a comprehensive optical, transport, and thermodynamic study of the Zintl compound Yb{sub 14}MnSb{sub 11}, demonstrating that it is the first ferromagnetic Kondo lattice compound in the underscreened limit. We propose a scenario whereby the combination of Kondo and Jahn-Teller effects provides a consistent explanation of both transport and optical data.
Reappearance of the Kondo effect in serially coupled symmetric triple quantum dots
NASA Astrophysics Data System (ADS)
Cheng, Yongxi; Wei, Jianhua; Yan, Yijing
2015-12-01
We investigate the spectral properties of a serially coupled triple quantum dot (STQD) system by means of the hierarchical equations of motion (HEOM) approach. We find that with the increase of the interdot coupling t, the first Kondo screening is followed by another Kondo effect reappearing due to the transition from the respective Kondo singlet state of individual QD to the coherence bonding state generated among the three QDs. The reappearance of the Kondo effect results in the three-peak structure of the spectral functions of peripheral QD-1(3). By investigating the susceptibility χ, we find that the local susceptibility of intermediate QD-2 is a positive value at weak interdot coupling, while it changes into a negative value at strong interdot coupling, at which the STQD system gives rise to the reappearance of the Kondo effect. We also find that the slopes of 1/χ will deviate from a straight line behaviour at low temperature in the reappearing Kondo regime. In addition, the influence of temperature and dot-lead coupling strength on the reappearing Kondo effect as well as the Kondo-correlated transport properties are afterwards exploited in detail.
Scanning tunneling spectroscopy of a magnetic atom on graphene in the Kondo regime
Zhuang, Huai -Bin; Sun, Qing -feng; Xie, X. C.
2009-06-23
In this study, the Kondo effect in the system consisting of a magnetic adatom on the graphene is studied. By using the non-equilibrium Green function method with the slave-boson mean field approximation, the local density of state (LDOS) and the conductance are calculated. For a doped graphene, the Kondo phase is present at all time. Surprisingly, two kinds of Kondo regimes are revealed. But for the undoped graphene, the Kondo phase only exists if the adatom’s energy level is beyond a critical value. The conductance is similar to the LDOS, thus, the Kondo peak in the LDOS can be observedmore » with the scanning tunneling spectroscopy. In addition, in the presence of a direct coupling between the STM tip and the graphene, the conductance may be dramatically enhanced, depending on the coupling site.« less
Scanning tunneling spectroscopy of a magnetic atom on graphene in the Kondo regime
Zhuang, Huai -Bin; Sun, Qing -feng; Xie, X. C.
2009-06-23
In this study, the Kondo effect in the system consisting of a magnetic adatom on the graphene is studied. By using the non-equilibrium Green function method with the slave-boson mean field approximation, the local density of state (LDOS) and the conductance are calculated. For a doped graphene, the Kondo phase is present at all time. Surprisingly, two kinds of Kondo regimes are revealed. But for the undoped graphene, the Kondo phase only exists if the adatom’s energy level is beyond a critical value. The conductance is similar to the LDOS, thus, the Kondo peak in the LDOS can be observed with the scanning tunneling spectroscopy. In addition, in the presence of a direct coupling between the STM tip and the graphene, the conductance may be dramatically enhanced, depending on the coupling site.
Exploring the phase diagram of the two-impurity Kondo problem
NASA Astrophysics Data System (ADS)
Spinelli, A.; Gerrits, M.; Toskovic, R.; Bryant, B.; Ternes, M.; Otte, A. F.
2015-11-01
A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present a study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. The pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third-order transport model, allows us to independently determine the degree of Kondo screening in each phase.
From four- to two-channel Kondo effect in junctions of XY spin chains
NASA Astrophysics Data System (ADS)
Giuliano, Domenico; Sodano, Pasquale; Tagliacozzo, Arturo; Trombettoni, Andrea
2016-08-01
We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a "critical" line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair) channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.
Analysis of the antiferromagnetic phase transitions of the 2D Kondo lattice
NASA Astrophysics Data System (ADS)
Jones, Barbara
2010-03-01
The Kondo lattice continues to present an interesting and relevant challenge, with its interactions between Kondo, RKKY, and coherent order. We present our study[1] of the antiferromagnetic quantum phase transitions of a 2D Kondo-Heisenberg square lattice. Starting from the nonlinear sigma model as a model of antiferromagnetism, we carry out a renormalization group analysis of the competing Kondo-RKKY interaction to one-loop order in an ɛ-expansion. We find a new quantum critical point (QCP) strongly affected by Kondo fluctuations. Near this QCP, there is a breakdown of hydrodynamic behavior, and the spin waves are logarithmically frozen out. The renormalization group results allow us to propose a new phase diagram near the antiferromagnetic fixed point of this 2D Kondo lattice model. The T=0 phase diagram contains four phases separated by a tetracritical point, the new QCP. For small spin fluctuations, we find a stable local magnetic moment antiferromagnet. For stronger coupling, region II is a metallic quantum disordered paramagnet. We find in region III a paramagnetic phase driven by Kondo interactions, with possible ground states of a heavy fermion liquid or a Kondo driven spin-liquid. The fourth phase is a spiral phase, or a large-Fermi-surface antiferromagnetic phase. We will describe these phases in more detail, including possible experimental confirmation of the spiral phase. The existence of the tetracritical point found here would be expected to affect the phase diagram at finite temperatures as well. In addition, It is hoped that these results, and particularly the Kondo interaction paramagnetic phase, will serve to bridge to solutions starting from the opposite limit, of a Kondo effect leading to a heavy fermion ground state. Work in collaboration with T. Tzen Ong. [4pt] [1] T. Ong and B. A. Jones, Phys. Rev. Lett. 103, 066405 (2009).
Unconventional superconductivity from local spin fluctuations in the Kondo lattice.
Bodensiek, Oliver; Žitko, Rok; Vojta, Matthias; Jarrell, Mark; Pruschke, Thomas
2013-04-01
The explanation of heavy-fermion superconductivity is a long-standing challenge to theory. It is commonly thought to be connected to nonlocal fluctuations of either spin or charge degrees of freedom and therefore of unconventional type. Here we present results for the Kondo-lattice model, a paradigmatic model to describe heavy-fermion compounds, obtained from dynamical mean-field theory which captures local correlation effects only. Unexpectedly, we find robust s-wave superconductivity in the heavy-fermion state. We argue that this novel type of pairing is tightly connected to the formation of heavy quasiparticle bands and the presence of strong local spin fluctuations. PMID:25167017
Transport through side-coupled multilevel double quantum dots in the Kondo regime
NASA Astrophysics Data System (ADS)
Andrade, J. A.; Cornaglia, Pablo S.; Aligia, A. A.
2014-03-01
We analyze the transport properties of a double quantum dot device in the side-coupled configuration. A small quantum dot (QD), having a single relevant electronic level, is coupled to source and drain electrodes. A larger QD, whose multilevel nature is considered, is tunnel-coupled to the small QD. A Fermi-liquid analysis shows that the low-temperature conductance of the device is determined by the total electronic occupation of the double QD. When the small dot is in the Kondo regime, an even number of electrons in the large dot leads to a conductance that reaches the unitary limit, while for an odd number of electrons a two-stage Kondo effect is observed and the conductance is strongly suppressed. The Kondo temperature of the second-stage Kondo effect is strongly affected by the multilevel structure of the large QD. For increasing level spacing, a crossover from a large Kondo temperature regime to a small Kondo temperature regime is obtained when the level spacing becomes of the order of the large Kondo temperature.
Application of the S=1 underscreened Anderson lattice model to Kondo uranium and neptunium compounds
NASA Astrophysics Data System (ADS)
Thomas, Christopher; da Rosa Simões, Acirete S.; Iglesias, J. R.; Lacroix, C.; Perkins, N. B.; Coqblin, B.
2011-01-01
Magnetic properties of uranium and neptunium compounds showing the coexistence of the Kondo screening effect and ferromagnetic order are investigated within the Anderson lattice Hamiltonian with a two-fold degenerate f level in each site, corresponding to 5f2 electronic configuration with S=1 spins. A derivation of the Schrieffer-Wolff transformation is presented and the resulting Hamiltonian has an effective f-band term, in addition to the regular exchange Kondo interaction between the S=1 f spins and the s=1/2 spins of the conduction electrons. The resulting effective Kondo lattice model can describe both the Kondo regime and a weak delocalization of the 5f electrons. Within this model we compute the Kondo and Curie temperatures as a function of model parameters, namely the Kondo exchange interaction constant JK, the magnetic intersite exchange interaction JH, and the effective f bandwidth. We deduce, therefore, a phase diagram of the model which yields the coexistence of the Kondo effect and ferromagnetic ordering and also accounts for the pressure dependence of the Curie temperature of uranium compounds such as UTe.
Entanglement probe of two-impurity Kondo physics in a spin chain.
Bayat, Abolfazl; Bose, Sougato; Sodano, Pasquale; Johannesson, Henrik
2012-08-10
We propose that real-space properties of the two-impurity Kondo model can be obtained from an effective spin model where two single-impurity Kondo spin chains are joined via an Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the two impurity spins. We then use a density matrix renormalization group approach, valid in all ranges of parameters, to study its features using two complementary quantum-entanglement measures, the negativity and the von Neumann entropy. This nonperturbative approach enables us to uncover the precise dependence of the spatial extent ξ(K) of the Kondo screening cloud with the Kondo and RKKY couplings. Our results reveal an exponential suppression of the Kondo temperature T(K)~1/ξ(K) with the size of the effective impurity spin in the limit of large ferromagnetic RKKY coupling, a striking display of "Kondo resonance narrowing" in the two-impurity Kondo model. We also show how the antiferromagnetic RKKY interaction produces an effective decoupling of the impurities from the bulk already for intermediate strengths of this interaction, and, furthermore, exhibit how the non-Fermi liquid quantum critical point is signaled in the quantum entanglement between various parts of the system. PMID:23006288
Interaction effect in the Kondo energy of the periodic Anderson-Hubbard model
NASA Astrophysics Data System (ADS)
Itai, K.; Fazekas, P.
1996-07-01
We extend the periodic Anderson model by switching on a Hubbard U for the conduction band. The nearly integral valent limit of the Anderson-Hubbard model is studied with the Gutzwiller variational method. The lattice Kondo energy shows U dependence both in the prefactor and the exponent. Switching on U reduces the Kondo scale, which can be understood to result from the blocking of hybridization. At half filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator. Our findings should be relevant for a number of correlated two-band models of recent interest.
Noise characteristics of the Fano effect and the Fano-Kondo effect in triple quantum dots.
Tanamoto, T; Nishi, Y; Fujita, S
2009-04-01
We theoretically compare transport properties of the Fano-Kondo effect with those of the Fano effect, focusing on the effect of a two-level state in a triple quantum dot (QD) system. We analyze shot noise characteristics in the Fano-Kondo region at zero temperature, and discuss the effect of strong electronic correlation in QDs. We found that the modulation of the Fano dip is strongly affected by the on-site Coulomb interaction in QDs, and stronger Coulomb interaction (Fano-Kondo case) induces larger noise. PMID:21825341
Magnetic Flux Effect on a Kondo-Induced Electric Polarization in a Triangular Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Koga, Mikito; Matsumoto, Masashige; Kusunose, Hiroaki
2014-08-01
A magnetic flux effect is studied theoretically on an electric polarization induced by the Kondo effect in a triangular triple-quantum-dot system, where one of the three dots is connected to a metallic lead. This electric polarization exhibits an Aharonov-Bohm oscillation as a function of the magnetic flux penetrating through the triangular loop. The numerical renormalization group analysis reveals how the oscillation pattern depends on the Kondo coupling of a local spin with lead electrons, which is sensitive to the point contact with the lead. It provides an experimental implication that the Kondo effect is the origin of the emergent electric polarization.
The Kondo effect in three-dimensional topological insulators
NASA Astrophysics Data System (ADS)
Xin, Xianhao; Yeh, Mao-Chuang
2013-07-01
We investigate the role of magnetic impurities in the transport properties of surface states on a three-dimensional topological insulator. First, we use second-order perturbation theory and the Boltzmann transport equation to calculate the magnetically induced resistivity in a topological insulator. Our result shows a non-perturbative behavior when conducting electrons and magnetic impurities’ spins are antiferromagnetically coupled. The surface resistivity is found to display an oscillatory rather than isotropic behavior compared to the conventional Kondo effect. Both the variational method and renormalization group (RG) analysis are employed to compute the Kondo temperature, through which the non-perturbative behavior is confirmed. We further study the RG flows and demonstrate that the RG trajectories flow into a strong coupling regime if coupling is antiferromagnetic. Our work is motivated by the recent transport experiments with surface currents on topological insulators. Our calculation is qualitatively consistent with the low temperature dip observed in the experimental R-T curve and might be one of the possible origins of the dip.
A Quantum Electrodynamics Kondo Circuit with Orbital and Spin Entanglement
NASA Astrophysics Data System (ADS)
Schiro, Marco; Deng, Guang-Wei; Henriet, Loic; Wei, Da; Li, Shu-Xiao; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guang-Can; Le Hur, Karyn; Guo, Guo-Ping
Recent progress in nanotechnology allows to engineer hybrid mesoscopic devices comprising on chip an artificial atom or quantum dot, capacitively coupled to a microwave (superconducting) resonator and to biased metallic leads. Here, we build such a prototype system where the artificial atom is a graphene double quantum dot (DQD) to probe non-equilibrium aspects of strongly-entangled many body states between light and matter at the nanoscale. Controlling the coupling of the photon field and the charge states of the DQD, we measure the microwave reflection spectrum of the resonator. When the DQD is at the charge degeneracy points, experimental results are consistent with a Kondo impurity model entangling charge, spin and orbital degrees of freedom with the quantum fluctuations of the cavity photon. The light coming out from the resonator reveals the formation of the Kondo or Abrikosov-Suhl resonance at low temperatures. We also explore other routes to investigate nonlinear transport by increasing the microwave power, the bias and gate voltages.
Entanglement structure of the two-channel Kondo model
NASA Astrophysics Data System (ADS)
Alkurtass, Bedoor; Bayat, Abolfazl; Affleck, Ian; Bose, Sougato; Johannesson, Henrik; Sodano, Pasquale; Sørensen, Erik S.; Le Hur, Karyn
2016-02-01
Two electronic channels competing to screen a single impurity spin, as in the two-channel Kondo model, are expected to generate a ground state with a nontrivial entanglement structure. We exploit a spin-chain representation of the two-channel Kondo model to probe the ground-state block entropy, negativity, tangle, and Schmidt gap, using a density matrix renormalization group approach. In the presence of symmetric coupling to the two channels, we confirm field-theory predictions for the boundary entropy difference ln(gUV/gIR) =ln(2 ) /2 between the ultraviolet and infrared limits and the leading ln(x )/x impurity correction to the block entropy. The impurity entanglement Simp is shown to scale with the characteristic length ξ2 CK. We show that both the Schmidt gap and the entanglement of the impurity with one of the channels—as measured by the negativity—faithfully serve as order parameters for the impurity quantum phase transition appearing as a function of channel asymmetry, allowing for explicit determination of critical exponents, ν ≈2 and β ≈0.2 . Remarkably, we find the emergence of tripartite entanglement only in the vicinity of the critical channel-symmetric point.
Holographic optical traps for atom-based topological Kondo devices
NASA Astrophysics Data System (ADS)
Buccheri, F.; Bruce, G. D.; Trombettoni, A.; Cassettari, D.; Babujian, H.; Korepin, V. E.; Sodano, P.
2016-07-01
The topological Kondo (TK) model has been proposed in solid-state quantum devices as a way to realize non-Fermi liquid behaviors in a controllable setting. Another motivation behind the TK model proposal is the demand to demonstrate the quantum dynamical properties of Majorana fermions, which are at the heart of their potential use in topological quantum computation. Here we consider a junction of crossed Tonks–Girardeau gases arranged in a star-geometry (forming a Y-junction), and we perform a theoretical analysis of this system showing that it provides a physical realization of the TK model in the realm of cold atom systems. Using computer-generated holography, we experimentally implement a Y-junction suitable for atom trapping, with controllable and independent parameters. The junction and the transverse size of the atom waveguides are of the order of 5 μm, leading to favorable estimates for the Kondo temperature and for the coupling across the junction. Since our results show that all the required theoretical and experimental ingredients are available, this provides the demonstration of an ultracold atom device that may in principle exhibit the TK effect.
Kondo route to spin inhomogeneities in the honeycomb Kitaev model
NASA Astrophysics Data System (ADS)
Das, S. D.; Dhochak, K.; Tripathi, V.
2016-07-01
Paramagnetic impurities in a quantum spin liquid give rise to Kondo effects with highly unusual properties. We have studied the effect of locally coupling a paramagnetic impurity with the spin-1/2 honeycomb Kitaev model in its gapless spin-liquid phase. The (impurity) scaling equations are found to be insensitive to the sign of the coupling. The weak and strong coupling fixed points are stable, with the latter corresponding to a noninteracting vacancy and an interacting, spin-1 defect for the antiferromagnetic and ferromagnetic cases, respectively. The ground state in the strong coupling limit in both cases has a nontrivial topology associated with a finite Z2 flux at the impurity site. For the antiferromagnetic case, this result has been obtained straightforwardly owing to the integrability of the Kitaev model with a vacancy. The strong-coupling limit of the ferromagnetic case is, however, nonintegrable, and we address this problem through exact-diagonalization calculations with finite Kitaev fragments. Our exact diagonalization calculations indicate that the weak-to-strong coupling transition and the topological phase transition occur rather close to each other and are possibly coincident. We also find an intriguing similarity between the magnetic response of the defect and the impurity susceptibility in the two-channel Kondo problem.
Spin fluctations and heavy fermions in the Kondo lattice
Khaliullin, G.G.
1994-09-01
This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodic lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.
Quantum phase transitions in the Kondo-necklace model
NASA Astrophysics Data System (ADS)
Ghassemi, Nader; Hemmatiyan, Shayan; Rahimi Movassagh, Mahsa; Kargarian, Mahdi; Rezakhani, Ali T.; Langari, Abdollah
2015-03-01
Kondo-necklace model can describe the magnetic low-energy limit of strongly correlated heavy fermion materials. There exist multiple energy scales in this model corresponding to each phase of the system. Here, we study quantum phase transitions between these different phases, and show the effect of anisotropies in terms of quantum information properties and vanishing energy gap. We employ the perturbative unitary transformations to calculate the energy gap and spin-spin correlations for the model one, two, and three spatial dimensions as well as for the spin ladders. In particular, we show that the method, although being perturbative, can predict the expected quantum critical point by imposing the spontaneous symmetry breaking, which is in good agreement with the results of numerical and Green's function analyses. We also use concurrence, a bipartite entanglement measure, to study the criticality of the model. Absence of singularities in the derivative of the concurrence in 2d and 3d in Kondo-necklace model shows this model has multipartite entanglement. We also discuss the crossover from the one-dimensional to the two-dimensional model via the ladder structure. Sharif University of Technology.
Co adatoms on Cu surfaces: Ballistic conductance and Kondo temperature
NASA Astrophysics Data System (ADS)
Baruselli, P. P.; Requist, R.; Smogunov, A.; Fabrizio, M.; Tosatti, E.
2015-07-01
The Kondo zero-bias anomaly of Co adatoms probed by scanning tunneling microscopy is known to depend on the height of the tip above the surface, and this dependence is different on different low index Cu surfaces. On the (100) surface, the Kondo temperature first decreases then increases as the tip approaches the adatom, while on the (111) surface it is virtually unaffected. These trends are captured by combined density functional theory and numerical renormalization-group calculations. The adatoms are found to be described by an S =1 Anderson model on both surfaces, and ab initio calculations help identify the symmetry of the active d orbitals. We correctly reproduce the Fano line shape of the zero-bias anomaly for Co/Cu(100) in the tunneling regime but not in the contact regime, where it is probably dependent on the details of the tip and contact geometry. The line shape for Co/Cu(111) is presumably affected by the presence of surface states, which are not included in our method. We also discuss the role of symmetry, which is preserved in our model scattering geometry but most likely broken in experimental conditions.
Kondo bahavior in antiferromagnetic NpPdSn
NASA Astrophysics Data System (ADS)
Shrestha, K.; Prokes, K.; Griveau, J.-C.; Jardin, R.; Colineau, E.; Caciuffo, R.; Eloirdi, R.; Gofryk, K.
Actinide-based intermetallics show a large variety of exotic physical phenomena mainly coming from 5f hybridization with both on-site and neighboring ligand states. Depending on the strength of these process unusual behaviors such as long-range magnetic order, Kondo effect, heavy-fermion ground state, valence fluctuations, and/or superconductivity have been observed. Here we report results of our extensive studies on NpPdSn. The compound crystalizes in hexagonal ZrNiAl-type of crystal structure and is studied by means of x-ray and neutron diffraction, magnetization, heat capacity, electrical resistivity, and thermoelectric power measurements, performed over a wide range of temperatures and applied magnetic fields. All the results revealed Kondo lattice behavior and antiferromagnetic ordering below 19 K. NpPdSn can be classified as a moderately enhanced heavy-fermion system, one of very few known amidst Np-based intermetallics. Work at Idaho National Laboratory was supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division.
Alternative Kondo breakdown mechanism: Orbital-selective orthogonal metal transition
NASA Astrophysics Data System (ADS)
Zhong, Yin; Liu, Ke; Wang, Yong-Qiang; Luo, Hong-Gang
2012-09-01
In a recent paper of Nandkishore, Metlitski, and Senthil [Phys. Rev. B1098-012110.1103/PhysRevB.86.045128 86, 045128 (2012)], a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We extend this concept to study the corresponding quantum phase transition in the extended Anderson lattice model. It is found that the disordered state of slave spins in this model is an orbital-selective orthogonal metal, a generalization of the concept of the orthogonal metal in the Hubbard model. The quantum critical behaviors are multiscale and dominated by a z=3 and z=2 critical modes in the high- and low-temperature regime, respectively. Such behaviors are obviously in contrast to the naive expectation in the Hubbard model. The result provides alternative Kondo breakdown mechanism for heavy fermion compounds underlying the physics of the orbital-selective orthogonal metal in the disordered state, which is different from the conventional Kondo breakdown mechanism with the fractionalized Fermi-liquid picture. This work is expected to be useful in understanding the quantum criticality happening in some heavy fermion materials and other related strongly correlated systems.
Local moment formation and Kondo screening in impurity trimers.
Mitchell, Andrew K; Jarrold, Thomas F; Galpin, Martin R; Logan, David E
2013-10-24
We study theoretically a triangular cluster of three magnetic impurities, hybridizing locally with conduction electrons of a metallic host. Such a cluster is the simplest to exhibit frustration, an important generic feature of many complex molecular systems in which different interactions compete. Here, low-energy doublet states of the trimer are favored by effective exchange interactions produced by strong electronic repulsion in localized impurity orbitals. Parity symmetry protects a level crossing of such states on tuning microscopic parameters, while an avoided crossing arises in the general distorted case. Upon coupling to a metallic host, the behavior is shown to be immensely rich because collective quantum many-body effects now also compete. In particular, impurity degrees of freedom are totally screened at low temperatures in a Kondo-screened Fermi liquid phase, while degenerate ground states persist in a local moment phase. Local frustration drives the quantum phase transition between the two, which may be first order or of Kosterlitz-Thouless type, depending on symmetries. Unusual mechanisms for local moment formation and Kondo screening are found due to the orbital structure of the impurity trimer. Our results are of relevance for triple quantum dot devices. The problem is studied by a combination of analytical arguments and the numerical renormalization group. PMID:23527540
NASA Astrophysics Data System (ADS)
Goswami, Pallab; Si, Qimiao
2014-01-01
Heavy-fermion systems represent a prototypical setting to study magnetic quantum phase transitions. A particular focus has been on the physics of Kondo destruction, which captures quantum criticality beyond the Landau framework of order-parameter fluctuations. In this context, we study the spin one-half Kondo-Heisenberg model on a honeycomb lattice at half filling. The problem is approached from the Kondo-destroyed, antiferromagnetically ordered insulating phase. We describe the local moments in terms of a coarse grained quantum nonlinear sigma model, and show that the skyrmion defects of the antiferromagnetic order parameter host a number of competing order parameters. In addition to the spin Peierls, charge and current density wave order parameters, we identify for the first time Kondo singlets as the competing orders of the antiferromagnetism. We show that the antiferromagnetism and various competing singlet orders can be related to each other via generalized chiral transformations of the underlying fermions. We also show that the conduction electrons acquire a Berry phase through their coupling to the hedgehog configurations of the Néel order, which cancels the Berry phase of the local moments. Our results demonstrate the competition between the Kondo singlet formation and spin-Peierls order when the antiferromagnetic order is suppressed, thereby shedding new light on the global phase diagram of heavy-fermion systems at zero temperature.
Measurement of Valley Kondo Effect in a Si/SiGe Quantum Dot
NASA Astrophysics Data System (ADS)
Yuan, Mingyun; Yang, Zhen; Tang, Chunyang; Rimberg, A. J.; Joynt, R.; Savage, D. E.; Lagally, M. G.; Eriksson, M. A.
2013-03-01
The Kondo effect in Si/SiGe QDs can be enriched by the valley degree of freedom in Si. We have observed resonances showing temperature dependence characteristic of the Kondo effect in two consecutive Coulomb diamonds. These resonances exhibit unusual magnetic field dependence that we interpret as arising from Kondo screening of the valley degree of freedom. In one diamond two Kondo peaks due to screening of the valley index exist at zero magnetic field, revealing a zero-field valley splitting of Δ ~ 0.28 meV. In a non-zero magnetic field the peaks broaden and coalesce due to Zeeman splitting. In the other diamond, a single resonance at zero bias persists without Zeeman splitting for non-zero magnetic field, a phenomenon characteristic of valley non-conservation in tunneling. This research is supported by the NSA and ARO.
Kondo physics in the Josephon junction with DIII-class topological and s-wave superconductors
NASA Astrophysics Data System (ADS)
Gao, Z.; Gong, W. J.
2015-12-01
We discuss the Kondo effect in the Josephson junction formed by the indirect coupling between a one-dimensional DIII-class topological and s-wave superconductors via a quantum dot. By performing the Schrieffer-Wolff transformation, we find that the single-electron occupation in the quantum dot induces various correlation modes, such as the Kondo and singlet-triplet correlations between the quantum dot and the s-wave superconductor and the spin-exchange correlation between the dot and Majorana doublet. Also, it modifies the Josephson effect by introducing the high-order anisotropic Kondo-like correlation and extra spin-exchange correlations. However, the Kondo temperature is still governed by the antiferromagnetic correlation between the dot and s-wave superconductor. We believe that this work shows the fundamental property of the DIII-class topological superconductor.
Gate-tunable split Kondo effect in a carbon nanotube quantum dot
NASA Astrophysics Data System (ADS)
Eichler, A.; Weiss, M.; Schönenberger, C.
2011-07-01
We show a detailed investigation of the split Kondo effect in a carbon nanotube quantum dot with multiple gate electrodes. Two conductance peaks, observed at finite bias in nonlinear transport measurements, are found to approach each other for increasing magnetic field, to result in a recovered zero bias Kondo resonance at finite magnetic field. Surprisingly, in the same charge state, but under different gate configurations, the splitting does not disappear for any value of the magnetic field, but we observe an avoided crossing. We think that our observations can be understood in terms of a two-impurity Kondo effect with two spins coupled antiferromagnetically. The exchange coupling between the two spins can be influenced by a local gate, and the non-recovery of the Kondo resonance for certain gate configurations is explained by the existence of a small antisymmetric contribution to the exchange interaction between the two spins.
Surface-State Spin Textures and Mirror Chern Numbers in Topological Kondo Insulators
NASA Astrophysics Data System (ADS)
Legner, Markus; Rüegg, Andreas; Sigrist, Manfred
2015-10-01
The recent discovery of topological Kondo insulators has triggered renewed interest in the well-known Kondo insulator samarium hexaboride, which is hypothesized to belong to this family. In this Letter, we study the spin texture of the topologically protected surface states in such a topological Kondo insulator. In particular, we derive close relationships between (i) the form of the hybridization matrix at certain high-symmetry points, (ii) the mirror Chern numbers of the system, and (iii) the observable spin texture of the topological surface states. In this way, a robust classification of topological Kondo insulators and their surface-state spin texture is achieved. We underpin our findings with numerical calculations of several simplified and realistic models for systems like samarium hexaboride.
Surface-State Spin Textures and Mirror Chern Numbers in Topological Kondo Insulators.
Legner, Markus; Rüegg, Andreas; Sigrist, Manfred
2015-10-01
The recent discovery of topological Kondo insulators has triggered renewed interest in the well-known Kondo insulator samarium hexaboride, which is hypothesized to belong to this family. In this Letter, we study the spin texture of the topologically protected surface states in such a topological Kondo insulator. In particular, we derive close relationships between (i) the form of the hybridization matrix at certain high-symmetry points, (ii) the mirror Chern numbers of the system, and (iii) the observable spin texture of the topological surface states. In this way, a robust classification of topological Kondo insulators and their surface-state spin texture is achieved. We underpin our findings with numerical calculations of several simplified and realistic models for systems like samarium hexaboride. PMID:26550740
Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance
NASA Astrophysics Data System (ADS)
Song, Taegeun; Kiselev, Mikhail N.; Kikoin, Konstantin; Shekhter, Robert I.; Gorelik, Leonid Y.
2014-03-01
We investigate the instability and dynamical properties of nanoelectromechanical systems represented by a single-electron device containing movable quantum dots attached to a vibrating cantilever via asymmetric tunnel contacts. The Kondo resonance in electron tunneling between the source and shuttle facilitates self-sustained oscillations originating from the strong coupling of mechanical and electronic/spin degrees of freedom. We analyze a stability diagram for the two-channel Kondo shuttling regime due to limitations given by the electromotive force acting on a moving shuttle, and find that the saturation oscillation amplitude is associated with the retardation effect of the Kondo cloud. The results shed light on possible ways to experimentally realize the Kondo-cloud dynamical probe by using high mechanical dissipation tunability as well as supersensitive detection of mechanical displacement.
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
NASA Astrophysics Data System (ADS)
Barzykin, Victor
2006-03-01
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D. Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that thermodynamic and transport properties of Kondo lattices below coherence temperature can be very successfully described in terms of a two-fluid model, with Kondo impurity and heavy electron Fermi liquid contributions. We analyze thermodynamic properties of Kondo lattices using 1/N slave boson treatment of the periodic Anderson model and show that these two contributions indeed arise below the coherence temperature. We find that the Kondo impurity contribution to thermodynamics corresponds to thermal excitations into the flat portion of the energy spectrum.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-01
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature TD. At TD, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near TD.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-29
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}. PMID:27176534
Interdiffusion-controlled Kondo suppression of injection efficiency in metallic nonlocal spin valves
NASA Astrophysics Data System (ADS)
O'Brien, L.; Spivak, D.; Jeong, J. S.; Mkhoyan, K. A.; Crowell, P. A.; Leighton, C.
2016-01-01
Nonlocal spin valves (NLSVs) generate pure spin currents, providing unique insight into spin injection and relaxation at the nanoscale. Recently it was shown that the puzzling low temperature nonmonotonicity of the spin accumulation in all-metal NLSVs occurs due to a manifestation of the Kondo effect arising from dilute local-moment-forming impurities in the nonmagnetic material. Here it is demonstrated that precise control over interdiffusion in Fe/Cu NLSVs via thermal annealing can induce dramatic increases in this Kondo suppression of injection efficiency, observation of injector/detector separation-dependent Kondo effects in both charge and spin channels simultaneously, and, in the limit of large interdiffusion, complete breakdown of standard Valet-Fert-based models. The Kondo effect in the charge channel enables extraction of the exact interdiffusion profile, quantifying the influence of local moment density on the injection efficiency and presenting a well-posed challenge to theory.
The Kondo temperature of a two-dimensional electron gas with Rashba spin-orbit coupling.
Chen, Liang; Sun, Jinhua; Tang, Ho-Kin; Lin, Hai-Qing
2016-10-01
We use the Hirsch-Fye quantum Monte Carlo method to study the single magnetic impurity problem in a two-dimensional electron gas with Rashba spin-orbit coupling. We calculate the spin susceptibility for various values of spin-orbit coupling, Hubbard interaction, and chemical potential. The Kondo temperatures for different parameters are estimated by fitting the universal curves of spin susceptibility. We find that the Kondo temperature is almost a linear function of Rashba spin-orbit energy when the chemical potential is close to the edge of the conduction band. When the chemical potential is far away from the band edge, the Kondo temperature is independent of the spin-orbit coupling. These results demonstrate that, for single impurity problems in this system, the most important reason to change the Kondo temperature is the divergence of density of states near the band edge, and the divergence is induced by the Rashba spin-orbit coupling. PMID:27494800
Kondo effect of trivalent Tm in Y 0.9Tm 0.1S
NASA Astrophysics Data System (ADS)
Haen, P.; Lapierre, F.; Mignot, J. M.; Flouquet, J.; Holtzberg, F.; Penney, T.
1983-02-01
The existence of a Kondo effect in a trivalent alloy Y 0.9Tm 0.1 S is shown by the Curie-Weiss behavior of the susceptibility and by a ln T decrease of Δϱ = ϱ alloy - ϱ YS above ˜ 12 K comparable with that observed in TmS. Comparisons are made with the Kondo dilute alloys of the intermediate valent system (Y,Tm)Se.
NASA Technical Reports Server (NTRS)
1996-01-01
Through Goddard Space Flight Center and Jet Propulsion Laboratory Small Business Innovation Research contracts, Irvine Sensors developed a three-dimensional memory system for a spaceborne data recorder and other applications for NASA. From these contracts, the company created the Memory Short Stack product, a patented technology for stacking integrated circuits that offers higher processing speeds and levels of integration, and lower power requirements. The product is a three-dimensional semiconductor package in which dozens of integrated circuits are stacked upon each other to form a cube. The technology is being used in various computer and telecommunications applications.
A fully controllable Kondo system: Coupling a flux qubit and an ultracold Fermi gas
NASA Astrophysics Data System (ADS)
Patton, Kelly
We show that a composite spin-1/2 Kondo system can be formed by coupling a superconducting quantum interference device (SQUID) to the internal hyperfine states of a trapped ultracold atomic Fermi gas. Here, the SQUID, or flux qubit, acts as an effective magnetic impurity that induces spin-flip scattering near the Fermi energies of the trapped gas. Although the ultracold gas and SQUID are at vastly different temperatures, the formation of a strongly correlated Kondo state between the two systems is found when the gas is cooled below the Kondo temperature. We find that the Kondo temperature of this hybrid system is within current experimental limits. Furthermore, the momentum distribution of the trapped fermions is calculated. We find that it clearly contains an experimental signature of this correlated state and the associated Kondo screening length. In addition to probing Kondo physics, the con- trollability of this system can be used to systematically explore the relaxation and equilibration of a strongly correlated system that has been initially prepared in a selected nonequilibrium state.
Fully controllable Kondo system: Coupling a flux qubit and an ultracold Fermi gas
NASA Astrophysics Data System (ADS)
Patton, Kelly R.
2016-02-01
We show that a composite spin-½ Kondo system can be formed by coupling a superconducting quantum interference device (SQUID) to the internal hyperfine states of a trapped ultracold atomic Fermi gas. Here, the SQUID, or flux qubit, acts as an effective magnetic impurity that induces spin-flip scattering near the Fermi energies of the trapped gas. Although the ultracold gas and SQUID are at vastly different temperatures, the formation of a strongly correlated Kondo state between the two systems is found when the gas is cooled below the Kondo temperature. We find that the Kondo temperature of this hybrid system is within current experimental limits. Furthermore, the momentum distribution of the trapped fermions is calculated, which clearly shows an experimental signature of the Kondo screening length. In addition to probing Kondo physics, the controllability of this system can be used to systematically explore the relaxation and equilibration of a strongly correlated system that has been initially prepared in a selected nonequilibrium state.
Local susceptibility and Kondo scaling in the presence of finite bandwidth
NASA Astrophysics Data System (ADS)
Hanl, Markus; Weichselbaum, Andreas
2014-02-01
The Kondo scale TK for impurity systems is expected to guarantee universal scaling of physical quantities. However, in practice, not every definition of TK necessarily supports this notion away from the strict scaling limit. Specifically, this paper addresses the role of finite bandwidth D in the strongly correlated Kondo regime. For this, various theoretical definitions of TK are analyzed based on the inverse magnetic impurity susceptibility at zero temperature. While conventional definitions in that respect quickly fail to ensure universal Kondo scaling for a large range of D, this paper proposes an altered definition of TKsc that allows universal scaling of dynamical or thermal quantities for a given fixed Hamiltonian. If the scaling is performed with respect to an external parameter that directly enters the Hamiltonian, such as magnetic field, the corresponding TKsc,B for universal scaling differs, yet becomes equivalent to TKsc in the scaling limit. The only requirement for universal scaling in the full Kondo parameter regime with a residual error of less than 1% is a well-defined isolated Kondo feature with TK≲0.01D irrespective of specific other impurity parameter settings. By varying D over a wide range relative to the bare energies of the impurity, for example, this allows a smooth transition from the Anderson to the Kondo model.
Discovery of a 3d-transition-metal-based ferromagnetic Kondo lattice system
NASA Astrophysics Data System (ADS)
Us Saleheen, Ahmad; Samanta, Tapas; Lepkowski, Daniel; Shankar, Alok; Prestigiacomo, Joseph; Dubenko, Igor; Quetz, Abdiel; McDougald, Roy, Jr.; McCandless, Gregory; Chan, Julia; Adams, Philip; Young, David; Ali, Naushad; Stadler, Shane
2015-03-01
The formation of a Kondo lattice results in a wide variety of exotic phenomena associated with the competition between the Kondo effect and the RKKY interaction, such as heavy fermions, non-Fermi liquid behavior, unconventional superconductivity, and so on. A quantum critical point (QCP) has been frequently observed at the boundaries of competing phases for antiferromagnetic materials. However, the existence of a ferromagnetic (FM) QCP is unclear. Moreover, FM Kondo lattices are rare. Here we report the discovery of a FM Kondo lattice system Mn1-xFexCoGe, which is the first example of a 3d-metal-based system (i.e., not rare-earth-based). Resistivity, magnetic susceptibility, heat capacity and thermopower studies on a single crystal sample indicate that the anisotropic FM kondo lattice has formed along c-axis. The signature of a spin density wave transition was also observed above the Kondo minimum, below which the resistivity follows a log(T) behavior. This work was supported by the U.S. Department of Energy (Grant Nos. DE-FG02-13ER46946 and DE-FG02-06ER46291).
Kondo cloud mediated long-range entanglement after local quench in a spin chain
NASA Astrophysics Data System (ADS)
Sodano, Pasquale; Bayat, Abolfazl; Bose, Sougato
2010-03-01
We show that, in the gapless Kondo regime, a single local quench at one end of a Kondo spin chain induces a fast and long-lived oscillatory dynamics. This quickly establishes a high-quality entanglement between the spins at the opposite ends of the chain. This entanglement is mediated by the Kondo cloud, attains a constant high value independent of the length for large chains, and shows thermal robustness. In contrast, when the Kondo cloud is absent, e.g., in the gapped dimer regime, only finite-size end to end effects can create some entanglement on a much longer time scale for rather short chains. By decoupling one end of the chain during the dynamics, one can distinguish between this end-end effect which vanishes, and the global Kondo cloud mediated entanglement, which persists. This quench approach paves the way to detect the elusive Kondo cloud through the entanglement between two individual spins. Our results show that nonperturbative cooperative phenomena from condensed matter may be exploited for quantum information.
Kondo effect in a quantum dot side-coupled to a topological superconductor
NASA Astrophysics Data System (ADS)
Lee, Minchul; Lim, Jong Soo; López, Rosa
2013-06-01
We investigate the dynamical and transport features of a Kondo dot side coupled to a topological superconductor (TS). The Majorana fermion states (MFSs) formed at the ends of the TS are found to be able to alter the Kondo physics profoundly: For an infinitely long wire where the MFSs do not overlap (ɛm=0) a finite dot-MFS coupling (Γm) reduces the unitary-limit value of the linear conductance by exactly a factor 3/4 in the weak-coupling regime (Γm
How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder.
Hamidian, Mohammad H; Schmidt, Andrew R; Firmo, Inês A; Allan, Milan P; Bradley, Phelim; Garrett, Jim D; Williams, Travis J; Luke, Graeme M; Dubi, Yonatan; Balatsky, Alexander V; Davis, J C
2011-11-01
Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a "Kondo-hole". No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559-12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857-6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu(2)Si(2). At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the "hybridization gapmap" technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. PMID:22006302
How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder
Hamidian, Mohammad H.; Schmidt, Andrew R.; Firmo, Inês A.; Allan, Milan P.; Bradley, Phelim; Garrett, Jim D.; Williams, Travis J.; Luke, Graeme M.; Dubi, Yonatan; Balatsky, Alexander V.; Davis, J. C.
2011-01-01
Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a “Kondo-hole”. No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559–12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857–6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu2Si2. At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the “hybridization gapmap” technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. PMID:22006302
Quantum Phases of the Shastry-Sutherland Kondo Lattice
NASA Astrophysics Data System (ADS)
Pixley, Jedediah; Yu, Rong; Si, Qimiao
2013-03-01
Motivated by the discovery of the geometrically frustrated heavy fermion metal Yb2Pt2Pb, which has a quasi two dimensional Shastry-Sutherland lattice structure, we consider the Heisenberg-Kondo lattice model on a two dimensional Shastry-Sutherland geometry. Using a large-N method, we obtain the phase diagram and, in particular, the quantum transitions between a valence bond solid phase and a heavy Fermi liquid phase. Interestingly, we find intermediate states that break the C4 symmetry. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related 221 materials, as well as the possible placement of these systems in a proposed global phase diagram for heavy fermion metals.
Anomalous Hall effect on the surface of topological Kondo insulators
NASA Astrophysics Data System (ADS)
König, E. J.; Ostrovsky, P. M.; Dzero, M.; Levchenko, A.
2016-07-01
We calculate the anomalous Hall conductivity σx y of the surface states in cubic topological Kondo insulators. We consider a generic model for the surface states with three Dirac cones on the (001) surface. The Fermi velocity, the Fermi momentum, and the Zeeman energy in different Dirac pockets may be unequal. The microscopic impurity potential mediates mixed intra- and interband extrinsic scattering processes. Our calculation of σx y is based on the Kubo-Streda diagrammatic approach. It includes diffractive skew scattering contributions originating from the rare two-impurity complexes. Remarkably, these contributions yield anomalous Hall conductivity that is independent of impurity concentration, and thus is of the same order as other known extrinsic side jump and skew scattering terms. We discuss various special cases of our results and the experimental relevance of our study in the context of the recent hysteretic magnetotransport data in SmB6 samples.
Kondo Effect in a Triple Quantum-Dot Array
NASA Astrophysics Data System (ADS)
Oguri, Akira; Nisikawa, Yunori; Hewson, A. C.
2006-09-01
We study the ground-state properties of a triple quantum dot based on a three-site Hubbard model connected to two non-interacting leads. Using the numerical renormalization group (NRG), the many-body phase shifts and dc conductance are calculated away from half-filling as a function of the onsite energy ɛd, which corresponds to the gate voltage. The results for conductance g show the typical Kondo plateaus of the Unitary limit g ≈ 2e2/h at some finite ranges of the gate-voltage corresponding to odd Nel (≈ 1, 3 and 5), where Nel is the total number of electrons in the triple dot. The conductance shows broad minima for even Nel(≈ 2 and 4). The local charge Nel shows a staircase behavior as a function of ɛd.
Superconductivity from spoiling magnetism in the Kondo lattice model
NASA Astrophysics Data System (ADS)
Asadzadeh, Mohammad Zhian; Fabrizio, Michele; Becca, Federico
2014-11-01
We find evidence that superconductivity intrudes into the paramagnetic-to-magnetic transition of the Kondo lattice model if magnetic frustration is added. Specifically, we study by the variational method the model on a square lattice in the presence of both nearest-neighbor (t ) and next-nearest-neighbor (t') hopping of the conduction electrons. We find that, when t'/t >0 , a d -wave superconducting dome emerges between the magnetic and paramagnetic metal phases and close to the compensated regime, i.e., the number of conduction electrons equals the number of localized spin-1/2 moments. Superconductivity is further strengthened by a direct antiferromagnetic exchange, JH, between the localized moments, to such an extent that we observe coexistence with magnetic order.
Surface-Supported Hydrocarbon π Radicals Show Kondo Behavior
2013-01-01
Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7–50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support. PMID:23539333
Kondo Effects in Single Layer Transition Metal Dichalcogenides
NASA Astrophysics Data System (ADS)
Phillips, Michael; Aji, Vivek
2015-03-01
Inversion symmetry breaking and strong spin orbit coupling in two dimensional transition metal dichalcogenides leads to interesting new phenomena such as the valley hall and spin hall effects. They display optical circular dichroism and the ability to generate excitation with valley specificity. In this talk we report on the consequences of these properties on correlated states in hole doped systems focussing on the physics of the screening of magnetic impurities. Unlike typical metals, the breaking of inversion symmetry leads to the mixing of a triplet component to the Kondo cloud. Using a variational wave function approach we determine the nature of the many body state. With the ground state in hand we analyze the excitations generated by valley discriminating perturbations. Graduate Student.
Kondo Breakdown and Quantum Oscillations in SmB6
NASA Astrophysics Data System (ADS)
Erten, Onur; Ghaemi, Pouyan; Coleman, Piers
2016-01-01
Recent quantum oscillation experiments on SmB6 pose a paradox, for while the angular dependence of the oscillation frequencies suggest a 3D bulk Fermi surface, SmB6 remains robustly insulating to very high magnetic fields. Moreover, a sudden low temperature upturn in the amplitude of the oscillations raises the possibility of quantum criticality. Here we discuss recently proposed mechanisms for this effect, contrasting bulk and surface scenarios. We argue that topological surface states permit us to reconcile the various data with bulk transport and spectroscopy measurements, interpreting the low temperature upturn in the quantum oscillation amplitudes as a result of surface Kondo breakdown and the high frequency oscillations as large topologically protected orbits around the X point. We discuss various predictions that can be used to test this theory.
Nonuniversal weak antilocalization effect in cubic topological Kondo insulators
NASA Astrophysics Data System (ADS)
Dzero, Maxim; Vavilov, Maxim G.; Kechedzhi, Kostyantyn; Galitski, Victor M.
2015-10-01
We study the quantum correction to conductivity on the surface of cubic topological Kondo insulators with multiple Dirac bands. We consider the model of time-reversal invariant disorder which induces the scattering of the electrons within the Dirac bands as well as between the bands. When only intraband scattering is present we find three long-range diffusion modes leading to weak antilocalization correction to conductivity which remains independent of the microscopic details such as Fermi velocities and relaxation times. Interband scattering gaps out two diffusion modes leaving only one long-range mode. We find that depending on the value of the phase coherence time, either three or only one long-range diffusion modes contribute to weak localization correction rendering the quantum correction to conductivity nonuniversal. We provide an interpretation for the results of the recent transport experiments on samarium hexaboride where weak antilocalization has been observed.
Anomalous Hall Effect on the surface of topological Kondo insulators
NASA Astrophysics Data System (ADS)
König, Elio; Ostrovsky, Pavel; Dzero, Maxim; Levchenko, Alex
We calculate the anomalous Hall conductivity σxy of surface states on three dimensional topological Kondo insulators with cubic symmetry and multiple Dirac cones. We treat a generic model in which the Fermi velocity, the Fermi momentum and the Zeeman energy in different pockets may be unequal and in which the microscopic impurity potential is short ranged on the scale of the smallest Fermi wavelength. Our calculation of σxy to the zeroth (i.e. leading) order in impurity concentration is based on the Kubo-Smrcka-Streda diagrammatic approach. It also includes certain extrinsic contributions with a single cross of impurity lines, which are of the same order in impurity concentration and were, to the best of our knowledge, scrutinized in a single band model, only. We discuss various special cases of our result and the experimental relevance of our study in the context of recent hysteretic magnetotransport data in SmB6 samples.
One-dimensional Kondo lattice model at quarter filling
NASA Astrophysics Data System (ADS)
Xavier, J. C.; Miranda, E.
2008-10-01
We revisit the problem of the quarter-filled one-dimensional Kondo lattice model, for which the existence of a dimerized phase and a nonzero charge gap had been reported by Xavier [Phys. Rev. Lett. 90, 247204 (2003)]. Recently, some objections were raised claiming that the system is neither dimerized nor has a charge gap. In the interest of clarifying this important issue, we show that these objections are based on results obtained under conditions in which the dimer order is artificially suppressed. We use the incontrovertible dimerized phase of the Majumdar-Ghosh point of the J1-J2 Heisenberg model as a paradigm with which to illustrate this artificial suppression. Finally, by means of extremely accurate density-matrix renormalization-group calculations, we show that the charge gap is indeed nonzero in the dimerized phase.
Entanglement switching via the Kondo effect in triple quantum dots
NASA Astrophysics Data System (ADS)
Tooski, S. B.; Bułka, Bogdan R.; Žitko, Rok; Ramšak, Anton
2014-06-01
We consider a triple quantum dot system in a triangular geometry with one of the dots connected to metallic leads. Using Wilson's numerical renormalization group method, we investigate quantum entanglement and its relation to the thermodynamic and transport properties in the regime where each of the dots is singly occupied on average, but with non-negligible charge fluctuations. It is shown that even in the regime of significant charge fluctuations the formation of the Kondo singlets induces switching between separable and perfectly entangled states. The quantum phase transition between unentangled and entangled states is analyzed quantitatively and the corresponding phase diagram is explained by exactly solvable spin model. In the framework of an effective model we also explain smearing of the entanglement transition for cases when the symmetry of the triple quantum dot system is relaxed.
Kondo effect and STM spectroscopy of Dirac electrons in graphene
NASA Astrophysics Data System (ADS)
Sengupta, Krishnendu
2011-03-01
We show that graphene, whose low-energy quasiparticles display Dirac like behavior, may exhibit a two-channel Kondo effect in the presence of magnetic impurities. We present a large N analysis for a generic spin S local moment coupled to Dirac electrons in graphene and demonstrate that the corresponding Kondo temperature can be tuned by an experimentally controllable applied gate voltage. We also study the STM spectra of these Dirac electrons in the presence of such impurities and demonstrate that such spectra depend qualitatively on the position of the impurity atom in the graphene matrix. More specifically, for impurity atoms atop the hexagon center, the zero-bias tunneling conductance, as measured by a STM, shows a peak; for those atop a graphene site, it shows a dip. We provide a qualitative theoretical explanation of this phenomenon and show that this unconventional behavior is a consequence of conservation/breaking of pseudospin symmetry of the Dirac quasiparticles by the impurity. We also predict that tuning the Fermi energy to zero by a gate voltage would not lead to qualitative change in the shape of the conductance spectra when the impurity is atop the hexagon center. A similar tuning of the Fermi energy for the impurity atop a site, however, would lead to a change in the tunneling conductance from a dip to a peak via an antiresonance. We discuss some recent experiments on a doped graphene sample that seem to have qualitative agreement with our theory and suggest further experiments to test our predictions. DST, India.
NASA Astrophysics Data System (ADS)
Kirchner, Stefan; Munoz, Enrique; Bolech, C. J.
2012-02-01
The non-linear conductance of semiconductor heterostructures and single molecule devices exhibiting Kondo physics has recently attracted attention [1,2]. We address the observed sample-dependence across various systems by considering additional electronic contributions present in the effective low-energy model underlying these experiments. To this end we develop a novel version of the superperturbation theory [3] in terms of dual fermions on the Keldysh contour. We analyze the role of particle hole asymmetry on the transport coefficients. Our approach [4] systematically extends the work of Yamada and Yosida and others to the particle-hole asymmetric Anderson model and reproduce the exactly solvable resonant level model and the special case considered in [5]. It correctly describes the strong coupling physics and is free of internal inconsistencies that would lead to a breakdown of current conservation. [4pt] [1] M. Grobis et al., Phys. Rev. Lett. 100, 246601 (2008).[0pt] [2] G. D. Scott et al., Phys. Rev. B 79, 165413 (2009).[0pt] [3] H. Hafermann et al., EPL 85, 27007 (2009).[0pt] [4] Enrique Munoz, C.J. Bolech, and Stefan Kirchner, submitted (2011).[0pt] [5] K. Yamada, Prog. Theo. Phys. 62, 354 (1979).
Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films
Zhu, L. J.; Nie, S. H.; Xiong, P.; Schlottmann, P.; Zhao, J. H.
2016-02-24
The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- tomore » square-root temperature dependence and deviation from it in three distinct temperature regimes. Lastly, our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons.« less
Lateral spin-orbit coupling and the Kondo effect in quantum dots
NASA Astrophysics Data System (ADS)
Vernek, Edson; Ngo, Anh; Ulloa, Sergio
2010-03-01
We present studies of the Coulomb blockade and Kondo regimes of transport of a quantum dot connected to current leads through spin-polarizing quantum point contacts (QPCs) [1]. This configuration, arising from the effect of lateral spin-orbit fields, results in spin-polarized currents even in the absence of external magnetic fields and greatly affects the correlations in the dot. Using an equation-of-motion technique and numerical renormalization group calculations we obtain the conductance and spin polarization for this system under different parameter regimes. Our results show that both the Coulomb blockade and Kondo regimes exhibit non-zero spin-polarized conductance. We analyze the role that the spin-dependent tunneling amplitudes of the QPC play in determining the charge and net magnetic moment in the dot. We find that the Kondo regime exhibits a strongly dependent Kondo temperature on the QPC polarizability. These effects, controllable by lateral gate voltages, may provide a new approach for exploring Kondo correlations, as well as possible spin devices. Supported by NSF DMR-MWN and PIRE. [1] P. Debray et al., Nature Nanotech. 4, 759 (2009).
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system.
Wang, Yu; Zheng, Xiao; Li, Bin; Yang, Jinlong
2014-08-28
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied dz(2) orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems. PMID:25173036
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system
Wang, Yu; Zheng, Xiao Li, Bin; Yang, Jinlong
2014-08-28
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied d{sub z{sup 2}} orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems.
Effect of Spin-Orbit Coupling on Kondo Phenomena in f7-Electron Systems
NASA Astrophysics Data System (ADS)
Hotta, Takashi
2015-11-01
In order to promote our basic understanding of the Kondo behavior recently observed in europium compounds, we analyze an impurity Anderson model with seven f electrons at an impurity site by employing a numerical renormalization group method. The local part of the model consists of Coulomb interactions among f electrons, spin-orbit coupling λ, and crystalline electric field (CEF) potentials, while we consider the hybridization V between local f electrons and single-band conduction electrons with au symmetry. For λ = 0, we observe underscreening Kondo behavior for appropriate values of V, characterized by an entropy change from ln 8 to ln 7, in which one of the seven f electrons is screened by conduction electrons. When λ is increased, we obtain two types of behavior depending on the value of V. For large V, we find an entropy release of ln 7 at low temperatures, determined by the level splitting energy due to the hybridization. For small V, we also observe an entropy change from ln 8 to ln 2 by the level splitting due to the hybridization, but at low temperatures, ln 2 entropy is found to be released, leading to the Kondo effect. We emphasize that the Kondo behavior for small V is observed for realistic values of λ on the order of 0.1 eV. We also discuss the effect of CEF potentials and the multipole properties in the Kondo behavior reported in this paper.
Study of ultrasonic attenuation for the Kondo and magnetic effects in heavy fermion systems
NASA Astrophysics Data System (ADS)
Baral, Purna Chandra; Rout, Govind Chandra
2013-05-01
The heavy fermion (HF) systems draw considerable attention due to their cooperative phenomena and anomalous properties arising out of the huge effective mass. A heavy fermion system is described by a model Hamiltonian consisting of the Kondo lattice model in addition to the Heisenberg-type spin-spin interaction among the localised electrons. The Hamiltonian is treated in the mean-field approximation to find the Kondo singlet parameter λ and the short-ranged f-electron correlation parameter Γ. In order to investigate ultrasonic absorption in the system, we consider the phonon interaction with the bare f-electrons, and the phonon coupling to the Kondo singlets. Further, the phonon Hamiltonian is considered in the harmonic approximation. The phonon Green's function is calculated in closed form. The imaginary part of the phonon self-energy describes the ultrasonic attenuation for the HF systems. The calculated ultrasonic attenuation clearly displays the f-electron correlation region separated by the Kondo singlet state at low temperatures. The correlation transition temperature and the Kondo temperature are located at dips in the temperature-dependent ultrasonic attenuation. The parameter dependence of the attenuation is investigated by varying the physical parameters of the HF systems and the wave frequency, and the experimental observations are explained on the basis of the model calculations.
Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films
Zhu, L. J.; Nie, S. H.; Xiong, P.; Schlottmann, P.; Zhao, J. H.
2016-01-01
The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- to square-root temperature dependence and deviation from it in three distinct temperature regimes. Our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons. PMID:26905518
Exploring the phase diagram of the two-impurity Kondo problem
Spinelli, A.; Gerrits, M.; Toskovic, R.; Bryant, B.; Ternes, M.; Otte, A. F.
2015-01-01
A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present a study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. The pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third-order transport model, allows us to independently determine the degree of Kondo screening in each phase. PMID:26616044
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system
NASA Astrophysics Data System (ADS)
Wang, Yu; Zheng, Xiao; Li, Bin; Yang, Jinlong
2014-08-01
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied d_{z^2} orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems.
Terahertz transmission and reflection studies of the topological Kondo insulator candidate SmB6
NASA Astrophysics Data System (ADS)
Morris, Christopher M.; Laurita, N. J.; Koopayeh, S.; Cottingham, P.; Phelan, W. A.; Schoop, L.; McQueen, T. M.; Armitage, N. P.
2015-03-01
The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures (T < 10 K) and high pressures. At low temperatures, a plateau is observed in the resistivity, contrary to the logarithmic divergence expected for a normal Kondo insulator. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator, a material with a Kondo insulating bulk, but topologically protected metallic surface states. Here, time domain terahertz spectroscopy (TDTS) is used to investigate the temperature dependent optical conductivity of single crystals of SmB6. A saturation of the transmission is observed associated with the resistance plateau as the bulk becomes insulating. A secondary bulk conduction mechanism remains down to the lowest measured temperature, 1.6 K. Additionally, FTIR measurements have been performed that show the Kondo gap of SmB6 opening at low temperatures. Work supported by The Institute of Quantum Matter under DOE Grant DE-FG02-08ER46544 and by the Gordon and Betty Moore Foundation.
SU(2)–SU(4) Kondo Crossover and Emergent Electric Polarization in a Triangular Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Koga, Mikito; Matsumoto, Masashige; Kusunose, Hiroaki
2016-06-01
We study an orbitally degenerate Kondo effect in a triangular triple quantum dot (TTQD), where the three dots are connected vertically with a single metallic lead through electron tunneling. Both spin and orbital degrees of freedom play an important role in the SU(4) Kondo effect. This is demonstrated by an equilateral TTQD Kondo system at half-filling, by Wilson's numerical renormalization group method. We show how an emergent electric polarization of the TTQD is associated with a crossover from SU(4) to SU(2) symmetry in the low-temperature state. A marked sign reversal of the electric polarization is generated by the fine-tuning of Kondo coupling with degenerate orbitals, which can be utilized to reveal orbital dynamics in the SU(4) Kondo effect.
Spin dynamics and Kondo physics in optical tweezers
NASA Astrophysics Data System (ADS)
Lin, Yiheng; Lester, Brian J.; Brown, Mark O.; Kaufman, Adam M.; Long, Junling; Ball, Randall J.; Isaev, Leonid; Wall, Michael L.; Rey, Ana Maria; Regal, Cindy A.
2016-05-01
We propose to use optical tweezers as a toolset for direct observation of the interplay between quantum statistics, kinetic energy and interactions, and thus implement minimum instances of the Kondo lattice model in systems with few bosonic rubidium atoms. By taking advantage of strong local exchange interactions, our ability to tune the spin-dependent potential shifts between the two wells and complete control over spin and motional degrees of freedom, we design an adiabatic tunneling scheme that efficiently creates a spin-singlet state in one well starting from two initially separated atoms (one atom per tweezer) in opposite spin state. For three atoms in a double-well, two localized in the lowest vibrational mode of each tweezer and one atom in an excited delocalized state, we plan to use similar techniques and observe resonant transfer of two-atom singlet-triplet states between the wells in the regime when the exchange coupling exceeds the mobile atom hopping. Moreover, we argue that such three-atom double-tweezers could potentially be used for quantum computation by encoding logical qubits in collective spin and motional degrees of freedom. Current address: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Fano-Andreev effect in Quantum Dots in Kondo regime
NASA Astrophysics Data System (ADS)
Orellana, Pedro; Calle, Ana Maria; Pacheco, Monica; Apel, Victor
In the present work, we investigate the transport through a T-shaped double quantum dot system coupled to two normal leads and to a superconducting lead. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot and by means of a slave boson mean field approximation at low temperature regime. We inquire into the influence of intradot interactions in the electronic properties of the system as well. Our results show that Fano resonances due to Andreev bound states are exhibited in the transmission from normal to normal lead as a consequence of quantum interference and proximity effect. This Fano effect produced by Andreev bound states in a side quantum dot was called Fano-Andreev effect, which remains valid even if the electron-electron interaction are taken into account, that is, the Fano-Andreev effect is robust against e-e interactions even in Kondo regime. We acknowledge the financial support from FONDECYT program Grants No. 3140053 and 11400571.
Kondo physics in non-local metallic spin transport devices
NASA Astrophysics Data System (ADS)
O'Brien, L.; Erickson, M. J.; Spivak, D.; Ambaye, H.; Goyette, R. J.; Lauter, V.; Crowell, P. A.; Leighton, C.
2014-05-01
The non-local spin-valve is pivotal in spintronics, enabling separation of charge and spin currents, disruptive potential applications and the study of pressing problems in the physics of spin injection and relaxation. Primary among these problems is the perplexing non-monotonicity in the temperature-dependent spin accumulation in non-local ferromagnetic/non-magnetic metal structures, where the spin signal decreases at low temperatures. Here we show that this effect is strongly correlated with the ability of the ferromagnetic to form dilute local magnetic moments in the NM. This we achieve by studying a significantly expanded range of ferromagnetic/non-magnetic combinations. We argue that local moments, formed by ferromagnetic/non-magnetic interdiffusion, suppress the injected spin polarization and diffusion length via a manifestation of the Kondo effect, thus explaining all observations. We further show that this suppression can be completely quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer.
Kondo physics in non-local metallic spin transport devices.
O'Brien, L; Erickson, M J; Spivak, D; Ambaye, H; Goyette, R J; Lauter, V; Crowell, P A; Leighton, C
2014-01-01
The non-local spin-valve is pivotal in spintronics, enabling separation of charge and spin currents, disruptive potential applications and the study of pressing problems in the physics of spin injection and relaxation. Primary among these problems is the perplexing non-monotonicity in the temperature-dependent spin accumulation in non-local ferromagnetic/non-magnetic metal structures, where the spin signal decreases at low temperatures. Here we show that this effect is strongly correlated with the ability of the ferromagnetic to form dilute local magnetic moments in the NM. This we achieve by studying a significantly expanded range of ferromagnetic/non-magnetic combinations. We argue that local moments, formed by ferromagnetic/non-magnetic interdiffusion, suppress the injected spin polarization and diffusion length via a manifestation of the Kondo effect, thus explaining all observations. We further show that this suppression can be completely quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer. PMID:24873934
Kondo hole route to incoherence in the periodic Anderson model
NASA Astrophysics Data System (ADS)
Kumar, Pramod; Vidhyadhiraja, N. S.
2013-03-01
The interplay of disorder and interactions in strongly correlated electronic systems is a subject of perennial interest. In this work, we have investigated the effect of Kondo-hole type disorder on the dynamics and transport properties of heavy fermion systems. We employ the periodic Anderson model within the framework of coherent potential approximation and dynamical mean field theory. The crossover from lattice coherent behaviour to an incoherent single-impurity behaviour is reflected in all aspects: a highly frequency (ω)-dependent hybridization becomes almost flat, the coherence peak in resistivity (per impurity) gives way to a Hammann form that saturates at low temperature (T); the Drude peak and the mid-infrared peak in the optical conductivity vanish almost completely. The zero temperature resistivity can be captured in a closed form expression, and we show how the Nordheim's rule gets strongly modified in these systems. The thermopower exhibits a characteristic peak, which changes sign with increasing disorder, and its location is shown to correspond to the low energy scale of the system (ωL). In fact, the thermopower appears to be much more sensitive to disorder variations than the resistivity. A comparison to experiments yields quantitative agreement. JNCASR and CSIR
Broken SU(4) symmetry in a Kondo-correlated carbon nanotube
NASA Astrophysics Data System (ADS)
Schmid, Daniel R.; Smirnov, Sergey; Margańska, Magdalena; Dirnaichner, Alois; Stiller, Peter L.; Grifoni, Milena; Hüttel, Andreas K.; Strunk, Christoph
2015-04-01
Understanding the interplay between many-body phenomena and nonequilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nanoelectronics. We demonstrate that the combination of Coulomb interaction, spin-orbit coupling, and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a field-theoretical Keldysh approach to the nonequilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.
Kondo interactions from band reconstruction in YbInCu4
Jarrige, I.; Kotani, A.; Yamaoka, H.; Tsujii, N.; Ishii, K.; Upton, M.; Casa, D.; Kim, J.; Gog, T.; Hancock, J. N.
2015-03-27
We combine resonant inelastic X-ray scattering (RIXS) and model calculations in the Kondo lattice compound YbInCu₄, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. In this study, the bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasi-gap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.
Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6
NASA Astrophysics Data System (ADS)
Xu, Nan; Ding, Hong; Shi, Ming
2016-09-01
Topological Kondo insulators are a new class of topological insulators in which metallic surface states protected by topological invariants reside in the bulk band gap at low temperatures. Unlike other 3D topological insulators, a truly insulating bulk state, which is critical for potential applications in next-generation electronic devices, is guaranteed by many-body effects in the topological Kondo insulator. Furthermore, the system has strong electron correlations that can serve as a testbed for interacting topological theories. This topical review focuses on recent advances in the study of SmB6, the most promising candidate for a topological Kondo insulator, from the perspective of spin- and angle-resolved photoemission spectroscopy with highlights of some important transport results.
Spin- and angle-resolved photoemission on the topological Kondo insulator candidate: SmB6.
Xu, Nan; Ding, Hong; Shi, Ming
2016-09-14
Topological Kondo insulators are a new class of topological insulators in which metallic surface states protected by topological invariants reside in the bulk band gap at low temperatures. Unlike other 3D topological insulators, a truly insulating bulk state, which is critical for potential applications in next-generation electronic devices, is guaranteed by many-body effects in the topological Kondo insulator. Furthermore, the system has strong electron correlations that can serve as a testbed for interacting topological theories. This topical review focuses on recent advances in the study of SmB6, the most promising candidate for a topological Kondo insulator, from the perspective of spin- and angle-resolved photoemission spectroscopy with highlights of some important transport results. PMID:27391865
Phonon-assisted tunneling and two-channel Kondo physics in molecular junctions
Dias Da Silva, Luis G; Dagotto, Elbio R
2009-01-01
The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. We present theoretical results for a single molecule in the Kondo regime connected to left and right metallic leads, creating the usual coupling to a conduction channel with left-right parity even. A center-of-mass vibrational mode introduces an additional phonon-assisted tunneling through the antisymmetric odd channel. A non-Fermi-liquid fixed point, reminiscent of the two-channel Kondo effect, appears at a critical value of the phonon-mediated coupling strength. Our numerical renormalization-group calculations for this system reveal non-Fermi-liquid behavior at low temperatures over lines of critical points. Signatures of this strongly correlated state are prominent in the thermodynamic properties and in the linear conductance.
Kondo decoherence : finding the right spin model for iron impurities in gold and silver.
Costi, T. A.; Bergqvist, L.; Weichselbaum, A.; von Delft, J.; Micklitz, T.; Rosch, A.; Mavropoulos, P.; Dederichs, P. H.; Mallet, F.; Saminadayar, L.; Bauerle, C.
2009-02-01
We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a long-standing question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin, and orbital degrees of freedom? Previous studies suggest a fully screened spin S Kondo model, but the value of S remained ambiguous. We perform density functional theory calculations that suggest S=3/2. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi-one-dimensional wires to numerical renormalization group predictions for S=1/2, 1, and 3/2, finding excellent agreement for S=3/2.
Kondo-type transport through a quantum dot under magnetic fields
Dong, Bing; Lei, X. L.
2001-06-15
In this paper, we investigate the Kondo correlation effects on linear and nonlinear transport in a quantum dot connected to reservoirs under finite magnetic fields, using the slave-boson mean field approach suggested by Kotliar and Ruckenstein [Phys. Rev. Lett. >57, 1362 (1986)]. A brief comparison between the present formulation and other slave-boson formulation is presented to justify this approach. The numerical results show that the linear conductance near electron-hole symmetry is suppressed by the application of the magnetic fields, but an anomalous enhancement is predicted in the nonsymmetry regime. The effect of external magnetic fields on the nonlinear differential conductances is discussed for the Kondo system. A significant reduction of the peak splitting is observed due to the strong Kondo correlation, which agrees well with experimental data.
Block entropy and quantum phase transition in the anisotropic Kondo necklace model
Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.
2010-06-15
We study the von Neumann block entropy in the Kondo necklace model for different anisotropies {eta} in the XY interaction between conduction spins using the density matrix renormalization group method. It was found that the block entropy presents a maximum for each {eta} considered, and, comparing it with the results of the quantum criticality of the model based on the behavior of the energy gap, we observe that the maximum block entropy occurs at the quantum critical point between an antiferromagnetic and a Kondo singlet state, so this measure of entanglement is useful for giving information about where a quantum phase transition occurs in this model. We observe that the block entropy also presents a maximum at the quantum critical points that are obtained when an anisotropy {Delta} is included in the Kondo exchange between localized and conduction spins; when {Delta} diminishes for a fixed value of {eta}, the critical point increases, favoring the antiferromagnetic phase.
Kondo interactions from band reconstruction in YbInCu(4).
Jarrige, I; Kotani, A; Yamaoka, H; Tsujii, N; Ishii, K; Upton, M; Casa, D; Kim, J; Gog, T; Hancock, J N
2015-03-27
We combine resonant inelastic x-ray scattering and model calculations in the Kondo lattice compound YbInCu_{4}, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. The bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasigap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system. PMID:25860761
Kondo phase shift at the zero-bias anomaly of quantum point contacts
NASA Astrophysics Data System (ADS)
Brun, Boris; Martins, Frederico; Faniel, Sébastien; Hackens, Benoit; Cavanna, Antonella; Ulysse, Christian; Ouerghi, Albdelkarim; Gennser, Ulf; Mailly, Dominique; Simon, Pascal; Huant, Serge; Bayot, Vincent; Sanquer, Marc; Sellier, Hermann
The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts.
Can magnetic noise from Kondo traps explain high frequency flux noise in superconducting qubits?
NASA Astrophysics Data System (ADS)
Dias da Silva, Luis; de Sousa, Rogerio
2015-03-01
In solid state devices, charge and magnetic noise have common microscopic origin. Both occur due to the presence of Kondo traps nearby metallic wires. We use numerical renormalization group calculations to show that, despite their common origin, charge and magnetic noise have opposing behavior controlled by completely different energy scales. While magnetic noise follows an universal scaling with the Kondo temperature, charge noise remains well described by non-interacting theory even when the trap is deep into the Kondo regime. We show how these results may explain the high frequency (f= 1-10 GHz) Ohmic flux noise observed in SQUIDs and superconducting qubits. LGDS acknowledges support from Brazilian agencies FAPESP (2013/50220-7), CNPq (307107/2013-2) and PRP-USP NAP-QNano. RdS acknowledges support from the Canadian program NSERC-Discovery and a FAPESP-UVic exchange award.
Kondo state for a compact Cr trimer on a metallic surface.
Kudasov, Yu B; Uzdin, V M
2002-12-30
The ground state of a Cr trimer supported on the Au(111) surface is investigated by means of a variational approach to the Coqblin-Schrieffer Hamiltonian. The temperature of Kondo-resonance formation (T(K)) for equilateral trimers increases drastically as compared to T(K) for a single Cr adatom. The Kondo state of a Cr trimer proves to be very sensitive to geometry and a small shift of any atom from the symmetrical position leads to a rapid decrease in T(K). These results are in good agreement with recent observations of the Kondo response of a single antiferromagnetic chromium trimer [T. Jamneala, Phys. Rev. Lett. 87, 256804 (2001)
Kondo effect in alkaline-earth-metal atomic gases with confinement-induced resonances
NASA Astrophysics Data System (ADS)
Zhang, Ren; Zhang, Deping; Cheng, Yanting; Chen, Wei; Zhang, Peng; Zhai, Hui
2016-04-01
Alkaline-earth-metal atoms have a long-lived electronic excited state, and when atoms in this excited state are localized in the Fermi sea of ground-state atoms by an external potential, they serve as magnetic impurities, due to the spin-exchange interaction between the excited- and the ground-state atoms. This can give rise to the Kondo effect. However, in order to achieve this effect in current atomic gas experiments, it requires the Kondo temperature to be increased to a sizable portion of the Fermi temperature. In this paper we calculate the confinement-induced resonance (CIR) for the spin-exchanging interaction between the ground and the excited states of the alkaline-earth-metal atoms and propose that the spin-exchange interaction can be strongly enhanced by utilizing the CIR. We analyze this system by the renormalization-group approach and show that near a CIR, the Kondo temperature can be significantly enhanced.
Replicas of the Kondo peak due to electron-vibration interaction in molecular transport properties
NASA Astrophysics Data System (ADS)
Roura-Bas, P.; Tosi, L.; Aligia, A. A.
2016-03-01
The low temperature properties of single level molecular quantum dots including both electron-electron and electron-vibration interactions, are theoretically investigated. The calculated differential conductance in the Kondo regime exhibits not only the zero bias anomaly but also side peaks located at bias voltages which coincide with multiples of the energy of vibronic mode V ˜ℏ Ω /e . We obtain that the evolution with temperature of the two main satellite conductance peaks follows the corresponding one of the Kondo peak when ℏ Ω ≫kBTK , TK being the Kondo temperature, in agreement with recent transport measurements in molecular junctions. However, we find that this is no longer valid when ℏ Ω is of the order of a few times kBTK .
Two-channel orbital Kondo effect in a quantum dot with SO(n) symmetry
NASA Astrophysics Data System (ADS)
Kuzmenko, T.; Kikoin, K.; Avishai, Y.
2013-09-01
A scenario for the formation of non-Fermi-liquid (NFL) Kondo effect (KE) with spin variable enumerating Kondo channels is suggested and worked out. In a doubly occupied symmetric triple quantum dot within parallel geometry, the NFL low-energy regime arises provided the device possesses both source-drain and left-right parity. Kondo screening follows a multistage renormalization group mechanism: reduction of the energy scale is accompanied by the change of the relevant symmetry group from SO(8) to SO(5). At low energy, three phases compete: (1) an underscreening spin-triplet (conventional) KE, (2) a spin-singlet potential scattering, and (3) a NFL phase where the roles of spin and orbital degrees of freedom are swapped.
Observation of the Kondo effect in a spin-3/2 hole quantum dot
Klochan, O.; Micolich, A. P.; Hamilton, A. R.; Trunov, K.; Reuter, D.; Wieck, A. D.
2013-12-04
We report the observation of the Kondo effect in a spin-3/2 hole quantum dot formed near pinch-off in a GaAs quantum wire. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the zero-bias peak in the differential conductance splits an in-plane magnetic field and the splitting is independent of gate voltage. Second, the splitting rate is twice as large as that for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly anisotropic and attribute this to the strong spin-orbit interaction for holes in GaAs.
Emergent p-Wave Kondo Coupling in Multi-Orbital Bands with Mirror Symmetry Breaking
NASA Astrophysics Data System (ADS)
Rhim, Jun Won; Han, Jung Hoon
2013-10-01
Kondo effect in the periodic Anderson model is examined for situations where the conduction bands are of multi-orbital character and subject to mirror-symmetry-breaking electric field. Taking p-orbital-based model for analysis, we find that a new hybridization channel opens up between p-orbital electrons and the local moments, leading to Kondo-coupled phases with nematic, or two-fold symmetry, although the microscopic Hamiltonian has the full square symmetry. The reduced symmetry in the band structure should be readily observable in spectroscopic or transport measurements for heavy fermion system in a multilayer environment such as successfully grown recently.
Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth
Craco, Luis; Leoni, Stefano
2015-01-01
Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA + DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals. PMID:26358556
Multipeak Kondo effect in one- and two-electron quantum dots.
Vidan, A; Stopa, M; Westervelt, R M; Hanson, M; Gossard, A C
2006-04-21
We have fabricated a few-electron quantum dot that can be tuned down to zero electrons while maintaining strong coupling to the leads. Using a nearby quantum point contact as a charge sensor, we can determine the absolute number of electrons in the quantum dot. We find several sharp peaks in the differential conductance, occurring at both zero and finite source-drain bias, for the one- and two-electron quantum dot. We attribute the peaks at finite bias to a Kondo effect through excited states of the quantum dot and investigate the magnetic field dependence of these Kondo resonances. PMID:16712183
NASA Astrophysics Data System (ADS)
Koga, M.; Matsumoto, M.; Kusunose, H.
2015-03-01
The Kondo effect plays an important role in emergence of electric polarization in a triangular triple-quantum-dot system, where one of the three dots is point-contacted with a single lead, and a magnetic flux penetrates through the triangular loop. The Kondo-induced electric polarization exhibits an Aharonov-Bohm type oscillation as a function of the magnetic flux. Our theoretical study shows various oscillation patterns associated with the field-dependent mixing of twofold orbitally degenerate ground states and their sensitivity to the point contact.
NASA Astrophysics Data System (ADS)
Heyder, Jan; Bauer, Florian; Schubert, Enrico; Borowsky, David; Schuh, Dieter; Wegscheider, Werner; von Delft, Jan; Ludwig, Stefan
2015-11-01
Quantum point contacts (QPCs) and quantum dots (QDs), two elementary building blocks of semiconducting nanodevices, both exhibit famously anomalous conductance features: the 0.7 anomaly in the former case, the Kondo effect in the latter. For both the 0.7 anomaly and the Kondo effect, the conductance shows a remarkably similar low-energy dependence on temperature T , source-drain voltage Vsd, and magnetic field B . In a recent publication [F. Bauer et al., Nature (London) 501, 73 (2013), 10.1038/nature12421], we argued that the reason for these similarities is that both a QPC and a Kondo QD (KQD) feature spin fluctuations that are induced by the sample geometry, confined in a small spatial regime, and enhanced by interactions. Here, we further explore this notion experimentally and theoretically by studying the geometric crossover between a QD and a QPC, focusing on the B -field dependence of the conductance. We introduce a one-dimensional model with local interactions that reproduces the essential features of the experiments, including a smooth transition between a KQD and a QPC with 0.7 anomaly. We find that in both cases the anomalously strong negative magnetoconductance goes hand in hand with strongly enhanced local spin fluctuations. Our experimental observations include, in addition to the Kondo effect in a QD and the 0.7 anomaly in a QPC, Fano interference effects in a regime of coexistence between QD and QPC physics, and Fabry-Perot-type resonances on the conductance plateaus of a clean QPC. We argue that Fabry-Perot-type resonances occur generically if the electrostatic potential of the QPC generates a flatter-than-parabolic barrier top.
Photoelectrosynthesis at semiconductor electrodes
Nozik, A. J.
1980-12-01
The general principles of photoelectrochemistry and photoelectrosynthesis are reviewed and some new developments in photoelectrosynthesis are discussed. Topics include energetics of semiconductor-electrolyte interfaces(band-edge unpinning); hot carrier injection at illuminated semiconductor-electrolyte junctions; derivatized semiconductor electrodes; particulate photoelectrochemical systems; layered compounds and other new materials; and dye sensitization. (WHK)
Photorefractive Semiconductors and Applications
NASA Technical Reports Server (NTRS)
Chen, Li-Jen; Luke, Keung L.
1993-01-01
Photorefractive semiconductors are attractive for information processing, becuase of fast material response, compatibility with semiconductor lasers, and availability of cross polarization diffraction for enhancing signal-to-noise ration. This paper presents recent experimental results on information processing using photorefractive GaAs, InP and CdTe, including image processing with semiconductor lasers.
Competing Kondo and e-e interaction in Ce2.1Nd0.9Al
NASA Astrophysics Data System (ADS)
Singh, Durgesh; Samatham, S. Shanmukharao; Venkateshwarlu, D.; Gangrade, Mohan; Ganesan, V.
2013-02-01
We report electrical resistivity of Ce2.1Nd0.9Al compound under applied magnetic fields. Magnetic field effect on the structural transition and Kondo ordering is studied. 30% Nd doping in Ce3Al makes TS = TK˜25K. Resistivity fits at low temperatures at different magnetic fields reveal a clear competition between Kondo and e-e interactions. It is demonstrated that Kondo interactions are weakened by the applied magnetic field and thus enhancing the e-e interaction. There seems a characteristic field where both the interactions contribute equally and for this sample it is around 6T.
State identification and tunable Kondo effect of MnPc on Ag(001)
NASA Astrophysics Data System (ADS)
Kügel, Jens; Karolak, Michael; Krönlein, Andreas; Senkpiel, Jacob; Hsu, Pin-Jui; Sangiovanni, Giorgio; Bode, Matthias
2015-06-01
We present a detailed investigation of spectroscopic features located at the central metal ion of MnPc (where Pc represents phthalocyanine) on Ag(001) by means of scanning tunneling spectroscopy (STS) and first-principles theory. STS data taken close to the Fermi level reveal an asymmetric feature that cannot be fitted with a single Fano function representing a one-channel Kondo effect. Instead, our data indicate the existence of a second superimposed feature. Two potential physical origins, a second Kondo channel related to the dx z /y z orbitals, and a spectral feature of the dz2 orbital itself, are discussed. A systematic experimental and theoretical comparison of MnPc with CoPc and FePc indicates that the second feature observed on MnPc is caused by the dz2 orbital. This conclusion is corroborated by STM-induced dehydrogenation experiments on FePc and MnPc which in both cases result in a gradual shift towards more positive binding energies and a narrowing of the Kondo resonance. Theoretical analysis reveals that the latter is caused by the reduced hybridization between the d orbital and the substrate. Spatially resolved differential conductivity maps taken close to the respective peak positions show that the intensity of both features is highest over the central Mn ion, thereby providing further evidence against a second Kondo channel originating from the dx z /y z orbital of the central Mn ion.
Environment-modulated Kondo phenomena in FePc/Au(111) adsorption systems
NASA Astrophysics Data System (ADS)
Wang, Yu; Zheng, Xiao; Yang, Jinlong
2016-03-01
Recent scanning tunneling microscopy experiments on electron transport through iron(II) phthalocyanine (FePc) molecules adsorbed on the Au(111) surface have revealed that the measured Kondo conductance signature depends strongly on the specific adsorption site. To understand the physical origin of experimental observations, particularly the variation of Kondo features with the molecular adsorption site, we employ a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach to investigate the electronic structure and Kondo correlation in FePc/Au(111) composite systems. The calculation results indicate that, for the on-top adsorption configuration, the two degenerate spin-unpaired dπ orbitals on the Fe center are coupled indirectly through substrate band states, leading to the Fano-like antiresonance line shape in the d I /d V spectra, while for the bridge adsorption configuration, the environment-induced couplings are largely suppressed because of the two different spin-unpaired d orbitals. Therefore, our work suggests that the environment-induced coupling as an essential physical factor could greatly influence the Fano-Kondo features in magnetic molecule/metal composites, and the crucial role of local orbital degeneracy and symmetry is discovered. These findings provide important insights into the electron correlation effects in complex solid-state systems. The usefulness and practicality of the combined DFT+HEOM method is also highlighted.
Analytical expression of Kondo temperature in quantum dot embedded in Aharonov-Bohm ring.
Yoshii, Ryosuke; Eto, Mikio
2011-01-01
We theoretically study the Kondo effect in a quantum dot embedded in an Aharonov-Bohm ring, using the "poor man's" scaling method. Analytical expressions of the Kondo temperature TK are given as a function of magnetic flux Φ penetrating the ring. In this Kondo problem, there are two characteristic lengths, Lc=ℏvF∕|ε̃0| and LK = ħvF = TK, where vF is the Fermi velocity and ε̃0 is the renormalized energy level in the quantum dot. The former is the screening length of the charge fluctuation and the latter is that of the spin fluctuation, i.e., size of Kondo screening cloud. We obtain diferent expressions of TK(Φ) for (i) Lc ≪ LK ≪ L, (ii) Lc ≪ L ≪ LK, and (iii) L ≪ Lc ≪ LK, where L is the size of the ring. TK is remarkably modulated by Φ in cases (ii) and (iii), whereas it hardly depends on Φ in case (i).PACS numbers: PMID:22112300
Stefański, Piotr
2013-02-27
A system composed of two quantum dots, i.e. a strongly interacting Kondo dot and a noninteracting one, placed in the arms of the Aharonov-Bohm ring, is investigated theoretically. The ring is coupled to normal leads. This configuration is mapped on the system of a correlated impurity embedded in a host with energy and flux dependent density of states. Additionally, the presence of the Rashba field allows a spin selective opening of the pseudogap in the density of states of the host, when the level of the noninteracting dot is tuned to the Fermi energy. This selectively diminishes electron correlations in the Kondo dot and creates resultant spin polarization at the Fermi level. It is shown that this polarization arises in the absence of any exchange field. Interestingly, this Rashba-correlation-induced spin polarization reaches its maximum for the position of the Kondo dot level corresponding to the Kondo temperature of the Anderson impurity in the host with constant density of states. PMID:23370331
Intersite coupling effects in a Kondo lattice near an antiferromagnetic instability
NASA Astrophysics Data System (ADS)
Nakatsuji, Satoru
2003-03-01
Critcal fluctuations due to the proximity to a magnetic instability are believed to be the origin of a variety of non-Fermi-liquid behavior and unconventional superconductivity observed in heavy fermion systems. Near the quantum critical points, prominent effect of intersite coupling in Kondo lattice systems may appear. With this in mind, we studied the La dilution effects in CeCoIn_5, a heavy fermion superconductor located near an antiferromangetic instability [1,2]. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single impurity Kondo temperature TK and an intersite spin-liquid temperature T. The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with T^*. These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case. This work was supported by NSF DMR-9527035. [1] C. Petrovic ´it et al., J.Phys.: Condens. Matter ´bf 13, L337 (2001). [2] S. Nakatsuji ´it et al., Phys. Rev. Lett. 89, 106402 (2002) ^´ast Work done in collaboration with Zachary Fisk, Sunmog Yeo, Luis Balicas, Pedro Schlottmann, Pagliuso G. Pagliuso, Nelson O. Moreno, John L. Sarrao, and Joe D. Thompson
Blocking transport resonances via Kondo many-body entanglement in quantum dots
Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena
2016-01-01
Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) ⊗ SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin. PMID:27526870
Sub-molecular modulation of a 4f driven Kondo resonance by surface-induced asymmetry
NASA Astrophysics Data System (ADS)
Warner, Ben; El Hallak, Fadi; Atodiresei, Nicolae; Seibt, Philipp; Pruser, Henning; Caciuc, Vasile; Waters, Michael; Fisher, Andrew J.; Blugel, Stefan; van Slageren, Joris; Hirjibehedin, Cyrus F.
Coupling between a magnetic impurity and an external bath can give rise to many-body quantum phenomena, including Kondo and Hund's Impurity states in metals, and Yu-Shiba-Rusinov states in superconductors. While advances have been made in probing the magnetic properties of d-shell impurities on surfaces, the confinement of f orbitals makes them much more difficult to access directly. Here we show that a 4f driven Kondo resonance can be modulated spatially by asymmetric coupling between a metallic surface and a molecule containing a 4f-like moment. Strong hybridisation of dysprosium double-decker phthalocyanine (DyPc2) with Cu(001) induces Kondo screening of the central magnetic moment. Misalignment between the symmetry axes of the molecule and the surface induces asymmetry in the molecule's electronic structure, spatially mediating electronic access to the magnetic moment through the Kondo resonance. This work demonstrates the important role that molecular ligands play in mediating electronic and magnetic coupling and in accessing many-body quantum states.
Kondo physics in a Ni impurity embedded in O-doped Au chains
NASA Astrophysics Data System (ADS)
Di Napoli, S.; Barral, M. A.; Roura-Bas, P.; Manuel, L. O.; Llois, A. M.; Aligia, A. A.
2015-08-01
By means of ab initio calculations we study the effect of O doping of Au chains containing a nanocontact represented by a Ni atom as a magnetic impurity. In contrast to pure Au chains, we find that with a minimum O doping the 5 dx z ,y z states of Au are pushed up, crossing the Fermi level. We also find that for certain O configurations, the Ni atom has two holes in the degenerate 3 dx z ,y z orbitals, forming a spin S =1 due to a large Hund interaction. The coupling between the 5 dx z ,y z Au bands and the 3 dx z ,y z of Ni states leads to a possible realization of a two-channel S =1 Kondo effect. While this kind of Kondo effect is commonly found in bulk systems, it is rarely observed in low dimensions. The estimated Kondo scale of the system lies within the present achievable experimental resolution in transport measurements. Another possible scenario for certain atomic configurations is that one of the holes resides in a 3 dz2 orbital, leading to a two-stage Kondo effect, the second one with SU(4) symmetry.
Blocking transport resonances via Kondo many-body entanglement in quantum dots.
Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena
2016-01-01
Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) ⊗ SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin. PMID:27526870
Ciudad D.; Arena D.; We, Z.-C.; Hindmarch, A.T.; Negusse, E.; Han, X.-F.Han; Marrows, C.H.
2012-06-07
The transition between Kondo and Coulomb blockade effects in discontinuous double magnetic tunnel junctions is explored as a function of the size of the CoPt magnetic clusters embedded between AlO{sub x} tunnel barriers. A gradual competition between cotunneling enhancement of the tunneling magnetoresistance (TMR) and the TMR suppression due to the Kondo effect has been found in these junctions, with both effects having been found to coexist even in the same sample. It is possible to tune between these two states with temperature (at a temperature far below the cluster blocking temperature). In addition, when further decreasing the size of the CoPt clusters, another gradual transition between the Kondo effect and direct tunneling between the electrodes takes place. This second transition shows that the spin-flip processes found in junctions with impurities in the barrier are in fact due to the Kondo effect. A simple theoretical model able to account for these experimental results is proposed.
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
NASA Astrophysics Data System (ADS)
Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.
Terahertz transmission studies of the topological Kondo insulator candidate SmB6
NASA Astrophysics Data System (ADS)
Laurita, Nicholas J.; Morris, Christopher M.; Koopayeh, Seyed; Cottingham, Patrick; Phelan, W. Adam; Schoop, Leslie; McQueen, Tyrel M.; Armitage, N. Peter
2014-03-01
The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures (T < 10 K) and high pressures. At low temperatures, a plateau is observed in the resistivity, contrary to the divergence expected for a normal Kondo insulator. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator, a material with a Kondo insulating bulk, but topologically protected metallic surface states. Here, time domain terahertz spectroscopy (TDTS) is used to investigate the temperature dependent low frequency optical conductivity of single crystals of SmB6. We find evidence for a substantial bulk conductivity at a frequency of a few hundred GHz, which challenges the notion of this material as having a clean gap. The evidence for topological surface states and their properties will be discussed. Work supported by The Institute of Quantum Matter under DOE grant DE-FG02-08ER46544 and by the Gordon and Betty Moore Foundation through Grant GBMF2628.
Quantum phase transitions, frustration, and the Fermi surface in the Kondo lattice model
NASA Astrophysics Data System (ADS)
Eidelstein, Eitan; Moukouri, S.; Schiller, Avraham
2011-07-01
The quantum phase transition from a spin-Peierls phase with a small Fermi surface to a paramagnetic Luttinger-liquid phase with a large Fermi surface is studied in the framework of a one-dimensional Kondo-Heisenberg model that consists of an electron gas away from half filling, coupled to a spin-1/2 chain by Kondo interactions. The Kondo spins are further coupled to each other with isotropic nearest-neighbor and next-nearest-neighbor antiferromagnetic Heisenberg interactions which are tuned to the Majumdar-Ghosh point. Focusing on three-eighths filling and using the density-matrix renormalization-group (DMRG) method, we show that the zero-temperature transition between the phases with small and large Fermi momenta appears continuous, and involves a new intermediate phase where the Fermi surface is not well defined. The intermediate phase is spin gapped and has Kondo-spin correlations that show incommensurate modulations. Our results appear incompatible with the local picture for the quantum phase transition in heavy fermion compounds, which predicts an abrupt change in the size of the Fermi momentum.
Unitary lens semiconductor device
Lear, K.L.
1997-05-27
A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.
Unitary lens semiconductor device
Lear, Kevin L.
1997-01-01
A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.
Kondo effects in a triangular triple quantum dot with lower symmetries
NASA Astrophysics Data System (ADS)
Oguri, A.; Amaha, S.; Nishikawa, Y.; Numata, T.; Shimamoto, M.; Hewson, A. C.; Tarucha, S.
2011-05-01
We study the low-energy properties and characteristic Kondo energy scale of a triangular triple quantum dot, connected to two non-interacting leads, in a wide parameter range of a gate voltage and distortions which lower the symmetry of an equilateral structure, using the numerical renormalization group approach. For large Coulomb interactions, the ground states with different characters can be classified according to the plateaus of Θ≡(δe-δo)(2/π), where δe and δo are the phase shifts for the even and odd partial waves. At these plateaus of Θ, both Θ and the occupation number Ntot≡(δe+δo)(2/π) take values close to integers, and thus the ground states can be characterized by these two integers. The Kondo effect with a local moment with total spin S=1 due to a Nagaoka mechanism appears on the plateau, which can be identified by Θ≃2.0 and Ntot≃4.0. For large distortions, however, the high-spin moment disappears through a singlet-triplet transition occurring within the four-electron region. It happens at a crossover to the adjacent plateaus for Θ≃0.0 and Θ≃4.0, and the two-terminal conductance has a peak in the transient regions. For weak distortions, the SU(4) Kondo effect also takes place for Ntot≃3.0. It appears as a sharp conductance valley between the S=1/2 Kondo ridges on both sides. We also find that the characteristic energy scale T* reflect these varieties of the Kondo effect. Particularly, T* is sensitive to the distribution of the charge and spin in the triangular triple dot.
Magnetic impurities in nanotubes: From density functional theory to Kondo many-body effects
NASA Astrophysics Data System (ADS)
Baruselli, P. P.; Fabrizio, M.; Smogunov, A.; Requist, R.; Tosatti, E.
2013-12-01
Low-temperature electronic conductance in nanocontacts, scanning tunneling microscopy (STM), and metal break junctions involving magnetic atoms or molecules is a growing area with important unsolved theoretical problems. While the detailed relationship between contact geometry and electronic structure requires a quantitative ab initio approach such as density functional theory (DFT), the Kondo many-body effects ensuing from the coupling of the impurity spin with metal electrons are most properly addressed by formulating a generalized Anderson impurity model to be solved with, for example, the numerical renormalization group (NRG) method. Since there is at present no seamless scheme that can accurately carry out that program, we have in recent years designed a systematic method for semiquantitatively joining DFT and NRG. We apply this DFT-NRG scheme to the ideal conductance of single wall (4,4) and (8,8) nanotubes with magnetic adatoms (Co and Fe), both inside and outside the nanotube, and with a single carbon atom vacancy. A rich scenario emerges, with Kondo temperatures generally in the Kelvin range, and conductance anomalies ranging from a single channel maximum to destructive Fano interference with cancellation of two channels out of the total four. The configuration yielding the highest Kondo temperature (tens of Kelvins) and a measurable zero-bias anomaly is that of a Co or Fe impurity inside the narrowest nanotube. The single atom vacancy has a spin, but a very low Kondo temperature is predicted. The geometric, electronic, and symmetry factors influencing this variability are all accessible, which makes this approach methodologically instructive and highlights many delicate and difficult points in the first-principles modeling of the Kondo effect in nanocontacts.
Kondo conductance across the smallest spin 1/2 radical molecule
Requist, Ryan; Modesti, Silvio; Baruselli, Pier Paolo; Smogunov, Alexander; Fabrizio, Michele; Tosatti, Erio
2014-01-01
Molecular contacts are generally poorly conducting because their energy levels tend to lie far from the Fermi energy of the metal contact, necessitating undesirably large gate and bias voltages in molecular electronics applications. Molecular radicals are an exception because their partly filled orbitals undergo Kondo screening, opening the way to electron passage even at zero bias. Whereas that phenomenon has been experimentally demonstrated for several complex organic radicals, quantitative theoretical predictions have not been attempted so far. It is therefore an open question whether and to what extent an ab initio-based theory is able to make accurate predictions for Kondo temperatures and conductance lineshapes. Choosing nitric oxide (NO) as a simple and exemplary spin 1/2 molecular radical, we present calculations based on a combination of density functional theory and numerical renormalization group (DFT+NRG), predicting a zero bias spectral anomaly with a Kondo temperature of 15 K for NO/Au(111). A scanning tunneling spectroscopy study is subsequently carried out to verify the prediction, and a striking zero bias Kondo anomaly is confirmed, still quite visible at liquid nitrogen temperatures. Comparison shows that the experimental Kondo temperature of about 43 K is larger than the theoretical one, whereas the inverted Fano lineshape implies a strong source of interference not included in the model. These discrepancies are not a surprise, providing in fact an instructive measure of the approximations used in the modeling, which supports and qualifies the viability of the density functional theory and numerical renormalization group approach to the prediction of conductance anomalies in larger molecular radicals. PMID:24367113
Thermoelectric effect in the Kondo dot side-coupled to a Majorana mode
NASA Astrophysics Data System (ADS)
Khim, Heunghwan; López, Rosa; Lim, Jong Soo; Lee, Minchul
2015-06-01
We investigate the linear thermoelectric response of an interacting quantum dot side-coupled by one of two Majorana modes hosted by a topological superconducting wire. We employ the numerical renormalization group technique to obtain the thermoelectrical conductance L in the Kondo regime while the background temperature T, the Majorana-dot coupling Γm, and the overlap ɛm between the two Majorana modes are tuned. We distinguish two transport regimes in which L displays different features: the weak- (Γm
Kondo conductance across the smallest spin 1/2 radical molecule.
Requist, Ryan; Modesti, Silvio; Baruselli, Pier Paolo; Smogunov, Alexander; Fabrizio, Michele; Tosatti, Erio
2014-01-01
Molecular contacts are generally poorly conducting because their energy levels tend to lie far from the Fermi energy of the metal contact, necessitating undesirably large gate and bias voltages in molecular electronics applications. Molecular radicals are an exception because their partly filled orbitals undergo Kondo screening, opening the way to electron passage even at zero bias. Whereas that phenomenon has been experimentally demonstrated for several complex organic radicals, quantitative theoretical predictions have not been attempted so far. It is therefore an open question whether and to what extent an ab initio-based theory is able to make accurate predictions for Kondo temperatures and conductance lineshapes. Choosing nitric oxide (NO) as a simple and exemplary spin 1/2 molecular radical, we present calculations based on a combination of density functional theory and numerical renormalization group (DFT+NRG), predicting a zero bias spectral anomaly with a Kondo temperature of 15 K for NO/Au(111). A scanning tunneling spectroscopy study is subsequently carried out to verify the prediction, and a striking zero bias Kondo anomaly is confirmed, still quite visible at liquid nitrogen temperatures. Comparison shows that the experimental Kondo temperature of about 43 K is larger than the theoretical one, whereas the inverted Fano lineshape implies a strong source of interference not included in the model. These discrepancies are not a surprise, providing in fact an instructive measure of the approximations used in the modeling, which supports and qualifies the viability of the density functional theory and numerical renormalization group approach to the prediction of conductance anomalies in larger molecular radicals. PMID:24367113
Rakhmilevitch, D; Korytár, R; Bagrets, A; Evers, F; Tal, O
2014-12-01
The interaction of individual electrons with vibrations has been extensively studied. However, the nature of electron-vibration interaction in the presence of many-body electron correlations such as a Kondo state has not been fully investigated. Here, we present transport measurements on a Copper-phthalocyanine molecule, suspended between two silver electrodes in a break-junction setup. Our measurements reveal both zero bias and satellite conductance peaks, which are identified as Kondo resonances with a similar Kondo temperature. The relation of the satellite peaks to electron-vibration interaction is corroborated using several independent spectroscopic indications, as well as ab initio calculations. Further analysis reveals that the contribution of vibration-induced inelastic current is significant in the presence of a Kondo resonance. PMID:25526145
Anderson, Iain; Teshima, Hazuki; Nolan, Matt; Lapidus, Alla L.; Tice, Hope; Glavina Del Rio, Tijana; Cheng, Jan-Fang; Han, Cliff; Tapia, Roxanne; Goodwin, Lynne A.; Pitluck, Sam; Liolios, Konstantinos; Mavromatis, K; Pagani, Ioanna; Ivanova, N; Mikhailova, Natalia; Pati, Amrita; Chen, Amy; Palaniappan, Krishna; Land, Miriam L; Rohde, Manfred; Lang, Elke; Detter, J. Chris; Goker, Markus; Woyke, Tanja; Bristow, James; Eisen, Jonathan; Markowitz, Victor; Hugenholtz, Philip; Kyrpides, Nikos C; Klenk, Hans-Peter
2013-01-01
rateuria aurantia (ex Kondo and Ameyama 1958) Swings et al. 1980 is a member of the bispecific genus Frateuria in the family Xanthomonadaceae, which is already heavily targeted for non-type strain genome sequencing. Strain Kondo 67(T) was initially (1958) identified as a member of 'Acetobacter aurantius', a name that was not considered for the approved list. Kondo 67(T) was therefore later designated as the type strain of the newly proposed acetogenic species Frateuria aurantia. The strain is of interest because of its triterpenoids (hopane family). F. aurantia Kondo 67(T) is the first member of the genus Frateura whose genome sequence has been deciphered, and here we describe the features of this organism, together with the complete genome sequence and annotation. The 3,603,458-bp long chromosome with its 3,200 protein-coding and 88 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2–δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z. -A.; Thompson, J. D.
2015-10-19
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2–δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressuremore » and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 e–/formular unit in CeNi2–δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. Here, the small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.« less
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.
2015-01-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.
Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D
2015-11-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
NASA Astrophysics Data System (ADS)
Grundmann, Marius
The historic development of semiconductor physics and technology began in the second half of the 19th century. Interesting discussions of the early history of the physics and chemistry of semiconductors can be found in treatises of G. Busch [2] and Handel [3]. The history of semiconductor industry can be followedin the text of Morris [4] and Holbrook et al. [5]. In 1947, the realization of the transistor was the impetus to a fast-paced development that created the electronics and photonics industries. Products founded on the basis of semiconductor devices such as computers (CPUs, memories), optical-storage media (lasers for CD, DVD), communication infrastructure (lasers and photodetectors for optical-fiber technology, high frequency electronics for mobile communication), displays (thin film transistors, LEDs), projection (laser diodes) and general lighting (LEDs) are commonplace. Thus, fundamental research on semiconductors and semiconductor physics and its offspring in the form of devices has contributed largely to the development of modern civilization and culture.
NASA Astrophysics Data System (ADS)
Lo, Po-Wei; Guo, Guang-Yu; Anders, Frithjof B.
2014-05-01
Motivated by the recent observation of the Kondo effect in graphene in transport experiments, we investigate the resistivity and dephasing rate in the Kondo regime due to magnetic impurities in graphene with different chemical potentials (μ). The Kondo effect due to either carbon vacancies or magnetic adatoms in graphene is described by the single-orbital pseudogap asymmetric Anderson impurity model which is solved by the accurate numerical renormalization group method. We find that although the Anderson impurity model considered here is a mixed-valence system, it can be driven into either the Kondo [μ >μc (critical value) >0], mixed-valency (μ ≈μc), or empty-orbital (μ <μc) regime by a gate voltage, giving rise to characteristic features in resistivity and dephasing rate in each regime. Specifically, in the case of μ <μc, the shapes of the resistivity (dephasing rate) curves for different μ are nearly identical. However, as temperature decreases, they start to increase to their maxima at a lower T /TK, but more rapidly [as (TK/T)3/2] than in normal metals [here, T (TK) denotes the (Kondo) temperature]. As T further decreases, after reaching the maximum, the dephasing rate drops more quickly than in normal metals, behaving as (T/TK)3 instead of (T/TK)2. Furthermore, the resistivity has a distinct peak above the saturation value near TK. In the case of μ >μc, in contrast, the resistivity curve has an additional broad shoulder above 10TK and the dephasing rate exhibits an interesting shoulder-peak shape. In the narrow boundary region (μ ≈μc), both the resistivity and dephasing rate curves are similar to the corresponding ones in normal metals. This explains the conventional Kondo-like resistivity from recent experiments on graphene with defects, although the distinct features in the resistivity in the other cases (μ <μc or μ >μc) were not seen in the experiments. The interesting features in the resistivity and dephasing rate are analyzed in
Semiconductor microcavity lasers
Gourley, P.L.; Wendt, J.R.; Vawter, G.A.; Warren, M.E.; Brennan, T.M.; Hammons, B.E.
1994-02-01
New kinds of semiconductor microcavity lasers are being created by modern semiconductor technologies like molecular beam epitaxy and electron beam lithography. These new microcavities exploit 3-dimensional architectures possible with epitaxial layering and surface patterning. The physical properties of these microcavities are intimately related to the geometry imposed on the semiconductor materials. Among these microcavities are surface-emitting structures which have many useful properties for commercial purposes. This paper reviews the basic physics of these microstructured lasers.
Semiconductor bridge (SCB) detonator
Bickes, Jr., Robert W.; Grubelich, Mark C.
1999-01-01
The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length.
Semiconductor bridge (SCB) detonator
Bickes, R.W. Jr.; Grubelich, M.C.
1999-01-19
The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge (SCB) igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length. 3 figs.
Interconnected semiconductor devices
Grimmer, Derrick P.; Paulson, Kenneth R.; Gilbert, James R.
1990-10-23
Semiconductor layer and conductive layer formed on a flexible substrate, divided into individual devices and interconnected with one another in series by interconnection layers and penetrating terminals.
Quantum critical Mott transitions in a bilayer Kondo insulator-metal model system
NASA Astrophysics Data System (ADS)
Sen, Sudeshna; Vidhyadhiraja, N. S.
2016-04-01
A bilayer system comprising a Kondo insulator coupled to a simple metal (KI-M) is considered. Employing the framework of dynamical mean-field theory, the model system is shown to exhibit a surface of quantum critical points (QCPs) that separates a Kondo screened, Fermi liquid phase from a local moment, Mott insulating phase. The quantum critical nature of these Mott transitions is characterized by the vanishing of (a) the coherence scale on the Fermi liquid side, and (b) the Mott gap on the MI side. In contrast to the usual "large-to-small" Fermi surface (FS) QCPs in heavy-fermion systems, the bilayer KI-M system exhibits a complete FS destruction.
Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model
NASA Astrophysics Data System (ADS)
Irkhin, Valentin Yu.
2016-05-01
Scaling equations for the Kondo lattice in the paramagnetic and magnetically ordered phases are derived to next-leading order with account of spin dynamics. The results are applied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in the multichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region. The corresponding temperature dependences of electronic and magnetic properties are discussed. The model describes naturally formation of a magnetic state with soft boson mode and small moment value. An important role of Van Hove singularities in the magnon spectral function is demonstrated. The results are rather sensitive to the type of magnetic ordering and space dimensionality, the conditions for NFL behavior being more favorable in the antiferromagnetic and 2D cases.
Kondo effect in the presence of van Hove singularities: A numerical renormalization group study
NASA Astrophysics Data System (ADS)
Zhuravlev, A. K.; Irkhin, V. Yu.
2011-12-01
A numerical renormalization-group investigation of the one-center t-t' Kondo problem is performed for the square lattice accounting for logarithmic Van Hove singularities (VHS) in the electron density of states near the Fermi level. The magnetic susceptibility, entropy, and specific heat are calculated. The temperature dependencies of the thermodynamic properties in the presence of VHS turn out to be nontrivial. When the distance Δ between VHS and the Fermi level decreases, the inverse logarithm of the corresponding Kondo temperature TK demonstrates a crossover from the standard linear to square-root dependence on the s-d exchange coupling. The low-temperature behavior of the magnetic susceptibility and specific heat are investigated, and the Wilson ratio is obtained. For Δ→0 the Fermi-liquid behavior is broken.
NASA Astrophysics Data System (ADS)
Hagymási, I.; Sólyom, J.; Legeza, Ö.
2015-07-01
We study the ground-state properties of an extended periodic Anderson model to understand the role of Hund's coupling between localized and itinerant electrons using the density-matrix renormalization group algorithm. By calculating the von Neumann entropies we show that two phase transitions occur and two new phases appear as the hybridization is increased in the symmetric half-filled case due to the competition between Kondo effect and Hund's coupling. In the intermediate phase, which is bounded by two critical points, we found a dimerized ground state, while in the other spatially homogeneous phases the ground state is Haldane-like and Kondo-singlet-like, respectively. We also determine the entanglement spectrum and the entanglement diagram of the system by calculating the mutual information thereby clarifying the structure of each phase.
Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire.
Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A; Gu, Genda; Mason, Nadya
2016-01-01
Zero-bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero-bias peaks in nanowires--for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential-conductance peaks at zero-bias voltage in non-superconducting electronic transport through a 3D topological insulator (Bi(1.33)Sb(0.67))Se3 nanowire. The zero-bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which are signatures of the Kondo effect in quantum dots. We characterize the zero-bias peaks and discuss their origin. PMID:26911258
Buildup of the Kondo effect from real-time effective action for the Anderson impurity model
NASA Astrophysics Data System (ADS)
Bock, Sebastian; Liluashvili, Alexander; Gasenzer, Thomas
2016-07-01
The nonequilibrium time evolution of a quantum dot is studied by means of dynamic equations for time-dependent Green's functions derived from a two-particle-irreducible (2PI) effective action for the Anderson impurity model. Coupling the dot between two leads at different voltages, the dynamics of the current through the dot is investigated. We show that the 2PI approach is capable of describing the dynamical buildup of the Kondo effect, which shows up as a sharp resonance in the spectral function, with a width exponentially suppressed in the electron self-coupling on the dot. An external voltage applied to the dot is found to deteriorate the Kondo effect at the hybridization scale. The dynamic equations are evaluated within different nonperturbative resummation schemes, within the direct, particle-particle, and particle-hole channels, as well as their combination, and the results compared with those from other methods.
Anomalous Temperature Dependence of the Dephasing Time in Mesoscopic Kondo Wires
NASA Astrophysics Data System (ADS)
Schopfer, Félicien; Bäuerle, Christopher; Rabaud, Wilfried; Saminadayar, Laurent
2003-02-01
We present measurements of the magnetoconductance of long and narrow quasi-one-dimensional gold wires containing magnetic iron impurities in a temperature range extending from 15mK to 4.2K. The dephasing rate extracted from the weak antilocalization shows a pronounced plateau in a temperature region of 300 800mK, associated with the phase breaking due to the Kondo effect. Below the Kondo temperature, the dephasing rate decreases linearly with temperature, in contradiction with standard Fermi-liquid theory. Our data suggest that the formation of a spin glass due to the interactions between the magnetic moments is responsible for the observed anomalous temperature dependence.
Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire
Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Mason, Nadya
2016-01-01
Zero-bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero-bias peaks in nanowires—for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential-conductance peaks at zero-bias voltage in non-superconducting electronic transport through a 3D topological insulator (Bi1.33Sb0.67)Se3 nanowire. The zero-bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which are signatures of the Kondo effect in quantum dots. We characterize the zero-bias peaks and discuss their origin. PMID:26911258
NASA Astrophysics Data System (ADS)
Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team
One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3
Interplay between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction
NASA Astrophysics Data System (ADS)
Prüser, Henning; Dargel, Piet E.; Bouhassoune, Mohammed; Ulbrich, Rainer G.; Pruschke, Thomas; Lounis, Samir; Wenderoth, Martin
2014-11-01
The interplay between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect is expected to provide the driving force for the emergence of many phenomena in strongly correlated electron materials. Two magnetic impurities in a metal are the smallest possible system containing all these ingredients and define a bottom-up approach towards a long-term understanding of concentrated/dense systems. Here we report on the experimental and theoretical investigation of iron dimers buried below a Cu(100) surface by means of low-temperature scanning tunnelling spectroscopy combined with density functional theory and numerical renormalization group calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl resonance, is strongly altered or even suppressed due to magnetic coupling between the impurities. It oscillates as a function of dimer separation revealing that it is related to indirect exchange interactions mediated by the conduction electrons.
Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire
Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Mason, Nadya
2016-02-25
Zero-bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero-bias peaks in nanowires—for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential-conductance peaks at zero-bias voltage in non-superconducting electronic transport through a 3D topological insulator (Bi1.33Sb0.67)Se3 nanowire. The zero-bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which are signatures of the Kondo effect in quantum dots. As a result, we characterize the zero-bias peaks and discuss their origin.
Bohm-Aharonov and Kondo effects on tunneling currents in a mesoscopic ring
Davidovich, M.A.; Anda, E.V.; Chiappe, G.
1997-03-01
We present an analysis of the Kondo effect on the Bohm-Aharonov oscillations of the tunneling currents in a mesoscopic ring with a quantum dot inserted in one of its arms. The system is described by an Anderson-impurity tight-binding Hamiltonian where the electron-electron interaction is restricted to the dot. The currents are obtained using nonequilibrium Green functions calculated through a cumulant diagrammatic expansion in the chain approximation. It is shown that at low temperature, even with the system out of resonance, the Kondo peak provides a channel for the electron to tunnel through the dot, giving rise to the Bohm-Aharonov oscillations of the current. At high temperature these oscillations are important only if the dot level is aligned to the Fermi level, when the resonance condition is satisfied. {copyright} {ital 1997} {ital The American Physical Society}
Field-Controlled Spin and Charge Distributions in Kondo System with a Triangular Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Koga, Mikito; Matsumoto, Masashige; Kusunose, Hiroaki
2013-09-01
The Kondo effect plays an important role in the emergence of electric polarization in a triangular triple-quantum-dot system, where one of the three dots is connected to a metallic lead through a point contact. The interplay between spin and charge distributions is investigated on the basis of an impurity Anderson model where the impurity-site cluster is described by a three-site Hubbard model. The numerical renormalization group analysis demonstrates that an applied magnetic field suppresses the Kondo effect and that the three-site spin correlations lead to an abrupt change in the local electric and magnetic polarizations. The controllability of this multiferroic behavior on the nanoscale is also discussed.
Phase diagram of the Kondo lattice model with a superlattice potential
NASA Astrophysics Data System (ADS)
Silva-Valencia, J.; Franco, R.; Figueira, M. S.
2016-02-01
We study the ground state of a Kondo lattice model where the free carries undergo a superlattice potential. Using the density matrix renormalization group method, we establish that the model exhibits a ferromagnetic phase and spiral phase whose boundaries in the phase diagram depend on the depth of the potential. Also, we observed that the spiral to ferromagnetic quantum phase transition can be tuned by changing the local coupling or the superlattice strength.
Competition between Kondo and RKKY correlations in the presence of strong randomness.
Tran, Minh-Tien; Kim, Ki-Seok
2011-10-26
We propose that competition between Kondo and magnetic correlations results in a novel universality class for heavy fermion quantum criticality in the presence of strong randomness. Starting from an Anderson lattice model with disorder, we derive an effective local field theory in the dynamical mean-field theory approximation, where randomness is introduced into both hybridization and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Performing the saddle-point analysis in the U(1) slave-boson representation, we reveal its phase diagram which shows a quantum phase transition from a spin liquid state to a local Fermi liquid phase. In contrast with the clean limit case of the Anderson lattice model, the effective hybridization given by holon condensation turns out to vanish, resulting from the zero mean value of the hybridization coupling constant. However, we show that the holon density becomes finite when the variance of the hybridization is sufficiently larger than that of the RKKY coupling, giving rise to the Kondo effect. On the other hand, when the variance of the hybridization becomes smaller than that of the RKKY coupling, the Kondo effect disappears, resulting in a fully symmetric paramagnetic state, adiabatically connected to the spin liquid state of the disordered Heisenberg model. We investigate the quantum critical point beyond the mean-field approximation. Introducing quantum corrections fully self-consistently in the non-crossing approximation, we prove that the local charge susceptibility has exactly the same critical exponent as the local spin susceptibility, suggesting an enhanced symmetry at the local quantum critical point. This leads us to propose novel duality between the Kondo singlet phase and the critical local moment state beyond the Landau-Ginzburg-Wilson paradigm. The Landau-Ginzburg-Wilson forbidden duality serves the mechanism of electron fractionalization in critical impurity dynamics, where such fractionalized excitations are
Spin injection into semiconductors
NASA Astrophysics Data System (ADS)
Oestreich, M.; Hübner, J.; Hägele, D.; Klar, P. J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D. E.; Lunn, B.
1999-03-01
The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.
Quantum Critical Behavior of the Bose-Fermi Kondo Model with Ising Anisotropy
NASA Astrophysics Data System (ADS)
Park, Tae-Ho
2005-03-01
The existence of a continous quantum phase transition of the Bose-Fermi Kondo Model (BFKM) with a self-consistently determined bosonic bath has been demonstrated within the Extended Dynamical Mean Field Approach to the anisotropic Kondo lattice model and φ/T-scaling near the quantum critical point(QCP)was found[1,2]. We study the quantum critical properties of the anisotropic BFKM with specified bath spectral function, where the spectrum of the bosonic bath vanishes in a power-law fashion with exponent γ for small frequencies. Motivated by very recent results that the quantum to classical mapping for a related class of models fails[3,4]. We determine the critical local susceptibility using both the classical and quantum Monte Carlo approaches of Ref.5. Our results cover several values of γ below and above the upper critical dimension of the classical model for temperatures down to 1% of the bare Kondo scale. [1]D. Grempel and Q. Si, Phys. Rev. Lett. 91, 026402 (2003). [2]J.Zhu, D. Grempel, and Q. Si, Phys. Rev. Lett. 91, 156404 (2003). [3]L. Zhu, S. Kirchner, Q. Si nad A. Georges, Phys. Rev. Lett. in press (cond-mat/0406293). [4]M. Vojta, N. Tong, and R. Bulla, cond-mat/0410132. [5]D. Grempel and M. Rozenberg, Phys. Rev. B 60, 4702 (1999).
NASA Astrophysics Data System (ADS)
Wang, Xiaoli; Hou, Dong; Zheng, Xiao; Yan, YiJing
2016-01-01
The magnetic anisotropy and Kondo phenomena in a mechanically stretched magnetic molecular junction are investigated by combining the density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. The system is comprised of a magnetic complex Co(tpy-SH)2 sandwiched between adjacent gold electrodes, which is mechanically stretched in experiments done by Parks et al. [Science 328, 1370 (2010)]. The electronic structure and mechanical property of the stretched system are investigated via the DFT calculations. The HEOM approach is then employed to characterize the Kondo resonance features, based on the Anderson impurity model parameterized from the DFT results. It is confirmed that the ground state prefers the S = 1 local spin state. The structural properties, the magnetic anisotropy, and corresponding Kondo peak splitting in the axial stretching process are systematically evaluated. The results reveal that the strong electron correlations and the local magnetic properties of the molecule magnet are very sensitive to structural distortion. This work demonstrates that the combined DFT+HEOM approach could be useful in understanding and designing mechanically controlled molecular junctions.
Interplay between Kondo screening and local singlets in SU (N) -symmetric cold atoms
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Rey, Ana Maria
2015-03-01
We study collective phenomena in strongly interacting fermionic alkaline-earth atoms (AEAs) loaded in an optical lattice. Owing to the strong decoupling between electronic orbital and nuclear-spin degrees of freedom, AEAs prepared in the two lowest electronic states are predicted to obey an accurate SU (N > 2 I + 1) symmetry in their two-body collisions (I is the nuclear spin). The SU (N) symmetric models offer a great opportunity to generate exotic many-body behavior emerging from the increased degeneracy and strict conservation laws. We focus on a parameter regime that realizes an SU (N > 2) (Coqblin-Schrieffer) generalization of the usual Kondo lattice model, and show that for band fillings above one atom per site, the system exhibits a peculiar interplay between Kondo screening and formation of singlets between localized atoms. In the limit of large Kondo coupling, we derive an effective Hamiltonian and determine its phase diagram. Our results can be tested in experiments with ultracold 173 Yb or 87 Sr atoms and are relevant for the physics of heavy-fermion materials with magnetic frustration. Supported by AFOSR, MURI-AFOSR and NSF.
Controlling Kondo-like Scattering at the SrTiO3-based Interfaces
Han, K.; Palina, N.; Zeng, S. W.; Huang, Z.; Li, C. J.; Zhou, W. X.; Wan, D.-Y.; Zhang, L. C.; Chi, X.; Guo, R.; Chen, J. S.; Venkatesan, T.; Rusydi, A.; Ariando, A
2016-01-01
The observation of magnetic interaction at the interface between nonmagnetic oxides has attracted much attention in recent years. In this report, we show that the Kondo-like scattering at the SrTiO3-based conducting interface is enhanced by increasing the lattice mismatch and growth oxygen pressure PO2. For the 26-unit-cell LaAlO3/SrTiO3 (LAO/STO) interface with lattice mismatch being 3.0%, the Kondo-like scattering is observed when PO2 is beyond 1 mTorr. By contrast, when the lattice mismatch is reduced to 1.0% at the (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 (LSAT/STO) interface, the metallic state is always preserved up to PO2 of 100 mTorr. The data from Hall measurement and X-ray absorption near edge structure (XANES) spectroscopy reveal that the larger amount of localized Ti3+ ions are formed at the LAO/STO interface compared to LSAT/STO. Those localized Ti3+ ions with unpaired electrons can be spin-polarized to scatter mobile electrons, responsible for the Kondo-like scattering observed at the LAO/STO interface. PMID:27147407
Orbital signatures of Fano-Kondo line shapes in STM adatom spectroscopy
NASA Astrophysics Data System (ADS)
Frank, Sebastian; Jacob, David
2015-12-01
We investigate the orbital origin of the Fano-Kondo line shapes measured in STM spectroscopy of magnetic adatoms on metal substrates. To this end we calculate the low-bias tunnel spectra of a Co adatom on the (001) and (111) Cu surfaces with our density functional theory-based ab initio transport scheme augmented by local correlations. In order to associate different d orbitals with different Fano line shapes we only correlate individual 3 d orbitals instead of the full Co 3 d shell. We find that Kondo peaks arising in different d levels indeed give rise to different Fano features in the conductance spectra. Hence, the shape of measured Fano features allows us to draw some conclusions about the orbital responsible for the Kondo resonance, although the actual shape is also influenced by temperature, effective interaction, and charge fluctuations. Comparison with a simplified model shows that line shapes are mostly the result of interference between tunneling paths through the correlated d orbital and the s p -type orbitals on the Co atom. Very importantly, the amplitudes of the Fano features vary strongly among orbitals, with the 3 z2 orbital featuring by far the largest amplitude due to its strong direct coupling to the s -type conduction electrons.
Robust topological surface state in Kondo insulator SmB{sub 6} thin films
Yong, Jie Jiang, Yeping; Zhang, Xiaohang; Greene, Richard L.; Usanmaz, Demet; Curtarolo, Stefano; Li, Linze; Pan, Xiaoqing; Shin, Jongmoon; Takeuchi, Ichiro
2014-12-01
Fabrication of smooth thin films of topological insulators with true insulating bulk are extremely important for utilizing their novel properties in quantum and spintronic devices. Here, we report the growth of crystalline thin films of SmB{sub 6}, a topological Kondo insulator with true insulating bulk, by co-sputtering both SmB{sub 6} and B targets. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicate films that are polycrystalline with a (001) preferred orientation. When cooling down, resistivity ρ shows an increase around 50 K and saturation below 10 K, consistent with the opening of the hybridization gap and surface dominated transport, respectively. The ratio ρ{sub 2K}/ρ{sub 300K} is only about two, much smaller than that of bulk, which indicates a much larger surface-to-bulk ratio. Point contact spectroscopy using a superconductor tip on SmB{sub 6} films shows both a Kondo Fano resonance and Andeev reflection, indicating an insulating Kondo lattice with metallic surface states.
Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model
Joyce, J.J.; Arko, A.J.; Andrews, A.B.
1993-09-01
The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.
Momentum-resolved evolution of the Kondo lattice into "hidden order" in URu2Si2.
Boariu, F L; Bareille, C; Schwab, H; Nuber, A; Lejay, P; Durakiewicz, T; Reinert, F; Santander-Syro, A F
2013-04-12
We study, using high-resolution angle-resolved photoemission spectroscopy, the evolution of the electronic structure in URu2Si2 at the Γ, Z, and X high-symmetry points from the high-temperature Kondo-screened regime to the low-temperature hidden-order (HO) state. At all temperatures and symmetry points, we find structures resulting from the interaction between heavy and light bands related to the Kondo-lattice formation. At the X point, we directly measure a hybridization gap of 11 meV already open at temperatures above the ordered phase. Strikingly, we find that while the HO induces pronounced changes at Γ and Z, the hybridization gap at X does not change, indicating that the hidden-order parameter is anisotropic. Furthermore, at the Γ and Z points, we observe the opening of a gap in momentum in the HO state, and show that the associated electronic structure results from the hybridization of a light electron band with the Kondo-lattice bands characterizing the paramagnetic state. PMID:25167291
Spin fluctuations in the anisotropic Kondo insulator CeRu4 Sn6
NASA Astrophysics Data System (ADS)
Fuhrman, Wesley T.; Haenel, J.; Rodriguez, J.; Paschen, S.; Broholm, C. L.
We report and model anisotropic quasi-elastic magnetic neutron scattering from single crystalline CeRu4Sn6. For T ~ 2 K the magnetic neutron scattering is broad in momentum (Q) with a persistent 1 / ℏω spectrum throughout the Brillouin zone. This indicates a lack of spatial coherence and no characteristic energy scale beyond the 0.2 meV resolution of the measurement. We find the Q-dependence of the scattering can be modeled by a Kondo-Heisenberg Hamiltonian that describes residual carriers and incompletely compensated localized electrons. These findings support the interpretation of tetragonal CeRu4Sn6 as an anisotropic or nodal Kondo insulator, markedly different from typical cubic Kondo insulators. We further discuss potential topological implications. Work at IQM was supported by the U.S. Department of Energy, office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER4654. W.T.F. thanks the ARCS foundation and Lockheed Martin for additional support.
Natural orbitals renormalization group approach to the two-impurity Kondo critical point
NASA Astrophysics Data System (ADS)
He, Rong-Qiang; Dai, Jianhui; Lu, Zhong-Yi
2015-04-01
The problem of two magnetic impurities in a normal metal exposes the two opposite tendencies in the formation of a singlet ground state, driven respectively by the single-ion Kondo effect with conduction electrons to screen impurity spins or the Ruderman-Kittel-Kasuya-Yosida interaction between the two impurities to directly form impurity spin singlet. However, whether the competition between these two tendencies can lead to a quantum critical point has been debated over more than two decades. Here, we study this problem by applying the newly proposed natural orbitals renormalization group method to a lattice version of the two-impurity Kondo model with a direct exchange K between the two impurity spins. The method allows for unbiased access to the ground state wave functions and low-lying excitations for sufficiently large system sizes. We demonstrate the existence of a quantum critical point, characterized by the power-law divergence of impurity staggered susceptibility with critical exponent γ =0.60 (1 ) , on the antiferromagnetic side of K when the interimpurity distance R is even lattice spacing, while a crossover behavior is recovered when R is odd lattice spacing. These results have ultimately resolved the long-standing discrepancy between the numerical renormalization group and quantum Monte Carlo studies, confirming a link of this two-impurity Kondo critical point to a hidden particle-hole symmetry predicted by the local Fermi liquid theory.
Controlling Kondo-like Scattering at the SrTiO3-based Interfaces
NASA Astrophysics Data System (ADS)
Han, K.; Palina, N.; Zeng, S. W.; Huang, Z.; Li, C. J.; Zhou, W. X.; Wan, D.-Y.; Zhang, L. C.; Chi, X.; Guo, R.; Chen, J. S.; Venkatesan, T.; Rusydi, A.; Ariando
2016-05-01
The observation of magnetic interaction at the interface between nonmagnetic oxides has attracted much attention in recent years. In this report, we show that the Kondo-like scattering at the SrTiO3-based conducting interface is enhanced by increasing the lattice mismatch and growth oxygen pressure PO2. For the 26-unit-cell LaAlO3/SrTiO3 (LAO/STO) interface with lattice mismatch being 3.0%, the Kondo-like scattering is observed when PO2 is beyond 1 mTorr. By contrast, when the lattice mismatch is reduced to 1.0% at the (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 (LSAT/STO) interface, the metallic state is always preserved up to PO2 of 100 mTorr. The data from Hall measurement and X-ray absorption near edge structure (XANES) spectroscopy reveal that the larger amount of localized Ti3+ ions are formed at the LAO/STO interface compared to LSAT/STO. Those localized Ti3+ ions with unpaired electrons can be spin-polarized to scatter mobile electrons, responsible for the Kondo-like scattering observed at the LAO/STO interface.
Controlling Kondo-like Scattering at the SrTiO3-based Interfaces.
Han, K; Palina, N; Zeng, S W; Huang, Z; Li, C J; Zhou, W X; Wan, D-Y; Zhang, L C; Chi, X; Guo, R; Chen, J S; Venkatesan, T; Rusydi, A; Ariando
2016-01-01
The observation of magnetic interaction at the interface between nonmagnetic oxides has attracted much attention in recent years. In this report, we show that the Kondo-like scattering at the SrTiO3-based conducting interface is enhanced by increasing the lattice mismatch and growth oxygen pressure PO2. For the 26-unit-cell LaAlO3/SrTiO3 (LAO/STO) interface with lattice mismatch being 3.0%, the Kondo-like scattering is observed when PO2 is beyond 1 mTorr. By contrast, when the lattice mismatch is reduced to 1.0% at the (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 (LSAT/STO) interface, the metallic state is always preserved up to PO2 of 100 mTorr. The data from Hall measurement and X-ray absorption near edge structure (XANES) spectroscopy reveal that the larger amount of localized Ti(3+) ions are formed at the LAO/STO interface compared to LSAT/STO. Those localized Ti(3+) ions with unpaired electrons can be spin-polarized to scatter mobile electrons, responsible for the Kondo-like scattering observed at the LAO/STO interface. PMID:27147407
Two-channel Kondo effect and phonon-assisted transport in single-molecular junctions
NASA Astrophysics Data System (ADS)
Dias da Silva, Luis; Dagotto, Elbio
2009-03-01
The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. In this theoretical work, we study such interplay in a system consisting of a single molecule in a metallic break junction tuned (by gate voltages) to be in an ``odd-N'' coulomb blockade valley (Kondo-prone). The connection to left and right metallic leads creates the usual coupling to a conduction channel with left-right symmetry (the ``even"-parity channel). A center-of-mass vibrational mode introduces an additional, phonon-assisted tunneling through the asymmetric (``odd''-parity channel). Our numerical renormalization-group calculations reveal that the phonon-mediated coupling to the odd channel leads to the appearance of a two-channel Kondo (2chK) effect, characterized by a non-Fermi-liquid (NFL) fixed point. The ground-state has NFL properties for a critical value of the phonon-mediated coupling strength and critical lines are present for wide range of parameters, including the regime away from particle-hole symmetry. Signatures of this 2chK non-Fermi-liquid behavior are prominent in the thermodynamic properties as well as in the linear conductance.
Semiconductor materials: From gemstone to semiconductor
NASA Astrophysics Data System (ADS)
Nebel, Christoph E.
2003-07-01
For diamond to be a viable semiconductor it must be possible to change its conductivity by adding impurities - known as dopants. With the discovery of a new dopant that generates electron conductivity at room temperature, diamond emerges as an electronic-grade material.
NASA Astrophysics Data System (ADS)
Sundar, Bhuvanesh; Mueller, Erich
2015-05-01
We propose an experimental protocol to directly observe the Kondo effect by scattering ultracold atoms with spin-dependent interactions. The Kondo effect is a transport anomaly which occurs when conduction electrons interact with magnetic impurities. We consider an ultracold system consisting of a gas of fermionic 6Li atoms and a gas of bosonic 87Rb atoms, where 6Li atoms play the role of conduction electrons and 87Rb atoms play the role of magnetic impurities. We propose a method to engineer Kondo-like interactions between them. To measure the Kondo effect, we imagine launching the 87Rb gas into the 6Li gas, and calculate the momentum transferred to the 6Li gas. We show that the temperature dependence of this momentum is logarithmic at low temperatures and has a minimum, characteristic of the Kondo effect and analogous to the behavior of electrical resistance of magnetic alloys. Experimental implementation of our proposal will give a new perspective on an iconic problem.
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Lee, Ting-Kuo; Mou, Chung-Yu
The energy gap in Dirac materials controls the topology and critical behaviors of the quantum phase transition associated with the critical point when the gap vanishes. However, it is often difficult to access the critical point as it requires tunablity of electronic structures. Here by exploiting the many-body screening interaction of localized spins and conduction electrons in a Kondo lattice, we demonstrate that the electronic band structures in a Kondo lattice are tunable in temperature. When spin-orbit interactions are included, we find that below the Kondo temperature, the Kondo lattice is a strong topological insulator at low temperature and undergoes a topological transition to a weak topological insulator at a higher temperature TD. At TD, Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our results indicate that the topological phase transition though a Dirac semi-metallic phase at finite temperatures also manifests profound physics and results in critical-like behavior both in magnetic and transport properties near TD. We acknowledge support from NCTS and Ministry of Science and Technology (MoST), Taiwan.
Sarkar, T. P.; Gopinadhan, K.; Motapothula, M.; Saha, S.; Huang, Z.; Dhar, S.; Patra, A.; Lu, W. M.; Telesio, F.; Pallecchi, I.; Ariando; Marré, D.; Venkatesan, T.
2015-01-01
We report the observation of spatially separated Kondo scattering and ferromagnetism in anatase Ta0.06Ti0.94O2 thin films as a function of thickness (10–200 nm). The Kondo behavior observed in thicker films is suppressed on decreasing thickness and vanishes below ~25 nm. In 200 nm film, transport data could be fitted to a renormalization group theory for Kondo scattering though the carrier density in this system is lower by two orders of magnitude, the magnetic entity concentration is larger by a similar magnitude and there is strong electronic correlation compared to a conventional system such as Cu with magnetic impurities. However, ferromagnetism is observed at all thicknesses with magnetic moment per unit thickness decreasing beyond 10 nm film thickness. The simultaneous presence of Kondo and ferromagnetism is explained by the spatial variation of defects from the interface to surface which results in a dominantly ferromagnetic region closer to substrate-film interface while the Kondo scattering is dominant near the surface and decreasing towards the interface. This material system enables us to study the effect of neighboring presence of two competing magnetic phenomena and the possibility for tuning them. PMID:26265554
Photoemission and magnetic circular dichroism studies of magnetic semiconductors
NASA Astrophysics Data System (ADS)
Fujimori, Atsushi
2005-03-01
Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.
Isotopically controlled semiconductors
Haller, E.E.
2004-11-15
A review of recent research involving isotopically controlled semiconductors is presented. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, can be considered the most important one for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples. Manuel Cardona, the longtime editor-in-chief of Solid State Communications has been and continues to be one of the major contributors to this field of solid state physics and it is a great pleasure to dedicate this review to him.
NASA Astrophysics Data System (ADS)
Huo, Dong-Ming
2015-10-01
We present nonequilibrium Green function calculations for electronic transport through a laterally coupled carbon-nanotube quantum-dot system. In this system, a one-dimensional double carbon nanotube quantum dot attached to polarised electrodes forms a main channel for electronic tunnelling. Each carbon nanotube quantum dot in the main channel couples to a dangling carbon nanotube quantum dot. Then, the conductance spectrum is calculated. The insulating band and resonance peak in this spectrum, due to Fano antiresonance and Kondo resonance, are discussed. The intradot electron's Coulomb interaction effect on the insulating band is also investigated. By controlling the coupling coefficient between the quantum dots, we can realise mutual transformation between Kondo resonance and Fano antiresonance at the Fermi level. The spin-orbit coupling and magnetic field's influence on the Kondo resonance peak are discussed in detail. Finally, spin magnetic moment and orbital magnetic moment of electrons in the quantum dot by applying parallel magnetic field are also predicted.
Non-Kondo-like electronic structure in the correlated rare-earth hexaboride YbB(6).
Neupane, Madhab; Xu, Su-Yang; Alidoust, Nasser; Bian, Guang; Kim, D J; Liu, Chang; Belopolski, I; Chang, T-R; Jeng, H-T; Durakiewicz, T; Lin, H; Bansil, A; Fisk, Z; Hasan, M Z
2015-01-01
We present angle-resolved photoemission studies on the rare-earth-hexaboride YbB(6), which has recently been predicted to be a topological Kondo insulator. Our data do not agree with the prediction and instead show that YbB(6) exhibits a novel topological insulator state in the absence of a Kondo mechanism. We find that the Fermi level electronic structure of YbB(6) has three 2D Dirac cone like surface states enclosing the Kramers's points, while the f orbital that would be relevant for the Kondo mechanism is ∼1 eV below the Fermi level. Our first-principles calculation shows that the topological state that we observe in YbB(6) is due to an inversion between Yb d and B p bands. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials. PMID:25615485
Vojta, Matthias; Mitchell, Andrew K; Zschocke, Fabian
2016-07-15
Kitaev's honeycomb-lattice compass model describes a spin liquid with emergent fractionalized excitations. Here, we study the physics of isolated magnetic impurities coupled to the Kitaev spin-liquid host. We reformulate this Kondo-type problem in terms of a many-state quantum impurity coupled to a multichannel bath of Majorana fermions and present the numerically exact solution using Wilson's numerical renormalization group technique. Quantum phase transitions occur as a function of Kondo coupling and locally applied field. At zero field, the impurity moment is partially screened only when it binds an emergent gauge flux, while otherwise it becomes free at low temperatures. We show how Majorana degrees of freedom determine the fixed-point properties, make contact with Kondo screening in pseudogap Fermi systems, and discuss effects away from the dilute limit. PMID:27472132
NASA Astrophysics Data System (ADS)
Vojta, Matthias; Mitchell, Andrew K.; Zschocke, Fabian
2016-07-01
Kitaev's honeycomb-lattice compass model describes a spin liquid with emergent fractionalized excitations. Here, we study the physics of isolated magnetic impurities coupled to the Kitaev spin-liquid host. We reformulate this Kondo-type problem in terms of a many-state quantum impurity coupled to a multichannel bath of Majorana fermions and present the numerically exact solution using Wilson's numerical renormalization group technique. Quantum phase transitions occur as a function of Kondo coupling and locally applied field. At zero field, the impurity moment is partially screened only when it binds an emergent gauge flux, while otherwise it becomes free at low temperatures. We show how Majorana degrees of freedom determine the fixed-point properties, make contact with Kondo screening in pseudogap Fermi systems, and discuss effects away from the dilute limit.
NMR evidence of anisotropic Kondo liquid behavior in CeIrIn5
NASA Astrophysics Data System (ADS)
Shockley, A. C.; Shirer, K. R.; Crocker, J.; Dioguardi, A. P.; Lin, C. H.; Nisson, D. M.; apRoberts-Warren, N.; Klavins, P.; Curro, N. J.
2015-08-01
We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4 f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.
Two-channel Kondo effect and the low-temperature crossover
NASA Astrophysics Data System (ADS)
Keller, Andrew; Peeters, Lucas; Weymann, Ireneusz; Moca, Cătălin Paşcu; Mahalu, Diana; Umansky, Vladimir; Zaránd, Gergely; Goldhaber-Gordon, David
2015-03-01
The two-channel Kondo (2CK) state, where a spin-1/2 impurity is equally exchange-coupled to two independent reservoirs, is a canonical non-Fermi liquid state. Experimental observations are rare because of its sensitivity to common and hard-to-control perturbations. We implement experimentally a 2CK state in a coupled dot-grain system (Potok, et al., doi:10.1038/nature05556), and explore the physics of the low-temperature crossover: how magnetic field and gate voltage drive the system towards a Fermi liquid ground state. Our experimental findings are corroborated by detailed numerical renormalization group modeling of our device.
Ferromagnetic Kondo lattice CeRuSi{sub 2} with non-Fermi-liquid behavior
Nikiforov, V. N.; Baran, M.; Irkhin, V. Yu.
2013-05-15
The structure, electronic, thermodynamic, and magnetic properties of the CeRuSi{sub 2} Kondo lattice with ferromagnetic ordering characterized by a small moment of the ground state are investigated. Anomalies in the temperature dependences of heat capacity and resistivity (unusual power or logarithmic behavior) observed in the low-temperature range indicate a non-Fermi-liquid behavior. The results are compared with those for other Ce{sub l}Ru{sub n}X{sub m} compounds and anomalous systems based on rare-earth elements and actinides that had been studied earlier.
Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB6
NASA Astrophysics Data System (ADS)
Butch, Nicholas P.; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A.; Booth, Corwin H.; Jeffries, Jason R.
2016-04-01
Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f -electron occupancy in the Kondo insulator SmB6 . Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.
Growth and Intrinsic Physical Properties of the Kondo Insulator SmB6
NASA Astrophysics Data System (ADS)
Phelan, William; Koohpayeh, Seyed; Cottingham, Patrick; Schoop, Leslie; Cava, Robert; Broholm, Collin; McQueen, Tyrel
2014-03-01
SmB6 is a long-studied Kondo Insulator that has come back into focus recently following theoretical predictions that it may harbor topologically protected surface states. Materials containing such surface states are referred to as topological insulators, and may impact technologically important areas such as quantum computing and spintronics. We report the preparation of single crystals of SmB6 via the floating zone technique, and the impact of growth conditions on the physical properties, including low temperature electrical transport. These results provide insights into the nature of the anomalous low temperature state of SmB6.
Interplay of localized and itinerant behavior in the one-dimensional Kondo-Heisenberg model
NASA Astrophysics Data System (ADS)
Xie, Neng; Yang, Yi-feng
2015-05-01
We use the density matrix renormalization group method to study the interplay of the localized and itinerant behaviors in the one-dimensional Kondo-Heisenberg model. We find signatures of simultaneously localized and itinerant behaviors of the local spins and attribute this duality to their simultaneous entanglement within the spin chain and with conduction electrons due to incomplete hybridization. We propose a microscopic definition of the hybridization parameter that measures this "partial" itinerancy. Our results provide a microscopic support for the dual nature of f electrons and the resulting two-fluid behavior widely observed in heavy electron materials.
Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB_{6}.
Butch, Nicholas P; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A; Booth, Corwin H; Jeffries, Jason R
2016-04-15
Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB_{6}. Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure. PMID:27127976
A low-temperature derivation of spin spin exchange in Kondo lattice model
NASA Astrophysics Data System (ADS)
Feng, Sze-Shiang; Mochena, Mogus
2005-11-01
Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-1/2 > and for spin-3/2, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t.
{ital Ab Initio} Calculation of Crystalline Electric Fields and Kondo Temperatures in Ce Compounds
Han, J.; Alouani, M.; Cox, D.; Han, J.; Cox, D.; Alouani, M.
1997-02-01
We have calculated the band-f hybridizations for Ce{sub x}La{sub 1-x}M{sub 3} compounds (x=1 and x{r_arrow}0; M=Pb,In,Sn,Pd) within the local density approximation and fed this into a noncrossing approximation for the Anderson impurity model applied to both dilute and concentrated limits. Our calculations produce crystalline electric field splittings and Kondo temperatures with trends in good agreement with experiment and demonstrate the need for detailed electronic structure information on hybridization to describe the diverse behaviors of these Ce compounds. {copyright} {ital 1997} {ital The American Physical Society}
Method of doping a semiconductor
Yang, Chiang Y.; Rapp, Robert A.
1983-01-01
A method for doping semiconductor material. An interface is established between a solid electrolyte and a semiconductor to be doped. The electrolyte is chosen to be an ionic conductor of the selected impurity and the semiconductor material and electrolyte are jointly chosen so that any compound formed from the impurity and the semiconductor will have a free energy no lower than the electrolyte. A potential is then established across the interface so as to allow the impurity ions to diffuse into the semiconductor. In one embodiment the semiconductor and electrolyte may be heated so as to increase the diffusion coefficient.
GUARD RING SEMICONDUCTOR JUNCTION
Goulding, F.S.; Hansen, W.L.
1963-12-01
A semiconductor diode having a very low noise characteristic when used under reverse bias is described. Surface leakage currents, which in conventional diodes greatly contribute to noise, are prevented from mixing with the desired signal currents. A p-n junction is formed with a thin layer of heavily doped semiconductor material disposed on a lightly doped, physically thick base material. An annular groove cuts through the thin layer and into the base for a short distance, dividing the thin layer into a peripheral guard ring that encircles the central region. Noise signal currents are shunted through the guard ring, leaving the central region free from such currents. (AEC)
Superconductivity in doped semiconductors
NASA Astrophysics Data System (ADS)
Bustarret, E.
2015-07-01
A historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike.
Kondo effect in a carbon nanotube with spin-orbit interaction and valley mixing: A DM-NRG study
NASA Astrophysics Data System (ADS)
Mantelli, Davide; Paşcu Moca, Cătălin; Zaránd, Gergely; Grifoni, Milena
2016-03-01
We investigate the effects of spin-orbit interaction (SOI) and valley mixing on the transport and dynamical properties of a carbon nanotube (CNT) quantum dot in the Kondo regime. As these perturbations break the pseudo-spin symmetry in the CNT spectrum but preserve time-reversal symmetry, they induce a finite splitting Δ between formerly degenerate Kramers pairs. Correspondingly, a crossover from the SU(4) to the SU(2)-Kondo effect occurs as the strength of these symmetry breaking parameters is varied. Clear signatures of the crossover are discussed both at the level of the spectral function as well as of the conductance. In particular, we demonstrate numerically and support with scaling arguments that the Kondo temperature scales inversely with the splitting Δ in the crossover regime. In presence of a finite magnetic field, time reversal symmetry is also broken. We investigate the effects of both parallel and perpendicular fields (with respect to the tube's axis) and discuss the conditions under which Kondo revivals may be achieved.
Tuning the Magnetic Quantum Criticality of Artificial Kondo Superlattices CeRhIn_{5}/YbRhIn_{5}.
Ishii, T; Toda, R; Hanaoka, Y; Tokiwa, Y; Shimozawa, M; Kasahara, Y; Endo, R; Terashima, T; Nevidomskyy, A H; Shibauchi, T; Matsuda, Y
2016-05-20
The effects of reduced dimensions and the interfaces on antiferromagnetic quantum criticality are studied in epitaxial Kondo superlattices, with alternating n layers of heavy-fermion antiferromagnet CeRhIn_{5} and seven layers of normal metal YbRhIn_{5}. As n is reduced, the Kondo coherence temperature is suppressed due to the reduction of effective Kondo screening. The Néel temperature is gradually suppressed as n decreases and the quasiparticle mass is strongly enhanced, implying dimensional control toward a quantum critical point. Magnetotransport measurements reveal that a quantum critical point is reached for the n=3 superlattice by applying small magnetic fields. Remarkably, the anisotropy of the quantum critical field is opposite to the expectations from the magnetic susceptibility in bulk CeRhIn_{5}, suggesting that the Rashba spin-orbit interaction arising from the inversion symmetry breaking at the interface plays a key role for tuning the quantum criticality in the two-dimensional Kondo lattice. PMID:27258878
NASA Astrophysics Data System (ADS)
Hayashi, Yuya; Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Ochiai, Akira
2016-03-01
We have measured the electrical resistivity of cerium monochalcogenides, CeS, CeSe, and CeTe, under high pressures of up to 8 GPa. The pressure dependences of the antiferromagnetic ordering temperature TN, crystal field splitting, and the ln T anomaly of the Kondo effect have been studied to cover the entire region from the magnetic ordering regime at low pressure to the Fermi liquid regime at high pressure. TN initially increases with increasing pressure, and starts to decrease at high pressure as expected from Doniach’s diagram. Simultaneously, the ln T behavior in the resistivity is enhanced, indicating the enhancement of the Kondo effect by pressure. It is also characteristic of CeXc that the crystal field splitting rapidly decreases at a common rate of -12.2 K/GPa. This leads to the increase in the degeneracy of the f state and the further enhancement of the Kondo effect. It is shown that the pressure-dependent degeneracy of the f state is a key factor for understanding the pressure dependence of TN, the Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.
Tuning the Magnetic Quantum Criticality of Artificial Kondo Superlattices CeRhIn5 /YbRhIn5
NASA Astrophysics Data System (ADS)
Ishii, T.; Toda, R.; Hanaoka, Y.; Tokiwa, Y.; Shimozawa, M.; Kasahara, Y.; Endo, R.; Terashima, T.; Nevidomskyy, A. H.; Shibauchi, T.; Matsuda, Y.
2016-05-01
The effects of reduced dimensions and the interfaces on antiferromagnetic quantum criticality are studied in epitaxial Kondo superlattices, with alternating n layers of heavy-fermion antiferromagnet CeRhIn5 and seven layers of normal metal YbRhIn5 . As n is reduced, the Kondo coherence temperature is suppressed due to the reduction of effective Kondo screening. The Néel temperature is gradually suppressed as n decreases and the quasiparticle mass is strongly enhanced, implying dimensional control toward a quantum critical point. Magnetotransport measurements reveal that a quantum critical point is reached for the n =3 superlattice by applying small magnetic fields. Remarkably, the anisotropy of the quantum critical field is opposite to the expectations from the magnetic susceptibility in bulk CeRhIn5 , suggesting that the Rashba spin-orbit interaction arising from the inversion symmetry breaking at the interface plays a key role for tuning the quantum criticality in the two-dimensional Kondo lattice.
Non-equilibrium conductance through a benzene molecule in the Kondo regime
NASA Astrophysics Data System (ADS)
Tosi, L.; Roura-Bas, P.; Aligia, A. A.
2012-09-01
Starting from exact eigenstates for a symmetric ring, we derive a low-energy effective generalized Anderson Hamiltonian which contains two spin doublets with opposite momenta and a singlet for the neutral molecule. For benzene, the singlet (doublets) represent the ground state of the neutral (singly charged) molecule. We calculate the non-equilibrium conductance through a benzene molecule, doped with one electron or a hole (i.e. in the Kondo regime), and connected to two conducting leads at different positions. We solve the problem using the Keldysh formalism and the non-crossing approximation. When the leads are connected in the para position (at 180°), the model is equivalent to the ordinary impurity Anderson model and its known properties are recovered. For other positions, there is a partial destructive interference in the co-tunneling processes involving the two doublets and, as a consequence, the Kondo temperature and the height and width of the central peak (for bias voltage Vb near zero) of the differential conductance G = dI/dVb (where I is the current) are reduced. In addition, two peaks at finite Vb appear. We study the position of these peaks, the temperature dependence of G and the spectral densities. Our formalism can also be applied to carbon nanotube quantum dots with intervalley mixing.
Influence of Rashba spin-orbit coupling on the Kondo effect
NASA Astrophysics Data System (ADS)
Wong, Arturo; Ulloa, Sergio E.; Sandler, Nancy; Ingersent, Kevin
2016-02-01
An Anderson model for a magnetic impurity in a two-dimensional electron gas with bulk Rashba spin-orbit interaction is solved using the numerical renormalization group under two different experimental scenarios. For a fixed Fermi energy, the Kondo temperature TK varies weakly with Rashba coupling λR, as reported previously. If instead the band filling is low and held constant, increasing λR can drive the system into a helical regime with exponential enhancement of TK. Under either scenario, thermodynamic properties at low temperatures T exhibit the same dependencies on T /TK as are found for λR=0 . Unlike the conventional Kondo effect, however, the impurity exhibits static spin correlations with conduction electrons of nonzero orbital angular momentum about the impurity site. We also consider a magnetic field that Zeeman splits the conduction band but not the impurity level, an effective picture that arises under a proposed route to access the helical regime in a driven system. The impurity contribution to the system's ground-state angular momentum is found to be a universal function of the ratio of the Zeeman energy to a temperature scale that is not TK (as would be the case in a magnetic field that couples directly to the impurity spin), but rather is proportional to TK divided by the impurity hybridization width. This universal scaling is explained via a perturbative treatment of field-induced changes in the electronic density of states.
Breakdown of the Kondo insulating state in SmB6 by introducing Sm vacancies
NASA Astrophysics Data System (ADS)
Valentine, Michael E.; Koohpayeh, Seyed; Phelan, W. Adam; McQueen, Tyrel M.; Rosa, Priscila F. S.; Fisk, Zachary; Drichko, Natalia
2016-08-01
We explore the stability of the hybridization gap in SmB6 to the presence of a small number of Sm vacancies typical for this material, and demonstrate the extreme fragility of the Kondo insulating state. For the most stoichiometric sample we detect the hybridization gap which appears below 50 K as a depressed electronic Raman intensity below about 30 meV. The spectral weight that shifts to higher frequencies on the opening of the hybridization gap forms two electronic maxima at 100 and 41 meV. We assign these maxima to the excitations between hybridized 4 f -5 d bands using recent band structure calculations. Below 30 K, in-gap exciton modes with long lifetimes protected by the hybridization gap develop at 16-18 meV. With the increase of the number of Sm vacancies the exciton features broaden, evidencing a decrease in the lifetime due to the presence of electronic states in the gap. At a concentration of Sm vacancies of only about 1% the in-gap exciton is completely quenched, and the hybridization gap is not fully opened. We suggest that only the most stoichiometric SmB6 samples possess a bulk gap necessary for the topological Kondo insulator state.
Magnetotransport in (Ce1-xNdx)Cu6 Kondo alloys
NASA Astrophysics Data System (ADS)
Strydom, André M.; du Plessis, Paul de V.
1999-03-01
The results of electrical resistivity ρ(T) and magnetoresistivity MR(T, B) for Kondo lattice is characterized through coherence effects in ρ(T) at low temperatures. The ρ(T) data above room temperature are used to resolve the electron-phonon scattering, and it is indicated that the single-ion Kondo interaction dominates both ρ(T) and MR(B) for a wide range of intermediate Ce concentrations. Based on this, the MR(B) data for different isotherms and alloy compositions are analysed according to the Bethe- ansatz description. We also discuss the observed deviations of our data from the preceding theoretical description due to the onset of magnetic order in alloys with high Nd content, and to phase coherence at low temperatures.
Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide
NASA Astrophysics Data System (ADS)
Luo, Yongkang; Pourovskii, Leonid; Rowley, S. E.; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'An; Si, Qimiao; Ong, N. P.
2014-08-01
A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems.
Non-Kondo Mechanism of Resistivity Minimum in Frustrated Itinerant Mangets
NASA Astrophysics Data System (ADS)
Batista, Cristian; Wang, Zhentao; Barros, Kipton; Chern, Gia-Wei
Frustration can induce novel phenomena in the transport properties of itinerant magnets. The ''amount of frustration'' is typically quantified by the | ΘCW | / TC ratio. A large value of this ratio corresponds to a broad temperature regime TC < T <ΘCW , where the spins are in spin liquid state, i.e., the magnetic structure factor is not flat, as in the gas (T >ΘCW) state and it does not contain Bragg peaks, as in the ordered or ''solid'' state at TTC . We demonstrate that when interaction between magnetic moments is mediated by the conduction electrons, the electronic resistivity increases upon lowering temperature, due to enhanced scattering rate for k <= 2kF . To illustrate this phenomenon we consider a triangular Kondo lattice model with classical local moments. By using both analytical and numerical methods, we unambiguously demonstrate that the electronic resistivity grows upon lowering temperature inside the spin liquid regime. This growth necessarily leads to a resistivity minimum when electron-electron and electron-phonon scattering are included. We note that the origin of this resistivity minimum is radically different from the well-known minimum induced by the Kondo effect.
Critical-field theory of the Kondo lattice model in two dimensions
Kim, Ki-Seok
2005-05-15
In the context of the U(1) slave-boson theory we derive a critical-field theory near the quantum-critical point of the Kondo lattice model in two spatial dimensions. First, we argue that strong gauge fluctuations in the U(1) slave-boson theory give rise to confinement between spinons and holons, thus causing 'neutralized' spinons in association with the slave-boson U(1) gauge field. Second, we show that critical fluctuations of Kondo singlets near the quantum-critical point result in a new U(1) gauge field. This emergent gauge field has nothing to do with the slave-boson U(1) gauge field. Third, we find that the slave-boson U(1) gauge field can be exactly integrated out in the low-energy limit. As a result we find a critical-field theory in terms of renormalized conduction electrons and neutralized spinons interacting via the new emergent U(1) gauge field. Based on this critical-field theory we obtain the temperature dependence of the specific heat and the imaginary part of the self-energy of the renormalized electrons. These quantities display non-Fermi-liquid behavior near the quantum-critical point.
Possible undercompensation effect in the Kondo insulator (Yb,Tm)B12
NASA Astrophysics Data System (ADS)
Alekseev, P. A.; Nemkovski, K. S.; Mignot, J.-M.; Clementyev, E. S.; Ivanov, A. S.; Rols, S.; Bewley, R. I.; Filipov, V. B.; Shitsevalova, N. Yu.
2014-03-01
The effects of Tm substitution on the dynamical magnetic response of Yb1-xTmxB12 (x=0, 0.08, 0.15, and 0.75) and Lu0.92Tm0.08B12 compounds have been studied using time-of-flight inelastic neutron scattering. Major changes were observed in the spectral structure and temperature evolution of the Yb contribution to the inelastic response for a rather low content of magnetic Tm ions. A sizable influence of the RB12 host (YbB12, as compared to LuB12 or pure TmB12) on the crystal-field splitting of the Tm3+ ion is also reported. The results point to a specific effect of impurities carrying a magnetic moment (Tm, as compared to Lu or Zr) in a Kondo insulator, which is thought to reflect the "undercompensation" of Yb magnetic moments, originally Kondo screened in pure YbB12. A parallel is made with the strong effect of Tm substitution on the temperature dependence of the Seebeck coefficient in Yb1-xTmxB12, which was reported previously.
NMR investigations on single crystals of U2Ru2Sn: A Kondo insulator
NASA Astrophysics Data System (ADS)
Rajarajan, A. K.; Rabis, A.; Baenitz, M.; Gippius, A. A.; Morozova, E. N.; Mydosh, J. A.; Steglich, F.
2005-04-01
U2Ru2Sn is unique among all Kondo insulators because of its tetragonal structure and an energy gap of about 150 K being the smallest of all the uranium-based Kondo insulators. We report Knight shift K(T) and relaxation rate T1-1 measurements from 119Sn(I={1}/{2})-NMR for the first time in single crystals and oriented micro-crystallites. At low temperatures the anisotropy in K(T) increases ( K∥/K⊥(4.2 K)≈2), a trend observed also in χ(T) and ρ(T). K(H⊥c) exhibits a smooth variation, whereas for K(H ∥ c) a change of slope occurs at 150 K with a more rapid decrease below. The anisotropy is not as prominent in T1-1(T). The hyperfine coupling constant exhibits a cross-over behaviour from one linear regime of K(T) vs. χ(T) to another around a characteristic temperature.
Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy.
Brun, B; Martins, F; Faniel, S; Hackens, B; Bachelier, G; Cavanna, A; Ulysse, C; Ouerghi, A; Gennser, U; Mailly, D; Huant, S; Bayot, V; Sanquer, M; Sellier, H
2014-01-01
Quantum point contacts exhibit mysterious conductance anomalies in addition to well-known conductance plateaus at multiples of 2e(2)/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position. PMID:24978440
Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy
NASA Astrophysics Data System (ADS)
Brun, B.; Martins, F.; Faniel, S.; Hackens, B.; Bachelier, G.; Cavanna, A.; Ulysse, C.; Ouerghi, A.; Gennser, U.; Mailly, D.; Huant, S.; Bayot, V.; Sanquer, M.; Sellier, H.
2014-06-01
Quantum point contacts exhibit mysterious conductance anomalies in addition to well-known conductance plateaus at multiples of 2e2/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position.
Excitonic and nematic instabilities on the surface of topological Kondo insulators
NASA Astrophysics Data System (ADS)
Roy, Bitan; Hofmann, Johannes; Stanev, Valentin; Sau, Jay D.; Galitski, Victor
2015-12-01
We study the effects of strong electron-electron interactions on the surface of cubic topological Kondo insulators (such as samarium hexaboride, SmB6). Cubic topological Kondo insulators generally support three copies of massless Dirac nodes on the surface, but only two of them are energetically degenerate and exhibit an energy offset relative to the third one. With a tunable chemical potential, when the surface states host electron and hole pockets of comparable size, strong interactions may drive this system into rotational symmetry breaking nematic and translational symmetric breaking excitonic spin- or charge-density-wave phases, depending on the relative chirality of the Dirac cones. Taking a realistic surface band structure into account we analyze the associated Ginzburg-Landau theory and compute the mean-field phase diagram for interacting surface states. Beyond mean-field theory, this system can be described by a two-component isotropic Ashkin-Teller model at finite temperature, and we outline the phase diagram of this model. Our theory provides a possible explanation of recent measurements which detect a twofold symmetric magnetoresistance and an upturn in surface resistivity with tunable gate voltage in SmB6. Our discussion can also be germane to other cubic topological insulators, such as ytterbium hexaboride (YbB6) and plutonium hexaboride (PuB6).
Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study
Kovaleva, N. N.; Kugel, K. I.; Bazhenov, A. V.; Fursova, T. N.; Löser, W.; Xu, Y.; Behr, G.; Kusmartsev, F. V.
2012-01-01
Magnetic materials are usually divided into two classes: those with localised magnetic moments, and those with itinerant charge carriers. We present a comprehensive experimental (spectroscopic ellipsomerty) and theoretical study to demonstrate that these two types of magnetism do not only coexist but complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material the itinerant charge carriers interact with large localised magnetic moments of Tb(4f) states, forming complex magnetic lattices at low temperatures, which we associate with self-organisation of magnetic clusters. The formation of magnetic clusters results in low-energy optical spectral weight shifts, which correspond to opening of the pseudogap in the conduction band of the itinerant charge carriers and development of the low- and high-spin intersite electronic transitions. This phenomenon, driven by self-trapping of electrons by magnetic fluctuations, could be common in correlated metals, including besides Kondo-lattice metals, Fe-based and cuprate superconductors. PMID:23189239
Visualizing the formation of the Kondo lattice and the hidden order in URu2Si2
Aynajian, Pegor; da Silva Neto, Eduardo H.; Parker, Colin V.; Huang, Yingkai; Pasupathy, Abhay; Mydosh, John; Yazdani, Ali
2010-01-01
Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope to examine the novel electronic states that emerge from the uranium f states in URu2Si2. We find that, as the temperature is lowered, partial screening of the f electrons’ spins gives rise to a spatially modulated Kondo–Fano resonance that is maximal between the surface U atoms. At T = 17.5 K, URu2Si2 is known to undergo a second-order phase transition from the Kondo lattice state into a phase with a hidden order parameter. From tunneling spectroscopy, we identify a spatially modulated, bias-asymmetric energy gap with a mean-field temperature dependence that develops in the hidden order state. Spectroscopic imaging further reveals a spatial correlation between the hidden order gap and the Kondo resonance, suggesting that the two phenomena involve the same electronic states. PMID:20498090
Kondo effect in a neutral and stable all organic radical single molecule break junction
NASA Astrophysics Data System (ADS)
Burzuri, Enrique; Gaudenzi, Rocco; Frisenda, Riccardo; Franco, Carlos; Mas-Torrent, Marta; Rovira, Concepcio; Veciana, Jaume; Alcon, Isaac; Bromley, Stefan T.; van der Zant, Herre S. J.
Organic radicals are neutral, purely organic molecules exhibiting an intrinsic magnetic moment due to the presence of an unpaired electron in the molecule in its ground state. This property, added to the low spin-orbit coupling makes organic radicals good candidates for molecular spintronics insofar as the radical character is stable in solid state electronic devices. We show that the paramagnetism of the PTM radical molecule, in the shape of a Kondo anomaly is preserved in two- and three-terminal solid-state devices, regardless of mechanical and electrostatic changes. Indeed, our results demonstrate that the Kondo anomaly is robust under electrodes displacement and changes of the electrostatic environment, pointing to a localized orbital in the radical as the source of magnetism. Strong support to this picture is provided by density functional calculations and measurements of the corresponding nonradical specie. We further study polyradical systems, where several unpaired spins interact in the same molecule. This work was supported by the EU FP7 program through project 618082 ACMOL and ERC grant advanced Mols@Mols. It was also supported by the Dutch funding organization NWO (VENI).
Magnetic structure of the Kondo lattice compound CeZn0.6Sb2
NASA Astrophysics Data System (ADS)
Chen, Y.; Lynn, J. W.; Lee, H.; Klavins, P.; Fisk, Z.; Nakatsuji, S.; Bao, W.; Thompson, J.; Park, T.; Macaluso, R.; Chan, J.; Carter, B.
2006-03-01
The new Kondo lattice compound CeZn0.6Sb2 has a tetragonal structure with space group P4/nmm and shows ferromagnetic behavior below 2.5 K. The Curie-Weiss temperature is 22 K along the tetragonal ab plane, indicating ferromagnetic interactions in the plane. Along the c axis, however, the Curie-Weiss temperature is -145 K, suggesting antiferromagnetic exchange interaction in this direction [1]. We determined the magnetic structure of CeZn0.6Sb2 using single crystal neutron diffraction. (h,0,l) and (h,h,l) scattering planes were investigated. We found CeZn0.6Sb2 orders ferromagnetically at TC=2.5 K. The magnetic structure is collinear with a low temperature ordered Ce moment of 1.3 (1) μB that lies in the ab plane. In addition, we measured the order parameter of the ferromagnetic transition. [1] Studies of the ferromagnetic Kondo lattice system of single crystal CeZnSb2, H. Lee, S. Nakatsuji, Y. Chen, W. Bao, R. Macaluso, J. Chan, T. Park, B. Carter, P. Klavins, J. Thompson, Z. Fisk, BAPS, Session L41, 2005.
NASA Astrophysics Data System (ADS)
Allerdt, Andrew; Büsser, C. A.; Martins, G. B.; Feiguin, A. E.
2015-02-01
Magnetic impurities embedded in a metal interact via an effective Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mediated by the conduction electrons, which is commonly assumed to be long ranged, with an algebraic decay in the interimpurity distance. However, they can also form a Kondo screened state that is oblivious to the presence of other impurities. We study the competition mechanisms between both effects on the square and cubic lattices by introducing an exact mapping onto an effective one-dimensional problem that we can solve with the density matrix renormalization group method. We show a dramatic departure from the conventional RKKY theory, that can be attributed to the dimensionality and different densities of states, as well as the quantum nature of the magnetic moments. In particular, for dimension d >1 , Kondo physics dominates even at short distances, while the ferromagnetic RKKY state is energetically unfavorable. Our findings can have clear implications in the interpretation of experiments and for tailoring the magnetic properties of surfaces.
Magnetic-field-tunable Kondo effect in alkaline-earth cold atoms
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Rey, Ana Maria
We study quantum magnetism and emergent Kondo physics in strongly interacting fermionic alkaline-earth atoms in an optical lattice with two Bloch bands: one localized and one itinerant. For a fully filled narrow band (two atoms per lattice site) we demonstrate that an applied magnetic field provides an efficient control of the ground state degeneracy due to the field-induced crossing of singlet and triplet state of the localized atomic pairs. We exploit this singlet-triplet resonance, as well as magnetically tunable interactions of atoms in different electronic states via the recently-discovered inter-orbital Feshbach resonance, and demonstrate that the system exhibits a magnetic field-induced Kondo phase characterized by delocalization of local singlets and a large Fermi surface. We also determine the phase diagram of the system within an effective low-energy model that incorporates the above magnetic-field effect as well as atomic interactions in the two optical lattice bands. Our results can be tested with ultracold 173 Yb , and provide a model for the magnetic field-induced heavy-fermion state in filled skutterudites such as PrOs4Sb12 . This work was supported by the NSF (PIF-1211914 and PFC-1125844), AFOSR, AFOSR-MURI, NIST and ARO individual investigator awards.
Photoemission spectroscopy and X-ray diffraction analysis of 3D topological and Kondo insulators
NASA Astrophysics Data System (ADS)
Shibayev, Pavel
2015-03-01
The advantage of studying 3D topological insulators (TIs), compounds that have attracted the attention of many in the condensed matter field, is the ability for their existence at room temperature and no magnetic fields, allowing both for resolving their band structure via angle-resolved photoemission spectroscopy (ARPES) and understanding electrical transport and other properties via X-ray diffraction (XRD) and point-contact spectroscopy (PCS). A comprehensive quantitative analysis of Bi2Se3, a 3D TI, was carried out using these methods. The Bi2Se3\\ crystals were synthesized in-house at Princeton University. A first-principles calculation based on density functional theory, DFT, was performed using the Abinit software. The band structure of the crystal was then resolved via ARPES at the Advanced Light Source in LBNL, resulting in a surprisingly stark and clear single Dirac cone. A large band gap was confirmed, suggesting an increased potential for applications. In contrast, Kondo insulators are found in rare-earth based materials with f-electron degrees of freedom. Photon energy dependent dispersion relationships and temperature dependence studies were performed on a Kondo candidate CeB6 via ARPES, showing an even number of Dirac cones and a non-TI behavior. Analysis of I-V characteristics through PCS will follow, in addition to characterization via Bruker XRD for both compounds. Research group led by Professor M. Zahid Hasan (Princeton University).
Kondo physics in the presence of Rashba spin-orbit interactions
NASA Astrophysics Data System (ADS)
Wong, Arturo; Ulloa, Sergio; Sandler, Nancy; Ingersent, Kevin
Recent theoretical studies have shown that Rashba spin-orbit interactions in a two-dimensional electron gas (2DEG) affect the thermodynamics of the impurity Kondo effect only through changes in the host density of states. These changes are generally modest, but yield exponential enhancement of the Kondo temperature TK if the 2DEG can be tuned to a helical regime in which all electrons at the Fermi surface have the same relation between the directions of their spin and momentum. It has been proposed to access the helical regime using irradiation with circularly polarized light, giving rise to an effective Zeeman splitting of the conduction band without any direct splitting of the impurity level. We show that under this scenario, the impurity contribution to the system's net angular momentum is a universal function of the Zeeman energy divided by a temperature scale that (surprisingly at first sight) is not TK, but rather is proportional to TK divided by the impurity hybridization width. This universal scaling can be understood via a perturbative treatment of irradiation-induced changes in the electron densities of states
4 f excitations in Ce Kondo lattices studied by resonant inelastic x-ray scattering
NASA Astrophysics Data System (ADS)
Amorese, A.; Dellea, G.; Fanciulli, M.; Seiro, S.; Geibel, C.; Krellner, C.; Makarova, I. P.; Braicovich, L.; Ghiringhelli, G.; Vyalikh, D. V.; Brookes, N. B.; Kummer, K.
2016-04-01
The potential of resonant inelastic soft x-ray scattering to measure 4 f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4 ,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
NASA Astrophysics Data System (ADS)
Batley, J. T.; Rosamond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
2015-12-01
The temperature dependence of the spin diffusion length typically reflects the scattering mechanism responsible for spin relaxation. Within nonmagnetic metals it is reasonable to expect the Elliot-Yafet mechanism to play a role and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. In lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. By measuring the transport properties of lateral Py/Cu/Py spin valves, fabricated from Cu with magnetic impurities of <1 ppm and ˜4 ppm, we extract a spin diffusion length which shows this suppression below 30 K only in the presence of the Kondo effect. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. We find the spin-flip probability of a magnetic impurity to be 34%. Our analysis demonstrates the dominant role of Kondo scattering in spin relaxation, even in low concentrations of order 1 ppm, and hence illustrates its importance to the reduction in spin diffusion length observed by ourselves and others.
Amorphous semiconductor solar cell
Dalal, Vikram L.
1981-01-01
A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.
Kansas Advanced Semiconductor Project
Baringer, P.; Bean, A.; Bolton, T.; Horton-Smith, G.; Maravin, Y.; Ratra, B.; Stanton, N.; von Toerne, E.; Wilson, G.
2007-09-21
KASP (Kansas Advanced Semiconductor Project) completed the new Layer 0 upgrade for D0, assumed key electronics projects for the US CMS project, finished important new physics measurements with the D0 experiment at Fermilab, made substantial contributions to detector studies for the proposed e+e- international linear collider (ILC), and advanced key initiatives in non-accelerator-based neutrino physics.
Chemically Derivatized Semiconductor Photoelectrodes.
ERIC Educational Resources Information Center
Wrighton, Mark S.
1983-01-01
Deliberate modification of semiconductor photoelectrodes to improve durability and enhance rate of desirable interfacial redox processes is discussed for a variety of systems. Modification with molecular-based systems or with metals/metal oxides yields results indicating an important role for surface modification in devices for fundamental study…
Physics of Organic Semiconductors
NASA Astrophysics Data System (ADS)
Brütting, Wolfgang
2004-05-01
Organic semiconductors are of steadily growing interest as active components in electronics and optoelectronics. Due to their flexibility, low cost and ease-of-production they represent a valid alternative to conventional inorganic semiconductor technology in a number of applications, such as flat panel displays and illumination, plastic integrated circuits or solar energy conversion. Although first commercial applications of this technology are being realized nowadays, there is still the need for a deeper scientific understanding in order to achieve optimum device performance.This special issue of physica status solidi (a) tries to give an overview of our present-day knowledge of the physics behind organic semiconductor devices. Contributions from 17 international research groups cover various aspects of this field ranging from the growth of organic layers and crystals, their electronic properties at interfaces, their photophysics and electrical transport properties to the application of these materials in different devices like organic field-effect transistors, photovoltaic cells and organic light-emitting diodes.Putting together such a special issue one soon realizes that it is simply impossible to fully cover the whole area of organic semiconductors. Nevertheless, we hope that the reader will find the collection of topics in this issue useful for getting an up-to-date review of a field which is still developing very dynamically.
Semiconductor radiation detector
Patt, Bradley E.; Iwanczyk, Jan S.; Tull, Carolyn R.; Vilkelis, Gintas
2002-01-01
A semiconductor radiation detector is provided to detect x-ray and light photons. The entrance electrode is segmented by using variable doping concentrations. Further, the entrance electrode is physically segmented by inserting n+ regions between p+ regions. The p+ regions and the n+ regions are individually biased. The detector elements can be used in an array, and the p+ regions and the n+ regions can be biased by applying potential at a single point. The back side of the semiconductor radiation detector has an n+ anode for collecting created charges and a number of p+ cathodes. Biased n+ inserts can be placed between the p+ cathodes, and an internal resistor divider can be used to bias the n+ inserts as well as the p+ cathodes. A polysilicon spiral guard can be implemented surrounding the active area of the entrance electrode or surrounding an array of entrance electrodes.
Doped semiconductor nanocrystal junctions
NASA Astrophysics Data System (ADS)
Borowik, Ł.; Nguyen-Tran, T.; Roca i Cabarrocas, P.; Mélin, T.
2013-11-01
Semiconductor junctions are the basis of electronic and photovoltaic devices. Here, we investigate junctions formed from highly doped (ND≈1020-1021cm-3) silicon nanocrystals (NCs) in the 2-50 nm size range, using Kelvin probe force microscopy experiments with single charge sensitivity. We show that the charge transfer from doped NCs towards a two-dimensional layer experimentally follows a simple phenomenological law, corresponding to formation of an interface dipole linearly increasing with the NC diameter. This feature leads to analytically predictable junction properties down to quantum size regimes: NC depletion width independent of the NC size and varying as ND-1/3, and depleted charge linearly increasing with the NC diameter and varying as ND1/3. We thus establish a "nanocrystal counterpart" of conventional semiconductor planar junctions, here however valid in regimes of strong electrostatic and quantum confinements.
Light amplification using semiconductors
Dupuis, R.D.
1987-06-01
During the summer of 1953, John von Neumann discussed his ideas concerning light amplification using semiconductors with Edward Teller. In September of that year, von Neumann sent a manuscript containing his ideas and calculations on this subject to Teller for his comments. To the best of our knowledge, von Neumann did not take time to work further on these ideas, and the manuscript remained unpublished. These previously unpublished writings of John von Neumann on the subject of light amplification in semiconductors are printed as a service to the laser community. While von Neumann's original manuscript and his letter to Teller are available to anyone who visits the Library of Congress, it is much more convenient to have this paper appear in an archival journal.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi_{2–δ}As_{2}
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z. -A.; Thompson, J. D.
2015-10-19
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi_{2–δ}As_{2} (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 e^{–}/formular unit in CeNi_{2–δ}As_{2} leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. Here, the small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.
Isotopically controlled semiconductors
Haller, Eugene E.
2006-06-19
The following article is an edited transcript based on the Turnbull Lecture given by Eugene E. Haller at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his 'pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations'. The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin-film heterostructures. Isotopic composition affects several properties such as phonon energies, band structure, and lattice constant in subtle, but, for their physical understanding, significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photoluminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for simultaneous self- and dopant-diffusion studies. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.
NASA Technical Reports Server (NTRS)
Taghavi-Larigani, Shervin (Inventor); Vanzyl, Jakob J. (Inventor); Yariv, Amnon (Inventor)
2006-01-01
Tunable semiconductor lasers are disclosed requiring minimized coupling regions. Multiple laser embodiments employ ring resonators or ring resonator pairs using only a single coupling region with the gain medium are detailed. Tuning can be performed by changing the phase of the coupling coefficient between the gain medium and a ring resonator of the laser. Another embodiment provides a tunable laser including two Mach-Zehnder interferometers in series and a reflector coupled to a gain medium.
MacKinnon, Barry A.; Ruffell, John P.
2011-06-01
In 1953 the Raytheon CK722 transistor was priced at $7.60. Based upon this, an Intel Xeon Quad Core processor containing 820,000,000 transistors should list at $6.2 billion. Particle accelerator technology plays an important part in the remarkable story of why that Intel product can be purchased today for a few hundred dollars. Most people of the mid twentieth century would be astonished at the ubiquity of semiconductors in the products we now buy and use every day. Though relatively expensive in the nineteen fifties they now exist in a wide range of items from high-end multicore microprocessors like the Intel product to disposable items containing 'only' hundreds or thousands like RFID chips and talking greeting cards. This historical development has been fueled by continuous advancement of the several individual technologies involved in the production of semiconductor devices including Ion Implantation and the charged particle beamlines at the heart of implant machines. In the course of its 40 year development, the worldwide implanter industry has reached annual sales levels around $2B, installed thousands of dedicated machines and directly employs thousands of workers. It represents in all these measures, as much and possibly more than any other industrial application of particle accelerator technology. This presentation discusses the history of implanter development. It touches on some of the people involved and on some of the developmental changes and challenges imposed as the requirements of the semiconductor industry evolved.
NASA Astrophysics Data System (ADS)
MacKinnon, Barry A.; Ruffell, John P.
2011-06-01
In 1953 the Raytheon CK722 transistor was priced at 7.60. Based upon this, an Intel Xeon Quad Core processor containing 820,000,000 transistors should list at 6.2 billion! Particle accelerator technology plays an important part in the remarkable story of why that Intel product can be purchased today for a few hundred dollars. Most people of the mid twentieth century would be astonished at the ubiquity of semiconductors in the products we now buy and use every day. Though relatively expensive in the nineteen fifties they now exist in a wide range of items from high-end multicore microprocessors like the Intel product to disposable items containing `only' hundreds or thousands like RFID chips and talking greeting cards. This historical development has been fueled by continuous advancement of the several individual technologies involved in the production of semiconductor devices including Ion Implantation and the charged particle beamlines at the heart of implant machines. In the course of its 40 year development, the worldwide implanter industry has reached annual sales levels around 2B, installed thousands of dedicated machines and directly employs thousands of workers. It represents in all these measures, as much and possibly more than any other industrial application of particle accelerator technology. This presentation discusses the history of implanter development. It touches on some of the people involved and on some of the developmental changes and challenges imposed as the requirements of the semiconductor industry evolved.
NASA Astrophysics Data System (ADS)
Vernek, Edson; Ruiz-Tijerina, David; da Silva, Luis D.; Egues, José Carlos
2015-09-01
Quantum dot attached to topological wires has become an interesting setup to study Majorana bound state in condensed matter[1]. One of the major advantage of using a quantum dot for this purpose is that it provides a suitable manner to study the interplay between Majorana bound states and the Kondo effect. Recently we have shown that a non-interacting quantum dot side-connected to a 1D topological superconductor and to metallic normal leads can sustain a Majorana mode even when the dot is empty. This is due to the Majorana bound state of the wire leaking into the quantum dot. Now we investigate the system for the case in which the quantum dot is interacting[3]. We explore the signatures of a Majorana zero-mode leaking into the quantum dot, using a recursive Green's function approach. We then study the Kondo regime using numerical renormalization group calculations. In this regime, we show that a "0.5" contribution to the conductance appears in system due to the presence of the Majorana mode, and that it persists for a wide range of the dot parameters. In the particle-hole symmetric point, in which the Kondo effect is more robust, the total conductance reaches 3e^2/2h, clearly indicating the coexistence of a Majorana mode and the Kondo resonance in the dot. However, the Kondo effect is suppressed by a gate voltage that detunes the dot from its particle-hole symmetric point as well as by a Zeeman field. The Majorana mode, on the other hand, is almost insensitive to both of them. We show that the zero-bias conductance as a function of the magnetic field follows a well-known universal curve. This can be observed experimentally, and we propose that this universality followed by a persistent conductance of 0.5,e^2/h are evidence for the presence of Majorana-Kondo physics. This work is supported by the Brazilians agencies FAPESP, CNPq and FAPEMIG. [1] A. Y. Kitaev, Ann.Phys. {bf 303}, 2 (2003). [2] E. Vernek, P.H. Penteado, A. C. Seridonio, J. C. Egues, Phys. Rev. B {bf
Landau quantization and spin-momentum locking in topological Kondo insulators
NASA Astrophysics Data System (ADS)
Schlottmann, P.
2016-05-01
SmB6 has been predicted to be a strong topological Kondo insulator and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. Quantum oscillations and ARPES measurements revealed several Dirac cones on the (001) and (101) surfaces of the crystal. We considered three types of surface Dirac cones with an additional parabolic dispersion and studied their Landau quantization and the expectation value of the spin of the electrons. The Landau quantization is quite similar in all three cases and would give rise to very similar de Haas-van Alphen oscillations. The spin-momentum locking, on the other hand, differs dramatically. Without the additional parabolic dispersion the spins are locked in the plane of the surface. The parabolic dispersion, however, produces a gradual canting of the spins out of the surface plane.
Kondo effect and thermoelectric transport in CePd3Be x
NASA Astrophysics Data System (ADS)
Gumeniuk, Roman; Schnelle, Walter; Kvashnina, Kristina O.; Leithe-Jasper, Andreas
2016-04-01
The physical properties of the series CePd3Be x (0≤slant x≤slant 0.47 ) have been studied. Introducing Be into CePd3 results in a drastic reduction of the Seebeck coefficient from 100 μV K-1 at 300 K to -2 μV K-1, respectively. Paramagnetism of Ce3+ free ions and metallic conduction dominate the physical properties. A structural transition at x = 0.25 is accompanied by a significant lowering of the Kondo temperature and leads to a successive suppression of the thermoelectric performance of CePd3Be x with increasing x.
NASA Astrophysics Data System (ADS)
Perfetto, E.; Stefanucci, G.
2012-08-01
We show that the energy functional of ensemble density functional theory (DFT) [Perdew , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.49.1691 49, 1691 (1982)] in systems with attractive interactions is a convex function of the fractional particle number N and is given by a series of straight lines joining a subset of ground-state energies. As a consequence the exchange-correlation (XC) potential is not discontinuous for all N. We highlight the importance of this exact result in the ensemble-DFT description of the negative-U Anderson model. In the atomic limit the discontinuity of the XC potential is missing for odd N while for finite hybridizations the discontinuity at even N is broadened. We demonstrate that the inclusion of these properties in any approximate XC potential is crucial to reproduce the characteristic signatures of the charge-Kondo effect in the conductance and charge susceptibility.
Variational Monte Carlo approach to the two-dimensional Kondo lattice model
NASA Astrophysics Data System (ADS)
Asadzadeh, Mohammad Zhian; Becca, Federico; Fabrizio, Michele
2013-05-01
We study the phase diagram of the Kondo lattice model with nearest-neighbor hopping in the square lattice by means of the variational Monte Carlo technique. Specifically, we analyze a wide class of variational wave functions that allow magnetic and superconducting order parameters, so as to assess the possibility that superconductivity might emerge close to the magnetic instability, as is often observed in heavy-fermion systems. Indeed, we do find evidence of d-wave superconductivity in the paramagnetic sector, i.e., when magnetic order is not allowed in the variational wave function. However, when magnetism is allowed, it completely covers the superconducting region, which thus disappears from the phase diagram.
Phase diagram of the Kondo lattice model on the kagome lattice
NASA Astrophysics Data System (ADS)
Ghosh, Shivam; O'Brien, Patrick; Henley, Christopher L.; Lawler, Michael J.
2016-01-01
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the underscreened kagome Kondo lattice model. At weak coupling, we show that incommensurate noncoplanar multiwave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduce competing interactions between the spins. At strong coupling, we find that such a complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling only commensurate orders seem to survive, but these orders still include noncoplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.
NASA Astrophysics Data System (ADS)
Ślebarski, A.; Goraus, J.
2012-12-01
We present the Ce 3d x-ray photoemission (XPS) spectra for CeM2Al10 (M=Ru, Os, Fe) from which we determined the on-site hybridization between the f and conduction electron states, Δcf, and the 4f-level occupancy, nf. Those parameters have been obtained using the Gunnarsson-Schönhammer approach. We found Δcf stronger for the Kondo insulator CeFe2Al10 than for the remaining compounds with Ru and Os. We discuss the type of behaviour of CeM2Al10 on the base of the earlier theoretical phase diagram obtained within the Anderson-lattice model.
Low-temperature magnetic fluctuations in the Kondo insulator SmB6
NASA Astrophysics Data System (ADS)
Biswas, P. K.; Salman, Z.; Neupert, T.; Morenzoni, E.; Pomjakushina, E.; von Rohr, F.; Conder, K.; Balakrishnan, G.; Hatnean, M. Ciomaga; Lees, M. R.; Paul, D. McK.; Schilling, A.; Baines, C.; Luetkens, H.; Khasanov, R.; Amato, A.
2014-04-01
We present the results of a systematic investigation of the magnetic properties of the three-dimensional Kondo topological insulator SmB6 using magnetization and muon-spin relaxation/rotation (μSR) measurements. The μSR measurements exhibit magnetic field fluctuations in SmB6 below ˜15 K due to electronic moments present in the system. However, no evidence for magnetic ordering is found down to 19 mK. The observed magnetism in SmB6 is homogeneous in nature throughout the full volume of the sample. Bulk magnetization measurements on the same sample show consistent behavior. The agreement between μSR, magnetization, and NMR results strongly indicate the appearance of intrinsic bulk magnetic in-gap states associated with fluctuating magnetic fields in SmB6 at low temperature.
NASA Astrophysics Data System (ADS)
Hoshino, Shintaro; Yada, Keiji; Tanaka, Yukio
2016-06-01
Junction systems of odd-frequency (OF) superconductors are investigated based on a mean-field Hamiltonian formalism. One-dimensional two-channel Kondo lattice (TCKL) is taken as a concrete example of OF superconductors. Properties of normal and Andreev reflections are examined in a normal metal/superconductor junction. Unlike conventional superconductors, normal reflection is always present due to the normal self energy that necessarily appears in the present OF pairing state. The conductance reflects the difference between repulsive and attractive potentials located at the interface, which is in contrast with the preexisting superconducting junctions. Josephson junction is also constructed by connecting TCKL with the other types of superconductors. The results can be understood from symmetry of the induced Cooper pairs at the edge in the presence of spin/orbital symmetry breaking. It has also been demonstrated that the symmetry argument for Cooper pairs is useful in explaining Meissner response in bulk.
Spiral to ferromagnetic transition in a Kondo lattice model with a double-well potential
NASA Astrophysics Data System (ADS)
Caro, R. C.; Franco, R.; Silva-Valencia, J.
2016-02-01
Using the density matrix renormalization group method, we study a system of 171Yb atoms confined in a one-dimensional optical lattice. The atoms in the 1So state undergo a double-well potential, whereas the atoms in the 3P0 state are localized. This system is modelled by the Kondo lattice model plus a double-well potential for the free carries. We obtain phase diagrams composed of ferromagnetic and spiral phases, where the critical points always increase with the interwell tunneling parameter. We conclude that this quantum phase transition can be tuned by the double-well potential parameters as well as by the common parameters: local coupling and density.
Constructive influence of the induced electron pairing on the Kondo state
NASA Astrophysics Data System (ADS)
Domański, T.; Weymann, I.; Barańska, M.; Górski, G.
2016-03-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon.
Spin-orbital and spin Kondo effects in parallel coupled quantum dots
NASA Astrophysics Data System (ADS)
Krychowski, D.; Lipiński, S.
2016-02-01
Strong electron correlations and interference effects are discussed in parallel-coupled single-level or orbitally doubly degenerate quantum dots. The finite-U mean-field slave boson approach is used to study many-body effects. The analysis is carried out in a wide range of parameter space including both atomic-like and molecular-like Kondo regimes and taking into account various perturbations, like interdot tunneling, interdot interaction, mixing of the electrode channels, and exchange interaction. We also discuss the influence of singularities of electronic structure and the impact of polarization of electrodes. Special attention is paid to potential spintronic applications of these systems showing how current polarization can be controlled by adjusting interference conditions and correlations by gate voltage. Simple proposals of double dot spin valve and bipolar electrically tunable spin filter are presented.
Low energy properties of the Kondo chain in the RKKY regime
D. H. Schimmel; Tsvelik, A. M.; Yevtushenko, O. M.
2016-05-03
We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman–Kittel–Kasuya–Yosida interaction. As has been recently shown (Tsvelik and Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing amore » competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. In conclusion, we discuss applicability of our theory and possible experiments which could support the theoretical findings.« less
Two-dimensional Fermi surfaces in Kondo insulator SmB₆.
Li, G; Xiang, Z; Yu, F; Asaba, T; Lawson, B; Cai, P; Tinsman, C; Berkley, A; Wolgast, S; Eo, Y S; Kim, Dae-Jeong; Kurdak, C; Allen, J W; Sun, K; Chen, X H; Wang, Y Y; Fisk, Z; Li, Lu
2014-12-01
In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6. PMID:25477456
Universality and Scaling in a Charge Two-Channel Kondo Device
NASA Astrophysics Data System (ADS)
Mitchell, A. K.; Landau, L. A.; Fritz, L.; Sela, E.
2016-04-01
We study a charge two-channel Kondo model, demonstrating that recent experiments [Z. Iftikhar et al, Nature (London) 526, 233 (2015)] realize an essentially perfect quantum simulation—not just of its universal physics, but also nonuniversal effects away from the scaling limit. Numerical renormalization group (RG) calculations yield conductance line shapes encoding RG flow to a critical point involving a free Majorana fermion. By mimicking the experimental protocol, the experimental curve is reproduced quantitatively over 9 orders of magnitude, although we show that far greater bandwidth/temperature separation is required to obtain the universal result. Fermi liquid instabilities are also studied: In particular, our exact analytic results for nonlinear conductance provide predictions away from thermal equilibrium, in the regime of existing experiments.
Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB_{6}
Fuhrman, W. T.; Leiner, Jonathan C.; Nikolić, P.; Granroth, Garrett E.; Stone, Matthew B.; Lumsden, Mark D.; DeBeer-Schmitt, Lisa M.; Alekseev, Pavel A.; Mignot, Jean-Michel; Koohpayeh, S. M.; Cottingham, P.; Phelan, William Adam; Schoop, L.; McQueen, T. M.; Broholm, C.
2015-01-21
In this paper, using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB_{6} and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering. Finally, we find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.
Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6
Fuhrman, W. T.; Leiner, Jonathan C.; Nikolić, P.; Granroth, Garrett E.; Stone, Matthew B.; Lumsden, Mark D.; DeBeer-Schmitt, Lisa M.; Alekseev, Pavel A.; Mignot, Jean-Michel; Koohpayeh, S. M.; et al
2015-01-21
In this paper, using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB6 and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering.more » Finally, we find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.« less
Low energy properties of the Kondo chain in the RKKY regime
NASA Astrophysics Data System (ADS)
Schimmel, D. H.; Tsvelik, A. M.; Yevtushenko, O. M.
2016-05-01
We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman–Kittel–Kasuya–Yosida interaction. As has been recently shown (Tsvelik and Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing a competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. We discuss applicability of our theory and possible experiments which could support the theoretical findings.
Constructive influence of the induced electron pairing on the Kondo state.
Domański, T; Weymann, I; Barańska, M; Górski, G
2016-01-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681
Constructive influence of the induced electron pairing on the Kondo state
Domański, T.; Weymann, I.; Barańska, M.; Górski, G.
2016-01-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681
Yang, Yifeng; Urbano, Ricardo; Nicholas, Curro; Pines, David
2009-01-01
We report Knight shift experiments on the superconducting heavy electron material CeCoIn{sub 5} that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the {sup 115}In nuclear quadrupole resonance (NQR) spin-lattice relaxation rate T{sub 1}{sup -1} measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point (QCP) located at slightly negative pressure in CeCoIn{sub 5} and provide additional evidence for significant similarities between the heavy electron materials and the high T{sub c} cuprates.
Low temperature transport properties of the quadrupolar Kondo lattice system PrTi2Al20
NASA Astrophysics Data System (ADS)
Sakai, Akito; Nakatsuji, Satoru
2013-08-01
We have investigated the low temperature transport properties of the cubic Γ3 compound PrTi2Al20. This is a quadrupolar Kondo lattice system where the nongmagnetic quadrupoles, which form a long-range order at low temperatures, have strong hybridization with the conduction electrons. A sharp drop of the resistivity due to a ferroquadrupole ordering is observed at T Q = 2.0 K. The T 2 dependence of the resistivity and the large Sommerfeld coefficient γ above T Q suggest the formation of a heavy-fermion state. The temperature dependence of the resistivity below T Q does not show a power law but exponential law behavior, indicating the emergence of an anisotropy gap Δ in the collective mode associated with the ferroquadrupole order below T Q. The Fisher-Langer relation holds around T Q, suggesting the higher order scattering processes than those in Born approximation are not dominant for this ferroquadrupole ordering.
Large high quality crystals of the Topological Kondo Insulator, SmB6
NASA Astrophysics Data System (ADS)
Balakrishnan, Geetha; Ciomaga Hatnean, Monica; Paul, D. Mck.; Lees, M. R.
2014-03-01
SmB6 has been predicted to be a Topological Kondo Insulator, the first strongly correlated heavy fermion material to exhibit topological surface states. High quality crystals are necessary to investigate the topological properties of this material. Single crystal growth of the rare earth hexaboride, SmB6, has been carried out by the floating zone technique using a high power xenon arc lamp image furnace. Large, high quality single-crystals are obtained by this technique. The crystals produced by the floating zone technique are free of contamination from flux materials and have been characterised by resistivity and magnetisation measurements. These crystals are ideally suited for the investigation of both the surface and bulk properties of SmB6.
Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6
NASA Astrophysics Data System (ADS)
Hatnean, M. Ciomaga; Lees, M. R.; Paul, D. M. K.; Balakrishnan, G.
2013-10-01
SmB6 has recently been predicted to be a Topological Kondo Insulator, the first strongly correlated heavy fermion material to exhibit topological surface states. High quality crystals are necessary to investigate the topological properties of this material. Single crystal growth of the rare earth hexaboride, SmB6, has been carried out by the floating zone technique using a high power xenon arc lamp image furnace. Large, high quality single-crystals are obtained by this technique. The crystals produced by the floating zone technique are free of contamination from flux materials and have been characterised by resistivity and magnetisation measurements. These crystals are ideally suited for the investigation of both the surface and bulk properties of SmB6.
Quantum phase transition and protected ideal transport in a Kondo chain
Tsvelik, A. M.; Yevtushenko, O. M.
2015-11-30
We study the low energy physics of a Kondo chain where electrons from a one-dimensional band interact with magnetic moments via an anisotropic exchange interaction. It is demonstrated that the anisotropy gives rise to two different phases which are separated by a quantum phase transition. In the phase with easy plane anisotropy, Z2 symmetry between sectors with different helicity of the electrons is broken. As a result, localization effects are suppressed and the dc transport acquires (partial) symmetry protection. This effect is similar to the protection of the edge transport in time-reversal invariant topological insulators. The phase with easy axis anisotropy corresponds to the Tomonaga-Luttinger liquid with a pronounced spin-charge separation. The slow charge density wave modes have no protection against localizatioin.
Quantum phase transition and protected ideal transport in a Kondo chain
Tsvelik, A. M.; Yevtushenko, O. M.
2015-11-30
We study the low energy physics of a Kondo chain where electrons from a one-dimensional band interact with magnetic moments via an anisotropic exchange interaction. It is demonstrated that the anisotropy gives rise to two different phases which are separated by a quantum phase transition. In the phase with easy plane anisotropy, Z2 symmetry between sectors with different helicity of the electrons is broken. As a result, localization effects are suppressed and the dc transport acquires (partial) symmetry protection. This effect is similar to the protection of the edge transport in time-reversal invariant topological insulators. The phase with easy axismore » anisotropy corresponds to the Tomonaga-Luttinger liquid with a pronounced spin-charge separation. The slow charge density wave modes have no protection against localizatioin.« less
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts. PMID:27376190
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics
NASA Astrophysics Data System (ADS)
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
Fermionology in the Kondo-Heisenberg model: the case of CeCoIn5
NASA Astrophysics Data System (ADS)
Zhong, Yin; Zhang, Lan; Lu, Han-Tao; Luo, Hong-Gang
2015-09-01
The Fermi surface of heavy electron systems plays a fundamental role in understanding their variety of puzzling phenomena, for example, quantum criticality, strange metal behavior, unconventional superconductivity and even enigmatic phases with yet unknown order parameters. The spectroscopy measurement of the typical heavy fermion superconductor CeCoIn5 has demonstrated multi-Fermi surface structure, which has not been studied in detail theoretically in a model system like the Kondo-Heisenberg model. In this work, we take a step toward such a theoretical model by revisiting the Kondo-Heisenberg model. It is found that the usual self-consistent calculation cannot reproduce the fermionology of the experimental observation of the system due to the sign binding between the hopping of the conduction electrons and the mean-field valence-bond order. To overcome such inconsistency, the mean-field valence-bond order is considered as a free/fitting parameter to correlate them with real-life experiments as performed in recent experiments [M.P. Allan, F. Massee, D.K. Morr, J. Van Dyke, A.W. Rost, A.P. Mackenzie, C. Petrovic, J.C. Davis, Nat. Phys. 9, 468 (2013); J. Van Dyke, F. Massee, M.P. Allan, J.C. Davis, C. Petrovic, D.K. Morr, Proc. Natl. Acad. Sci. 111, 11663 (2014)], which also explicitly reflects the intrinsic dispersion of local electrons observed in experimental measurements. Given the fermionology, the calculated effective mass enhancement, entropy, superfluid density and Knight shift are all in qualitative agreement with the experimental results of CeCoIn5, which confirms our assumption. Our result supports a d_{x^2 - y^2 }-wave pairing structure in the heavy fermion material CeCoIn5.
Theory of hydrogen in semiconductors
Walle, C.G. van de
1998-12-31
This paper treats the subject of hydrogen in semiconductors from various perspectives. First, a brief historical overview is given. Then, some basic principles governing the interaction between hydrogen and semiconductors are outlined. Finally, specific examples will emphasize the impact of hydrogen on technological applications. While the general treatment applies to interactions of hydrogen with any semiconductor, the applications will focus mainly on hydrogen interacting with silicon.
New developments in power semiconductors
NASA Technical Reports Server (NTRS)
Sundberg, G. R.
1983-01-01
This paper represents an overview of some recent power semiconductor developments and spotlights new technologies that may have significant impact for aircraft electric secondary power. Primary emphasis will be on NASA-Lewis-supported developments in transistors, diodes, a new family of semiconductors, and solid-state remote power controllers. Several semiconductor companies that are moving into the power arena with devices rated at 400 V and 50 A and above are listed, with a brief look at a few devices.
NASA Astrophysics Data System (ADS)
Pixley, J. H.; Yu, Rong; Si, Qimiao
2014-10-01
Considerable recent theoretical and experimental effort has been devoted to the study of quantum criticality and novel phases of antiferromagnetic heavy-fermion metals. In particular, quantum phase transitions have been discovered in heavy-fermion compounds with geometrical frustration. These developments have motivated us to study the competition between the Ruderman-Kittel-Kasuya-Yosida and Kondo interactions on the Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as a function of magnetic frustration and Kondo coupling within a slave-fermion approach. Pertinent phases include the valence bond solid and heavy Fermi liquid. In the presence of antiferromagnetic order, our zero-temperature phase diagram is remarkably similar to the global phase diagram proposed earlier based on general grounds. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related compounds.
Method of passivating semiconductor surfaces
Wanlass, M.W.
1990-06-19
A method is described for passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.
Method of passivating semiconductor surfaces
Wanlass, Mark W.
1990-01-01
A method of passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.
Antiferromagnetic order and Kondo-lattice behavior in single-crystalline Ce2RhSi3
NASA Astrophysics Data System (ADS)
Szlawska, M.; Kaczorowski, D.; Ślebarski, A.; Gulay, L.; Stępień-Damm, J.
2009-04-01
Single crystal of Ce2RhSi3 was investigated by means of x-ray diffraction, magnetization, electrical resistivity, and heat-capacity measurements. Moreover, its electronic structure was studied by cerium core-level x-ray photoemission spectroscopy. The results revealed that Ce2RhSi3 is an antiferromagnetic Kondo lattice due to the presence of stable trivalent Ce ions.
Semiconductor nanorod liquid crystals
Li, Liang-shi; Walda, Joost; Manna, Liberato; Alivisatos, A. Paul
2002-01-28
Rodlike molecules form liquid crystalline phases with orientational order and positional disorder. The great majority of materials in which liquid crystalline phases have been observed are comprised of organic molecules or polymers, even though there has been continuing and growing interest in inorganic liquid crystals. Recent advances in the control of the sizes and shapes of inorganic nanocrystals allow for the formation of a broad class of new inorganic liquid crystals. Here we show the formation of liquid crystalline phases of CdSe semiconductor nanorods. These new liquid crystalline phases may have great importance for both application and fundamental study.
Semiconductor cooling apparatus
NASA Technical Reports Server (NTRS)
Banks, Bruce A. (Inventor); Gaier, James R. (Inventor)
1993-01-01
Gas derived graphite fibers generated by the decomposition of an organic gas are joined with a suitable binder. This produces a high thermal conductivity composite material which passively conducts heat from a source, such as a semiconductor, to a heat sink. The fibers may be intercalated. The intercalate can be halogen or halide salt, alkaline metal, or any other species which contributes to the electrical conductivity improvement of the graphite fiber. The fibers are bundled and joined with a suitable binder to form a high thermal conductivity composite material device. The heat transfer device may also be made of intercalated highly oriented pyrolytic graphite and machined, rather than made of fibers.
Semiconductor superlattice photodetectors
NASA Technical Reports Server (NTRS)
Chuang, S. L.; Hess, K.; Coleman, J. J.; Leburton, J. P.
1984-01-01
A superlattice photomultiplier and a photodetector based on the real space transfer mechanism were studied. The wavelength for the first device is of the order of a micron or flexible corresponding to the bandgap absorption in a semiconductor. The wavelength for the second device is in the micron range (about 2 to 12 microns) corresponding to the energy of the conduction band edge discontinuity between an Al/(sub x)Ga(sub 1-x)As and GaAs interface. Both devices are described.
Semiconductor structure and devices
NASA Technical Reports Server (NTRS)
Dinkel, Nancy A. (Inventor); Goldstein, Bernard (Inventor); Ettenberg, Michael (Inventor)
1987-01-01
Semiconductor devices such as lasers which include a substrate with a channel therein with a clad layer overlying the substrate and filling the channel exhibit irregularities such as terraces in the surface of the clad layer which are detrimental to device performance. These irregularities are substantially eliminated by forming the channel in a surface of a buffer layer greater than about 4 micrometers thick on the substrate and forming the clad layer over the buffer layer and the channel. CW lasers incorporating the principles of the invention exhibit the highest output power in a single spatial mode and maximum output power which have been observed to date.
Isotopically controlled semiconductors
Haller, Eugene E.
2001-12-21
Semiconductor bulk crystals and multilayer structures with controlled isotopic composition have attracted much scientific and technical interest in the past few years. Isotopic composition affects a large number of physical properties, including phonon energies and lifetimes, bandgaps, the thermal conductivity and expansion coefficient and spin-related effects. Isotope superlattices are ideal media for self-diffusion studies. In combination with neutron transmutation doping, isotope control offers a novel approach to metal-insulator transition studies. Spintronics, quantum computing and nanoparticle science are emerging fields using isotope control.
Layered semiconductor neutron detectors
Mao, Samuel S; Perry, Dale L
2013-12-10
Room temperature operating solid state hand held neutron detectors integrate one or more relatively thin layers of a high neutron interaction cross-section element or materials with semiconductor detectors. The high neutron interaction cross-section element (e.g., Gd, B or Li) or materials comprising at least one high neutron interaction cross-section element can be in the form of unstructured layers or micro- or nano-structured arrays. Such architecture provides high efficiency neutron detector devices by capturing substantially more carriers produced from high energy .alpha.-particles or .gamma.-photons generated by neutron interaction.
Composite Semiconductor Substrates
NASA Technical Reports Server (NTRS)
Nouhi, Akbar; Radhakrishnan, Gouri; Katz, Joseph; Koliwad, Kris
1989-01-01
Epitaxial structure of three semiconductor materials - silicon, gallium arsenide, and cadmium telluride - makes possible integrated monolithic focal-plane arrays of photodectors. Silicon layer contains charge-coupled devices, gallium arsenide layer contains other fast electronic circuitry, and cadmium telluride layer serves as base for array of mercury cadmium telluride infrared sensors. Technique effectively combines two well-established techniques; metalorganic chemical-vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). Multilayer structure includes HgCdTe light sensors with Si readout devices and GaAs signal-processing circuits. CdTe layer provides base for building up HgCdTe layer.
NASA Astrophysics Data System (ADS)
Du, Shixuan
Control over charge and spin states at the single molecule level is crucial not only for a fundamental understanding of charge and spin interactions but also represents a prerequisite for development of molecular electronics and spintronics. In this talk, I will talk about the extended spin distribution in space beyond the central Mn ion, and onto the non-magnetic constituent atoms of the MnPc molecule. This extended spin distribution results in an extended Kondo effect, which can be explained by spin polarization induced by symmetry breaking of the molecular framework, as confirmed by DFT calculations. Measuring the evolution of the Kondo splitting with applied magnetic fields at different atomic sites, we find a spatial variation of the g-factor within a single molecule for the first time. The existence of atomic site-dependent g-factors can be attributed to specific molecular orbitals distributed over the entire molecule. This work not only open up a new opportunity for quantum information recording, but also provide a new route to explore the internal electronic and spin structure of complex molecules, hard to achieve otherwise. (L. W. Liu et al., Phys. Rev. Lett. 2015, 114, 126601. In collaboration with Liwei Liu, Kai Yang, Yuhang Jiang, Li Gao, Qi Liu, Boqun Song, Wende Xiao, Haitao Zhou, Hongjun Gao in CAS, Min Ouyang in MU, and A.H. Castro Neto in SNU.) Revealing the Atomic Site-Dependent g Factor within a Single Magnetic Molecule via the Extended Kondo Effect.
Non-Kondo-like electronic structure in the correlated rare-earth hexaboride YbB6
Neupane, Madhab; Xu, Su -Yang; Alidoust, Nasser; Bian, Guang; Kim, D. J.; Liu, Chang; Belopolski, I.; Chang, T. -R.; Jeng, H. -T.; Durakiewicz, T.; et al
2015-01-07
Here, we present angle-resolved photoemission studies on the rare-earth-hexaboride YbB6, which has recently been predicted to be a topological Kondo insulator. Our data do not agree with the prediction and instead show that YbB6 exhibits a novel topological insulator state in the absence of a Kondo mechanism. We find that the Fermi level electronic structure of YbB6 has three 2D Dirac cone like surface states enclosing the Kramers’s points, while the f orbital that would be relevant for the Kondo mechanism is ~1 eV below the Fermi level. Our first-principles calculation shows that the topological state that we observe inmore » YbB6 is due to an inversion between Yb d and B p bands. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials.« less
Patil, S.; Generalov, A.; Güttler, M.; Kushwaha, P.; Chikina, A.; Kummer, K.; Rödel, T. C.; Santander-Syro, A. F.; Caroca-Canales, N.; Geibel, C.; Danzenbächer, S.; Kucherenko, Yu.; Laubschat, C.; Allen, J. W.; Vyalikh, D. V.
2016-01-01
The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f 0 peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f 15/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices. PMID:26987899
Vernek, E.; Büsser, C. A.; Anda, E. V.; Feiguin, A. E.; Martins, G. B.
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 the 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.
Patil, S; Generalov, A; Güttler, M; Kushwaha, P; Chikina, A; Kummer, K; Rödel, T C; Santander-Syro, A F; Caroca-Canales, N; Geibel, C; Danzenbächer, S; Kucherenko, Yu; Laubschat, C; Allen, J W; Vyalikh, D V
2016-01-01
The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f (0) peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f (1)5/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices. PMID:26987899
From Kondo behavior to high temperature superconductivity in Sr(Ni1-xFex)2As2
NASA Astrophysics Data System (ADS)
Wakeham, Nicholas; Ni, Ni; Bauer, Eric; Thompson, Joe; Ronning, Filip
SrFe2As2 has an antiferromagnetic groundstate at ambient pressure that can be suppressed by chemical doping or pressure to produce unconventional superconductivity. SrNi2As2 is a non-magnetic conventional superconductor with Tc of 0.6 K. It has been shown that in Sr(Ni1-xFex)2As2 there is a dome of superconductivity between x = 0 . 95 and x = 0 . 9 . However, little is known about this doping series for small x values. We will present the study of the thermodynamic and transport properties of the doping series of Sr(Ni(1-x)Fex)2As2 for x <= 0 . 6 . In the dilute Fe limit (x <= 0 . 01) we find strong evidence for single-ion Kondo behaviour. As the concentration of Fe is increased, Fe-Fe interaction effects become significant and the Kondo scale increases. For 0 . 2 <= x <= 0 . 6 magnetic susceptibility measurements show the presence of a spin glass transition. The presence of Kondo behaviour in Sr(Ni(1-x)Fex)2As2 indicates the formation of local moments interacting with conduction electrons. Therefore, we will address the relevance of this result to the discussion of the itineracy of the magnetism in SrFe2As2, as well as the observed enhancement of the effective mass seen in many pnictide compounds.
NASA Astrophysics Data System (ADS)
Maurand, Romain; Meng, Tobias; Bonet, Edgar; Florens, Serge; Marty, Laëtitia; Wernsdorfer, Wolfgang
2012-01-01
We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic) dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.
NASA Astrophysics Data System (ADS)
Eder, R.; Wróbel, P.
2011-07-01
We study the two-dimensional Kondo lattice model with an additional Heisenberg exchange between localized spins. In a first step, we use mean-field theory with two order parameters. The first order parameter is a complex pairing amplitude between conduction electrons and localized spins that describes condensation of Kondo (or Zhang-Rice) singlets. A nonvanishing value implies that the localized spins contribute to the Fermi surface volume. The second-order parameter describes singlet pairing between the localized spins and competes with the Kondo-pairing order parameter. Reduction of the carrier density in the conduction band reduces the energy gain due to the formation of the large Fermi surface and induces a phase transition to a state with strong singlet correlations between the localized spins and a Fermi surface that comprises only the conduction electrons. The model thus shows a doping driven change of its Fermi surface volume. At intermediate doping and low temperature, there is a phase where both order parameters coexist, which has a gapped large Fermi surface and dx2-y2 superconductivity. The theory thus qualitatively reproduces the phase diagram of cuprate superconductors. In the second part of this paper, we show how the two phases with different Fermi surface volume emerge in a strong-coupling theory applicable in the limit of large Kondo exchange. The large Fermi surface phase corresponds to a “vacuum” of localized Kondo singlets with uniform phase, and the quasiparticles are spin-1/2 charge fluctuations around this fully paired state. In the small Fermi surface phase, the quasiparticles correspond to propagating Kondo singlets or triplets whereby the phase of a given Kondo singlet corresponds to its momentum. In this picture, a phase transition occurs for low filling of the conduction band as well.
NASA Astrophysics Data System (ADS)
Bellac, Michel Le
2014-11-01
In this chapter, we move on to the case of fermions, and we shall find out that fermions are no less interesting than bosons! In practice, electrons are the most important example of fermions, because they are responsible for electrical conductivity in metals and semiconductors. It is impossible to understand a phenomenon as familiar as electrical conductivity without appealing to quantum physics. Two properties play a fundamental role: first the propagation of electron waves in crystal lattices, and second the Pauli exclusion principle, which is a consequence of the fermionic character of the electrons. In Section 6.1, we introduce electron wave propagation in crystals which gives rise to the phenomenon of energy bands, and we describe the filling of these bands according to the Pauli principle. These results will be used in Section 6.2 to describe the electronic properties of semiconductors, on which almost all our modern technology (laser diodes, optical fiber communication, computers, smartphones and so forth) is grounded. Finally, in Sections 6.3 and 6.4, we shall describe the principles of light emitting diodes (LEDs) and laser diodes.
Doped semiconductor nanocrystal junctions
Borowik, Ł.; Mélin, T.; Nguyen-Tran, T.; Roca i Cabarrocas, P.
2013-11-28
Semiconductor junctions are the basis of electronic and photovoltaic devices. Here, we investigate junctions formed from highly doped (N{sub D}≈10{sup 20}−10{sup 21}cm{sup −3}) silicon nanocrystals (NCs) in the 2–50 nm size range, using Kelvin probe force microscopy experiments with single charge sensitivity. We show that the charge transfer from doped NCs towards a two-dimensional layer experimentally follows a simple phenomenological law, corresponding to formation of an interface dipole linearly increasing with the NC diameter. This feature leads to analytically predictable junction properties down to quantum size regimes: NC depletion width independent of the NC size and varying as N{sub D}{sup −1/3}, and depleted charge linearly increasing with the NC diameter and varying as N{sub D}{sup 1/3}. We thus establish a “nanocrystal counterpart” of conventional semiconductor planar junctions, here however valid in regimes of strong electrostatic and quantum confinements.
Doping semiconductor nanocrystals.
Erwin, Steven C; Zu, Lijun; Haftel, Michael I; Efros, Alexander L; Kennedy, Thomas A; Norris, David J
2005-07-01
Doping--the intentional introduction of impurities into a material--is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn can be incorporated into nanocrystals of CdS and ZnSe (refs 7-9), but not into CdSe (ref. 12)--despite comparable bulk solubilities of near 50 per cent. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to 'self-purification', an allegedly intrinsic mechanism whereby impurities are expelled. Here we show instead that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth. We find that adsorption--and therefore doping efficiency--is determined by three main factors: surface morphology, nanocrystal shape, and surfactants in the growth solution. Calculated Mn adsorption energies and equilibrium shapes for several nanocrystals lead to specific doping predictions. These are confirmed by measuring how the Mn concentration in ZnSe varies with nanocrystal size and shape. Finally, we use our predictions to incorporate Mn into previously undopable CdSe nanocrystals. This success establishes that earlier difficulties with doping are not intrinsic, and suggests that a variety of doped nanocrystals--for applications from solar cells to spintronics--can be anticipated. PMID:16001066
Semiconductor cylinder fiber laser
NASA Astrophysics Data System (ADS)
Sandupatla, Abhinay; Flattery, James; Kornreich, Philipp
2015-12-01
We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In2Te3 semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2 μm, an outside diameter of 126 μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In2Te3 gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of -73 dB.
Isotopically engineered semiconductors
NASA Astrophysics Data System (ADS)
Haller, E. E.
1995-04-01
Scientific interest, technological promise, and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This review of mostly recent activities begins with an introduction to some past classical experiments which have been performed on isotopically controlled semiconductors. A review of the natural isotopic composition of the relevant elements follows. Some materials aspects resulting in part from the high costs of enriched isotopes are discussed next. Raman spectroscopy studies with a number of isotopically pure and deliberately mixed Ge bulk crystals show that the Brillouin-zone-center optical phonons are not localized. Their lifetime is almost independent of isotopic disorder, leading to homogeneous Raman line broadening. Studies with short period isotope superlattices consisting of alternating layers of n atomic planes of 70Ge and 74Ge reveal a host of zone-center phonons due to Brillouin-zone folding. At n≳40 one observes two phonon lines at frequencies corresponding to the bulk values of the two isotopes. In natural diamond, isotope scattering of the low-energy phonons, which are responsible for the thermal conductivity, is very strongly affected by small isotope disorder. Isotopically pure 12C diamond crystals exhibit thermal conductivities as high as 410 W cm-1 K-1 at 104 K, leading to projected values of over 2000 W cm-1 K-1 near 80 K. The changes in phonon properties with isotopic composition also weakly affect the electronic band structures and the lattice constants. The latter isotope dependence is most relevant for future standards of length based on crystal lattice constants. Capture of thermal neutrons by isotope nuclei followed by nuclear decay produces new elements, resulting in a very large number of possibilities for isotope selective doping of semiconductors. This neutron transmutation of isotope nuclei, already used
Semiconductor devices incorporating multilayer interference regions
Biefeld, R.M.; Drummond, T.J.; Gourley, P.L.; Zipperian, T.E.
1987-08-31
A semiconductor high reflector comprising a number of thin alternating layers of semiconductor materials is electrically tunable and may be used as a temperature insensitive semiconductor laser in a Fabry-Perot configuration. 8 figs.
Semiconductor devices incorporating multilayer interference regions
Biefeld, Robert M.; Drummond, Timothy J.; Gourley, Paul L.; Zipperian, Thomas E.
1990-01-01
A semiconductor high reflector comprising a number of thin alternating layers of semiconductor materials is electrically tunable and may be used as a temperature insensitive semiconductor laser in a Fabry-Perot configuration.
Fibre ring cavity semiconductor laser
Duraev, V P; Medvedev, S V
2013-10-31
This paper presents a study of semiconductor lasers having a polarisation maintaining fibre ring cavity. We examine the operating principle and report main characteristics of a semiconductor ring laser, in particular in single- and multiple-frequency regimes, and discuss its application areas. (lasers)
Process for producing chalcogenide semiconductors
Noufi, R.; Chen, Y.W.
1985-04-30
A process for producing chalcogenide semiconductor material is disclosed. The process includes forming a base metal layer and then contacting this layer with a solution having a low pH and containing ions from at least one chalcogen to chalcogenize the layer and form the chalcogenide semiconductor material.
Process for producing chalcogenide semiconductors
Noufi, Rommel; Chen, Yih-Wen
1987-01-01
A process for producing chalcogenide semiconductor material is disclosed. The process includes forming a base metal layer and then contacting this layer with a solution having a low pH and containing ions from at least one chalcogen to chalcogenize the layer and form the chalcogenide semiconductor material.
Variable temperature semiconductor film deposition
Li, X.; Sheldon, P.
1998-01-27
A method of depositing a semiconductor material on a substrate is disclosed. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.
Variable temperature semiconductor film deposition
Li, Xiaonan; Sheldon, Peter
1998-01-01
A method of depositing a semiconductor material on a substrate. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.
Physics with isotopically controlled semiconductors
Haller, E. E.
2010-07-15
This paper is based on a tutorial presentation at the International Conference on Defects in Semiconductors (ICDS-25) held in Saint Petersburg, Russia in July 2009. The tutorial focused on a review of recent research involving isotopically controlled semiconductors. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, is the most prominent effect for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples.
Various Kondo Effects for a Model Cerium Impurity in Normal Metals
NASA Astrophysics Data System (ADS)
Kim, Tae-Suk
1995-11-01
In this dissertation, we study a realistic extension of the conventional simple approach to the Kondo effect for Cerium(Ce^{3+}) ions, including the finite Coulomb interaction, the strong spin -orbit coupling, the crystal electric field effect, and multiple configurations in their simplest form. In the conventional approach, the f^2 configuration was removed from the problem, assuming the infinite on-site Coulomb interaction. Then only the one-channel exchange interaction is present between f ^0 and f^1 configurations for Ce ions. Relaxing the infinite on-site Coulomb interaction and including the detailed atomic energy structure leads to rich physics. Keeping the lowest lying doublet in the f^1 configuration, we find various exchange interactions which were missing in the conventional theory. In the hybridization between f^1 and f^2 configurations, we find with the impurity pseudospin S_ {I} = 1/2: (i) a two-channel exchange interaction with the conduction electron pseudo spin S _{c} = 1/2; (ii) a one-channel exchange interaction with the conduction electron pseudo spin S_{c} 3/2; (iii) One-channel ferromagnetic or antiferromagnetic exchange interactions with the conduction electron pseudo spin S_{c} = 1/2; (iv) Mixing exchange interactions among the conduction electrons belonging to the different partial wave channels. We analyze various exchange interactions using the scaling theory to study the stability of non-Fermi liquid fixed points. In this model study, we find only three types of stable fixed points. The well-studied one -channel strong coupling fixed point is stable. The two -channel fixed point of model (i) remains stable even in the presence of the channel symmetry breaking and channel mixing interactions. The unexpected three-channel fixed point of the combined model for (i) and (iii) is stable. Furthermore, we discovered a "zoo" of unstable fixed points where all kinds of exchange interactions are realized. Using the non-crossing approximation, we
Kondo Physics at Interfaces in Metallic Non-Local Spin Transport Devices
NASA Astrophysics Data System (ADS)
Leighton, Chris
2015-03-01
Despite the maturity of metallic spintronics there remain large gaps in our understanding of spin transport in metals, particularly with injection of spins across ferromagnetic/non-magnetic (FM/NM) interfaces, and their subsequent diffusion and relaxation. Unresolved issues include the limits of applicability of Elliott-Yafet spin relaxation, quantification of the influence of defects, surfaces, and interfaces on spin relaxation at nanoscopic dimensions, and the importance of magnetic and spin-orbit scattering. The non-local spin-valve is an enabling device in this context as, in addition to offering potentially disruptive applications, it allows for the separation of charge and spin currents. One particularly perplexing issue in metallic non-local spin valves is the widely observed non-monotonicity in the T-dependent spin accumulation, where the spin signal actually decreases at low T, in contrast to simple expectations. In this work, by studying an expanded range of FM/NM combinations (encompassing Ni80Fe20, Ni, Fe, Co, Cu, and Al), we demonstrate that this effect is not a property of a given FM or NM, but rather of the FM/NM pair. The non-monotonicity is in fact strongly correlated with the ability of the FM to form a dilute local magnetic moment in the NM. We show that local moments, resulting in this case from the ppm-level tail of the FM/NM interdiffusion profile, suppress the injected spin polarization and diffusion length via a novel manifestation of the Kondo effect, explaining all observations associated with the low T downturn in spin accumulation. We further show: (a) that this effect can be promoted by thermal annealing, at which point the conventional charge transport Kondo effect is simultaneously detected in the NM, and (b) that this suppression in spin accumulation can be quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer. Important implications for room temperature
Functionalization of Semiconductor Nanoparticles
NASA Astrophysics Data System (ADS)
Baraton, M.-I.
Functionalization of nanoparticles surface by attachment of organic entities is used to achieve and tailor many new properties, such as lubrication, optical response, chemical sensing, or biocompatibility. But because at the nanometer scale the surface properties significantly contribute to the overall properties, the consequences of the surface modifications have to be thoroughly evaluated. This paper demonstrates the relevance of Fourier transform infrared spectroscopy to the study of the surface reactions leading to the functionalization, and of the stability of the functionalized surface under the expected working conditions. In the case of semiconductor nanoparticles, this technique additionally allows the analysis of the impact of the functionalization on the electrical properties. This will be illustrated by the case study of tin oxide nanoparticles for chemical gas sensors. The correlation between surface chemistry and electrical properties is critical to optimize the nanoparticles functionalization for the targeted properties.
Hydrogen on semiconductor surfaces
Schaefer, J.A.; Balster, T.; Polyakov, V.; Rossow, U.; Sloboshanin, S.; Starke, U.; Tautz, F.S.
1998-12-31
The authors review structural and electronic aspects of the reaction of hydrogen with semiconductor surfaces. Among others, they address the Si(100), Ge{sub x}Si{sub 1{minus}x}(100), GaAs(100), InP(100), SiC(100), SiC(0001) and SiC(000{bar 1}) surfaces. It is demonstrated that high resolution electron energy loss spectroscopy (HREELS) in conjunction with a number of other surface sensitive techniques like low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS/UPS) can yield important information about the surface atomic structure, the effects of hydrogen passivation and etching and on electronic properties of the surfaces. 67 refs., 7 figs., 3 tabs.
Photocatalysis Using Semiconductor Nanoclusters
Thurston, T.R.; Wilcoxon,J.P.
1999-01-21
We report on experiments using nanosize MoS{sub 2} to photo-oxidize organic pollutants in water using visible light as the energy source. We have demonstrated that we can vary the redox potentials and absorbance characteristics of these small semiconductors by adjusting their size, and our studies of the photooxidation of organic molecules have revealed that the rate of oxidation increases with increasing bandgap (i.e. more positive valence band and more negative conduction band potentials). Because these photocatalysis reactions can be performed with the nanoclusters fully dispersed and stable in solution, liquid chromatography can be used to determine both the intermediate reaction products and the state of the nanoclusters during the reaction. We have demonstrated that the MoS{sub 2} nanoclusters remain unchanged during the photooxidation process by this technique. We also report on studies of MoS{sub 2} nanoclusters deposited on TiO{sub 2} powder.
NASA Astrophysics Data System (ADS)
Eaton, Samuel W.; Fu, Anthony; Wong, Andrew B.; Ning, Cun-Zheng; Yang, Peidong
2016-06-01
The discovery and continued development of the laser has revolutionized both science and industry. The advent of miniaturized, semiconductor lasers has made this technology an integral part of everyday life. Exciting research continues with a new focus on nanowire lasers because of their great potential in the field of optoelectronics. In this Review, we explore the latest advancements in the development of nanowire lasers and offer our perspective on future improvements and trends. We discuss fundamental material considerations and the latest, most effective materials for nanowire lasers. A discussion of novel cavity designs and amplification methods is followed by some of the latest work on surface plasmon polariton nanowire lasers. Finally, exciting new reports of electrically pumped nanowire lasers with the potential for integrated optoelectronic applications are described.
Semiconductor radiation detector
Bell, Zane W.; Burger, Arnold
2010-03-30
A semiconductor detector for ionizing electromagnetic radiation, neutrons, and energetic charged particles. The detecting element is comprised of a compound having the composition I-III-VI.sub.2 or II-IV-V.sub.2 where the "I" component is from column 1A or 1B of the periodic table, the "II" component is from column 2B, the "III" component is from column 3A, the "IV" component is from column 4A, the "V" component is from column 5A, and the "VI" component is from column 6A. The detecting element detects ionizing radiation by generating a signal proportional to the energy deposited in the element, and detects neutrons by virtue of the ionizing radiation emitted by one or more of the constituent materials subsequent to capture. The detector may contain more than one neutron-sensitive component.
One-dimensional edge state transport in a topological Kondo insulator
NASA Astrophysics Data System (ADS)
Nakajima, Yasuyuki; Syers, Paul; Wang, Xiangfeng; Wang, Renxiong; Paglione, Johnpierre
2016-03-01
Topological insulators, with metallic boundary states protected against time-reversal-invariant perturbations, are a promising avenue for realizing exotic quantum states of matter, including various excitations of collective modes predicted in particle physics, such as Majorana fermions and axions. According to theoretical predictions, a topological insulating state can emerge from not only a weakly interacting system with strong spin-orbit coupling, but also in insulators driven by strong electron correlations. The Kondo insulator compound SmB6 is an ideal candidate for realizing this exotic state of matter, with hybridization between itinerant conduction electrons and localized f-electrons driving an insulating gap and metallic surface states at low temperatures. Here we exploit the existence of surface ferromagnetism in SmB6 to investigate the topological nature of metallic surface states by studying magnetotransport properties at very low temperatures. We find evidence of one-dimensional surface transport with a quantized conductance value of e2/h originating from the chiral edge channels of ferromagnetic domain walls, providing strong evidence that topologically non-trivial surface states exist in SmB6.
Magnetic doping and kondo effect in bi(2)se(3) nanoribbons.
Cha, Judy J; Williams, James R; Kong, Desheng; Meister, Stefan; Peng, Hailin; Bestwick, Andrew J; Gallagher, Patrick; Goldhaber-Gordon, David; Cui, Yi
2010-03-10
A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surface-to-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically doped Bi2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than approximately 2%, low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics. PMID:20131918
Goker, A
2015-05-01
We study the optical absorption of a system consisting of a diatomic molecule that exhibits strong electron correlations coupled to metal nanoparticles possessing plasmon resonances by invoking the time-dependent non-crossing approximation. We investigate the evolution of the Fano resonance arising from the plasmon-exciton coupling when both atoms are Coulomb blockaded. We found that the Fano resonance rapidly dwindles as the ambient temperature exceeds the Kondo temperature of the singly occupied discrete state with higher energy and vanishes entirely at elevated temperatures. Our results show that even boosting the plasmon-exciton coupling above this temperature scale fails to revive the Fano resonance. We propose a microscopic model that accounts for these results. We suggest that a possible remedy for observation of the Fano resonance at high ambient temperatures is to position the singly occupied discrete state with the higher energy as close as possible to the Fermi level of the contacts while keeping the emitter resonance constant to prevent the merger of the Fano and plasmon resonances. PMID:25858207
Incomplete Protection of the Surface Weyl Cones of Kondo Insulators: Spin Exciton Scattering
NASA Astrophysics Data System (ADS)
Riseborough, Peter; Kapilevich, Gary A.>; Gray, Alex; Gulacsi, Miklos; Durakiewicz, Tomasz; Smith, James L.
The material SmB6 is a Kondo Insulator, where the lowest-energy bulk electronic excitations are spin excitons. The material also has surface states which are subjected to strong spin-orbit coupling. It has been suggested that SmB6 is also a topological insulator. Here we show that, despite the absence of time-reversal symmetry breaking and the presence of strong spin-orbit coupling, the chiral spin texture of the Weyl cone is not completely protected. In particular, we show that the spin-exciton mediated scattering produces features in the surface electronic spectrum at energies separated from the surface Fermi-energy by the spin-exciton energy. Despite the features being far removed from the surface Fermi-energy, the features are extremely temperature dependent. The temperature variation occurs over a characteristic scale determined by the dispersion of the spin exciton. The structures may be observed by electron spectroscopy at low temperatures. US Department of Energy, Office of Basic Energy Science, via the Award DE-FG02-01ER45872.
Topological surface states in Kondo insulator SmB6 via planar tunneling spectroscopy*
NASA Astrophysics Data System (ADS)
Park, Wan Kyu; Sun, Lunan; Noddings, Alex; Greene, Laura; Kim, Dae-Jeong; Fisk, Zachary
Samarium hexaboride (SmB6) belongs to a class of materials called Kondo insulators in which the hybridization between itinerant electrons and local moments leads to an emergent state of matter. With inherently large spin-orbit coupling along with strong correlation, SmB6 has been recently predicted to be topological meaning that topologically robust conducting states should exist at its surfaces. Although extensive investigations have provided growing evidence for the existence of such states, corroborative spectroscopic evidences are still lacking unlike in the weakly correlated counterparts. We adopt planar tunneling spectroscopy to unveil their detailed nature and behavior utilizing its inherently high energy resolution. Measurements of tunneling conductance on two different crystal surfaces (001) and (011) reveal the expected linear density of states for two and one Dirac cones, respectively. Moreover, it is found that these topological states cease to be protected well before they merge into the bulk states at the gap edges. Microscopic modeling of the tunneling processes accounting for the interaction with spin excitons as predicted by a recent theory provide consistent explanations for all the observed features, corroborating the proposed picture on the incompletely protected surface states in SmB6
Strong correlations in Kondo topological insulators: Two-dimensional heavy fermions, and beyond
NASA Astrophysics Data System (ADS)
Nikolic, Predrag
Samarium hexaboride (SmB6) is a candidate topological insulator with strong electron correlations. Empowered by the time-reversal (TR) symmetry and topology, the low-energy surface states of hybridized samarium's d and f orbitals can exhibit a rich two-dimensional heavy-fermion phenomenology. This talk will survey several interesting possibilities for correlated surface states, which depend on microscopic surface conditions. A pronounced participation of the f orbitals is expected to create a heavy-fermion Dirac metal, possibly unstable to spin density waves, superconductivity, or exotic Mott insulators (e.g. algebraic and non-Abelian spin liquids). The opposite limit of ``localized magnetic moments'' can produce a non-Fermi liquid of d electrons that exhibits two-dimensional quantum electrodynamics. Ultrathin films made from topological Kondo insulators can host lattices of SU(2) vortices, which need not break the TR symmetry. Landau-Ginzburg theory and numerical model calculations reveal the nature and stability of such vortex lattices, while field theory arguments predict that their quantum melting could yield novel incompressible quantum liquids with non-Abelian fractional excitations.
Two-dimensional Fermi surfaces in Kondo insulating SmB6
NASA Astrophysics Data System (ADS)
Li, Gang
There has been renewed interest in Samarium Hexaboride, which is a strongly correlated heavy Fermion material. Hybridization between itinerant electrons and localized orbitals lead to an opening of charge gap at low temperature. However, the resistivity of SmB6 does not diverge at low temperature. Former studies suggested that this residual conductance is contributed by various origins. Recent theoretical developments suggest that the particular symmetry of energy bands of SmB6 may host a topologically non-trivial surface state, i.e., a topological Kondo insulator. To probe the Fermiology of the possible metallic surface state, we use sensitive torque magnetometry to detect the de Haas van Alphen (dHvA) effect due to Landau level quantization on flux-grown crystals, down to He-3 temperature and up to 45 Tesla. Our angular and temperature dependent data suggest two-dimensional Fermi Surfaces lie in both crystalline (001) and (101) surface planes of SmB6.
Magnetic-field-tunable Kondo effect in alkaline-earth cold atoms
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Rey, Ana Maria
2015-05-01
We study quantum magnetism in strongly interacting fermionic alkaline-earth atoms (AEAs). Due to the decoupling of electronic and nuclear degrees of freedom, AEAs in two lowest electronic states (1S0 and 3P0) obey an accurate SU(N 2 I + 1) symmetry in their two-body collisions (I is the nuclear spin). We consider a system that realizes the simplest SU(2) case (for atoms prepared in two nuclear-spin states) in an optical lattice with two bands: one localized and one itinerant. For the fully filled narrow band (two atoms per lattice site) we demonstrate that an applied magnetic field provides an efficient control of the local ground state degeneracy due to mixing of spin and orbital two-body states. We derive an effective low-energy model that includes this magnetic-field effect as well as atomic interactions in the two optical lattice bands, and show that it exhibits a peculiar phenomenon of a magnetic field-induced Kondo effect, so far observed only in Coulomb blockaded quantum dots. We expect that our results can be tested with ultracold 173 Yb or 87 Sr atoms. Supported by JILA-NSF-PFC-1125844, NSF-PIF-1211914, ARO, AFOSR, AFOSR-MURI.
Guerrero, M.; Yu, C.C.
1995-04-15
In order to better understand Kondo insulators, we have studied both the symmetric and asymmetric Anderson lattices at half filling in one dimension using the density-matrix formulation of the numerical renormalization group. The asymmetric case is treated in the mixed-valence regime. We have calculated the charge gap, the spin gap, and the quasiparticle gap as a function of the repulsive interaction {ital U} using open boundary conditions for lattices as large as 24 sites. We find that the charge gap is larger than the spin gap for all {ital U} for both the symmetric and asymmetric cases. Ruderman-Kittel-Kasuya-Yosida interactions are evident in the {ital f}-spin--{ital f}-spin correlation functions at large {ital U} in the symmetric case, but are suppressed in the asymmetric case as the {ital f} level approaches the Fermi energy. This suppression can also be seen in the staggered susceptibility {chi}({ital q}=2{ital k}{sub {ital F}}) and it is consistent with neutron scattering measurements of {chi}({ital q}) in CeNiSn.
YbNi Si3 : An antiferromagnetic Kondo lattice with strong exchange interaction
NASA Astrophysics Data System (ADS)
Avila, M. A.; Sera, M.; Takabatake, T.
2004-09-01
We report on the structural, thermodynamic, and transport properties of high quality single crystals of YbNiSi3 grown by the flux method. This compound crystallizes in the SmNiGe3 layered structure type of the Cmmm space group. The general physical behavior is that of a Kondo lattice showing an antiferromagnetic ground state below TN=5.1K . This is among the highest ordering temperatures for a Yb-based intermetallic, indicating strong exchange interaction between the Yb ions, which are in or very close to +3 valency based on the effective moment of 4.45μB/f.u . The compound has moderately heavy-electron behavior with a Sommerfeld coefficient of 190mJ/molK2 . Resistivity is highly anisotropic and for I⊥b exhibits the signature logarithmic increase below a local minimum, followed by a sharp decrease in the coherent/magnetically ordered state, resulting in a residual resistivity of 1.5μΩcm and a residual resistivity ratio of 40. Fermi-liquid behavior consistent with a ground-state doublet is clearly observed below 1K .
Semiconductor Nanocrystals for Biological Imaging
Fu, Aihua; Gu, Weiwei; Larabell, Carolyn; Alivisatos, A. Paul
2005-06-28
Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission feature. Semiconductor nanocrystals, on the other hand, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.
Kondo interactions from band reconstruction in ${\mathrm{YbInCu}}_{4}$
Jarrige, I.; Kotani, A.; Yamaoka, H.; Tsujii, N.; Ishii, K.; Upton, M.; Casa, D.; Kim, J.; Gog, T.; Hancock, J. N.
2015-03-27
We combine resonant inelastic X-ray scattering (RIXS) and model calculations in the Kondo lattice compound YbInCu₄, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. In this study, the bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasi-gap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.
Sopori, Bhushan; Rangappan, Anikara
2014-11-25
Systems and methods for semiconductor device PN junction fabrication are provided. In one embodiment, a method for fabricating an electrical device having a P-N junction comprises: depositing a layer of amorphous semiconductor material onto a crystalline semiconductor base, wherein the crystalline semiconductor base comprises a crystalline phase of a same semiconductor as the amorphous layer; and growing the layer of amorphous semiconductor material into a layer of crystalline semiconductor material that is epitaxially matched to the lattice structure of the crystalline semiconductor base by applying an optical energy that penetrates at least the amorphous semiconductor material.
Semiconductor technology program. Progress briefs
NASA Technical Reports Server (NTRS)
Bullis, W. M.
1980-01-01
Measurement technology for semiconductor materials, process control, and devices is reviewed. Activities include: optical linewidth and thermal resistance measurements; device modeling; dopant density profiles; resonance ionization spectroscopy; and deep level measurements. Standardized oxide charge terminology is also described.
Metal-Insulator-Semiconductor Photodetectors
Lin, Chu-Hsuan; Liu, Chee Wee
2010-01-01
The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III–V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows. PMID:22163382
Semiconductor crystal high resolution imager
NASA Technical Reports Server (NTRS)
Levin, Craig S. (Inventor); Matteson, James (Inventor)
2011-01-01
A radiation imaging device (10). The radiation image device (10) comprises a subject radiation station (12) producing photon emissions (14), and at least one semiconductor crystal detector (16) arranged in an edge-on orientation with respect to the emitted photons (14) to directly receive the emitted photons (14) and produce a signal. The semiconductor crystal detector (16) comprises at least one anode and at least one cathode that produces the signal in response to the emitted photons (14).
Impurity gettering in semiconductors
Sopori, B.L.
1995-06-20
A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.
Impurity gettering in semiconductors
Sopori, Bhushan L.
1995-01-01
A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.
Semiconductor film Cherenkov lasers
NASA Astrophysics Data System (ADS)
Walsh, John E.
1994-12-01
The technical achievements for the project 'Semiconductor Film Cherenkov Lasers' are summarized. Described in the fourteen appendices are the operation of a sapphire Cherenkov laser and various grating-coupled oscillators. These coherent radiation sources were operated over the spectral range extending from 3 mm down to 400 micrometers. The utility of various types of open, multi-grating resonators and mode-locked operation were also demonstrated. In addition to these experiments, which were carried out with a 10-100 kV pulse generator, a low-energy (3-3.6 MeV) Van de Graaff generator and a low-energy RF linac (2.8 MeV) were used to investigate the properties of continuum incoherent Smith-Purcell radiation. It was shown that levels of intensity comparable to the infrared beam lines on a synchrotron could be obtained and thus that grating-coupled sources are potentially an important new source for Fourier transform spectroscopy. Finally, a scanning electron microscope was adapted for investigating mu-electron-beam-driven far-infrared sources. At the close of the project, spontaneous emission over the 288-800 micrometers band had been observed. Intensity levels were in accord with expectations based on theory. One or more of the Appendices address these topics in detail.
Survey of cryogenic semiconductor devices
Talarico, L.J.; McKeever, J.W.
1996-04-01
Improved reliability and electronic performance can be achieved in a system operated at cryogenic temperatures because of the reduction in mechanical insult and in disruptive effects of thermal energy on electronic devices. Continuing discoveries of new superconductors with ever increasing values of T{sub c} above that of liquid nitrogen temperature (LNT) have provided incentive for developing semiconductor electronic systems that may also operate in the superconductor`s liquid nitrogen bath. Because of the interest in high-temperature superconductor (HTS) devices, liquid nitrogen is the cryogen of choice and LNT is the temperature on which this review is focused. The purpose of this survey is to locate and assemble published information comparing the room temperature (298 K), performance of commercially available conventional and hybrid semiconductor device with their performance at LNT (77K), to help establish their candidacy as cryogenic electronic devices specifically for use at LNT. The approach to gathering information for this survey included the following activities. Periodicals and proceedings were searched for information on the behavior of semiconductor devices at LNT. Telephone calls were made to representatives of semiconductor industries, to semiconductor subcontractors, to university faculty members prominent for their research in the area of cryogenic semiconductors, and to representatives of the National Aeronautics and Space Administration (NASA) and NASA subcontractors. The sources and contacts are listed with their responses in the introduction, and a list of references appears at the end of the survey.
EDITORIAL: Oxide semiconductors
NASA Astrophysics Data System (ADS)
Kawasaki, M.; Makino, T.
2005-04-01
Blue or ultraviolet semiconducting light-emitting diodes have the potential to revolutionize illumination systems in the near-future. Such industrial need has propelled the investigation of several wide-gap semiconducting materials in recent years. Commercial applications include blue lasers for DVD memory and laser printers, while military applications are also expected. Most of the material development has so far been focused on GaN (band gap 3.5 eV at 2 K), and ZnSe (2.9 eV) because these two representative direct transition semiconductors are known to be bright emitting sources. GaN and GaN-based alloys are emerging as the winners in this field because ZnSe is subject to defect formation under high current drive. On the other hand, another II-VI compound, ZnO, has also excited substantial interest in the optoelectronics-oriented research communities because it is the brightest emitter of all, owing to the fact that its excitons have a 60 meV binding energy. This is compared with 26 meV for GaN and 20 meV for ZnSe. The stable excitons could lead to laser action based on their recombination even at temperatures well above room temperature. ZnO has additional major properties that are more advantageous than other wide-gap materials: availability of large area substrates, higher energy radiation stability, environmentally-friendly ingredients, and amenability to wet chemical etching. However, ZnO is not new to the semiconductor field as exemplified by several studies made during the 1960s on structural, vibrational, optical and electrical properties (Mollwo E 1982 Landolt-Boernstein New Series vol 17 (Berlin: Springer) p 35). In terms of devices, the luminescence from light-emitting diode structures was demonstrated in which Cu2O was used as the p-type material (Drapak I T 1968 Semiconductors 2 624). The main obstacle to the development of ZnO has been the lack of reproducible p-type ZnO. The possibility of achieving epitaxial p-type layers with the aid of thermal
Field dependence of the magnon dispersion in the Kondo lattice CeCu2 up to 12 T
NASA Astrophysics Data System (ADS)
Schedler, R.; Witte, U.; Rotter, M.; Loewenhaupt, M.; Schmidt, W.
2005-05-01
CeCu2 can be classified as a Kondo lattice which shows antiferromagnetic (AF) order below TN=3.5K [R. Trump et al., J. Appl. Phys. 69, 4699 (1991)]. The orthorhombic crystal and the simple AF magnetic structure with two magnetic moments in the primitive unit cell requires two magnon modes which are observed in zero and low magnetic fields and well described by spin wave theory. However, at higher fields, at and above 3T, an unexpected, additional magnetic excitation is observed. In contrast to the two low-energy magnon modes, it exhibits a steeper (factor 2) field dependence and a flat dispersion. Its origin is unclear.
NASA Astrophysics Data System (ADS)
Pillet, J.-D.; Joyez, P.; Žitko, Rok; Goffman, M. F.
2013-07-01
We performed tunneling spectroscopy of a carbon nanotube quantum dot (QD) coupled to a metallic reservoir either in the normal or in the superconducting state. We explore how the Kondo resonance, observed when the QD's occupancy is odd and the reservoir is normal, evolves towards Andreev bound states (ABS) in the superconducting state. Within this regime, the ABS spectrum observed is consistent with a quantum phase transition from a singlet to a degenerate magnetic doublet ground state, in quantitative agreement with a single-level Anderson model with superconducting leads.
Chinthavali, M.S.
2005-11-22
With the increase in demand for more efficient, higher-power, and higher-temperature operation of power converters, design engineers face the challenge of increasing the efficiency and power density of converters [1, 2]. Development in power semiconductors is vital for achieving the design goals set by the industry. Silicon (Si) power devices have reached their theoretical limits in terms of higher-temperature and higher-power operation by virtue of the physical properties of the material. To overcome these limitations, research has focused on wide-bandgap materials such as silicon carbide (SiC), gallium nitride (GaN), and diamond because of their superior material advantages such as large bandgap, high thermal conductivity, and high critical breakdown field strength. Diamond is the ultimate material for power devices because of its greater than tenfold improvement in electrical properties compared with silicon; however, it is more suited for higher-voltage (grid level) higher-power applications based on the intrinsic properties of the material [3]. GaN and SiC power devices have similar performance improvements over Si power devices. GaN performs only slightly better than SiC. Both SiC and GaN have processing issues that need to be resolved before they can seriously challenge Si power devices; however, SiC is at a more technically advanced stage than GaN. SiC is considered to be the best transition material for future power devices before high-power diamond device technology matures. Since SiC power devices have lower losses than Si devices, SiC-based power converters are more efficient. With the high-temperature operation capability of SiC, thermal management requirements are reduced; therefore, a smaller heat sink would be sufficient. In addition, since SiC power devices can be switched at higher frequencies, smaller passive components are required in power converters. Smaller heat sinks and passive components result in higher-power-density power converters
Optical pumping in semiconductors
NASA Astrophysics Data System (ADS)
Hermann, C.; Lampel, G.; Safarov, V. I.
Optical Pumping in Semiconductors (OPS) arises from the transfer of angular momentum from light to the localized states of a semiconductor. Spin polarized electrons are thus excited in the conduction band; their polarization is convenient measured through the circular polarization of photoluminescence. This review gives an insight of the various studies based on OPS. After describing the first OPS experiment, we show that this technique allows the determination of band structure properties, and the optical detection of conduction electron spin resonance. The nuclei are polarized by hyperfine interaction, which permits the optical detection of nuclear resonance. A magnetic field transverse to the direction of light propagation produces an electronic depolarization analogous to the Hanle effect. The electron lifetime and spin relaxation time are measured under steady-state conditions by comparison to their Larmor frequency in this transverse field. By activation to Negative Electron Affinity of a GaAs surface, electrons oriented by OPS can be photoemitted into vacuum, leading to a highly spin-polarized beam : we describe a collision experiment in which such a beam transfers angular momentum to atoms. Le Pompage Optique dans les semiconducteurs (POS) provient du transfert de moment angulaire de la lumière vers les états délocalisés d'un semiconducteur. On excite ainsi dans la bande de conduction des électrons polarisés de spin, dont on mesure commodément la polarisation à partir de la polarisation circulaire de la photoluminescence. Cet article de revue présente un aperçu des différentes études fondées sur le POS. Après avoir décrit la première expérience de POS, nous montrons que par cette technique on peut déterminer des propriétés liées à la structure de bande, et détecter optiquement la résonance de spin des électrons de conduction. Les noyaux sont polarisés grâce au couplage hyperfin qui permet également la détection optique de la r
Transport Spectroscopy of Coupled Quantum Dots in Conditions of the Kondo Effect
NASA Astrophysics Data System (ADS)
Glazman, Leonid
2005-03-01
We develop electron transport theory for novel devices [1,2], which are interesting in the context of correlated electrons physics. The device proposed in Ref. [1] is designed for an observation of a non-Fermi-liquid behavior of itinerant electrons. The device measured in Ref. [2] may serve a similar purpose, and also may become important for quantum computing.In the case of Ref. [1], our theory [3] provides a strategy for tuning to the non-Fermi-liquid fixed point -- a quantum critical point in the space of device parameters. We explore the corresponding quantum phase transition, and make explicit predictions for the behavior of differential conductance in the vicinity of the quantum critical point. Motivated by the measurements [2], we developed a theory of conductance of Kondo quantum dots coupled by the RKKY interaction [4]. Investigation of the differential conductance at fixed interaction strength may allow one to distinguish between the possible ground states of the system. Transition between the ground states is achieved by tuning the interaction strength; the nature of the transition (which includes a possibility of a non-Fermi-liquid point) can be extracted from the temperature dependence of the linear conductance.This research is supported by NSF grants DMR02-37296 and EIA02- 10736.1. Y. Oreg and D. Goldhaber-Gordon, Phys. Rev. Lett. 90, p. 136602 (2003). 2. N.J. Craig J.M. Taylor, E.A. Lester, C.M. Marcus, M.P. Hanson, and A.C. Gossard, Science 304, 565 (2004).3. M.G. Vavilov and L.I. Glazman, preprint cond-mat/0404366.4. M. Pustilnik, L. Borda, L.I. Glazman, and J. von Delft, Phys. Rev. B 69, 115316 (2004).
NMR relaxation in the topological Kondo insulator SmB6
NASA Astrophysics Data System (ADS)
Schlottmann, P.
2014-10-01
SmB6 has been predicted to be a strong topological Kondo insulator, and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. We study the temperature and magnetic field dependence of the NMR Knight shift and relaxation rate arising from the topological conduction states. For the clean surface the Landau quantization of the surface states gives rise to highly degenerate discrete levels for which the Knight shift is proportional to the magnetic field B and inversely proportional to the temperature T. The relaxation rate 1/T1 is not Korringa-like. For the more realistic case of a surface with a low concentration of defects (dirty limit) the scattering of the electrons leads to a broadening of the Landau levels and hence to a finite density of states. The mildly dirty surface case leads to a T-independent Knight shift proportional to B and a Korringa-like 1/T1 at low T. The wave functions of the surface states are expected to fall off exponentially with distance from the surface giving rise to a superposition of relaxation times, i.e., a stretched exponential. It is questionable that the experimental 11B Knight shift and relaxation rate arise from the surface states of the TKI. An alternative explanation is that the bulk susceptibility and the 11B NMR properties are the consequence of the in-gap bulk states originating from magnetic exciton bound states proposed by Riseborough [Phys. Rev. B 68, 235213 (2003), 10.1103/PhysRevB.68.235213].
Hydrogen in semiconductors and metals
Nickel, N.H.; Jackson, W.B.; Bowman, R.C.; Leisure, R.G.
1998-12-31
Major highlights of the conference include further understanding of the structure of extended hydrogen clusters in semiconductors, switchable optical properties of metal-hydride films, reversible changes in the magnetic coupling in metallic superlattices, and increased lifetime of integrated circuits due to deuterium device passivation. Continued progress has also been achieved in understanding hydrogenation of defects in compound semiconductors and on surfaces. Total energy calculations in semiconductors have progressed sufficiently to predict energetics and vibration frequencies as measured by experiment. Similarly, electronic structure calculations of hydrogen-metal systems provide a deeper understanding of stability, bonding, and phase changes. Various nuclear techniques have been refined to yield important information regarding the concentration and transport of hydrogen in condensed matter. Finally, the interaction of hydrogen to create thermal donors has been used to create deep p-n junctions without the need for deep diffusion of dopants. The volume has been organized along the order of presentation within the conference. Similar methods and subjects have been grouped together. The authors have attempted to keep similar metal and semiconductor papers together in order to further promote cross-fertilization between the fields. Major categories include hydrogen on surfaces, theory and thermodynamics, hydrogen transport phenomena, nuclear characterization techniques, compound semiconductors, metal bulk, devices and applications, bulk silicon, and carbon and carbon-like materials. Separate abstracts were prepared for most papers.
Nonlinear optical interactions in semiconductors
NASA Astrophysics Data System (ADS)
Salour, M. M.
1985-12-01
The optical pumping technique in GaAs has led to the development of a novel and highly sensitive optical temperature sensor. Completed is the experiment on two photon optical pumping in ZnO. An external cavity semiconductor laser involving ZnO as a gain medium was demonstrated under two-photon excitation. This laser should have a major impact on the development of tunable blue-green radiation for submarine communication. Completed is a paper on heat buildup in semiconductor platelets. New lasers are used to explore elementary excitation in optical thin film layers of semiconductors. This has led to the first demonstration of the feasibility of room temperature operation of a tunable coherent source involving multiple quantum well material. Completed is the construction of a simple remote (non-contact) temperature sensor to directly measure heat buildup in semiconductor materials as a result of high power optical laser excitation. Finally, an experiment involving optical frequency mixing to probe electrodynamics in the GaAlAs multiple quantumwell and superlattice structures, utilizing two recently constructed tunabel laser systems,has been successful. Attempts were focused on observing a number of new optical effects including nonlinear absorption and transmission phenomena, enhanced spontaneous and stimulated light scattering processes, etc. The construction of an external cavity semiconductor HgCdTe has been successful.
Gomez Sal, J.C.; Garcia Soldevilla, J.; Blanco, J.A.; Espeso, J.I.; Rodriguez Fernandez, J.; Luis, F.; Bartolome, F.; Bartolome, J.
1997-11-01
The low-temperature magnetic and transport properties of the orthorhombic CeNi{sub 0.4}Cu{sub 0.6} compound have been determined from the analysis of specific heat, ac magnetic susceptibility, electrical resistivity, elastic and inelastic neutron scattering. These measurements present intriguing experimental results that could not be explained within the usual phenomenology of Ce-based compounds. C{sub p} and {chi}{sub ac} present anomalies around 1 K corresponding to ferromagnetic order as confirmed by neutron diffraction. The magnetic structure is collinear with very reduced moments, 0.6{mu}{sub B}/Ce lying in the b direction. Additionally, a clear Kondo behavior is observed with a Kondo temperature T{sub K}=1.9K estimated from quasielastic neutron scattering. Above the ordering temperature, further anomalies are observed in C{sub p} and {chi}{sub ac} that could not be explained as originating from crystal electric field or Kondo effects. From the frequency and field dependence of the {chi}{sub ac}, above T{sub c}, a spin-glass state with a freezing temperature T{sub f}=2K is proposed for this compound. This unusual magnetic behavior is discussed in terms of mixed (positive and negative) Ruderman-Kittel-Kasuya-Yosida interactions, randomness (structural disorder), large hybridization (Kondo effect), and strong magnetocrystalline anisotropy (crystal electric field effects). {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Xu, N.; Shi, X.; Biswas, P. K.; Matt, C. E.; Dhaka, R. S.; Huang, Y.; Plumb, N. C.; Radović, M.; Dil, J. H.; Pomjakushina, E.; Conder, K.; Amato, A.; Salman, Z.; Paul, D. McK.; Mesot, J.; Ding, H.; Shi, M.
2013-09-01
Recent theoretical calculations and experimental results suggest that the strongly correlated material SmB6 may be a realization of a topological Kondo insulator. We have performed an angle-resolved photoemission spectroscopy study on SmB6 in order to elucidate elements of the electronic structure relevant to the possible occurrence of a topological Kondo insulator state. The obtained electronic structure in the whole three-dimensional momentum space reveals one electron-like 5d bulk band centered at the X point of the bulk Brillouin zone that is hybridized with strongly correlated f electrons, as well as the opening of a Kondo band gap (ΔB ˜ 20 meV) at low temperature. In addition, we observe electron-like bands forming three Fermi surfaces at the center Γ¯ point and boundary X¯ point of the surface Brillouin zone. These bands are not expected from calculations of the bulk electronic structure, and their observed dispersion characteristics are consistent with surface states. Our results suggest that the unusual low-temperature transport behavior of SmB6 is likely to be related to the pronounced surface states sitting inside the band hybridization gap and/or the presence of a topological Kondo insulating state.
NASA Astrophysics Data System (ADS)
Mantelli, Davide; Paşcu Moca, Cătălin; Zaránd, Gergely; Grifoni, Milena
2016-08-01
We investigate the effects of spin-orbit interaction (SOI) and valley mixing on the transport and dynamical properties of a carbon nanotube (CNT) quantum dot in the Kondo regime. As these perturbations break the pseudo-spin symmetry in the CNT spectrum but preserve time-reversal symmetry, they induce a finite splitting Δ between formerly degenerate Kramers pairs. Correspondingly, a crossover from the SU(4) to the SU(2)-Kondo effect occurs as the strength of these symmetry breaking parameters is varied. Clear signatures of the crossover are discussed both at the level of the spectral function as well as of the conductance. In particular, we demonstrate numerically and support with scaling arguments that the Kondo temperature scales inversely with the splitting Δ in the crossover regime. In presence of a finite magnetic field, time reversal symmetry is also broken. We investigate the effects of both parallel and perpendicular fields (with respect to the tube's axis) and discuss the conditions under which Kondo revivals may be achieved.
Field-dependent ordered phases and Kondo phenomena in the filled skutterudite compound PrOs4As12
Maple, M. B.; Butch, N. P.; Frederick, N. A.; Ho, P.-C.; Jeffries, J. R.; Sayles, T. A.; Yanagisawa, T.; Yuhasz, W. M.; Chi, Songxue; Kang, H. J.; Lynn, J. W.; Dai, Pengcheng; McCall, S. K.; McElfresh, M. W.; Fluss, M. J.; Henkie, Z.; Pietraszko, A.
2006-01-01
Electrical resistivity, specific heat, and magnetization measurements to temperatures as low as 80 mK and magnetic fields up to 16 T were made on the filled skutterudite compound PrOs4As12. The measurements reveal the presence of two ordered phases at temperatures below approximately 2.3 K and in fields below approximately 3 T. Neutron-scattering experiments in zero field establish an antiferromagnetic ground state <2.28 K. In the antiferromagnetically ordered state, the electronic-specific heat coefficient γ ≈ 1 J/mol·K2 below 1.6 K and 0 ≤ H ≤ 1.25 T. The temperature and magnetic-field dependence of the electrical resistivity and specific heat in the paramagnetic state are consistent with single-ion Kondo behavior with a low Kondo temperature on the order of 1 K. The electronic-specific heat in the paramagnetic state can be described by the resonance-level model with a large zero-temperature electronic-specific heat coefficient that decreases with increasing magnetic field from approximately 1 J/mol·K2 at 3 T to approximately 0.2 J/mol·K2 at 16 T. PMID:16632603
NASA Astrophysics Data System (ADS)
Schilling, James S.; Song, Jing; Soni, Vikas; Lim, Jinhyuk
Most elemental lanthanides order magnetically at temperatures To well below ambient, the highest being 292 K for Gd. Sufficiently high pressure is expected to destabilize the well localized magnetic 4 f state of the heavy lanthanides, leading to increasing influence of Kondo physics on the RKKY interaction. For pressures above 80 GPa, To for Dy and Tb begins to increase dramatically, extrapolating for Dy to a record-high value near 400 K at 160 GPa. This anomalous increase may be an heretofore unrecognized feature of the Kondo lattice state; if so, one would expect To to pass through a maximum and fall rapidly at even higher pressures. A parallel is suggested to the ferromagnet CeRh3B2 where To = 115 K at ambient pressure, a temperature more than 100-times higher than anticipated from simple de Gennes scaling. Here we discuss recent experiments on Nd where anomalous behavior in To (P) is found to occur at lower pressures, perhaps reflecting the fact that Nd's 4 f wave function is less localized. Work at Washington University is supported by NSF Grant DMR-1104742 and CDAC through NNSA/DOE Grant DE-FC52-08NA28554.
Kondo-type behavior of the Ru4 + lattice in LaCu3Ru4O12
NASA Astrophysics Data System (ADS)
Riegg, S.; Widmann, S.; Meir, B.; Sterz, S.; Günther, A.; Büttgen, N.; Ebbinghaus, S. G.; Reller, A.; von Nidda, H.-A. Krug; Loidl, A.
2016-03-01
Rare d -electron-derived heavy-fermion properties of the solid-solution series LaCu3RuxTi4 -xO12 were studied for 1 ≤x ≤4 by resistivity, susceptibility, specific-heat measurements, and magnetic-resonance techniques. Our results suggest the existence of a coherent Kondo lattice formed by localized Ru 4 d electrons leading to strongly enhanced effective electron masses. Pure ruthenate (x =4 ) is a heavy-fermion metal characterized by a resistivity proportional to T2 at low temperatures T . By increasing titanium substitution the coherent Fermi-liquid state is disturbed, yielding single-ion Kondo-type properties as in the paradigm 4 f -based heavy-fermion compound CexLa1 -xCu2.05Si2 [M. Ocko et al., Phys. Rev. B 64, 195106 (2001), 10.1103/PhysRevB.64.195106]. In LaCu3RuxTi4 -xO12 the heavy-fermion behavior finally breaks down upon crossing the metal-to-insulator transition close to x =2 .
Antiferromagnetic Kondo lattice in the layered compounds Re2NiGa9Ge2 (Re =Ce, Pr, Sm)
NASA Astrophysics Data System (ADS)
Zhu, Yanglin; Liu, Jinyu; Hu, Jin; Adams, Daniel; Spinu, Leonard; Mao, Zhiqiang
Intermetallic compounds containing rare-earth/actinide elements with 4f/5f electrons have formed a special family of strongly correlated materials, i.e. heavy fermion systems. We have recently found a new layered rare earth intermetallic system showing moderate heavy fermion behavior: Re2NiGa9Ge2 (Re =Ce, Sm, Pr). The Re =Ce and Sm members were previously synthesized, while their electronic properties have not been reported. We have recently grown single crystals of Re2NiGa9Ge2 (Re =Ce, Sm, Pr) and characterized their electronic and magnetic properties. We find all these materials are antiferromagnetic, with TN = 2.5 K, 5 K, 3.4 K respectively for Re =Ce, Pr and Sm. Moreover, they also exhibit large values of electronic specific coefficient: γ ~ 101 mJ mol-Ce-1 K-2 for Re =Ce, 368 mJ mol-Pr-1 K-2 for Re =Pr, and 196.4 mJ mol-Sm-1 K-2 for Re =Sm, indicating enhanced Kondo effect and the presence of AFM Kondo lattice. Our findings suggest that Re2NiGa9Ge2 (Re =Ce, Pr, Sm) could be interesting candidate materials for exploring novel exotic properties of correlated electrons through external parameter tuning such as chemical substitution and pressure.
Non-Fermi Liquid Behaviour in the Heavy-Fermion Kondo Lattice Ce2Rh3Al9
NASA Astrophysics Data System (ADS)
Falkowski, M.; Strydom, A. M.
2014-04-01
In the heavy fermion class of strongly correlated electron systems, the Landau Fermi liquid description of metals has become a rather fragile basis on which to formulate an understanding of their ground state. The proximity to cooperative phenomena such as magnetic order and superconductivity and the amenability of Ce- and Yb-based compounds to be tuned into quantum criticality have been found to have extraordinary effects on the T→0 thermal scaling of electronic and magnetic properties. A collection of non-Fermi liquid scaling relations have thus far been proposed in the search for universality. Here we report on the physical properties of the heavy fermion Kondo lattice Ce2Rh3Al9. The low-temperature specific heat and electrical resistivity are best described by power laws in their temperature dependence, and we model these according to the expectation for a system close to a magnetic phase transition. We demonstrate how applied magnetic fields drive the transition from the Kondo coherent state, through a cross-over phase, and into Fermi-liquid behaviour at high fields and low temperatures.
NASA Astrophysics Data System (ADS)
Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard; Averitt, Richard
We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound SmB6, a prototype Kondo insulator. Temperature dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ~T* =20 K, well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20K) indicates the emergence of a surface state with an effective electron mass of 0.1me. Conductivity dynamics following optical excitation are also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20K, indicative of another channel opening up in the low energy electrodynamics. Taken together, these results suggest the onset of a surface state well below the crossover temperature (100K) after long-range coherence of the f-electron Kondo lattice is established. JZ and RDA acknowledge support from DOE - Basic Energy Sciences under Grant No. DE-FG02-09ER46643, under which the THz measurements and data analysis were performed. JY, IT and RLG acknowledge support from ONR N00014-13-1-0635 and NSF DMR 1410665.
Magnetotransport study of Kondo compound Ce(Ni0.7Cu0.3)2Al3
NASA Astrophysics Data System (ADS)
Yadam, Sankararao; Singh, Durgesh; Venkateshwarlu, D.; Gangrade, Mohan Kumar; Samatham, S. Shanmukharao; Ganesan, V.
2015-06-01
CeNi2Al3 system has evolved in to a known thermoelectric material with a usable figure of merit at low temperatures. Kondo effect plays a crucial role in the enhancement of TEP in this system especially when the Ni site is substituted with non-magnetic elements like Cu. Effect of high magnetic fields on various properties of this system is yet to be explored. Ce(Ni0.7Cu0.3)2Al3 is a representative sample that has a significant enhancement of TEP whose reasons are being explored recently. Here we report the magnetoresistivity measurements on this sample down to 2K and fields upto 14T. The famous negative ln(T) rise with a minimum at 14.5 K is getting suppressed by the magnetic fields. Magnetic correlations are observed with increasing magnetic field strength in the form of a hump like behavior due to competition between Kondo and RKKY interactions. This hump is shifted to higher temperatures with increase in the field strength which indicates probable onset of ferromagnetic correlations that is being corroborated by the observed negative magnetoresistance at low temperatures.
Light induced suppression of Kondo effect at amorphous LaAlO3/SrTiO3 interface
NASA Astrophysics Data System (ADS)
Liu, G. Z.; Qiu, J.; Jiang, Y. C.; Zhao, R.; Yao, J. L.; Zhao, M.; Feng, Y.; Gao, J.
2016-07-01
We report photoelectric properties of two-dimensional electron gas (2DEG) at an amorphous LaAlO3/SrTiO3 interface. Under visible light illumination (650 nm), an enhancement of electric conductivity is observed over the temperature range from 2 to 300 K. Particularly, a resistance upturn appearing below 25 K, which is further proved to from the Kondo effect, is suppressed by the 650 nm visible light. From the results of light-assisted Hall measurements, light irradiation increases the carrier mobility rather than carrier density in the Kondo regime. It is suggested that light induces the decoherence effect of localized spin states, hence the electron scattering is weakened and the carrier mobility is improved accordingly. Moreover, the enhancement of electrical conductivity by visible light verifies that in-gap states located in the SrTiO3 side of the interface play an important role in the electrical transport of the amorphous SrTiO3-based oxide 2DEG system. Our results provide deeper insight into the photoinduced effects in the 2DEG system, paving the way for the design of optoelectronic devices based on oxides.
Park, Wan Kyu; Sun, Lunan; Noddings, Alexander; Kim, Dae-Jeong; Fisk, Zachary; Greene, Laura H
2016-06-14
Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3 Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6 The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6. PMID:27233936
Competition between Kondo and indirect exchange at the edges and bulk of graphene, and 2D materials
NASA Astrophysics Data System (ADS)
Allerdt, Andrew; Martins, George; Feiguin, Adrian
We study the problem of two magnetic impurities at the surface of graphene, BN, MoS2, phosphorene, silicene and germanene using exact numerical methods. We map the band structure of these materials onto one dimensional tight-binding chains in the same spirit as Wilson's numerical renormalization group. We use the density matrix renormalization group to solve the problem exactly, keeping all the information about the underlying lattice. Competition between Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions is non-trivial, due to strong non-perturbative effects. Depending on the presence of a pseudogap, or gap, we identify an important directionality and position dependence of the correlations. We present scenarios and regimes where impurities prefer to form their own Kondo clouds instead of an RKKY singlet state, or remain as uncoupled local moments. In the particular case of graphene, ferromagnetism is only stable at half-filling. In addition, we study the effects of spin-orbit coupling, and the presence of edge states.
NASA Astrophysics Data System (ADS)
Allerdt, Andrew; Feiguin, Adrian; Busser, Carlos; Martins, George
2015-03-01
Magnetic impurities embedded in a metal interact via an effective Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mediated by the conduction electrons, which is commonly assumed to be long ranged, with an algebraic decay in the inter-impurity distance. However, they can also form a Kondo screened state that is oblivious to the presence of other impurities. We study the competition mechanisms between both effects on the square and cubic lattices by introducing an exact mapping onto an effective one-dimensional problem that we can solve with the density matrix renormalization group method (DMRG). We show a dramatic departure from the conventional RKKY theory, that can be attributed to the dimensionality and different densities of states, as well as the quantum nature of the magnetic moments. In particular, for dimension d > 1 , Kondo physics dominates even at short distances, while the ferromagnetic RKKY state is energetically unfavorable. Our findings can have clear implications in the interpretation of experiments and for tailoring the magnetic properties of surfaces.
NASA Astrophysics Data System (ADS)
Bernal, Oscar Orlando
The intermetallic Kondo alloy system UCu _{5-x}Pd_{x } is one of a number of recently-discovered Kondo materials which exhibit deviations from Fermi liquid behavior in their thermodynamic and transport properties down to micro-Kelvin temperatures. Studying local electronic structure by nuclear magnetic resonance techniques (NMR) in this unconventional system, we find anomalous behavior of NMR parameters versus magnetic susceptibility chi in UCu_4Pd and UCu_{3.5}Pd_ {1.5}. Metallic alloys containing magnetic impurities usually display a linear relation between the susceptibility and the Knight shift and its distribution, the magnetic broadening. In UCu_{5 -x}Pd_{x}, as the temperature is lowered, it is found that for both concentrations the magnetic broadening of the ^{63}Cu NMR spectra grows non-linearly with respect to chi, reaching enhancements at the lowest temperatures of ~100% over the values expected from a high-temperature linear relation. Enhancement of the linewidth over the susceptibility might indicate the possibility of U-spin freezing, as observed in some dilute Kondo alloys. The absence of any anomalies in either the specific heat or the magnetic susceptibility of these samples suggests, however, that spin freezing does not account for the observations, and that the enhancement is related to intrinsic behavior of the paramagnetic alloys. Smaller but similar anomalies are found for the isotropic and axial components of the Knight shift {cal K} as functions chi in the two materials. {cal K} presents a linear relation with chi only down to ~30 K. Below this temperature, the absolute value of the Knight-shift components grows more slowly than would be expected from extrapolating their high temperature behavior, suggesting temperature-dependent transferred-hyperfine fields at the Cu sites or a temperature-dependent lineshape asymmetry. We interpret these observations in terms of disorder of the density of conduction-electron states (DOS). A simple model of
High mobility emissive organic semiconductor.
Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J
2015-01-01
The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm(2) V(-1) s(-1). Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m(-2) and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics. PMID:26620323
High mobility emissive organic semiconductor
Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J.
2015-01-01
The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V−1 s−1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m−2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics. PMID:26620323
High mobility emissive organic semiconductor
NASA Astrophysics Data System (ADS)
Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J.
2015-12-01
The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V-1 s-1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m-2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.
Selenium semiconductor core optical fibers
Tang, G. W.; Qian, Q. Peng, K. L.; Wen, X.; Zhou, G. X.; Sun, M.; Chen, X. D.; Yang, Z. M.
2015-02-15
Phosphate glass-clad optical fibers containing selenium (Se) semiconductor core were fabricated using a molten core method. The cores were found to be amorphous as evidenced by X-ray diffraction and corroborated by Micro-Raman spectrum. Elemental analysis across the core/clad interface suggests that there is some diffusion of about 3 wt % oxygen in the core region. Phosphate glass-clad crystalline selenium core optical fibers were obtained by a postdrawing annealing process. A two-cm-long crystalline selenium semiconductor core optical fibers, electrically contacted to external circuitry through the fiber end facets, exhibit a three times change in conductivity between dark and illuminated states. Such crystalline selenium semiconductor core optical fibers have promising utility in optical switch and photoconductivity of optical fiber array.
Device Concepts in Semiconductor Spintronics
NASA Astrophysics Data System (ADS)
Molenkamp, Laurens W.
Semiconductor spintronics has now reached a stage where the basic physical mechanisms controlling spin injection and detection are understood. Moreover, some critical technological issues involved in the growth and lithography of the magnetic semiconductors have been solved. This has allowed us to explore the physics of meanwhile quite complex spintronic devices. The lectures will start with an introduction to spin transport in metals and semiconductors. Building upon this, I will discuss various simple devices that demonstrate this basic physics in action. Subsequently, more advanced devices will be covered. For example, I will discuss resonant tunneling diodes (RTDs) fabricated from paramagnetic II-VI semiconductors that can be operated as a voltage controlled spin-switch. A quantum dot version of these RTDs exhibits, unexpectedly, remanent magnetism at zero external field, which we interpret as resulting from tunneling through a single magnetic polaron. In the ferromagnetic semiconductor (Ga, Mn)As we have observed a very large spin valve effect due to domain wall pinning at sub-10 nm sized constrictions. Furthermore, we have found a novel magnetoresistance effect in this material, dubbed tunnel anisotropic magnetoresistance (TAMR), which is due to the strongly (magneto-)anisotropic density of states in a ferromagnetic semiconductor. The effect leads to the observation of a spin valve-like behavior in tunnel structures containg a single ferromagnetic layer and also dominates the spin-valve signal obtained from structures containing two (Ga, Mn)As layers, where the effect may cause resistance changes of five orders of magnitude. Note from Publisher: This article contains the abstract only.
Exciton Transport in Organic Semiconductors
NASA Astrophysics Data System (ADS)
Menke, Stephen Matthew
Photovoltaic cells based on organic semiconductors are attractive for their use as a renewable energy source owing to their abundant feedstock and compatibility with low-cost coating techniques on flexible substrates. In contrast to photovoltaic cells based traditional inorganic semiconductors, photon absorption in an organic semiconductor results in the formation of a coulombically bound electron-hole pair, or exciton. The transport of excitons, consequently, is of critical importance as excitons mediate the interaction between charge and light in organic photovoltaic cells (OPVs). In this dissertation, a strong connection between the fundamental photophysical parameters that control nanoscopic exciton energy transfer and the mesoscopic exciton transport is established. With this connection in place, strategies for enhancing the typically short length scale for exciton diffusion (L D) can be developed. Dilution of the organic semiconductor boron subphthalocyanine chloride (SubPc) is found to increase the LD for SubPc by 50%. In turn, OPVs based on dilute layers of SubPc exhibit a 30% enhancement in power conversion efficiency. The enhancement in power conversion efficiency is realized via enhancements in LD, optimized optical spacing, and directed exciton transport at an exciton permeable interface. The role of spin, energetic disorder, and thermal activation on L D are also addressed. Organic semiconductors that exhibit thermally activated delayed fluorescence and efficient intersystem and reverse intersystem crossing highlight the balance between singlet and triplet exciton energy transfer and diffusion. Temperature dependent measurements for LD provide insight into the inhomogeneously broadened exciton density of states and the thermal nature of exciton energy transfer. Additional topics include energy-cascade OPV architectures and broadband, spectrally tunable photodetectors based on organic semiconductors.
A brief history of ... semiconductors
NASA Astrophysics Data System (ADS)
Jenkins, Tudor
2005-09-01
The development of studies in semiconductor materials is traced from its beginnings with Michael Faraday in 1833 to the production of the first silicon transistor in 1954, which heralded the age of silicon electronics and microelectronics. Prior to the advent of band theory, work was patchy and driven by needs of technology. However, the arrival of this successful quantum theory of solids, together with a concentration on the growth of pure silicon and germanium and an understanding of their properties, saw an explosion in activity in semiconductor studies that has continued to this day.
Wide band gap semiconductor templates
Arendt, Paul N.; Stan, Liliana; Jia, Quanxi; DePaula, Raymond F.; Usov, Igor O.
2010-12-14
The present invention relates to a thin film structure based on an epitaxial (111)-oriented rare earth-Group IVB oxide on the cubic (001) MgO terminated surface and the ion-beam-assisted deposition ("IBAD") techniques that are amendable to be over coated by semiconductors with hexagonal crystal structures. The IBAD magnesium oxide ("MgO") technology, in conjunction with certain template materials, is used to fabricate the desired thin film array. Similarly, IBAD MgO with appropriate template layers can be used for semiconductors with cubic type crystal structures.
Thermoelectric performance of granular semiconductors.
Glatz, A.; Beloborodov, I. S.; Materials Science Division; California State Univ.
2009-01-01
We study the effects of doping and confinement on the thermoelectric properties of nanocrystalline semiconductors. We calculate the thermopower and figure of merit for temperatures less than the charging energy. For weakly coupled semiconducting grains it is shown that the figure of merit is optimized for grain sizes of order 5 nm for typical materials, and that its value can be larger than one. Using the similarities between granular semiconductors and electron or Coulomb glasses allows for a quantitative description of inhomogeneous semiconducting thermoelectrics.
NASA Astrophysics Data System (ADS)
Adroja, D. T.; Hillier, A. D.; Ritter, C.; Bhattacharyya, A.; Khalyavin, D. D.; Strydom, A. M.; Peratheepan, P.; Fâk, B.; Koza, M. M.; Kawabata, J.; Yamada, Y.; Okada, Y.; Muro, Y.; Takabatake, T.; Taylor, J. W.
2015-09-01
The opening of a spin gap in the orthorhombic compounds Ce T2Al10 (T =Ru andOs ) is followed by antiferromagnetic ordering at TN=27 and 28.5 K, respectively, with a small ordered moment (0.29 -0.34 μB ) along the c axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with La doping in Ce1 -xLaxT2Al10 (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND), and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 and 10 meV in the 10% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 μB along the b axis in Ce0.9La0.1Ru2Al10 , however a moment of 0.23 μB still along the c axis in Ce0.9La0.1Os2Al10 . This contrasting behavior can be explained by a different degree of hybridization in CeRu2Al10 and CeOs2Al10 , being stronger in the latter than in the former. Muon spin rotation (μ SR ) studies on Ce1 -xLaxRu2Al10 (x =0 , 0.3, 0.5, and 0.7), reveal the presence of coherent frequency oscillations indicating a long-range magnetically ordered ground state for x =0 to 0.5, but an almost temperature independent Kubo-Toyabe response between 45 mK and 4 K for x =0.7 . We compare the results of the present investigations with those reported on the electron and hole doping in Ce T2Al10 .
Method of preparing nitrogen containing semiconductor material
Barber, Greg D.; Kurtz, Sarah R.
2004-09-07
A method of combining group III elements with group V elements that incorporates at least nitrogen from a nitrogen halide for use in semiconductors and in particular semiconductors in photovoltaic cells.
Semiconductor Reliability--Another Field for Physicists.
ERIC Educational Resources Information Center
Derman, Samuel; Anderson, Wallace T.
1994-01-01
Stresses that an important industrial area is product reliability, especially for semiconductors. Suggests that physics students would benefit from training in semiconductors: the many modes of failure, radiation effects, and electrical contact problems. (MVL)
Semiconductor electrode with improved photostability characteristics
Frank, Arthur J.
1987-01-01
An electrode is disclosed for use in photoelectrochemical cells having an electrolyte which includes an aqueous constituent. The electrode includes a semiconductor and a hydrophobic film disposed between the semiconductor and the aqueous constituent. The hydrophobic film is adapted to permit charges to pass therethrough while substantially decreasing the activity of the aqueous constituent at the semiconductor surface thereby decreasing the photodegradation of the semiconductor electrode.
Semiconductor nanocrystal-based phagokinetic tracking
Alivisatos, A Paul; Larabell, Carolyn A; Parak, Wolfgang J; Le Gros, Mark; Boudreau, Rosanne
2014-11-18
Methods for determining metabolic properties of living cells through the uptake of semiconductor nanocrystals by cells. Generally the methods require a layer of neutral or hydrophilic semiconductor nanocrystals and a layer of cells seeded onto a culture surface and changes in the layer of semiconductor nanocrystals are detected. The observed changes made to the layer of semiconductor nanocrystals can be correlated to such metabolic properties as metastatic potential, cell motility or migration.
Semiconductor electrode with improved photostability characteristics
Frank, A.J.
1985-02-19
An electrode is described for use in photoelectrochemical cells having an electrolyte which includes an aqueous constituent. The electrode consists of a semiconductor and a hydrophobic film disposed between the semiconductor and the aqueous constituent. The hydrophobic film is adapted to permit charges to pass therethrough while substantially decreasing the activity of the aqueous constituent at the semiconductor surface thereby decreasing the photodegradation of the semiconductor electrode.
Diode having trenches in a semiconductor region
Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth
2016-03-22
An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.
Semiconductor devices having a recessed electrode structure
Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth
2015-05-26
An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.
Semiconductor assisted metal deposition for nanolithography applications
Rajh, Tijana; Meshkov, Natalia; Nedelijkovic, Jovan M.; Skubal, Laura R.; Tiede, David M.; Thurnauer, Marion
2002-01-01
An article of manufacture and method of forming nanoparticle sized material components. A semiconductor oxide substrate includes nanoparticles of semiconductor oxide. A modifier is deposited onto the nanoparticles, and a source of metal ions are deposited in association with the semiconductor and the modifier, the modifier enabling electronic hole scavenging and chelation of the metal ions. The metal ions and modifier are illuminated to cause reduction of the metal ions to metal onto the semiconductor nanoparticles.
Semiconductor assisted metal deposition for nanolithography applications
Rajh, Tijana; Meshkov, Natalia; Nedelijkovic, Jovan M.; Skubal, Laura R.; Tiede, David M.; Thurnauer, Marion
2001-01-01
An article of manufacture and method of forming nanoparticle sized material components. A semiconductor oxide substrate includes nanoparticles of semiconductor oxide. A modifier is deposited onto the nanoparticles, and a source of metal ions are deposited in association with the semiconductor and the modifier, the modifier enabling electronic hole scavenging and chelation of the metal ions. The metal ions and modifier are illuminated to cause reduction of the metal ions to metal onto the semiconductor nanoparticles.
(Magnetic properties of doped semiconductors)
Not Available
1990-01-01
Research continued on the transport behavior of doped semiconductors on both sides of the metal-insulator transition, and the approach to the transition from both the insulating and the metallic side. Work is described on magneto resistance of a series of metallic Si:B samples and CdSe. (CBS)
Conductive Container for Semiconductor Devices
NASA Technical Reports Server (NTRS)
Rice, J. T.
1986-01-01
Container for semiconductor components not only protects them against mechanical damage but ensures they are not harmed by electrostatic discharges. Container holds components in fixed positions so they can be serialized and identified from their locations. Suitable for holding components during both storing and shipping. Originally developed for microwave diodes, container concept readily adaptable to transistors and integrated circuits.
Semiconductor-based optical refrigerator
Epstein, Richard I.; Edwards, Bradley C.; Sheik-Bahae, Mansoor
2002-01-01
Optical refrigerators using semiconductor material as a cooling medium, with layers of material in close proximity to the cooling medium that carries away heat from the cooling material and preventing radiation trapping. In addition to the use of semiconducting material, the invention can be used with ytterbium-doped glass optical refrigerators.
Electronic spectra of semiconductor nanocrystals
Alivisatos, A.P.
1993-12-31
Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.
Semiconductor technology program: Progress briefs
NASA Technical Reports Server (NTRS)
Galloway, K. F.; Scace, R. I.; Walters, E. J.
1981-01-01
Measurement technology for semiconductor materials, process control, and devices, is discussed. Silicon and silicon based devices are emphasized. Highlighted activities include semiinsulating GaAs characterization, an automatic scanning spectroscopic ellipsometer, linewidth measurement and coherence, bandgap narrowing effects in silicon, the evaluation of electrical linewidth uniformity, and arsenicomplanted profiles in silicon.
Mechanical scriber for semiconductor devices
Lin, Peter T.
1985-01-01
A mechanical scriber using a scribing tip, such as a diamond, provides controlled scriber forces with a spring-loaded compound lever arrangement. The scribing force and range of scribing depth are adjusted by a pair of adjustable micrometer heads. A semiconductor device, such as a multilayer solar cell, can be formed into scribed strips at each layer.
Mechanical scriber for semiconductor devices
Lin, P.T.
1985-03-05
A mechanical scriber using a scribing tip, such as a diamond, provides controlled scriber forces with a spring-loaded compound lever arrangement. The scribing force and range of scribing depth are adjusted by a pair of adjustable micrometer heads. A semiconductor device, such as a multilayer solar cell, can be formed into scribed strips at each layer. 5 figs.
A Brief History of ... Semiconductors
ERIC Educational Resources Information Center
Jenkins, Tudor
2005-01-01
The development of studies in semiconductor materials is traced from its beginnings with Michael Faraday in 1833 to the production of the first silicon transistor in 1954, which heralded the age of silicon electronics and microelectronics. Prior to the advent of band theory, work was patchy and driven by needs of technology. However, the arrival…
2010 Defects in Semiconductors GRC
Shengbai Zhang
2011-01-06
Continuing its tradition of excellence, this Gordon Conference will focus on research at the forefront of the field of defects in semiconductors. The conference will have a strong emphasis on the control of defects during growth and processing, as well as an emphasis on the development of novel defect detection methods and first-principles defect theories. Electronic, magnetic, and optical properties of bulk, thin film, and nanoscale semiconductors will be discussed in detail. In contrast to many conferences, which tend to focus on specific semiconductors, this conference will deal with point and extended defects in a broad range of electronic materials. This approach has proved to be extremely fruitful for advancing fundamental understanding in emerging materials such as wide-band-gap semiconductors, oxides, sp{sup 2} carbon based-materials, and photovoltaic/solar cell materials, and in understanding important defect phenomena such as doping bottleneck in nanostructures and the diffusion of defects and impurities. The program consists of about twenty invited talks and a number of contributed poster sessions. The emphasis should be on work which has yet to be published. The large amount of discussion time provides an ideal forum for dealing with topics that are new and/or controversial.
Semiconductor ac static power switch
NASA Technical Reports Server (NTRS)
Vrancik, J.
1968-01-01
Semiconductor ac static power switch has long life and high reliability, contains no moving parts, and operates satisfactorily in severe environments, including high vibration and shock conditions. Due to their resistance to shock and vibration, static switches are used where accidental switching caused by mechanical vibration or shock cannot be tolerated.
Electron beam pumped semiconductor laser
NASA Technical Reports Server (NTRS)
Hug, William F. (Inventor); Reid, Ray D. (Inventor)
2009-01-01
Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.
Optical bistability in semiconductor microcavities
Baas, A.; Karr, J.Ph.; Giacobino, E.; Eleuch, H.
2004-02-01
We report the observation of polaritonic bistability in semiconductor microcavities in the strong-coupling regime. The origin of bistability is the polariton-polariton interaction, which gives rise to a Kerr-like nonlinearity. The experimental results are in good agreement with a simple model taking transverse effects into account.
Semiconductor alloys - Structural property engineering
NASA Technical Reports Server (NTRS)
Sher, A.; Van Schilfgaarde, M.; Berding, M.; Chen, A.-B.
1987-01-01
Semiconductor alloys have been used for years to tune band gaps and average bond lengths to specific applications. Other selection criteria for alloy composition, and a growth technique designed to modify their structural properties, are presently considered. The alloys Zn(1-y)Cd(y)Te and CdSe(y)Te(1-y) are treated as examples.
Amphoteric native defects in semiconductors
Walukiewicz, W.
1989-05-22
We show that a new concept of amphoteric native defects with strongly Fermi level dependent defect formation energy provides the basis for a unified explanation of a large variety of phenomena in semiconductors. Formation of Schottky barriers, particle irradiation induced compensation, doping-induced superlattice intermixing, and limits of free-carrier concentration find for the first time a common simple explanation.
Semiconductor films on flexible iridium substrates
Goyal, Amit
2005-03-29
A laminate semiconductor article includes a flexible substrate, an optional biaxially textured oxide buffer system on the flexible substrate, a biaxially textured Ir-based buffer layer on the substrate or the buffer system, and an epitaxial layer of a semiconductor. Ir can serve as a substrate with an epitaxial layer of a semiconductor thereon.
Advanced Semiconductor Devices
NASA Astrophysics Data System (ADS)
Shur, Michael S.; Maki, Paul A.; Kolodzey, James
2007-06-01
I. Wide band gap devices. Wide-Bandgap Semiconductor devices for automotive applications / M. Sugimoto ... [et al.]. A GaN on SiC HFET device technology for wireless infrastructure applications / B. Green ... [et al.]. Drift velocity limitation in GaN HEMT channels / A. Matulionis. Simulations of field-plated and recessed gate gallium nitride-based heterojunction field-effect transistors / V. O. Turin, M. S. Shur and D. B. Veksler. Low temperature electroluminescence of green and deep green GaInN/GaN light emitting diodes / Y. Li ... [et al.]. Spatial spectral analysis in high brightness GaInN/GaN light emitting diodes / T. Detchprohm ... [et al.]. Self-induced surface texturing of Al2O3 by means of inductively coupled plasma reactive ion etching in Cl2 chemistry / P. Batoni ... [et al.]. Field and termionic field transport in aluminium gallium arsenide heterojunction barriers / D. V. Morgan and A. Porch. Electrical characteristics and carrier lifetime measurements in high voltage 4H-SiC PiN diodes / P. A. Losee ... [et al.]. Geometry and short channel effects on enhancement-mode n-Channel GaN MOSFETs on p and n- GaN/sapphire substrates / W. Huang, T. Khan and T. P. Chow. 4H-SiC Vertical RESURF Schottky Rectifiers and MOSFETs / Y. Wang, P. A. Losee and T. P. Chow. Present status and future Directions of SiGe HBT technology / M. H. Khater ... [et al.]Optical properties of GaInN/GaN multi-quantum Wells structure and light emitting diode grown by metalorganic chemical vapor phase epitaxy / J. Senawiratne ... [et al.]. Electrical comparison of Ta/Ti/Al/Mo/Au and Ti/Al/Mo/Au Ohmic contacts on undoped GaN HEMTs structure with AlN interlayer / Y. Sun and L. F. Eastman. Above 2 A/mm drain current density of GaN HEMTs grown on sapphire / F. Medjdoub ... [et al.]. Focused thermal beam direct patterning on InGaN during molecular beam epitaxy / X. Chen, W. J. Schaff and L. F. Eastman -- II. Terahertz and millimeter wave devices. Temperature-dependent microwave performance of
Controlled growth of semiconductor crystals
Bourret-Courchesne, E.D.
1992-07-21
A method is disclosed for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B[sub x]O[sub y] are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T[sub m1] of the oxide of boron (T[sub m1]=723 K for boron oxide B[sub 2]O[sub 3]), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T[sub m2] of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm[sup 2]. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 [mu]m. 7 figs.
Controlled growth of semiconductor crystals
Bourret-Courchesne, Edith D.
1992-01-01
A method for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B.sub.x O.sub.y are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T.sub.m1 of the oxide of boron (T.sub.m1 =723.degree. K. for boron oxide B.sub.2 O.sub.3), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T.sub.m2 of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm.sup.2. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 .mu.m.
Walukiewicz, W.
1988-07-01
The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration.
Walukiewicz, W.
1988-02-01
The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs.
Preservation of surface features on semiconductor surfaces
Wilt, D.P.
1989-02-14
A semiconductor laser is described comprising a Group III-V compound semiconductor body having a major surface, p1 an optical grating on the major surface, a protective coating on the grating, the coating including a transition metal, a Group III-V compound semiconductor heterostructure formed on the coating, the heterostructure having the shape of a mesa and including a Group III-V compound semiconductor active layer, a current-blocking Group III-V compound semiconductor structure laterally adjacent the mesa and effective to direct the primary flow of current through the mesa during operation of the laser, and means forming electrical contact to the laser.
Broad interband semiconductor laser diodes
NASA Astrophysics Data System (ADS)
Tan, Chee Loon
A semiconductor laser is a diode device that emits light via stimulated emission. Conventionally, light emitted from a semiconductor laser is spatially coherent or narrowband. The fundamental mechanism of stimulated emission process in general leads only to a single wavelength emission. However, there are some lasers emit light with a broad spectrum or different distinct wavelength subjected to various operating conditions such as external grating configuration with semiconductor laser, diode-pumped self-Q-switch fiber laser, ultrashort pulse excitation, photonic crystal fiber, ultrabroadband solid-state lasers, semiconductor optical amplifier-based multiwavelength tunable fiber lasers, nonlinear crystal, broadband semiconductor laser etc. This type of broadband laser is vital in many practical applications such as optical telecommunications, spectroscopy measurement, imaging technology, etc. Recently, an ultra-broadband semiconductor laser that utilizes intersubband optical transitions via quantum cascade configuration has been realized. Laser action with a Fabry-Perot spectrum covering all wavelengths from 6 to 8 microm simultaneously is demonstrated with this approach. More recently, broadband emission results from interband optical transitions via quantum-dot/dash nanostructures have been demonstrated in a simple p-i-n laser diode structure. To date, this latest approach offers the simplest design by proper engineering of quantized energy states as well as utilizing the high inhomogeneity of the dot/dash nanostructures, which is inherent from self-assembled growth technology. In this dissertation, modeling of semiconductor InGaAs/GaAs quantum-dot broadband laser utilizing the properties of inhomogeneous and homogeneous broadening effects on lasing spectral will be discussed, followed by a detail analysis of another type of broad interband semiconductor laser, which is InAs/InGaAlAs quantum-dash broadband laser. Based on the device characterization results
Luo, Yongkang; Chen, Hua; Dai, Jianhui; Xu, Zhu -an; Thompson, J. D.
2015-02-25
Motivated by the high sensitivity to Fermi surface topology and scattering mechanisms in magnetothermoelectric transport, we have measured the thermopower and Nernst effect on the (011) plane of the proposed topological Kondo insulator SmB6. These experiments, together with electrical resistivity and Hall effect measurements, suggest that the (011) plane also harbors a metallic surface with an effective mass on the order of 10–102 m0. The surface and bulk conductances are well distinguished in these measurements and are categorized into metallic and nondegenerate semiconducting regimes, respectively. As a result, electronic correlations play an important role in enhancing scattering and also contributemore » to the heavy surface state.« less
Anomalous Hall effect in L 10-MnAl films with controllable orbital two-channel Kondo effect
NASA Astrophysics Data System (ADS)
Zhu, L. J.; Nie, S. H.; Zhao, J. H.
2016-05-01
The anomalous Hall effect (AHE) in strongly disordered magnetic systems has been buried in persistent confusion despite its long history. We report the AHE in perpendicularly magnetized L 10-MnAl epitaxial films with a variable orbital two-channel Kondo (2CK) effect arising from the strong coupling of conduction electrons and the structural disorders of two-level systems. The AHE is observed to excellently scale with ρAH/f =a0ρx x 0+b ρxx 2 at high temperatures where phonon scattering prevails. In contrast, significant deviation occurs at low temperatures where the orbital 2CK effect becomes important, suggesting a negative AHE contribution. The deviation of the scaling agrees with the orbital 2CK effect in the breakdown temperatures and deviation magnitudes.
Emergent Kondo Lattice Behavior in Iron-Based Superconductors A Fe2As2 (A =K , Rb, Cs)
NASA Astrophysics Data System (ADS)
Wu, Y. P.; Zhao, D.; Wang, A. F.; Wang, N. Z.; Xiang, Z. J.; Luo, X. G.; Wu, T.; Chen, X. H.
2016-04-01
Here, we experimentally study the origin of d -electron heavy fermion (HF) behavior in iron-based superconductors (FeSCs) A Fe2As2 (A =K , Rb, Cs). Nuclear magnetic resonance on 75As reveals a universal coherent-incoherent crossover with a characteristic temperature T*. Below T*, a so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling behavior similar to f -electron HF materials. Furthermore, the scaling rule also regulates the manifestation of magnetic fluctuation. These results undoubtedly support an emergent Kondo lattice scenario for the d -electron HF behavior, which qualifies the A Fe2As2 (A =K , Rb, Cs) as d -electron HF superconductors.
Emergent Kondo Lattice Behavior in Iron-Based Superconductors AFe_{2}As_{2} (A=K, Rb, Cs).
Wu, Y P; Zhao, D; Wang, A F; Wang, N Z; Xiang, Z J; Luo, X G; Wu, T; Chen, X H
2016-04-01
Here, we experimentally study the origin of d-electron heavy fermion (HF) behavior in iron-based superconductors (FeSCs) AFe_{2}As_{2} (A=K, Rb, Cs). Nuclear magnetic resonance on ^{75}As reveals a universal coherent-incoherent crossover with a characteristic temperature T^{*}. Below T^{*}, a so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling behavior similar to f-electron HF materials. Furthermore, the scaling rule also regulates the manifestation of magnetic fluctuation. These results undoubtedly support an emergent Kondo lattice scenario for the d-electron HF behavior, which qualifies the AFe_{2}As_{2} (A=K, Rb, Cs) as d-electron HF superconductors. PMID:27104721
Th-doped URu 2Si 2: influence of “Kondo holes” on coexisting superconductivity and magnetism
NASA Astrophysics Data System (ADS)
de la Torre, A. Lopez; Visani, P.; Dalichaouch, Y.; Lee, B. W.; Maple, M. B.
1992-07-01
The effect of thorium impurities on superconductivity and antiferromagnetism, which coexist below the superconducting critical temperature Tc, has been investigated in the heavy electron compound URu 2Si 2. The substitution of up to 5 at% Th for U was found to (1) enhance the low temperature normal state magnetic susceptibility and electronic specific heat coefficient γ, (2) broaden the superconducting and antiferromagnetic transitions, (3) suppress the specific heat jump associated with the superconductivity at Tc and antiferromagnetism at the Néel temperature TN, and (4) induce a Kondo-like minimum in the electrical resistivity at low temperatures. The increase in γ and decrease in TN and the antiferromagnetic energy gap Δ with negative “chemical pressure” associated with the substitution of Th for U correlates with the decrease in γ and increase in TN and Δ upon application of an external pressure.
Back-side readout semiconductor photomultiplier
Choong, Woon-Seng; Holland, Stephen E
2014-05-20
This disclosure provides systems, methods, and apparatus related to semiconductor photomultipliers. In one aspect, a device includes a p-type semiconductor substrate, the p-type semiconductor substrate having a first side and a second side, the first side of the p-type semiconductor substrate defining a recess, and the second side of the p-type semiconductor substrate being doped with n-type ions. A conductive material is disposed in the recess. A p-type epitaxial layer is disposed on the second side of the p-type semiconductor substrate. The p-type epitaxial layer includes a first region proximate the p-type semiconductor substrate, the first region being implanted with p-type ions at a higher doping level than the p-type epitaxial layer, and a second region disposed on the first region, the second region being doped with p-type ions at a higher doping level than the first region.
Crystal-field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3
NASA Astrophysics Data System (ADS)
Anand, V. K.; Adroja, D. T.; Britz, D.; Strydom, A. M.; Taylor, J. W.; Kockelmann, W.
2016-07-01
Inelastic neutron scattering experiments have been carried out to determine the crystal-field states of the Kondo lattice heavy fermions CeRuSn3 and CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space group P m 3 ¯n ) in which the Ce atoms occupy two distinct crystallographic sites with cubic (m 3 ¯ ) and tetragonal (4 ¯m .2 ) point symmetries. The INS data of CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV, which is accounted by a model based on crystal electric field (CEF) excitations. On the other hand, the INS data of isostructural CeRhSn3 reveal three CEF excitations around 7.0, 12.2, and 37.2 meV. The neutron intensity sum rule indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3 + state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds are deduced. We estimate the Kondo temperature TK=3.1 (2 ) K for CeRuSn3 from neutron quasielastic linewidth in excellent agreement with that determined from the scaling of magnetoresistance which gives TK=3.2 (1 ) K. For CeRhSn3, the neutron quasielastic linewidth gives TK≈4.6 K. For both CeRuSn3 and CeRhSn3, the ground state of Ce3 + turns out to be a quartet for the cubic site and a doublet for the tetragonal site.
Semiconductor electrolyte photovoltaic energy converter
NASA Technical Reports Server (NTRS)
Anderson, W. W.; Anderson, L. B.
1975-01-01
Feasibility and practicality of a solar cell consisting of a semiconductor surface in contact with an electrolyte are evaluated. Basic components and processes are detailed for photovoltaic energy conversion at the surface of an n-type semiconductor in contact with an electrolyte which is oxidizing to conduction band electrons. Characteristics of single crystal CdS, GaAs, CdSe, CdTe and thin film CdS in contact with aqueous and methanol based electrolytes are studied and open circuit voltages are measured from Mott-Schottky plots and open circuit photo voltages. Quantum efficiencies for short circuit photo currents of a CdS crystal and a 20 micrometer film are shown together with electrical and photovoltaic properties. Highest photon irradiances are observed with the GaAs cell.
Coherent magnetic semiconductor nanodot arrays
2011-01-01
In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation. PMID:21711627
Dimensional crossover in semiconductor nanostructures.
McDonald, Matthew P; Chatterjee, Rusha; Si, Jixin; Jankó, Boldizsár; Kuno, Masaru
2016-01-01
Recent advances in semiconductor nanostructure syntheses provide unprecedented control over electronic quantum confinement and have led to extensive investigations of their size- and shape-dependent optical/electrical properties. Notably, spectroscopic measurements show that optical bandgaps of one-dimensional CdSe nanowires are substantially (approximately 100 meV) lower than their zero-dimensional counterparts for equivalent diameters spanning 5-10 nm. But what, exactly, dictates the dimensional crossover of a semiconductor's electronic structure? Here we probe the one-dimensional to zero-dimensional transition of CdSe using single nanowire/nanorod absorption spectroscopy. We find that carrier electrostatic interactions play a fundamental role in establishing dimensional crossover. Moreover, the critical length at which this transition occurs is governed by the aspect ratio-dependent interplay between carrier confinement and dielectric contrast/confinement energies. PMID:27577091
Hypersonic modes in nanophononic semiconductors.
Hepplestone, S P; Srivastava, G P
2008-09-01
Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized Si/Si{0.4}Ge{0.6} superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal. PMID:18851224
Optical conductivity for liquid semiconductors
NASA Astrophysics Data System (ADS)
Jain, Manish; Ko, Eunjung; Derby, J. J.; Chelikowsky, James
2002-03-01
We present calculations for the optical conductivity of several semiconductor liquids: SiGe, GaAs, CdTe, and ZnTe. We perform ab initio molecular dynamics for these liquids. The required interatomic forces are determined using the pseudopotential density functional method. We determine the optical conductivity by considering ensemble averages of the liquid state within the Kubo-Greenwood formalism. In the liquid phase, CdTe and ZnTe exhibit properties that are different from III-V and group IV semiconductors. CdTe and ZnTe remain semiconducting unlike SiGe and GaAs, which are metallic in the melt. These differences in optical conductivities are explained in terms of differences in the microstructure of the liquids. We also verify an empirical rule by Joffe and Regel. Their rule predicts the liquid will remain semiconducting if the short range order of the melt resembles that of the crystalline phase.
Cameras for semiconductor process control
NASA Technical Reports Server (NTRS)
Porter, W. A.; Parker, D. L.
1977-01-01
The application of X-ray topography to semiconductor process control is described, considering the novel features of the high speed camera and the difficulties associated with this technique. The most significant results on the effects of material defects on device performance are presented, including results obtained using wafers processed entirely within this institute. Defects were identified using the X-ray camera and correlations made with probe data. Also included are temperature dependent effects of material defects. Recent applications and improvements of X-ray topographs of silicon-on-sapphire and gallium arsenide are presented with a description of a real time TV system prototype and of the most recent vacuum chuck design. Discussion is included of our promotion of the use of the camera by various semiconductor manufacturers.
Compound semiconductor optical waveguide switch
Spahn, Olga B.; Sullivan, Charles T.; Garcia, Ernest J.
2003-06-10
An optical waveguide switch is disclosed which is formed from III-V compound semiconductors and which has a moveable optical waveguide with a cantilevered portion that can be bent laterally by an integral electrostatic actuator to route an optical signal (i.e. light) between the moveable optical waveguide and one of a plurality of fixed optical waveguides. A plurality of optical waveguide switches can be formed on a common substrate and interconnected to form an optical switching network.
Selective Etching of Semiconductor Glassivation
NASA Technical Reports Server (NTRS)
Casper, N.
1982-01-01
Selective etching technique removes portions of glassivation on a semi-conductor die for failure analysis or repairs. A periodontal needle attached to a plastic syringe is moved by a microprobe. Syringe is filled with a glass etch. A drop of hexane and vacuum pump oil is placed on microcircuit die and hexane is allowed to evaporate leaving a thin film of oil. Microprobe brings needle into contact with area of die to be etched.
Etching Of Semiconductor Wafer Edges
Kardauskas, Michael J.; Piwczyk, Bernhard P.
2003-12-09
A novel method of etching a plurality of semiconductor wafers is provided which comprises assembling said plurality of wafers in a stack, and subjecting said stack of wafers to dry etching using a relatively high density plasma which is produced at atmospheric pressure. The plasma is focused magnetically and said stack is rotated so as to expose successive edge portions of said wafers to said plasma.
Hybrid ferromagnetic-semiconductor structures
Prinz, G.A. )
1990-11-23
Ultrahigh-vacuum growth techniques are now being used to grow single-crystal films of magnetic materials. These growth procedures, carried out in the same molecular beam epitaxy systems commonly used for the growth of semiconductor films, have yielded a variety of new materials and structures that may prove useful for integrated electronics and integrated optical device applications. Examples are given for growth on GaAs and ZnSe, including magnetic sandwiches and patterned structures. 14 refs., 9 figs.
Upper critical field and Kondo effects in Fe(Te0.9Se0.1) thin films by pulsed field measurements
Salamon, Myron B.; Cornell, Nicholas; Jaime, Marcelo; Balakirev, Fedor F.; Zakhidov, Anvar; Huang, Jijie; Wang, Haiyan
2016-02-10
The transition temperatures of epitaxial films of Fe(Te0:9Se0:1) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields Bc2(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find Bc2(0) to be on the order of 45 T, similar to values in bulk material and still in excess of the paramagnetic limit. The same films show strong magnetoresistance in fields above Bc2(T), consistent with the observed Kondo minimum seen above Tc. Fits to the temperature dependence in the context of the WHH model, using the experimental value of the Maki parameter, require anmore » effective spin-orbit relaxation parameter of order unity. Lastly, we suggest that Kondo localization plays a similar role to spin-orbit pair breaking in making WHH fits to the data.« less
Upper Critical Field and Kondo Effects in Fe(Te0.9Se0.1) Thin Films by Pulsed Field Measurements
Salamon, Myron B.; Cornell, Nicholas; Jaime, Marcelo; Balakirev, Fedor F.; Zakhidov, Anvar; Huang, Jijie; Wang, Haiyan
2016-01-01
The transition temperatures of epitaxial films of Fe(Te0:9Se0:1) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields Bc2(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find Bc2(0) to be on the order of 45 T, similar to values in bulk material and still in excess of the paramagnetic limit. The same films show strong magnetoresistance in fields above Bc2(T), consistent with the observed Kondo minimum seen above Tc. Fits to the temperature dependence in the context of the WHH model, using the experimental value of the Maki parameter, require an effective spin-orbit relaxation parameter of order unity. We suggest that Kondo localization plays a similar role to spin-orbit pair breaking in making WHH fits to the data. PMID:26861588
Conductivity in transparent oxide semiconductors
NASA Astrophysics Data System (ADS)
King, P. D. C.; Veal, T. D.
2011-08-01
Despite an extensive research effort for over 60 years, an understanding of the origins of conductivity in wide band gap transparent conducting oxide (TCO) semiconductors remains elusive. While TCOs have already found widespread use in device applications requiring a transparent contact, there are currently enormous efforts to (i) increase the conductivity of existing materials, (ii) identify suitable alternatives, and (iii) attempt to gain semiconductor-engineering levels of control over their carrier density, essential for the incorporation of TCOs into a new generation of multifunctional transparent electronic devices. These efforts, however, are dependent on a microscopic identification of the defects and impurities leading to the high unintentional carrier densities present in these materials. Here, we review recent developments towards such an understanding. While oxygen vacancies are commonly assumed to be the source of the conductivity, there is increasing evidence that this is not a sufficient mechanism to explain the total measured carrier concentrations. In fact, many studies suggest that oxygen vacancies are deep, rather than shallow, donors, and their abundance in as-grown material is also debated. We discuss other potential contributions to the conductivity in TCOs, including other native defects, their complexes, and in particular hydrogen impurities. Convincing theoretical and experimental evidence is presented for the donor nature of hydrogen across a range of TCO materials, and while its stability and the role of interstitial versus substitutional species are still somewhat open questions, it is one of the leading contenders for yielding unintentional conductivity in TCOs. We also review recent work indicating that the surfaces of TCOs can support very high carrier densities, opposite to the case for conventional semiconductors. In thin-film materials/devices and, in particular, nanostructures, the surface can have a large impact on the total
Interfaces in semiconductor/metal radial superlattices
Deneke, Christoph; Sigle, Wilfried; Eigenthaler, Ulrike; Aken, Peter A. van; Schuetz, Gisela; Schmidt, Oliver G.
2007-06-25
Semiconductor/metal radial superlattices are produced by the roll-up of inherently strained InGaAs/Ti/Au as well as InAlGaAs/GaAs/Cr films. Cross sections of the obtained structures are prepared and investigated in detail by diverse transmission electron microscopy as well as microanalysis techniques. Special attention is paid to the interfaces of the semiconductor/metal hybrid superlattice. The study reveals amorphous, noncrystalline layers for the semiconductor/metal as well as for the metal/semiconductor interface. The chemical analysis suggests that the observed interlayers are oxides giving rise to a semiconductor/oxide/metal/oxide superlattice rather than a pure semiconductor/metal superlattice.