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Sample records for kondo semiconductor cerhas

  1. Stabilization of Kondo Semiconductor State by Sb Doping of CeNi1-σSn1+σ and the General Criterion of Its Appearance

    NASA Astrophysics Data System (ADS)

    Spałek, J.; Ślebarski, A.

    2008-07-01

    Semimetallic off-stoichiometric CeNi1-δSn1+δ-xSbx system with δ≈0.06 is shown to transform into a Kondo semiconductor upon the substitution of few percent of Sb for Sn. The full-gap formation is associated with f-electron localization induced by the combined effect of the collective Kondo-singlet formation and the atomic disorder. Namely, the extra valence electrons introduced with the Sb doping (one per Sb atom) contribute additionally to the formation of the collective Kondo spin-singlet state at low temperatures, as seen by a substantial reduction of the magnetic susceptibility. The precise general definition of the Kondo semiconductor is provided and the difference with either the simple band or the Mott-Hubbard insulators is stressed.

  2. Fe Substitution Effect on the High-Field Magnetization in the Kondo Semiconductor CeRu2Al10

    NASA Astrophysics Data System (ADS)

    Kondo, Akihiro; Kindo, Koichi; Nohara, Hiroki; Nakamura, Michio; Tanida, Hiroshi; Sera, Masafumi; Nishioka, Takashi

    2017-02-01

    The magnetization of the Fe substitution system in the Kondo semiconductor CeRu2Al10 was measured in high magnetic fields of up to 72 T with the magnetic field (H) along the a-axis. The magnetization curve indicates that the critical field from the antiferromagnetic (AFM) phase to the paramagnetic one (Hcp) shows an increase from ˜51 (x = 0) to ˜60 T (x = 0.7) owing to the Fe substitution. The Fe concentration dependence of Hcp is similar to that of the magnitude of the energy of the spin gap. The degree of the concave H dependence of the magnetization curve, which is the characteristic feature for H ∥ a in CeT2Al10 (T = Ru, Os), is not strongly enhanced by the Fe substitution. This may be due to the suppression of the strong anisotropy of the hybridization between the conduction band and the localized 4f shell along the a-axis. These results reveal that the spin gap of the present system consists of at least two components, the gap due to the spin (Kondo) singlet formation and the anisotropy gap of the AF magnon.

  3. Doping Effects on the Electronic Structure of an Anisotropic Kondo Semiconductor CeOs2Al10: An Optical Study with Re and Ir Substitution

    NASA Astrophysics Data System (ADS)

    Kimura, Shin-ichi; Takao, Hitoshi; Kawabata, Jo; Yamada, Yoshihiro; Takabatake, Toshiro

    2016-12-01

    An anisotropic Kondo semiconductor CeOs2Al10 exhibits an unusual antiferromagnetic order at rather high transition temperature T0 of 28.5 K. Two possible origins of the magnetic order have been proposed so far, one is the Kondo coupling of the hybridization between the conduction (c) and the 4f states and the other is the charge-density wave/charge ordering along the orthorhombic b-axis. To clarify the origin of the magnetic order, we have investigated the electronic structure of hole- and electron-doped CeOs2Al10 [Ce(Os1-yRey)2Al10 and Ce(Os1-xIrx)2Al10, respectively] by using optical conductivity spectra along the b-axis. The intensity of the c-f hybridization gap at ħω ˜ 50 meV continuously decreases from y = 0.10 to x = 0.12 via x = y = 0. On the other hand, the intensity of the charge excitation observed at ħω ˜ 20 meV has the maximum at x = y = 0 as similar with the doping dependence of T0. The fact that the charge excitation is strongly related to the magnetic order strengthens the possibility of the charge density wave/charge ordering as the origin of the magnetic order.

  4. Doping effects on the hybridization gap and antiferromagnetic order in the Kondo semiconductor CeO s2A l10 studied by break-junction experiments

    NASA Astrophysics Data System (ADS)

    Kawabata, J.; Ekino, T.; Yamada, Y.; Okada, Y.; Sugimoto, A.; Muro, Y.; Takabatake, T.

    2017-01-01

    The Kondo semiconductors Ce T2A l10 (T =Ru and Os) exhibit antiferromagnetic (AFM) orders at unexpectedly high temperatures TN=27.0 and 28.5 K, respectively, whose mechanism remains in debate. We report the break-junction experiments on 4 f /5 d -hole and 5 d -electron doped CeO s2A l10 as well as nondoped CeR u2A l10 . The differential conductance spectra d I /d V for T =Os and Ru show three gap structures; two hybridization gaps V1, V2 and an AFM gap VAF, whose magnitudes for T =Os are 15 -50 % larger than for T =Ru . Doping of 4 f /5 d holes and 5 d electrons in CeO s2A l10 changes the d I /d V spectrum in very different ways. Nevertheless, in all cases, the suppression of V1 is well correlated with those of VAF and TN. Furthermore, the zero-bias conductance decreases on cooling below T* (>TN ) only in the doping region where V1 and VAF coexist. This fact indicates that the unusual AFM order is preceded by the decrease in the density of states in the presence of V1.

  5. Drastic changes in electronic properties of Kondo semiconductor CeRu2Al10 induced by Rh doping: Anisotropic transport properties in the antiferromagnetic ordered state

    NASA Astrophysics Data System (ADS)

    Tanida, H.; Nohara, H.; Nakagawa, F.; Yoshida, K.; Sera, M.; Nishioka, T.

    2016-10-01

    Electrical resistivity (ρ ), thermopower, and specific heat measurements have been performed on the novel Kondo semiconductor Ce (Ru1-xRhx) 2Al10 (x =0 , 0.02, 0.03, and 0.05), which has been attracting a great deal of interest due to an unusual antiferromagnetic (AFM) order below T0, in order to clarify the Rh doping effect on the anisotropy of the electronic properties in the ordered state. In CeRu2Al10 , ρ shows an anisotropic increase below T0 independently of the electric current direction. We propose the existence of two different mechanisms to explain the anisotropic increase of ρ . One is an isotropic charge gap which enhances ρ below T0 isotropically, although its origin is not known at present. The other is an anisotropic suppression of ρ which originates from the anisotropic c-f hybridization and is largest along the orthorhombic a axis. By the Rh doping, the anisotropic temperature dependence of ρ below T0 is drastically changed. For I ∥b , the increase is almost completely suppressed and a metallic-like behavior is observed, whereas it is small and isotropic for I ∥a and c . From these results, we propose that as a result of the destruction of the spin-gap excitation by the Rh doping, a metallic-like electronic state is formed along the b axis and the small isotropic charge gap is opened in the a c plane. By taking into account the present results and the still high T0 even in x =0.05 , we conclude that the AFM order in the Rh-doped CeRu2Al10 should be viewed as unusual as the AFM order in CeRu2Al10 although the localized character of the Ce-4 f electron is apparently enhanced by the Rh doping. We have also examined the evolution of the AFM ordered state from x =0 to x =0.05 , where the AFM ordered moment (mAF) is aligned along the c axis in x =0 and a axis in x =0.05 . From the results of those experiments in magnetic field, we have revealed that the spin reorientation from mAF∥c to mAF∥a takes place quite abruptly just at xc˜0

  6. 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.

  7. Collapse of the G d3 + ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor CeF e4P12

    NASA Astrophysics Data System (ADS)

    Venegas, P. A.; Garcia, F. A.; Garcia, D. J.; Cabrera, G. G.; Avila, M. A.; Rettori, C.

    2016-12-01

    Recent experiments on G d3 + electron-spin resonance (ESR) in the filled skutterudite C e1 -xG dxF e4P12(x ≈0.001 ) , at temperatures where the host resistivity manifests a smooth insulator-metal crossover, provide evidence of the underlying Kondo physics associated with this system. At low temperatures (below T ≈160 K), C e1 -xG dxF e4P12 behaves as a Kondo insulator with a relatively large hybridization gap, and the G d3 + ESR spectra display a fine structure with Lorentzian line shape, typical of insulating media. In this work, based on previous experiments performed by the same group, we argue that the electronic gap may be attributed to the large hybridization present in the coherent regime of a Kondo lattice. Moreover, mean-field calculations suggest that the electron-phonon interaction is fundamental at explaining such hybridization. The resulting electronic structure is strongly temperature dependent, and at T*≈160 K the system undergoes an insulator-to-metal transition induced by the withdrawal of 4 f electrons from the Fermi volume, the system becoming metallic and nonmagnetic. The G d3 + ESR fine structure coalesces into a single Dysonian resonance, as in metals. Our simulations suggest that exchange narrowing via the usual Korringa mechanism is not enough to describe the thermal behavior of the G d3 + ESR spectra in the entire temperature region (4.2-300 K). We propose that the temperature activated fluctuating valence of the Ce ions is the key ingredient that fully describes this unique temperature dependence of the G d3 + ESR fine structure.

  8. Spin Relaxation in Kondo Lattice Systems with Anisotropic Kondo Interaction

    NASA Astrophysics Data System (ADS)

    Belov, S. I.; Kutuzov, A. S.

    2016-12-01

    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.

  9. Corrected Kondo temperature beyond the conventional Kondo scaling limit.

    PubMed

    Li, ZhenHua; Wei, JianHua; Zheng, Xiao; Yan, YiJing; Luo, Hong-Gang

    2017-02-20

    In the Kondo systems such as the magnetic impurity screened by the conduction electrons in a metal host, as well as the quantum dots connected by the leads, the low energy behaviors have universal dependence on the [Formula: see text] or [Formula: see text], where [Formula: see text] is the conventional Kondo temperature. However, it was shown that this scaling behavior is only valid at low-energy; this is called the Kondo scaling limit. Here we explore the extention of the scaling parameter range by introducing the corrected Kondo temperature T K, which may depend on the temperature and bias, as well as the other external parameters. We define the corrected Kondo temperature by scaling the local density of states near the Fermi level, obtained by accurate hierarchy of equations of motion approach at finite temperature and finite bias, and thus obtain a phenomenological expression of the corrected Kondo temperature. By using the corrected Kondo temperature as a characteristic energy scale, the conductance of the quantum dot can be well scaled in a wide parameter range, even two orders beyond the conventional scaling parameter range. Our work indicates that the Kondo scaling, although dominated by the conventional Kondo temperature in the low-energy of the Kondo system, could be extended to a higher energy regime, which is useful for analyzing the physics of the Kondo transport in non-equilibrium or high temperature cases.

  10. 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.

  11. Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system

    SciTech Connect

    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.

  12. 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.

  13. Spin polarization of the split Kondo state.

    PubMed

    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.

  14. A maximally supersymmetric Kondo model

    NASA Astrophysics Data System (ADS)

    Harrison, Sarah; Kachru, Shamit; Torroba, Gonzalo

    2012-10-01

    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.

  15. A Maximally Supersymmetric Kondo Model

    SciTech Connect

    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.

  16. Spatially dependent Kondo effect in Quantum Corrals

    NASA Astrophysics Data System (ADS)

    Rossi, Enrico; Morr, Dirk K.

    2007-03-01

    We study the Kondo screening of a single magnetic impurity placed inside a quantum corral consisting of non-magnetic impurities on the surface of a metallic host system. We show that the spatial structure of the corral's eigenmodes leads to a spatially dependent Kondo effect whose signatures are experimentally measurable spatial variations of the Kondo temperature, TK, and of the critical Kondo coupling, Jcr. Moreover we find that the screening of the magnetic impurity is accompanied by the formation of multiple Kondo resonances with characteristic spatial patterns that provide further experimental signatures of the spatially dependent Kondo effect. Our results demonstrate that quantum corrals provide new possibilities to manipulate and explore the Kondo effect.

  17. Magnetic field induced mixed level Kondo effect in two-level quantum dots

    NASA Astrophysics Data System (ADS)

    Wong, Arturo; Ngo, Anh; Ulloa, Sergio

    2012-02-01

    Semiconductor quantum dots provide an easily tunable environment in which to investigate the Kondo effect. As it is known, Kondo correlations are suppressed by magnetic fields, showing e.g. a drop in the conductance of a quantum dot device. However, certain systems may exhibit an increasing conductance as a function of an applied magnetic field [1]. In this work we use the numerical renormalization group method to study a two-level quantum dot system with on-level and interlevel Coulomb repulsion, coupled to a single channel. When there is a finite detuning between levels, and a local singlet develops in one of them, the linear conductance of the device shows a maximum structure as a function of an in-plane magnetic field, which depends on the temperature of the system. This maximum occurs at a magnetic field strength such that the spin up state of one of the levels and spin down of the other are degenerate, allowing a ``mixed level'' Kondo effect. The respective spectral functions feature a resonance at the Fermi energy, commensurate with the Kondo physics. We discuss the properties of this mixed level Kondo state in terms of the detuning and the other parameters of the system. [4pt] [1] R. Sakano and N. Kawakami, PRB 73, 155332 (2006)

  18. Kondo spin screening cloud in two-dimensional electron gas with spin-orbit couplings.

    PubMed

    Feng, Xiao-Yong; Zhang, Fu-Chun

    2011-03-16

    A spin-1/2 Anderson impurity in a semiconductor quantum well with Rashba and Dresselhaus spin-orbit couplings is studied by using a variational wavefunction method. The local magnetic moment is found to be quenched at low temperatures. The spin-spin correlations of the impurity and the conduction electron density show anisotropy in both spatial and spin spaces, which interpolates the Kondo spin screenings of a conventional metal and of a surface of three-dimensional topological insulators.

  19. The Kondo necklace model with planar anisotropy

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    2009-10-01

    We study the one-dimensional anisotropic Kondo necklace model at zero temperature through White's density matrix renormalization group technique. The ground state energy and the spin gap were calculated as a function of the exchange parameter for two anisotropy values. We found a finite critical point separating a Kondo singlet from an antiferromagnetic phase. The transition is highly congruent with a Kosterlitz-Thouless form. We observed that the critical point increases with the anisotropy.

  20. Spin versus charge noise from Kondo traps

    NASA Astrophysics Data System (ADS)

    da Silva, Luis G. G. V. Dias; de Sousa, Rogério

    2015-08-01

    Magnetic and charge noise have a common microscopic origin in solid-state devices, as described by a universal electron trap model. In spite of this common origin, magnetic (spin) and charge noise spectral densities display remarkably different behaviors when many-particle correlations are taken into account, leading to the emergence of the Kondo effect. We derive exact frequency sum rules for trap noise and perform numerical renormalization-group calculations to show that while spin noise is a universal function of the Kondo temperature, charge noise remains well described by single-particle theory even when the trap is deep in the Kondo regime. We obtain simple analytical expressions for charge and spin noise that account for Kondo screening in all frequency and temperature regimes, enabling the study of the impact of disorder and the emergence of magnetic 1 /f noise from Kondo traps. We conclude that the difference between charge and spin noise survives even in the presence of disorder, showing that noise can be more manageable in devices that are sensitive to magnetic (rather than charge) fluctuations and that the signature of the Kondo effect can be observed in spin noise spectroscopy experiments.

  1. Kondo Destruction in RKKY-Coupled Kondo Lattice and Multi-Impurity Systems

    NASA Astrophysics Data System (ADS)

    Nejati, Ammar; Ballmann, Katinka; Kroha, Johann

    2017-03-01

    In a Kondo lattice, the spin exchange coupling between a local spin and the conduction electrons acquires nonlocal contributions due to conduction electron scattering from surrounding local spins and the subsequent RKKY interaction. It leads to a hitherto unrecognized interference of Kondo screening and the RKKY interaction beyond the Doniach scenario. We develop a renormalization group theory for the RKKY-modified Kondo vertex. The Kondo temperature TK(y ) is suppressed in a universal way, controlled by the dimensionless RKKY coupling parameter y . Complete spin screening ceases to exist beyond a critical RKKY strength yc even in the absence of magnetic ordering. At this breakdown point, TK(y ) remains nonzero and is not defined for larger RKKY couplings y >yc. The results are in quantitative agreement with STM spectroscopy experiments on tunable two-impurity Kondo systems. The possible implications for quantum critical scenarios in heavy-fermion systems are discussed.

  2. Manipulating Kondo temperature via single molecule switching.

    PubMed

    Iancu, Violeta; Deshpande, Aparna; Hla, Saw-Wai

    2006-04-01

    Two conformations of isolated single TBrPP-Co molecules on a Cu(111) surface are switched by applying +2.2 V voltage pulses from a scanning tunneling microscope tip at 4.6 K. The TBrPP-Co has a spin-active cobalt atom caged at its center, and the interaction between the spin of this cobalt atom and free electrons from the Cu(111) substrate can cause a Kondo resonance. Tunneling spectroscopy data reveal that switching from the saddle to a planar molecular conformation enhances spin-electron coupling, which increases the associated Kondo temperature from 130 to 170 K. This result demonstrates that the Kondo temperature can be manipulated just by changing molecular conformation without altering chemical composition of the molecule.

  3. The physics of Kondo impurities in graphene.

    PubMed

    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.

  4. 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.

  5. Kondo lattice without Nozieres exhaustion effect.

    SciTech Connect

    Kikoin, K.; Kiselev, M. N.; Materials Science Division; Ben-Gurion Univ. of the Negev; Ludwig-Maximilians Univ.

    2006-01-01

    We discuss the properties of layered Anderson/Kondo lattices with metallic electrons confined in 2D xy planes and local spins in insulating layers forming chains in the z direction. Each spin in this model possesses its own 2D Kondo cloud, so that the Nozieres exhaustion problem does not occur. The high-temperature perturbational description is matched to exact low-T Bethe-ansatz solution. The excitation spectrum of the model is gapless both in charge and spin sectors. The disordered phases and possible experimental realizations of the model are briefly discussed.

  6. Kondo tunneling through real and artificial molecules.

    PubMed

    Kikoin, K; Avishai, Y

    2001-03-05

    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.

  7. 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 (TKKondo effect and ferromagnetism can be understood within this model.

  8. Interacting electrons and quenched randomness: From the mesoscopic Kondo problem to the depeleted Kondo lattice

    NASA Astrophysics Data System (ADS)

    Kaul, Ribhu

    The physics of strong electron-electron interactions in quantum many body physics is an exciting subject. An understanding of these effects is crucial for explaining the unusual behavior of many materials. These materials are interesting both from a fundamental view point and for application to future technologies. One of the simplest many-body phenomena is the interaction of a local "impurity" spin with a sea of electrons, the so-called "Kondo Impurity Problem," discovered about half a century ago. In the last two decades there has been a huge revival in the study of "Kondo" type phenomena. Experiments on two types of quantum materials have been responsible for this revival. On the one hand, fabrication of nano-meter scale electronic devices that act as "Kondo" impurities have provided flexible and tunable realizations of quantum impurities. On the other hand, the discovery of "Kondo" lattice materials (or "Heavy-Fermion" metals) have provided a window onto the physics of metals with a dense concentration of "Kondo" impurities. This thesis is concerned with physical problems relevant to both these types of materials. Part I of this thesis is concerned with manifestations of the interplay of quantum coherence and the Kondo effect in nano-structures. The effect of this interesting competition can be observed in a variety of nano-devices. In some set-ups the Kondo temperature itself becomes a mesoscopic quantity (Chapter 3), exhibiting huge sample to sample fluctuations, while in other set-ups the definition of the Kondo temperature itself becomes the question of interest (Chapter 4). We have also developed a new method to simulate general quantum impurity models using quantum Monte-Carlo methods (Chapter 5) and applied it to study the universal Kondo physics that takes place when the screening bath is placed in a finite-size box. Finally, we have proposed a new experimental set-up in which the finite-size spectrum of many interesting quantum impurity problems

  9. 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.

  10. 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.

  11. 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.

  12. Entanglement in the Anisotropic Kondo Necklace Model

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    We study the entanglement in the one-dimensional Kondo necklace model with exact diagonalization, calculating the concurrence as a function of the Kondo coupling J and an anisotropy η in the interaction between conduction spins, and we review some results previously obtained in the limiting cases η = 0 and 1. We observe that as J increases, localized and conduction spins get more entangled, while neighboring conduction spins diminish their concurrence; localized spins require a minimum concurrence between conduction spins to be entangled. The anisotropy η diminishes the entanglement for neighboring spins when it increases, driving the system to the Ising limit η = 1 where conduction spins are not entangled. We observe that the concurrence does not give information about the quantum phase transition in the anisotropic Kondo necklace model (between a Kondo singlet and an antiferromagnetic state), but calculating the von Neumann block entropy with the density matrix renormalization group in a chain of 100 sites for the Ising limit indicates that this quantity is useful for locating the quantum critical point.

  13. 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).

  14. The Kondo tip decorated by the Co atom

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Liu, Qin; Lai, Xinchun; Zhao, Aidi

    2016-11-01

    The Kondo effect of single Co adatoms on Ru(0001) is detected with two different kinds of co-decorated tip (Kondo tip) by using low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. We call the relatively separated two magnetic impurities in the tunneling region ‘two Kondo system’ to distinguish it from the ‘two-impurity Kondo system’. We find that the artificially constructed Kondo tips can be generally categorized into two types of Kondo resonances, which have distinct Fano line shapes with quantum interference factor |q| ≫ 1 and |q| ∼ 1, respectively. The tunneling spectra of six constructed two Kondo systems can be well fitted by summing the two Fano resonances of the two subsystems and a linear background. More interestingly, by extracting the amplitudes of the two Fano resonances in the spectra, we find that the electron transmission of such a two Kondo system in the tunneling region is dominated by the quantum interference of the Kondo tip, which is directly related to the geometric configuration of the adsorbed Kondo atom on the tip.

  15. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    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).

  16. Kondo force in shuttling devices: dynamical probe for a Kondo cloud.

    PubMed

    Kiselev, M N; Kikoin, K A; Gorelik, L Y; Shekhter, R I

    2013-02-08

    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.

  17. 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.

  18. Fano-Kondo and the Kondo box regimes crossover in a quantum dot coupled to a quantum box.

    PubMed

    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).

  19. Entanglement entropy near Kondo-destruction quantum critical points

    NASA Astrophysics Data System (ADS)

    Chowdhury, Tathagata; Wagner, Christopher; Ingersent, Kevin; Pixley, Jedediah

    Entanglement entropy is a measure of quantum-mechanical entanglement across the boundary created by partitioning a system into two subsystems. We study this quantity in Kondo impurity models that feature Kondo-destruction quantum critical points (QCPs). Recent work has shown that the entanglement entropy between a Kondo impurity of spin Simp and its environment is pinned at its maximum possible value Se = ln (2Simp + 1) throughout the Kondo phase. In the Kondo-destroyed phase, where the impurity spin acquires a nonzero expectation value Mloc, Se = ln (2Simp + 1) - a (Simp) Mloc2 irrespective of the properties of the host. Here, we report numerical renormalization-group results for Kondo models with a pseudogapped density of states under a different partition that separates the impurity and on-site conduction electrons from the rest of the system. Now, the entanglement entropy is affected by the nature of the environment beyond the information contained in Mloc, but Se still contains a critical part that exhibits power-law behavior in the vicinity of the Kondo-destruction QCP

  20. 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.

  1. 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.

  2. Pairing correlations near a Kondo-destruction quantum critical point

    NASA Astrophysics Data System (ADS)

    Pixley, J. H.; Deng, Lili; Ingersent, Kevin; Si, Qimiao

    2015-05-01

    Motivated by the unconventional superconductivity observed in heavy-fermion metals, we investigate pairing susceptibilities near a continuous quantum phase transition of the Kondo-destruction type. We solve two-impurity Bose-Fermi Anderson models with Ising and Heisenberg forms of the interimpurity exchange interaction using continuous-time quantum Monte Carlo and numerical renormalization-group methods. Each model exhibits a Kondo-destruction quantum critical point separating Kondo-screened and local-moment phases. For antiferromagnetic interimpurity exchange interactions, singlet pairing is found to be enhanced in the vicinity of the transition. Implications of this result for heavy-fermion superconductivity are discussed.

  3. Non-Kondo many-body physics in a Majorana-based Kondo type system

    NASA Astrophysics Data System (ADS)

    van Beek, Ian J.; Braunecker, Bernd

    2016-09-01

    We carry out a theoretical analysis of a prototypical Majorana system, which demonstrates the existence of a Majorana-mediated many-body state and an associated intermediate low-energy fixed point. Starting from two Majorana bound states, hosted by a Coulomb-blockaded topological superconductor and each coupled to a separate lead, we derive an effective low-energy Hamiltonian, which displays a Kondo-like character. However, in contrast to the Kondo model which tends to a strong- or weak-coupling limit under renormalization, we show that this effective Hamiltonian scales to an intermediate fixed point, whose existence is contingent upon teleportation via the Majorana modes. We conclude by determining experimental signatures of this fixed point, as well as the exotic many-body state associated with it.

  4. 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.

  5. Universal out-of-equilibrium transport in Kondo-correlated quantum dots: renormalized dual fermions on the Keldysh contour.

    PubMed

    Muñoz, Enrique; Bolech, C J; Kirchner, Stefan

    2013-01-04

    The nonlinear conductance of semiconductor heterostructures and single molecule devices exhibiting Kondo physics has recently attracted attention. We address the observed sample dependence of the measured steady state transport coefficients by considering additional electronic contributions in the effective low-energy model underlying these experiments that are absent in particle-hole symmetric setups. A novel version of the superperturbation theory of Hafermann et al. in terms of dual fermions is developed, which correctly captures the low-temperature behavior. We compare our results with the measured transport coefficients.

  6. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  7. 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.

  8. 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.

  9. Evidence of Kondo effect in organic radical nanoassemblies

    NASA Astrophysics Data System (ADS)

    Rashidi, Mohammad; Mullegger, Stefan; Fattinger, Michael; Koch, Reinhold

    2012-02-01

    The outstanding spatial resolution of low temperature (LT) scanning tunneling microscopy (STM) and spectroscopy (STS) enables to probe the frontier orbital electronic structure of single magnetic molecules and clusters adsorbed on substrates. Here, we study self-aligned nanostructures of (spin-1/2) hydrocarbon radicals on a metal surface by means of LT-STM and STS. Pronounced involvement of surface state electrons is observed in the frontier molecular orbital (MO) resonances. An empty hybrid state closely above the substrate Fermi level exhibits the characteristic properties of surface Kondo effect reported for similar systems in the literature. By identifying three electronic states as hybrids of molecular orbitals and surface state electrons (two of them directly related to the Kondo effect), we are able to present a modified picture of the surface Kondo effect. It is based on a valence-bond model, where the bonding state represents Kondo's virtual bound state and the antibonding state is the so called 'Kondo resonance' reported in STM studies of the surface Kondo effect. Furthermore, double occupation of the originally singly unoccupied MO by tunneling electrons leads to the third state well above the Fermi level due to Coulomb repulsion as described by the Anderson model.

  10. Mid-gap states and Kondo effect in disordered graphene

    NASA Astrophysics Data System (ADS)

    Lewenkopf, Caio; Miranda, Vladimir; Dias da Silva, Luis

    2012-02-01

    Recent experiments on graphene flakes with short range scattering defects have stengthen the interest on Kondo physics in graphene systems. The experimental data show a temperature dependence of the resistivity consistent with the low-temperature Kondo screening of local magnetic moments. While the linear dispersion in the density of states in graphene justify a pseudogap Kondo model showing a rich variety of quantum critical behavior as a function of the gate-controlled chemical potential, the presence of disorder can alter this effect in favor of the ``standard'' Kondo model, with a Fermi-liquid ground state. We study these effects with different numerical methods. Tight-binding calculations for diluted scattering defects show the appearance of quasi-localized midgap states in the local density of states at the vicinity of the charge neutrality point. This leads to the formulation a Anderson-like model of localized states within the graphene matrix, which may lead to a Kondo screening consistent with the experiments. To verify this hypothesis, we perform numerical renormalization group (NRG) calculations to study the gate-dependence of the Kondo temperature and the transport properties of this model.

  11. Kondo effect in bosonic spin liquids.

    PubMed

    Florens, Serge; Fritz, Lars; Vojta, Matthias

    2006-01-27

    In a metal, a magnetic impurity is fully screened by the conduction electrons at low temperature. In contrast, impurity moments coupled to spin-1 bulk bosons, such as triplet excitations in paramagnets, are only partially screened, even at the bulk quantum critical point. We argue that this difference is not due to the quantum statistics of the host particles but instead related to the structure of the impurity-host coupling, by demonstrating that frustrated magnets with bosonic spinon excitations can display a bosonic version of the Kondo effect. However, the Bose statistics of the bulk implies distinct behavior, such as a weak-coupling impurity quantum phase transition, and perfect screening for a range of impurity spin values. We discuss implications of our results for the compound Cs2CuCl4, as well as possible extensions to multicomponent bosonic gases.

  12. Shubnikov-de Haas oscillations in the Kondo semimetal CeNiSn

    NASA Astrophysics Data System (ADS)

    Terashima, Taichi; Terakura, Chieko; Uji, Shinya; Aoki, Haruyoshi; Echizen, Yuji; Takabatake, Toshiro

    2001-03-01

    The title compound CeNiSn was once classified as a Kondo insulator. However, recent studies have suggested that the energy gap opening in CeNiSn is a pseudogap with a finite density of states at the Fermi level (see, for example, Refs. 1-3). In the present work, we succeeded in observing Shubnikov-de Haas oscillations in low-temperature magnetoresistance, and thus directly proved that CeNiSn is a semimetal rather than a semiconductor. We discuss experimental results in terms of a hybridization gap picture. References 1. G. Nakamoto et al., J. Phys. Soc. Jpn. 64, 4834 (1995). 2. K. Nakamura et al., Phys. Rev. B 53, 6385 (1996). 3. K. Izawa et al., J. Phys. Soc. Jpn. 65, 3119 (1996).

  13. Vibration-mediated Kondo transport in molecular junctions: conductance evolution during mechanical stretching

    PubMed Central

    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

  14. Tuning magnetism by Kondo effect and frustration

    NASA Astrophysics Data System (ADS)

    Löhneysen, Hilbert V.

    2014-03-01

    Heavy-fermion systems are an ideal playground for studying the quantum phase transition (QPT) between paramagnetic and magnetically ordered ground states arising from the competition between Kondo and RKKY interactions. Two different routes have been identified by various experiments, i. e., the more traditional spin-density-wave (SDW) and the Kondo-breakdown approaches. However, up to now an a-priori assignment of a given system to these different routes has not been possible. Yet another route to quantum criticality not included in the above approaches might be geometric frustration of magnetic moments, a route well known for insulating magnets with competing interactions. First experiments on metallic systems have recently been conducted. In the canonical partially frustrated antiferromagnetic system CePd1-xNixAl, the Néel temperature TN(x) decreases, with TN --> 0 at the critical concentration xc ~ 0.144. The low-temperature specific heat C(T) evolves toward C/ Tα ln(T0/ T) for x -->xc. The unusual T dependence of C/ T is compatible with the Hertz-Millis-Moriya (HMM) scenario of quantum criticality if the quantum-critical fluctuations are two-dimensional in nature. Here two-dimensionality might arise from antiferromagnetic planes that are effectively decoupled by the frustrated Ce atoms in between. An exciting possibility is that the planes of frustrated Ce moments form a two-dimensional spin liquid. In the prototypical heavy-fermion system CeCu6-xAux the experiments by Schröder et al. provided the initial evidence of local quantum criticality. While concentration and pressure tuning of the quantum phase transition (QPT) are described by this scenario, magnetic-field tuning the QPT is in line with the SDW scenario. Elastic neutron scattering experiments on CeCu5.5Au0.5 under hydrostatic pressure p show that at p = 8 kbar, TN and the magnetic propagation vector attain almost the values of CeCu5.7Au0.3. This x - p analogy away from the QPT is highly remarkable

  15. Pattern of adsorption isotherms in Ono-Kondo coordinates.

    PubMed

    Sumanatrakul, Panita; Abaza, Sarah; Aranovich, Gregory L; Sangwichien, Chayanoot; Donohue, Marc D

    2012-02-15

    The Ono-Kondo lattice density functional theory is used to analyze adsorbate-adsorbate interactions for supercritical systems. In prior work, this approach has been used to study intermolecular interactions in subcritical adsorbed phases, and this has included the study of adsorbate-adsorbate repulsions in the regime of adsorption compression. In this paper, we present the general pattern of adsorption isotherms in Ono-Kondo coordinates; this has not been done in the past. For this purpose, experimental isotherms for adsorption of supercritical fluids (including nitrogen, methane, and carbon dioxide) are plotted in Ono-Kondo coordinates. In addition, we performed Grand Canonical Monte Carlo simulations of adsorption for Lennard-Jones molecules and plotted isotherms in Ono-Kondo coordinates. Our results indicate a pattern of isotherms with regimes of adsorbate-adsorbate attractions at low surface coverage and adsorbate-adsorbate repulsions at high surface coverage. When the generalized Ono-Kondo model is used over a wide range of pressures - from low pressures of the Henry's law regime to supercritical pressures - the slope of the isotherm varies from positive at low pressures to negative at high pressures. The linear sections of these graphs show when the adsorbate-adsorbate interaction energies are approximately constant. When these linear sections have negative slopes, it indicates that the system is in a state of adsorption compression.

  16. Entanglement entropy near Kondo-destruction quantum critical points

    NASA Astrophysics Data System (ADS)

    Pixley, J. H.; Chowdhury, Tathagata; Miecnikowski, M. T.; Stephens, Jaimie; Wagner, Christopher; Ingersent, Kevin

    2015-06-01

    We study the impurity entanglement entropy Se in quantum impurity models that feature a Kondo-destruction quantum critical point (QCP) arising from a pseudogap in the conduction-band density of states or from coupling to a bosonic bath. On the local-moment (Kondo-destroyed) side of the QCP, the entanglement entropy contains a critical component that can be related to the order parameter characterizing the quantum phase transition. In Kondo models describing a spin-Simp,Se assumes its maximal value of ln(2 Simp+1 ) at the QCP and throughout the Kondo phase, independent of features such as particle-hole symmetry and under- or overscreening. In Anderson models, Se is nonuniversal at the QCP and, at particle-hole symmetry, rises monotonically on passage from the local-moment phase to the Kondo phase; breaking this symmetry can lead to a cusp peak in Se due to a divergent charge susceptibility at the QCP. Implications of these results for quantum critical systems and quantum dots are discussed.

  17. Spin-valley Kondo effect in silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Shiau, Shiue Yuan

    Recent progress in the fabrication of silicon-based quantum dots opens the prospect of observing the Kondo effect associated with the valley degree of freedom. We compute the dot density of states using an Anderson impurity model, whose structure mimics the nonlinear conductance through a dot. The density of states is obtained as a function of temperature and applied magnetic field in the Kondo regime using an equation-of-motion approach. We show that there is a very complex peak structure near the Fermi energy in the N =1,2,3 Coulomb blockade regimes, but not in the N =4, with several signatures that distinguish this spin-valley Kondo effect from the usual spin Kondo effect seen in GaAs dots. We also show that the valley index is generally not conserved when electrons tunnel into a silicon dot, though the extent of this non-conservation is expected to be sample-dependent. This valley index non-conservation can be detected in principle from the valley Kondo effect. We identify features of the conductance that should enable experimenters to understand the interplay of Zeeman splitting and valley splitting, as well as the dependence of tunneling on the valley degree of freedom.

  18. Metallic ferromagnetism in the Kondo lattice

    PubMed Central

    Yamamoto, Seiji J.; Si, Qimiao

    2010-01-01

    Metallic magnetism is both ancient and modern, occurring in such familiar settings as the lodestone in compass needles and the hard drive in computers. Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still largely missing. The Stoner approach perturbatively treats Coulomb interactions when the latter need to be large, whereas the Nagaoka approach incorporates thermodynamically negligible holes into a half-filled band. Here, we show that the ferromagnetic order of the Kondo lattice is amenable to an asymptotically exact analysis over a range of interaction parameters. In this ferromagnetic phase, the conduction electrons and local moments are strongly coupled but the Fermi surface does not enclose the latter (i.e., it is “small”). Moreover, non-Fermi-liquid behavior appears over a range of frequencies and temperatures. Our results provide the basis to understand some long-standing puzzles in the ferromagnetic heavy fermion metals, and raise the prospect for a new class of ferromagnetic quantum phase transitions. PMID:20798053

  19. Semiconductor heterostructure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold John (Inventor); Woodall, Jerry MacPherson (Inventor)

    1978-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  20. Semiconductor structure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold J. (Inventor); Woodall, Jerry M. (Inventor)

    1979-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  1. Effective Kondo Model for a Trimer on a Metallic Surface

    NASA Astrophysics Data System (ADS)

    Aligia, A. A.

    2006-03-01

    I consider a Hubbard-Anderson model which describes localized orbitals in three different atoms hybridized both among themselves and with a continuum of extended states. Using a generalized Schrieffer-Wolf transformation, I derive an effective Kondo model for the interaction between the doublet ground state of the isolated trimer and the extended states. For an isoceles trimer with distances a, l, l between the atoms, the Kondo temperature is very small for la when a is small. The results agree with experiments for a Cr trimer on Au(111).

  2. Inelastic transport through Aharonov-Bohm interferometer in Kondo regime

    SciTech Connect

    Yoshii, Ryosuke; Eto, Mikio; Sakano, Rui; Affleck, Ian

    2013-12-04

    We formulate elastic and inelastic parts of linear conductance through an Aharonov-Bohm (AB) ring with an embedded quantum dot in the Kondo regime. The inelastic part G{sub inel} is proportional to T{sup 2} when the temperature T is much smaller than the Kondo temperature T{sub K}, whereas it is negligibly small compared with elastic part G{sub el} when T ≫ T{sub K}. G{sub inel} weakly depends on the magnetic flux penetrating the AB ring, which disturbs the precise detection of G{sub el}/(G{sub el}+G{sub inel}) by the visibility of AB oscillation.

  3. 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.

  4. Detecting the Kondo screening cloud around a quantum dot.

    PubMed

    Affleck, I; Simon, P

    2001-03-26

    A fundamental prediction of scaling theories of the Kondo effect is the screening of an impurity spin by a cloud of electrons spread out over a mesoscopic distance. This cloud has never been observed experimentally. Recently, aspects of the Kondo effect have been observed in experiments on quantum dots embedded in quantum wires. Since the length of the wire may be of order the size of the screening cloud, such systems provide an ideal opportunity to observe it. We point out that persistent current measurements in a closed ring provide a conceptually simple way of detecting this fundamental length scale.

  5. Two-point functions in a holographic Kondo model

    NASA Astrophysics Data System (ADS)

    Erdmenger, Johanna; Hoyos, Carlos; O'Bannon, Andy; Papadimitriou, Ioannis; Probst, Jonas; Wu, Jackson M. S.

    2017-03-01

    We develop the formalism of holographic renormalization to compute two-point functions in a holographic Kondo model. The model describes a (0 + 1)-dimensional impurity spin of a gauged SU( N ) interacting with a (1 + 1)-dimensional, large- N , strongly-coupled Conformal Field Theory (CFT). We describe the impurity using Abrikosov pseudo-fermions, and define an SU( N )-invariant scalar operator O built from a pseudo-fermion and a CFT fermion. At large N the Kondo interaction is of the form O^{\\dagger}O, which is marginally relevant, and generates a Renormalization Group (RG) flow at the impurity. A second-order mean-field phase transition occurs in which O condenses below a critical temperature, leading to the Kondo effect, including screening of the impurity. Via holography, the phase transition is dual to holographic superconductivity in (1 + 1)-dimensional Anti-de Sitter space. At all temperatures, spectral functions of O exhibit a Fano resonance, characteristic of a continuum of states interacting with an isolated resonance. In contrast to Fano resonances observed for example in quantum dots, our continuum and resonance arise from a (0 + 1)-dimensional UV fixed point and RG flow, respectively. In the low-temperature phase, the resonance comes from a pole in the Green's function of the form - i< O >2, which is characteristic of a Kondo resonance.

  6. Topological defects of Néel order and Kondo singlet formation for Kondo-Heisenberg model on a honeycomb lattice

    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.

  7. Kondo spin liquid in the Kondo necklace model: Classical disordered phase versus symmetry-protected topological state

    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.

  8. Kondo effect of D\\xAFs and D\\xAFs* mesons in nuclear matter

    NASA Astrophysics Data System (ADS)

    Yasui, Shigehiro; Sudoh, Kazutaka

    2017-03-01

    We study the Kondo effect for D¯s and D¯s* mesons as impurity particles in nuclear matter. The spin-exchange interaction between the D¯s or D¯s* meson and the nucleon induces the enhancement of the effective coupling in the low-energy scattering in the infrared region, whose energy scale of singularity is given by the Kondo scale. We investigate the Kondo scale in the renormalization group equation at nucleon one-loop level. We furthermore study the ground state with the Kondo effect in the mean-field approach, and present that the Kondo scale is related to the mixing strength between the D¯s or D¯s* meson and the nucleon in nuclear matter. We show the spectral function of the impurity when the Kondo effect occurs.

  9. Theory of Kondo suppression of spin polarization in nonlocal spin valves

    NASA Astrophysics Data System (ADS)

    Kim, K.-W.; O'Brien, L.; Crowell, P. A.; Leighton, C.; Stiles, M. D.

    2017-03-01

    We theoretically analyze contributions from the Kondo effect to the spin polarization and spin diffusion length in all-metal nonlocal spin valves. Interdiffusion of ferromagnetic atoms into the normal metal layer creates a region in which Kondo physics plays a significant role, giving discrepancies between experiment and existing theory. We start from a simple model and construct a modified spin drift-diffusion equation which clearly demonstrates how the Kondo physics not only suppresses the electrical conductivity but even more strongly reduces the spin diffusion length. We also present an explicit expression for the suppression of spin polarization due to Kondo physics in an illustrative regime. We compare this theory to previous experimental data to extract an estimate of the Elliot-Yafet probability for Kondo spin flip scattering of 0.7 ±0.4 , in good agreement with the value of 2/3 derived in the original theory of Kondo.

  10. Many-terminal Majorana island: From topological to multichannel Kondo model

    NASA Astrophysics Data System (ADS)

    Herviou, Loïc; Le Hur, Karyn; Mora, Christophe

    2016-12-01

    We study Kondo screening obtained by coupling Majorana bound states, located on a topological superconducting island, to interacting electronic reservoirs. At the charge degeneracy points of the island, we formulate an exact mapping onto the spin-1 /2 multichannel Kondo effect. The coupling to Majorana fermions transforms the tunneling terms into effective fermionic bilinear contributions with a Luttinger parameter K in the leads that is effectively doubled. For strong interactions K =1 /2 , the intermediate fixed point of the standard multichannel Kondo model is exactly recovered. It evolves with K and connects to strong coupling in the noninteracting case K =1 , with maximum conductance between the leads and robustness against channel asymmetries similarly to the topological Kondo effect. For a number of leads above four, there exists a window of Luttinger parameters in which a quantum phase transition can occur between the strong coupling topological Kondo state and the partially conducting multichannel Kondo state.

  11. Kondo screening of the spin and orbital magnetic moments of Fe impurities in Cu

    NASA Astrophysics Data System (ADS)

    Joly, L.; Kappler, J.-P.; Ohresser, P.; Sainctavit, Ph.; Henry, Y.; Gautier, F.; Schmerber, G.; Kim, D. J.; Goyhenex, C.; Bulou, H.; Bengone, O.; Kavich, J.; Gambardella, P.; Scheurer, F.

    2017-01-01

    We use x-ray magnetic circular dichroism to evidence the effect of correlations on the local impurity magnetic moment in an archetypal Kondo system, namely, a dilute Cu:Fe alloy. Applying the sum rules on the Fe L2 ,3 absorption edges, the evolution of the spin and orbital moments across the Kondo temperature are determined separately. The spin moment presents a crossover from a nearly temperature-independent regime below the Kondo temperature to a paramagneticlike regime above. Conversely, the weak orbital moment shows a temperature-independent behavior in the whole temperature range, suggesting different Kondo screening temperature scales for the spin and orbital moments.

  12. Model for overscreened Kondo effect in ultracold Fermi gas

    NASA Astrophysics Data System (ADS)

    Kuzmenko, I.; Kuzmenko, T.; Avishai, Y.; Kikoin, K.

    2015-04-01

    The feasibility of realizing the overscreened Kondo effect in ultracold Fermi gas of atoms with spin s ≥ 3/2 in the presence of a localized magnetic impurity atom is proved realistic. Specifying (as a mere example) a system of ultracold 22Na Fermi gas and a trapped 6Li impurity, the mechanism of exchange interaction between the Na and Li atoms is elucidated and the exchange constant is found to be positive (antiferromagnetic). The corresponding exchange Hamiltonian is derived, and the Kondo temperature is estimated at the order of 500 nK. Within a weak-coupling renormalization group scheme, it is shown that the coupling renormalizes to the non-Fermi-liquid fixed point. An observable displaying multichannel features even in the weak-coupling regime is the impurity magnetization that is negative for T ≫TK and becomes positive with decreasing temperature.

  13. Macroscopic quantum entanglement of a Kondo cloud at finite temperature.

    PubMed

    Lee, S-S B; Park, Jinhong; Sim, H-S

    2015-02-06

    We propose a variational approach for computing the macroscopic entanglement in a many-body mixed state, based on entanglement witness operators, and compute the entanglement of formation (EoF), a mixed-state generalization of the entanglement entropy, in single- and two-channel Kondo systems at finite temperature. The thermal suppression of the EoF obeys power-law scaling at low temperature. The scaling exponent is halved from the single- to the two-channel system, which is attributed, using a bosonization method, to the non-Fermi liquid behavior of a Majorana fermion, a "half" of a complex fermion, emerging in the two-channel system. Moreover, the EoF characterizes the size and power-law tail of the Kondo screening cloud of the single-channel system.

  14. Diagonal composite order in a two-channel Kondo lattice.

    PubMed

    Hoshino, Shintaro; Otsuki, Junya; Kuramoto, Yoshio

    2011-12-09

    A novel type of symmetry breaking is reported for the two-channel Kondo lattice where conduction electrons have spin and orbital (channel) degrees of freedom. Using the continuous-time quantum Monte Carlo and the dynamical mean-field theory, a spontaneous breaking of the orbital symmetry is observed. The tiny breakdown of orbital occupation number, however, vanishes if the conduction electrons have the particle-hole symmetry. The proper order parameter instead is identified as a composite quantity representing the orbital-selective Kondo effect. The single-particle spectrum of the selected orbital shows insulating property, while the other orbital behaves as a Fermi liquid. This composite order is the first example of odd-frequency order other than off-diagonal order (superconductivity), and is a candidate of hidden order in f-electron systems.

  15. 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.

  16. The Spin Glass-Kondo Competition in Disordered Cerium Systems

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F.; Coqblin, B.

    2013-10-01

    We discuss the competition between the Kondo effect, the spin glass state and a magnetic order observed in disordered Cerium systems. We present firstly the experimental situation of disordered alloys such as CeNi1 - xCux and then the different theoretical approaches based on the Kondo lattice model, with different descriptions of the intersite exchange interaction for the spin glass. After the gaussian approach of the Sherrington-Kirkpatrick model, we discuss the Mattis and the van Hemmen models. Then, we present simple cluster calculations in order to describe the percolative evolution of the clusters from the cluster spin glass to the inhomogeneous ferromagnetic order recently observed in CeNi1 - xCux disordered alloys and finally we discuss the effect of random and transverse magnetic field.

  17. Toward a new microscopic framework for Kondo lattice materials

    NASA Astrophysics Data System (ADS)

    Lonzarich, Gilbert; Pines, David; Yang, Yi-feng

    2017-02-01

    Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. From this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings.

  18. Low temperature properties of the Kondo insulator FeSi

    NASA Astrophysics Data System (ADS)

    Figueira, M. S.; Franco, R.

    2007-07-01

    In this paper we study the low temperature (T) properties of the Kondo insulator FeSi within the X-boson approach. We show that the ground state of the FeSi is metallic and highly correlated with a large effective mass; the low temperature contributions to the specific heat and the resistivity are of the Fermi-liquid type. The low temperature properties are governed by a reentrant transition into a metallic state, that occurs when the chemical potential crosses the gap and enters the conduction band, generating a metallic ground state. The movement of the chemical potential is due to the strong correlations present in the system. We consider the low temperature regime of the Kondo insulator FeSi, where the hybridization gap is completely open. In this situation we identify the two characteristic temperatures: the coherence temperature T0 and the Kondo temperature TKL. In the range T < T0, we identify a regime characterized by the formation of coherent states and Fermi-liquid behavior of the low temperature properties; in the range TKL > T > T0, we identify a regime characterized by an activation energy. Within the X-boson approach we study those low temperature regimes although we do not try to adjust parameters to recover the experimental energy scales.

  19. The low temperature spectral weight transfer problem in Kondo insulators

    NASA Astrophysics Data System (ADS)

    Franco, R.; Silva-Valencia, J.; Figueira, M. S.

    2009-01-01

    In this paper we address the problem of the spectral weight transfer in Kondo insulators (KI). We employ the X-boson approach for the periodic Anderson model, in the U →∞ limit. We calculate the two energy gaps of the system analytically: the indirect gap, Δind = Eg ≃ Emir, present in the density of states, and the direct one Δdir, associated with the minimum energy necessary to produce inter-band transitions. We find that the optical behavior of the system is governed by two energy scales: one of low frequency, characterized by Eg ≃ Emir, in the mid-infrared region (MIR), which is a reminiscent of the heavy fermion Emir peak, that appears in Kondo insulators as a broad maximum in the MIR region and that controls the low temperature transport properties, the gap opening in optical conductivity and the formation of the Drude peak, at ω = 0, in the intermediate temperature range. The other energy scale appears at high frequencies, and is characterized by the direct gap Δdir. According to our results, this peak controls the anomalous redistribution of spectral weight in the optical conductivity. We apply the theory in order to study the Kondo insulator FeSi, and we calculate the optical conductivity of the system and the spectral weight transfer in the optical conductivity.

  20. Kondo resonance from p-wave hybridization in graphene.

    PubMed

    Jafari, S A; Tohyama, T

    2014-10-15

    The p-wave hybridization in graphene present a distinct class of Kondo problem in pseudogap Fermi systems with bath density of states (DOS) ρ₀(ε) ∝ |ε|. The peculiar geometry of substitutional and hollow-site ad-atoms, and effectively the vacancies allow for a p-wave form of momentum dependence in the hybridization of the associated local orbital with the Dirac fermions of the graphene host which results in a different picture than the s-wave momentum independent hybridization. For the p-wave hybridization function, away from the Dirac point we find closed-form formulae for the Kondo temperature TK which in contrast to the s-wave case is non-zero for any value of hybridization strength V of the single impurity Anderson model (SIAM). At the Dirac point where the DOS vanishes, we find a conceivably small value of Vmin above which the Kondo screening takes place even in the presence of particle-hole symmetry. We also show that the non-Lorentzian line shape of the local spectrum arising from anomalous hybridization function leads to much larger TK in vacant graphene compared to a metallic host with similar bandwidth and SIAM parameters.

  1. Antiferromagnetic Kondo lattice compound CePt3P

    PubMed Central

    Chen, Jian; Wang, Zhen; Zheng, Shiyi; Feng, Chunmu; Dai, Jianhui; Xu, Zhu’an

    2017-01-01

    A new ternary platinum phosphide CePt3P was synthesized and characterized by means of magnetic, thermodynamic and transport measurements. The compound crystallizes in an antiperovskite tetragonal structure similar to that in the canonical family of platinum-based superconductors APt3P (A = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion superconductor CePt3Si. In contrast to all the superconducting counterparts, however, no superconductivity is observed in CePt3P down to 0.5 K. Instead, CePt3P displays a coexistence of antiferromagnetic ordering, Kondo effect and crystalline electric field effect. A field-induced spin-flop transition is observed below the magnetic ordering temperature TN1 of 3.0 K while the Kondo temperature is of similar magnitude as TN1. The obtained Sommerfeld coefficient of electronic specific heat is γCe = 86 mJ/mol·K2 indicating that CePt3P is a moderately correlated antiferromagnetic Kondo lattice compound. PMID:28157184

  2. Kondo physics from quasiparticle poisoning in Majorana devices

    DOE PAGES

    Plugge, S.; Tsvelik, A. M.; Zazunov, A.; ...

    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

  3. Kondo physics from quasiparticle poisoning in Majorana devices

    SciTech Connect

    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 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.

  4. 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.

  5. 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.

  6. Spins of adsorbed molecules investigated by the detection of Kondo resonance

    NASA Astrophysics Data System (ADS)

    Komeda, Tadahiro

    2014-12-01

    Surface magnetism has been one of the platforms to explore the magnetism in low dimensions. It is also a key component for the development of quantum information processes, which utilizes the spin degree of freedom. The Kondo resonance is a phenomenon that is caused by an interaction between an isolated spin and conduction electrons. First observed in the 1930s as an anomalous increase in the low-temperature resistance of metals embedded with magnetic atoms, the Kondo physics mainly studied the effects of bulk magnetic impurities in the resistivity. In the last 15 years it has undergone a revival by a scanning tunneling microscope (STM) which enables the measurement of the Kondo resonance at surfaces using an atomic scale point contact. The detection of the Kondo resonance can be a powerful tool to explore surface magnetism. In this article, I review recent studies of the surface spin of adsorbed molecules by the detection of the Kondo resonance. Researches on metal phthalocyanine (MPc) and porphyrin molecules will be examined. In addition, the Kondo resonance for double-decker lanthanoide Pc molecules will be discussed. Some of the double-decker Pc molecules show single-molecule magnet (SMM) behavior, which attracts attention as a material for electronic devices. For both classes, the ligand plays a crucial role in determining the parameters of the Kondo resonance, such as the Kondo temperature and the change of the shape from peak to Fano-dip. In addition, the spin in delocalized molecular orbital forms the Kondo resonance, which shows significant differences from the Kondo resonance formed by the metal spins. Since molecular orbital can be tuned in a flexible manner by the design of the molecule, the Kondo resonance formed by delocalized molecular orbital might expand the knowledge of this field.

  7. Emergence of a Kondo singlet state with Kondo temperature well beyond 1000 K in a proton-embedded electron gas

    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.

  8. Kondo correlations formation and the local magnetic moment dynamics in the Anderson model

    NASA Astrophysics Data System (ADS)

    Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

    2017-02-01

    We investigated the typical time scales of the Kondo correlations formation for the single-state Anderson model, when coupling to the reservoir is switched on at the initial time moment. The influence of the Kondo effect appearance on the system non-stationary characteristics was analyzed and discussed.

  9. 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.

  10. Fano–Andreev effect in a T-shape double quantum dot in the Kondo regime

    NASA Astrophysics Data System (ADS)

    Calle, A. M.; Pacheco, M.; Martins, G. B.; Apel, V. M.; Lara, G. A.; Orellana, P. A.

    2017-04-01

    In the present work, we investigate the electronic transport through a T-shape double quantum dot system coupled to two normal leads and to one superconducting lead. We explore the interplay between Kondo and Andreev states due to proximity effects. We find that Kondo resonance is modified by the Andreev bound states, which manifest through Fano antiresonances in the local density of states of the embedded quantum dot and normal transmission. This means that there is a correlation between Andreev bound states and Fano resonances that is robust under the influence of high electronic correlation. We have also found that the dominant couplings at the quantum dots are characterized by a crossover region that defines the range where the Fano–Kondo and the Andreev–Kondo effect prevail in each quantum dot. Likewise, we find that the interaction between Kondo and Andreev bound states has a notable influence on the Andreev transport.

  11. 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).

  12. 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.

  13. Thermoelectric properties of the Kondo insulator FeSb2

    NASA Astrophysics Data System (ADS)

    Figueira, M. S.; Silva-Valencia, J.; Franco, R.

    2012-06-01

    Recently it was shown [A. Bentien, S. Johnsen, G.K.H. Madsen, B.B. Iversen, F. Steglich, Europhys. Lett. 80, 17008 (2007)], that the strongly correlated Kondo insulator FeSb2 exhibits a colossal Seebeck coefficient; however, due to its large lattice thermal conductivity, the dimensionless thermoelectric figure of merit (zT) is only 0.005 at 12 K. This experimental result motivate us to perform a theoretical study of the thermoelectric properties of Kondo insulators, within the framework of the X-boson approach [R. Franco, M.S. Figueira, M.E. Foglio, Phys. Rev. B 66, 045112 (2002)] for the periodic Anderson model. We consider a set of parameters adequate for describing the compound FeSb2, and we calculate the resistivity, the thermoelectric power (Seebeck coefficient), the charge carrier thermal conductance, the thermoelectric factor power (zT), the Wiedemann-Franz law, the specific heat, and the Sommerfeld's γ coefficient. The result of the colossal maximum of the Seebeck coefficient, at low temperatures, has the same order of magnitude as the experimental result [A. Bentien, S. Johnsen, G.K.H. Madsen, B.B. Iversen, F. Steglich, Europhys. Lett. 80, 17008 (2007)]. We also show that those temperature region presents an intermediate valence behavior, characterized by a moderate increase of the Sommerfeld's γ coefficient.

  14. Unveiling the internal entanglement structure of the Kondo singlet

    NASA Astrophysics Data System (ADS)

    Yang, Chun; Feiguin, Adrian E.

    2017-03-01

    We disentangle all the individual degrees of freedom in the quantum impurity problem to deconstruct the Kondo singlet, both in real and 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" to quantify entanglement. We identify "projected natural orbitals" that allow us to individualize a single-particle electronic wave function that is responsible of more than 90 % of the impurity screening. In the weak coupling regime, the impurity is entangled to an electron at the Fermi level, while in the strong coupling regime, the impurity counterintuitively entangles mostly with the high energy electrons and disentangles completely from the low-energy states carving a "hole" around the Fermi level. This enables one to use concurrence as a pseudo order parameter to compute the characteristic "size" of the Kondo cloud, beyond which electrons are weakly correlated to the impurity and are dominated by the physics of the boundary.

  15. Single- or multi-flavor Kondo effect in graphene

    NASA Astrophysics Data System (ADS)

    Zhu, Zhen-Gang; Ding, Kai-He; Berakdar, Jamal

    2010-06-01

    Based on the tight-binding formalism, we investigate the Anderson and the Kondo model for an adatom magnetic impurity above graphene. Different impurity positions are analyzed. Employing a partial-wave representation we study the nature of the coupling between the impurity and the conducting electrons. The components from the two Dirac points are mixed while interacting with the impurity. Two configurations are considered explicitly: the adatom is above one atom (ADA), the other case is the adatom above the center the honeycomb (ADC). For ADA the impurity is coupled with one flavor for both A and B sublattice and both Dirac points. For ADC the impurity couples with multi-flavor states for a spinor state of the impurity. We show, explicitly for a 3d magnetic atom, dz2, (dxz,dyz), and (dx2- y2,dxy) couple respectively with the Γ1, Γ5(E1), and Γ6(E2) representations (reps) of C6v group in ADC case. The bases for these reps of graphene are also derived explicitly. For ADA we calculate the Kondo temperature.

  16. 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.

  17. Periodically driven Kondo impurity in nonequilibrium steady states

    NASA Astrophysics Data System (ADS)

    Iwahori, Koudai; Kawakami, Norio

    2016-12-01

    We study the nonequilibrium dynamics of a periodically driven anisotropic Kondo impurity model. The periodic time dependence is introduced for a local magnetic field which couples to the impurity spin and also for an in-plane exchange interaction. We obtain the exact results on the time evolution for arbitrary periodic time dependence at the special point in the parameter space known as the Toulouse limit. We first consider a specific case where the local magnetic field is periodically switched on and off. When the driving period is much shorter than the inverse of the Kondo temperature, an intriguing oscillating behavior (resonance phenomenon) emerges in the time average of the impurity spin polarization with increasing the local magnetic field intensity. By taking the high-frequency limit of the external driving, we elucidate that the system recovers the translational invariance in time and can be described by a mixture of the zero-temperature and infinite-temperature properties. In certain cases, the system is governed by either zero-temperature or infinite-temperature properties and, therefore, can be properly described by the corresponding equilibrium state.

  18. Spin fluctations and heavy fermions in the Kondo lattice

    SciTech Connect

    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.

  19. Competition between Kondo effect and RKKY physics in graphene magnetism

    NASA Astrophysics Data System (ADS)

    Allerdt, A.; Feiguin, A. E.; Das Sarma, S.

    2017-03-01

    The cooperative behavior of quantum impurities on two-dimensional (2D) materials, such as graphene and bilayer graphene, is characterized by a nontrivial competition between screening (Kondo effect) and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetism. In addition, due to the small density of states at the Fermi level, impurities may not couple to the conduction electrons at all, behaving as free moments. Employing a recently developed exact numerical method to study multi-impurity lattice systems, we obtain nonperturbative results that dramatically depart from expectations based on the conventional RKKY theory. At half filling and for weak coupling, impurities remain in the local moment regime when they are on opposite sublattices, up to a critical value of the interactions when they start coupling antiferromagnetically with correlations that decay very slowly with interimpurity distance. At finite doping, away from half filling, ferromagnetism is completely absent and the physics is dominated by a competition between antiferromagnetism and Kondo effect. In bilayer graphene, impurities on opposite layers behave as free moments, unless the interaction is of the order of the hopping or larger.

  20. 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.

  1. Inelastic tunneling spectroscopy for magnetic atoms and the Kondo resonance.

    PubMed

    Goldberg, E C; Flores, F

    2013-06-05

    The interaction between a single magnetic atom and the metal environment (including a magnetic field) is analyzed by introducing an ionic Hamiltonian combined with an effective crystal-field term, and by using a Green-function equation of motion method. This approach describes the inelastic electron tunneling spectroscopy and the Kondo resonances as due to atomic spin fluctuations associated with electron co-tunneling processes between the leads and the atom. We analyze in the case of Fe on CuN the possible spin fluctuations between states with S = 2 and 3/2 or 5/2 and conclude that the experimentally found asymmetries in the conductance with respect to the applied bias, and its marked structures, are well explained by the 2↔3/2 spin fluctuations. The case of Co is also considered and shown to present, in contrast with Fe, a resonance at the Fermi energy corresponding to a Kondo temperature of 6 K.

  2. 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.

  3. 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.

  4. Tunable pseudogap Kondo effect and quantum phase transitions in Aharonov-Bohm interferometers.

    PubMed

    Dias da Silva, Luis G G V; Sandler, Nancy; Simon, Pascal; Ingersent, Kevin; Ulloa, Sergio E

    2009-04-24

    We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. This system can be described by an effective one-impurity Anderson model with an energy- and flux-dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and transmission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.

  5. Tunable Pseudogap Kondo Effect and Quantum Phase Transitions in Aharonov-Bohm Interferometers

    SciTech Connect

    Dias Da Silva, Luis G; Sandler, Nancy; Simon, Pascal; Ingersent, Kevin; Ulloa, Sergio E

    2009-01-01

    We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. This system can be described by an effective one-impurity Anderson model with an energy- and flux- dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and trans- mission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.

  6. Semiconductor sensors

    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.

  7. 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.

  8. Topological defects of Néel order and Kondo singlet formation for the Kondo-Heisenberg model on a honeycomb lattice

    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.

  9. 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.

  10. Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.

    PubMed

    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}.

  11. A theoretical study of the cluster glass-Kondo-magnetic disordered alloys

    NASA Astrophysics Data System (ADS)

    Zimmer, F. M.; Magalhães, S. G.; Coqblin, B.

    2009-10-01

    The physics of disordered alloys, such as typically the well known case of CeNi1-xCux alloys, showing an interplay among the Kondo effect, the spin glass state and a magnetic order, has been studied firstly within an average description like in the Sherrington-Kirkpatrick model. Recently, a theoretical model [S.G. Magalhaes, F.M. Zimmer, P.R. Krebs, B. Coqblin, Phys. Rev. B 74 (2006) 014427] involving a more local description of the intersite interaction has been proposed to describe the phase diagram of CeNi1-xCux. This alloy is an example of the complex interplay between Kondo effect and frustration in which there is in particular the onset of a cluster-glass state. Although the model given in Magalhaes et al. [Phys. Rev. B 74 (2006) 014427] has reproduced the different phases relatively well, it is not able to describe the cluster-glass state. We study here the competition between the Kondo effect and a cluster glass phase within a Kondo-lattice model with an inter-cluster random Gaussian interaction. The inter-cluster term is treated within the cluster mean-field theory for spin glasses [C.M. Sokoulis, Phys. Rev. B 18 (1978) 3757], while, inside the cluster, an exact diagonalisation is performed including inter-site ferromagnetic and intra-site Kondo interactions. The cluster glass order parameters and the Kondo correlation function are obtained for different values of the cluster size, the intra-cluster ferromagnetic coupling and the Kondo intra-site coupling. We obtain that the increase of the Kondo coupling tends clearly to destroy the cluster glass phase.

  12. How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder

    PubMed Central

    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

  13. 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 (ΓmKondo temperature. In the strong-coupling regime (Γm>TK), on the other hand, the spin-split Kondo resonance takes place due to the MFS-induced Zeeman splitting, which is a genuine many-body effect of the strong Coulomb interaction and the topological superconductivity. We find that the original Kondo resonance is fully restored once the MFSs are strongly hybridized (ɛm>Γm). This unusual interaction between the Kondo effect and the MFS can thus serve to detect the Majorana fermions unambiguously and quantify the degree of overlap between the MFSs in the TS.

  14. How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder.

    PubMed

    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

    2011-11-08

    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.

  15. Thermopower and thermal conductance for a Kondo correlated quantum dot

    NASA Astrophysics Data System (ADS)

    Franco, R.; Silva-Valencia, J.; Figueira, M. S.

    We study the thermopower and thermal conductivity of a gate-defined quantum dot, with a very strong Coulomb repulsion inside the dot, employing the X-boson approach for the impurity Anderson model. Our results show a change in the sign of the thermopower as function of the energy level of the quantum dot (gate voltage), which is associated with an oscillatory behavior and a suppression of the thermopower magnitude at low temperatures. We identify two relevant energy scales: a low temperature scale dominated by the Kondo effect and a T˜Δ temperature scale characterized by charge fluctuations. We also discuss the Wiedemann-Franz relation and the thermoelectric figure of merit. Our results are in qualitative agreement with recent experimental reports and other theoretical treatments.

  16. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    DOE PAGES

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

  17. Quantum Oscillations in Kondo Insulator SmB6

    NASA Astrophysics Data System (ADS)

    Li, Lu

    2015-03-01

    In Kondo insulator samarium hexaboride SmB6, strong correlation and band hybridization lead to a diverging resistance at low temperature. The resistance divergence ends at about 3 Kelvin, a behavior recently demonstrated to arise from the surface conductance. However, questions remain whether and where a topological surface state exists. Quantum oscillations have not been observed to map the Fermi surface. We solve the problem by resolving the Landau Level quantization and Fermi surface topology using torque magnetometry. The observed angular dependence of the Fermi surface cross section suggests two-dimensional surface states on the (101) and (100) plane. Furthermore, similar to the quantum Hall states for graphene, the tracking of the Landau Levels in the infinite magnetic field limit points to -1/2, the Berry phase contribution from the 2D Dirac electronic state.

  18. Kondo Breakdown and Quantum Oscillations in SmB_{6}.

    PubMed

    Erten, Onur; Ghaemi, Pouyan; Coleman, Piers

    2016-01-29

    Recent quantum oscillation experiments on SmB_{6} pose a paradox, for while the angular dependence of the oscillation frequencies suggest a 3D bulk Fermi surface, SmB_{6} 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.

  19. 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.

  20. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    SciTech Connect

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.

  1. Interpretation of experimental results on Kondo systems with crystal field.

    PubMed

    Romero, M A; Aligia, A A; Sereni, J G; Nieva, G

    2014-01-15

    We present a simple approach to calculate the thermodynamic properties of single Kondo impurities including orbital degeneracy and crystal field effects (CFE) by extending a previous proposal by Schotte and Schotte (1975 Phys. Lett. 55A 38). Comparison with exact solutions for the specific heat of a quartet ground state split into two doublets shows deviations below 10% in the absence of CFE and a quantitative agreement for moderate or large CFE. As an application, we fit the measured specific heat of the compounds CeCu2Ge2, CePd3Si0.3, CePdAl, CePt, Yb2Pd2Sn and YbCo2Zn20. The agreement between theory and experiment is very good or excellent depending on the compound, except at very low temperatures due to the presence of magnetic correlations (not accounted for in the model).

  2. Excitations and magnetization density distribution in the dilute ferromagnetic semiconductor Yb14MnSb11

    NASA Astrophysics Data System (ADS)

    Stone, M. B.; Garlea, V. O.; Gillon, B.; Cousson, A.; Christianson, A. D.; Lumsden, M. D.; Nagler, S. E.; Mandrus, D.; Sales, B. C.

    2017-01-01

    Yb14MnSb11 is a rare example of a Kondo lattice compound with ferromagnetic dominated RKKY interactions. As a ferromagnetic semiconductor with Tc≈53 K, it is also a potential compound for exploration of spintronic devices. Here we describe measurements which answer remaining questions regarding the energy scales of the exchange interactions, the valence, and the magnetization density distribution in this system. We find that the system consists of RKKY exchange coupled Mn2 + sites with nearest and next nearest exchange interactions dominating the magnetic spectrum with no significant magnetization density localized on other atomic sites. The extended spread of a negative magnetization around each of the Mn ions supports a Kondo screening cloud scenario for Yb14MnSb11 .

  3. Topological Kondo Insulator (TKI) and related candidate materials: High-resolution ARPES studies

    NASA Astrophysics Data System (ADS)

    Hasan, M. Zahid

    2014-03-01

    In this talk, I plan to present ARPES (synchrotron and laser-based) studies of several mix valence and Kondo insulator phenomena in some of the rare earth heavy fermion compounds in connection to their non-trivial topology of band structures. Focus will be on SmB6 which has been predicted to be a TKI recently. By combining low-temperature and high energy-momentum resolution of the laser-based ARPES technique, for the first time, we accessed the surface electronic structure of the anomalous conductivity regime. At low T, we observe in-gap states within a 4 meV energy window of the Fermi level, which lie clearly within the bulk insulating gap. The in-gap states are found to be suppressed and eventually disappear, as the temperature is raised in approaching the coherent Kondo lattice hybridization (30 K), which proves that the in-gap states strongly depend on the existence of Kondo lattice hybridization and the effective Kondo gap, in agreement with their theoretical predicted origin of topological surface states within the Kondo insulating gap . Our Fermi mapping at the energy corresponding to these in-gap states shows distinct Fermi pockets that enclose the three Kramers' points the surface Brillouin zone, which are remarkably consistent with the theoretically predicted topological surface Fermi surface in the topological Kondo insulating phase within the level of energy resolution. The observed Fermi surface topology of the in-gap states, their temperature dependence across the transport anomaly and Kondo lattice hybridization temperatures, as well as their robustness against repeated thermal recycling, collectively not only provide a unique insight illuminating the nature of the residual conductivity anomaly but also serve as a strong experimental evidence to the predicted topological Kondo insulator phase. I also plan to present results on YbB6 and YbB12 both of which are mix valence compounds. This work is in collaboration with Madhab Neupane, N. Alidoust, S

  4. 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).

  5. Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities

    NASA Astrophysics Data System (ADS)

    Ruiz-Tijerina, David A.; Dias da Silva, Luis G. G. V.

    2017-03-01

    Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have, so far, proved elusive to experimental efforts. In this article we study the thermodynamic, spectral, and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's C3 v and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by T-2 resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the noncritical and Kondo regimes. By contrast, the resistivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back-gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.

  6. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    PubMed Central

    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

  7. Kondo effect in a quantum wire with spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    de Sousa, G. R.; Silva, Joelson F.; Vernek, E.

    2016-09-01

    The influence of spin-orbit interactions on the Kondo effect has been under debate recently. Studies conducted recently on a system composed of an Anderson impurity on a two-dimensional electron gas with a Rashba spin orbit have shown that it can enhance or suppress the Kondo temperature (TK), depending on the relative energy level position of the impurity with respect to the particle-hole symmetric point. Here, we investigate a system composed of a single Anderson impurity, side coupled to a quantum wire with spin-orbit coupling (SOC). We derive an effective Hamiltonian in which the Kondo coupling is modified by the SOC. In addition, the Hamiltonian contains two other scattering terms, the so-called Dzyaloshinskii-Moriya interaction, known to appear in these systems, and another one describing processes similar to the Elliott-Yafet scattering mechanisms. By performing a renormalization group analysis on the effective Hamiltonian, we find that the correction on the Kondo coupling due to the SOC favors the enhancement of the Kondo temperature even in the particle-hole symmetric point of the Anderson model, agreeing with the numerical renormalization group results. Moreover, away from the particle-hole symmetric point, TK always increases with the SOC, accordingly with a previous renormalization group analysis.

  8. Coupled Quantum Dots in the Kondo regime: interference and filtering effects.

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Luis; Sandler, Nancy; Ingersent, Kevin; Ulloa, Sergio

    2006-03-01

    Double quantum-dot systems (DQDs) provide a vast array of possibilities for both theoretical and experimental investigations of the Kondo regime. In this work, we propose DQDs as a possible experimental realization of a Kondo impurity coupled to an effective structured (non-constant) density of states (DoS). We consider a DQD in parallel configuration coupled to metallic leads. By changing the lead-dot and dot-dot couplings, the effective hybridization function for an individual dot displays sharp resonances and/or pseudogaps, allowing for an experimental probe into the transition between both regimes. Using numerical renormalization group methods, we calculate the dot's spectral function in different regimes. For a dot weakly coupled to the leads and strongly coupled to the second dot, the effective DoS has a sharp resonance with width δ and the spectral density shows a splitting in the Kondo resonance for TK>δ, although the Kondo singlet is preserved. Furthermore, for small inter-dot coupling, second order dot-dot interactions through the conduction electrons lead to the formation of a pseudo-gap. The spectral density goes to zero as a power-law |ɛ-ɛF|^2 and the Kondo screening is suppressed. Supported by NFS-NIRT.

  9. Ferromagnetism in the Kondo-lattice compound CePd2P2.

    PubMed

    Tran, Vinh Hung; Bukowski, Zbigniew

    2014-06-25

    We report physical properties of CePd2P2 crystallizing in the tetragonal ThCr2Si2-type structure (space group I4/mmm). Dc-magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistance measurements establish a ferromagnetic ordering below the Curie temperature TC = 28.4 ± 0.2 K. Critical analysis of isothermal and isofield magnetization yields critical exponents of β = 0.405 ± 0.005, γ = 1.11 ± 0.05 and δ = 3.74 ± 0.04. The ordered state is characterized by saturation moment Ms ∼ 0.98μB and magnon energy gap Δ/kB ∼25–35 K. The studied properties reflect a competing influence of the Kondo and crystalline electric field (CEF) interactions. The strength of the Kondo effect is assigned by a low-temperature Kondo scale TK ∼19 ± 10 K and a high-temperature Kondo scale TK ~ H 117 } 10 K. A model of the inelastic scattering of the conduction electrons with an exchanged CEF energy ΔCEF was applied to the magnetic resistivity. An average value ΔCEF = 260 ± 30 K is consistent in the relationships with TK and TK H. We argue that the CePd2P2 compound appears to be a new ferromagnetic Kondo-lattice among the Ce-based intermetallics.

  10. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    DOE PAGES

    Zhu, L. J.; Nie, S. H.; Xiong, P.; ...

    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

  11. Quantum interference and Kondo effects in an Aharonov-Bohm-Casher interferometer containing a laterally coupled double quantum dot

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Tokura, Y.; Tarucha, S.

    2010-01-01

    We theoretically investigate spin-dependent electron transport through an Aharonov-Bohm-Casher interferometer containing a laterally coupled double quantum dot. In particular, we numerically calculate the Aharonov-Bohm and Aharonov-Casher oscillations of the linear conductance in the Kondo regime. We show that the AC oscillation in the Kondo regime deviates from the sinusoidal form.

  12. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Electric-Current-Induced Heat Generation in Kondo Regime

    NASA Astrophysics Data System (ADS)

    Chen, Qiao; Zhang, Ya-Min

    2010-07-01

    Using the nonequilibrium Green's function technique, we investigate the current induced heat generation in Kondo regime. The Kondo effect influences the heat generation significantly. In the curve of heat generation versus the bias, a negative differential of the heat generation is exhibited. The symmetry of the heat generation is destroyed by the strong electron-electron interaction and the electron-phonon interaction.

  13. X-boson cumulant approach to the topological Kondo insulators

    NASA Astrophysics Data System (ADS)

    Ramos, E.; Franco, R.; Silva-Valencia, J.; Foglio, M. E.; Figueira, M. S.

    2014-12-01

    In this work we present a generalization of our previous work of the X-boson approach to the periodic Anderson model (PAM), adequate to study a novel class of intermetallic 4f and 5f orbitals materials: the topological Kondo insulators, whose paradigmatic material is the compound SmB6. For simplicity, we consider a version of the PAM on a 2D square lattice, adequate to describe Ce-based compounds in two dimensions. The starting point of the model is the 4f - Ce ions orbitals, with J = 5/2 multiplet, in the presence of spin-orbit coupling. Our technique works well for all of the parameters of the model and avoids the unwanted phase transitions of the slave boson mean field theory. We present a critical comparison of our results with those of the usual slave boson method, that has been intensively used to describe this class of materials. We also obtain a new valence first order transition which we attribute to the vec k dependence of the hybridization.

  14. 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.

  15. Gapped excitation in dense Kondo lattice CePtZn

    NASA Astrophysics Data System (ADS)

    Harriger, L.; Disseler, S. M.; Gunasekera, J.; Rodriguez-Rivera, J.; Pixley, J.; Manfrinetti, P.; Dhar, S. K.; Singh, D. K.

    2017-01-01

    We report on neutron scattering and muon spin relaxation measurements of dense Kondo lattice CePtZn. The system develops long-range incommensurate magnetic order as the temperature is reduced below TN=1.75 K. Interestingly, a Q -independent gap at E =0.65 meV in the energy spectrum is found to co-exist with the long-range magnetic order. The gap persists to a very high temperature of T ≃100 K. The Q -independent characteristic and its persistence to high temperature hint that the gapped excitation may be manifesting the excited state of the ground-state doublet of the crystal-field energy levels. However, the observed broadness in the linewidth with distinct temperature and field dependencies makes it a nontrivial phenomenon. Qualitative analysis of the experimental data suggests the possible co-existence of a local critical behavior, which is onset near the critical field of H ≃3 T, with the crystal-field excitation in the dynamic properties.

  16. 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.

  17. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Kondo effect in a deformed molecule coupled asymmetrically to ferromagnetic electrodes

    NASA Astrophysics Data System (ADS)

    Wang, Rui-Qiang; Jiang, Kai-Ming

    2009-12-01

    The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of the molecule is taken into account, modeled as interactions with a phonon system, and phonon-assisted Kondo satellites arise on both sides of the usual main Kondo peak. In the antiparallel electrode configuration, the Kondo satellites can be split only for the asymmetric dot-lead couplings, distinguished from the parallel configuration where splitting also exists, even though it is for symmetric case. We also analyze how to compensate the splitting and restore the suppressed zero-bias Kondo resonance. It is shown that one can change the TMR ratio significantly from a negative dip to a positive peak only by slightly modulating a local external magnetic field, whose value is greatly dependent on the electron-phonon coupling strength.

  18. Block entropy and quantum phase transition in the anisotropic Kondo necklace model

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    2010-06-01

    We study the von Neumann block entropy in the Kondo necklace model for different anisotropies η 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 η 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 Δ is included in the Kondo exchange between localized and conduction spins; when Δ diminishes for a fixed value of η, the critical point increases, favoring the antiferromagnetic phase.

  19. Preserved Kondo effect of small cobalt atomic chains on Ru(0001) surface

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Liu, Qin; Zhou, Chunsheng; Lai, Xinchun; Li, Bin; Zhao, Aidi

    2016-12-01

    The evolution of the Kondo effect from a cobalt monomer to a compact dimer, a linear trimer and then a triangular trimer on Ru(0001) surface was studied by atomic manipulation and scanning tunneling spectroscopy (STS). It is found that the Kondo resonances of a compact Co dimer and linear trimer still can be detected in their STS because of the weak ferromagnetic exchange interaction between the Co atoms. However, when the number of the nearest-neighbors for every Co atom in the compact Co clusters is larger than one, for the interaction between Co atoms enter into the regime of the strong ferromagnetic exchange interaction, the Kondo resonance disappear and a new state forms.

  20. Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers.

    PubMed

    Rostami, Habib; Moghaddam, Ali G; Asgari, Reza

    2016-12-21

    We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin-orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man's scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K, which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials.

  1. GW approach to Anderson model in and out of equilibrium : scaling properties in the Kondo regime.

    SciTech Connect

    Spataru, Dan Catalin

    2010-03-01

    The low-energy properties of the Anderson model for a single impurity coupled to two leads are studied using the GW approximation. We find that quantities such as the spectral function at zero temperature, the linear-response conductance as function of temperature or the differential conductance as function of bias voltage exhibit universal scaling behavior in the Kondo regime. We show how the form of the GW scaling functions relates to the form of the scaling functions obtained from the exact solution at equilibrium. We also compare the energy scale that goes inside the GW scaling functions with the exact Kondo temperature, for a broad range of the Coulomb interaction strength in the asymptotic regime. This analysis allows to clarify a presently suspended question in the literature, namely whether or not the GW solution captures the Kondo resonance.

  2. Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Rostami, Habib; Moghaddam, Ali G.; Asgari, Reza

    2016-12-01

    We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin-orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man’s scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K, which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials.

  3. Kondo physics in the single-electron transistor with ac driving

    NASA Astrophysics Data System (ADS)

    Nordlander, Peter; Wingreen, Ned S.; Meir, Yigal; Langreth, David C.

    2000-01-01

    Using a time-dependent Anderson Hamiltonian, a quantum dot with an ac voltage applied to a nearby gate is investigated. A rich dependence of the linear response conductance on the external frequency and driving amplitude is demonstrated. At low frequencies a sufficiently strong ac potential produces sidebands of the Kondo peak in the spectral density of the dot, and a slow, roughly logarithmic decrease in conductance over several decades of frequency. At intermediate frequencies, the conductance of the dot displays an oscillatory behavior due to the appearance of Kondo resonances of the satellites of the dot level. At high frequencies, the conductance of the dot can vary rapidly due to the interplay between photon-assisted tunneling and the Kondo resonance.

  4. Frequency Regimes of Kondo Dynamics in a Single-Electron Transistor

    NASA Astrophysics Data System (ADS)

    Hemingway, Bryan; Kogan, Andrei; Herbert, Stephen; Melloch, Michael

    2013-03-01

    It has been theoretically predicted that the Kondo temperature, TK, serves as the intrinsic timescale for the formation of Kondo correlations between conduction electrons and local spin moments. To probe this timescale, we have measured the time averaged differential conductance, =d /dVds, of a single electron transistor in the spin 1/2 Kondo regime in presence of an oscillating bias voltage, V(t)=Vds+VAC sin(2 πft). We present the amplitude dependent conductance over select frequencies spanning several orders of magnitude below TK to twice TK (TK ~ 16GHz). At frequencies above TK, we find good agreement with theory [Kaminski, et al. Phys. Rev. B 62, 8154 (2000)] in both the low (VAC ~ TK/10) and high (VAC ~ 10TK) amplitude regimes. The onset of non-adiabatic conductance behavior occurs well below prediction, f ~ TK, and becomes more apparent as the frequency nears TK. Supported by NSF DMR award Nos. 0804199 and 1206784.

  5. Quantum dots with even number of electrons: kondo effect in a finite magnetic field

    PubMed

    Pustilnik; Avishai; Kikoin

    2000-02-21

    We show that the Kondo effect can be induced by an external magnetic field in quantum dots with an even number of electrons. If the Zeeman energy B is close to the single-particle level spacing Delta in the dot, the scattering of the conduction electrons from the dot is dominated by an anisotropic exchange interaction. A Kondo resonance then occurs despite the fact that B exceeds by far the Kondo temperature T(K). As a result, at low temperatures T

  6. Kondo interactions from band reconstruction in YbInCu4

    DOE PAGES

    Jarrige, I.; Kotani, A.; Yamaoka, H.; ...

    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.

  7. Understanding the Josephson current through a Kondo-correlated quantum dot.

    PubMed

    Luitz, D J; Assaad, F F; Novotný, T; Karrasch, C; Meden, V

    2012-06-01

    We study the Josephson current 0-π transition of a quantum dot tuned to the Kondo regime. The physics can be quantitatively captured by the numerically exact continuous time quantum Monte Carlo method applied to the single-impurity Anderson model with Bardeen-Cooper-Schrieffer superconducting leads. For a comparison to an experiment, the tunnel couplings are determined by fitting the normal-state linear conductance. Excellent agreement for the dependence of the critical Josephson current on the level energy is achieved. For increased tunnel couplings the Kondo scale becomes comparable to the superconducting gap, and the regime of the strongest competition between superconductivity and Kondo correlations is reached; we predict the gate voltage dependence of the critical current in this regime.

  8. Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers

    NASA Astrophysics Data System (ADS)

    Lobos, A. M.; Aligia, A. A.

    2009-10-01

    We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.

  9. Gap formation and phase transition of the anisotropic Kondo necklace model: Density matrix renormalization group analysis

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    2010-01-01

    We analyze the one-dimensional Kondo necklace model, at zero temperature, with an anisotropy parameter η in the interaction of the conduction chain, by means of the density matrix renormalization group. We calculate the energy gap and estimate the quantum critical points that separate a Kondo singlet state from an antiferromagnetic state, assuming a Kosterlitz-Thouless tendency. We also observe the correlation functions and the structure factors that support our critical points. The resulting phase diagram is presented and compared to that reported previously using Lanczos calculations. It is shown that the quantum critical points vary very slowly with η , but when η approaches zero, they drop abruptly.

  10. Two-channel Kondo physics in a Majorana island coupled to a Josephson junction

    NASA Astrophysics Data System (ADS)

    Landau, L. A.; Sela, E.

    2017-01-01

    We study a Majorana island coupled to a bulk superconductor via a Josephson junction and to multiple external normal leads. In the absence of the Josephson coupling, the system displays a topological Kondo state, which had been largely studied recently. However, we find that this state is unstable even to small Josephson coupling, which instead leads at low temperature T to a new fixed point. Most interesting is the case of three external leads, forming a minimal electronic realization of the long sought two-channel Kondo effect. While the T =0 conductance corresponds to simple resonant Andreev reflection, the leading T dependence forms an experimental fingerprint for non-Fermi-liquid properties.

  11. Spin-orbit interactions in a helical Luttinger liquid with a Kondo impurity

    NASA Astrophysics Data System (ADS)

    Eriksson, Erik

    2013-03-01

    We study the transport properties of a helical Luttinger liquid with a Kondo impurity and spin-orbit interactions. Such a system, which may be realized at the edge of a quantum spin Hall insulator with a gate-induced electric field, provides a mechanism to electrically control the conductance. A Rashba spin-orbit interaction may even change the nature of the Kondo screening [Eriksson et al., Phys. Rev. B 86, 161103(R) (2012)]. Considering other types of spin-orbit interactions, together with an extended non-equilibrium analysis, we further improve the understanding of these phenomena.

  12. Observation of the Kondo effect in a spin-3/2 hole quantum dot

    SciTech Connect

    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.

  13. Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth

    PubMed Central

    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

  14. Relation between the 0.7 anomaly and the Kondo effect: Geometric crossover between a quantum point contact and a Kondo quantum dot

    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.

  15. Blocking transport resonances via Kondo many-body entanglement in quantum dots

    PubMed Central

    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

  16. 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.

  17. Strong spin Seebeck effect in Kondo T-shaped double quantum dots.

    PubMed

    Wójcik, K P; Weymann, I

    2017-02-08

    We investigate, taking a theoretical approach, the thermoelectric and spin thermoelectric properties of a T-shaped double quantum dot strongly coupled to two ferromagnetic leads, focusing on the transport regime in which the system exhibits the two-stage Kondo effect. We study the dependence of the (spin) Seebeck coefficient, the corresponding power factor and the figure of merit on temperature, leads' spin polarization and dot level position. We show that the thermal conductance fulfills a modified Wiedemann-Franz law, also in the regime of suppression of subsequent stages of the Kondo effect by the exchange field resulting from the presence of ferromagnets. Moreover, we demonstrate that the spin thermopower is enhanced at temperatures corresponding to the second stage of Kondo screening. Very interestingly, the spin-thermoelectric response of the system is found to be highly sensitive to the spin polarization of the leads. In some cases spin polarization of the order of 1% is sufficient for a strong spin Seebeck effect to occur. This is explained as a consequence of the interplay between the two-stage Kondo effect and the exchange field induced in the double quantum dot. Due to the possibility of tuning the exchange field by the choice of gate voltage, the spin thermopower may also be tuned to be maximal for desired spin polarization of the leads. All calculations are performed with the aid of the numerical renormalization group technique.

  18. 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.

  19. Two-channel Kondo physics from arsenic bond oscillations in zirconium arsenide selenide

    NASA Astrophysics Data System (ADS)

    Kirchner, Stefan; Cichorek, Tomasz; Bochenek, L.; Schmidt, Marcus; Niewa, Rainer; Czulucki, A.; Auffermann, G.; Steglich, Frank; Kniep, Ruediger

    2015-03-01

    The two-channel Kondo effect is a fascinating but extremely fragile many-body state that has been theoretically discussed extensively. we address metallic compounds of a specific (PbFCl) structure for which a - AT 1 / 2 term to ρ (T) is frequently observed, in line with the two-channel Kondo effect. The origin of this anomalous behavior has remained enigmatic since here, solely the interaction between electrons may account for this behavior, and the two-channel Kondo state is not expected to occur. By combining chemical and structural investigations with various physical property measurements we show that the magnetic field-independent - AT 1 / 2 term to the low-T resistivity observed over two decades in ZrAsxSey with 1.90 <= x + y <= 1.99 originates from vacancies in the layer exclusively built up by As. Furthermore, we can trace back the two-channel Kondo effect in this material to a dynamic Jahn-Teller effect operating at these vacancies. All physical properties of the investigated compounds support this conclusion. Our findings will be relevant also for other metallic systems with pnictogen-pnictogen bondings, e.g., cage-forming compounds like the skutterudites.

  20. Sub-molecular modulation of a 4f driven Kondo resonance by surface-induced asymmetry

    PubMed Central

    Warner, Ben; El Hallak, Fadi; Atodiresei, Nicolae; Seibt, Philipp; Prüser, Henning; Caciuc, Vasile; Waters, Michael; Fisher, Andrew J.; Blügel, Stefan; van Slageren, Joris; Hirjibehedin, Cyrus F.

    2016-01-01

    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 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 hybridization of dysprosium double-decker phthalocyanine 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 have in mediating electronic and magnetic coupling and in accessing many-body quantum states. PMID:27666413

  1. Analytical expression of Kondo temperature in quantum dot embedded in Aharonov-Bohm ring

    PubMed Central

    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∕|ε˜0| and LK = ħvF = TK, where vF is the Fermi velocity and ε˜0 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

  2. Strong spin Seebeck effect in Kondo T-shaped double quantum dots

    NASA Astrophysics Data System (ADS)

    Wójcik, K. P.; Weymann, I.

    2017-02-01

    We investigate, taking a theoretical approach, the thermoelectric and spin thermoelectric properties of a T-shaped double quantum dot strongly coupled to two ferromagnetic leads, focusing on the transport regime in which the system exhibits the two-stage Kondo effect. We study the dependence of the (spin) Seebeck coefficient, the corresponding power factor and the figure of merit on temperature, leads’ spin polarization and dot level position. We show that the thermal conductance fulfills a modified Wiedemann-Franz law, also in the regime of suppression of subsequent stages of the Kondo effect by the exchange field resulting from the presence of ferromagnets. Moreover, we demonstrate that the spin thermopower is enhanced at temperatures corresponding to the second stage of Kondo screening. Very interestingly, the spin-thermoelectric response of the system is found to be highly sensitive to the spin polarization of the leads. In some cases spin polarization of the order of 1% is sufficient for a strong spin Seebeck effect to occur. This is explained as a consequence of the interplay between the two-stage Kondo effect and the exchange field induced in the double quantum dot. Due to the possibility of tuning the exchange field by the choice of gate voltage, the spin thermopower may also be tuned to be maximal for desired spin polarization of the leads. All calculations are performed with the aid of the numerical renormalization group technique.

  3. Analytical expression of Kondo temperature in quantum dot embedded in Aharonov-Bohm ring.

    PubMed

    Yoshii, Ryosuke; Eto, Mikio

    2011-11-23

    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:

  4. A theoretical study of the spin glass-Kondo-magnetic disordered alloys in the presence of a random field

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2012-12-01

    We study here the influence of a random applied magnetic field on the competition between the Kondo effect, the spin glass phase and a ferromagnetic order in disordered cerium systems such as CeNi1-xCux. The model used here takes an intrasite Kondo coupling and an intersite random coupling; both the intersite random coupling and the random magnetic field are described within the Sherrington-Kirkpatrick model and the one-step replica symmetry breaking procedure is also used here. We present phase diagrams giving Temperature versus the Kondo exchange parameter and the random magnetic field makes decrease particularly the importance of the spin glass and ferromagnetic phases.

  5. Cyclotron dynamics of a Kondo singlet in a spin-orbit-coupled alkaline-earth-metal atomic gas

    NASA Astrophysics Data System (ADS)

    Jiang, Bo-Nan; Lv, Hao; Wang, Wen-Li; Du, Juan; Qian, Jun; Wang, Yu-Zhu

    2014-11-01

    We propose a scheme to investigate the interplay between the Kondo-exchange interaction and the quantum spin Hall effect with ultracold fermionic alkaline-earth-metal atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, although the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling.

  6. Genome sequence of Frateuria aurantia type strain (Kondo 67(T)), a xanthomonade isolated from Lilium auratium Lindl.

    SciTech Connect

    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.

  7. Origin of bulk quantum oscillations in the bulk Kondo insulating ground state of SmB6

    NASA Astrophysics Data System (ADS)

    Sebastian, Suchitra; Tan, B. S.; Hsu, Y.-T.; Zeng, B.; Ciomaga Hatnean, M.; Harrison, N.; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, M.; Johannes, M. D.; Murphy, T. P.; Park, J.-H.; Balicas, L.; Shitsevalova, N.; Lonzarich, G. G.; Balakrishnan, G.

    I will discuss our recent observation of quantum oscillations corresponding to a bulk Fermi surface in the Kondo insulator SmB6, and consider their possible origin. New complementary experimental results will be presented which raise the interesting question of whether the underlying ground state corresponds to a novel Kondo regime in which the spin channel is gapless while the charge channel is gapped.

  8. Heavy-Fermion Valence-Bond Liquids in Ultracold Atoms: Cooperation of the Kondo Effect and Geometric Frustration.

    PubMed

    Isaev, L; Rey, A M

    2015-10-16

    We analyze a microscopic mechanism behind the coexistence of a heavy Fermi liquid and geometric frustration in Kondo lattices. We consider a geometrically frustrated periodic Anderson model and demonstrate how orbital fluctuations lead to a Kondo-screened phase in the limit of extreme strong frustration when only local singlet states participate in the low-energy physics. We also propose a setup to realize and study this exotic state with SU(3)-symmetric alkaline-earth cold atoms.

  9. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2–δAs2

    DOE PAGES

    Luo, Yongkang; Ronning, F.; Wakeham, N.; ...

    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

  10. Numerical approach to time-dependent quantum transport and dynamical Kondo transition.

    PubMed

    Zheng, Xiao; Jin, Jinshuang; Welack, Sven; Luo, Meng; Yan, YiJing

    2009-04-28

    An accurate and efficient numerical approach is developed for the transient electronic dynamics of open quantum systems at low temperatures. The calculations are based on a formally exact hierarchical equations of motion quantum dissipation theory [J. S. Jin et al., J. Chem. Phys. 128, 234703 (2008)]. We propose a hybrid scheme that combines the Matsubara expansion technique and a frequency dispersion treatment to account for reservoir correlation functions. The new scheme not just admits various forms of reservoir spectral functions but also greatly reduces the computational cost of the resulting hierarchical equations, especially in the low temperature regime. Dynamical Kondo effects are obtained and the cotunneling induced Kondo transitions are resolved in the transient current in response to time-dependent external voltages.

  11. Superconductivity of composite particles in a two-channel Kondo lattice.

    PubMed

    Hoshino, Shintaro; Kuramoto, Yoshio

    2014-04-25

    Emergence of odd-frequency s-wave superconductivity is demonstrated in the two-channel Kondo lattice by means of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. Around half filling of the conduction bands, divergence of an odd-frequency pairing susceptibility is found, which signals instability toward the superconductivity. The corresponding order parameter is equivalent to a staggered composite-pair amplitude with even frequencies, which involves both localized spins and conduction electrons. A model wave function is constructed for the composite order with the use of symmetry operations such as charge conjugation and channel rotations. Given a certain asymmetry of the conduction bands, another s-wave superconductivity is found that has a uniform order parameter. The Kondo effect in the presence of two channels is essential for both types of unconventional superconductivity.

  12. Layered Kondo lattice model for quantum critical beta-YbAlB4.

    PubMed

    Nevidomskyy, Andriy H; Coleman, P

    2009-02-20

    We analyze the magnetic and electronic properties of the quantum critical heavy fermion superconductor beta-YbAlB4, calculating the Fermi surface and the angular dependence of the extremal orbits relevant to the de Haas-van Alphen measurements. Using a combination of the realistic materials modeling and single-ion crystal field analysis, we are led to propose a layered Kondo lattice model for this system, in which two-dimensional boron layers are Kondo coupled via interlayer Yb moments in a Jz=+/-5/2 state. This model fits the measured single-ion magnetic susceptibility and predicts a substantial change in the electronic anisotropy as the system is pressure tuned through the quantum critical point.

  13. Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire

    PubMed Central

    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

  14. The Kondo effect and coherent transport in stacking-faults-free wurtzite InAs nanowires

    NASA Astrophysics Data System (ADS)

    Kretinin, Andrey V.; Popovitz-Biro, Ronit; Mahalu, Diana; Oreg, Yuval; Heiblum, Moty; Shtrikman, Hadas

    2011-12-01

    The crystalline perfection of wurtzite InAs nanowires grown by the Vapor-Liquid-Solid Molecular Beam Epitaxy technique in combination with careful fabrication of nanowire-based FET devices allowed us to observe a variety of phenomena associated with mesoscopic coherent transport. When the single nanowire channel is nearly pinched-off the Coulomb blockade conductance oscillations exhibit well-pronounced Kondo effect approaching the conductance unitary limit. At some gate voltages the breaking of odd-even parity of the Kondo effect related to the formation of the triplet ground state is observed. At higher gate voltages when the channel is open we observe the Fabry-Pérot type conductance oscillations. The length of the Fabry-Pérot electron resonator deduced from the period of the oscillations is in agreement with the physical length of the nanowire device.

  15. Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature

    NASA Astrophysics Data System (ADS)

    Flores, F.; Goldberg, E. C.

    2017-02-01

    An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.

  16. Bohm-Aharonov and Kondo effects on tunneling currents in a mesoscopic ring

    SciTech Connect

    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}

  17. Spiral magnetic phases on the Kondo Lattice Model: A Hartree-Fock approach

    NASA Astrophysics Data System (ADS)

    Costa, N. C.; Lima, J. P.; dos Santos, Raimundo R.

    2017-02-01

    We study the Kondo Lattice Model (KLM) on a square lattice through a Hartree-Fock approximation in which the local spins are treated semi-classically, in the sense that their average values are modulated by a magnetic wavevector Q while they couple with the conduction electrons through fermion operators. In this way, we obtain a ground state phase diagram in which spiral magnetic phases (in which the wavevector depends on the coupling constants and on the density) interpolate between the low-density ferromagnetic phase and the antiferromagnetic phase at half filling; within small regions of the phase diagram commensurate magnetic phases can coexist with Kondo screening. We have also obtained 'Doniach-like' diagrams, showing the effect of temperature on the ground state phases, and established that for some ranges of the model parameters (the exchange coupling and conduction electron density) the magnetic wavevector changes with temperature, either continuously or abruptly (e.g., from spiral to ferromagnetic).

  18. Excitons in topological Kondo insulators: Theory of thermodynamic and transport anomalies in SmB6

    NASA Astrophysics Data System (ADS)

    Knolle, Johannes; Cooper, Nigel R.

    2017-03-01

    Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated—band versus Mott—insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction-induced band gap. The first discovered Kondo insulator (KI) SmB6 has been predicted to form a topological KI (TKI). However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes inside the charge gap are seen in specific heat, thermal transport, and quantum oscillation experiments in strong magnetic fields. Here, we show that TKIs are susceptible to the formation of excitons and magnetoexcitons. These charge neutral composite particles can account for long-standing anomalies in SmB6 .

  19. Theory of Fano Resonances in Graphene: The Kondo effect probed by STM

    SciTech Connect

    Wehling, T.O.

    2010-06-02

    We consider the theory of Kondo effect and Fano factor energy dependence for magnetic impurity (Co) on graphene. We have performed a first principles calculation and find that the two dimensional E{sub 1} representation made of d{sub xz}, d{sub yz} orbitals is likely to be responsible for the hybridization and ultimately Kondo screening for cobalt on graphene. There are few high symmetry sites where magnetic impurity atom can be adsorbed. For the case of Co atom in the middle of hexagon of carbon lattice we find anomalously large Fano q-factor, q {approx} 80 and strongly suppressed coupling to conduction band. This anomaly is a striking example of quantum mechanical interference related to the Berry phase inherent to graphene band structure.

  20. Jahn-Teller / Kondo Interplay in a Three-Terminal Quantum Dot

    NASA Astrophysics Data System (ADS)

    Toonen, R. C.; Qin, H.; Huettel, A. K.; Goswami, S.; van der Weide, D. W.; Eberl, K.; Blick, R. H.

    2006-03-01

    The Jahn-Teller effect is the spontaneous geometric distortion of a nonlinear molecular entity. The Kondo effect, an expression of asymptotic freedom, arises from the hybridization between localized states of a magnetic impurity and the itinerant states of its environment. The interplay of these two phenomena has attracted the attention of theorists studying the growth and interactions of heavy-fermion systems. Because of the technical difficulties associated with probing isolated impurities in bulk materials, this composite effect has remained experimentally unexplored. We have investigated co-tunneling transport phenomena in a three-terminal quantum dot with triangular symmetry. Our measurements of anomalous spectral signatures reveal interplay between the Jahn-Teller and Kondo effects. This discovery suggests a means of controlling the correlation of spatially separated pairs of entangled electrons (EPR pairs)---a necessary condition for the physical realization of a quantum computer (DiVincenzo's 7th requirement).

  1. Mass-Imbalanced Superconductivity in Effective Two-Channel Kondo Lattice

    NASA Astrophysics Data System (ADS)

    Kusunose, Hiroaki

    2016-11-01

    We propose that mass-imbalanced superconductivity is realized in an effective two-channel Kondo lattice, and its characteristic property appears in electromagnetic responses such as the Meissner effect. Starting from an effective two-channel Kondo lattice model as a low-energy effective theory, and approximating it with two mean-field order parameter components in a self-consistent fashion, it is shown that the balance of the two components is sensitively reflected in the magnitude of the Meissner kernel, while thermodynamic properties are little affected by the balance. This remarkable behavior is understood by the localized character of one partner in the Cooper pair, namely, the effect of the mass imbalance. We briefly mention the relevance to the huge enhancement of the upper critical field under pressure observed in Pr 1-2-20 systems.

  2. Kondo lattice on the edge of a 2D topological insulator

    NASA Astrophysics Data System (ADS)

    Maciejko, Joseph

    2012-02-01

    Much attention has been devoted recently to the experimental and theoretical study of the effect of magnetic impurities on the stability of the gapless boundary modes of topological insulators. When the quantum dynamics of the impurities is considered, those boundary modes constitute novel types of fermionic baths which may affect the nature of possible impurity phases and phase transitions. We study a regular one-dimensional array of quantum magnetic impurities interacting with the helical edge liquid of a two-dimensional time-reversal invariant topological insulator. Exact solutions at the special Toulouse and Luther-Emery points as well as a renormalization group analysis àla Anderson-Yuval allow us to construct a phase diagram in the space of Kondo coupling, electron-electron interaction strength, and electron density. We point out similarities and differences with the Kondo lattice in a ordinary one-dimensional electron gas.

  3. Excitons in topological Kondo insulators: Theory of thermodynamic and transport anomalies in SmB_{6}.

    PubMed

    Knolle, Johannes; Cooper, Nigel R

    2017-03-03

    Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated-band versus Mott-insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction-induced band gap. The first discovered Kondo insulator (KI) SmB_{6} has been predicted to form a topological KI (TKI). However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes inside the charge gap are seen in specific heat, thermal transport, and quantum oscillation experiments in strong magnetic fields. Here, we show that TKIs are susceptible to the formation of excitons and magnetoexcitons. These charge neutral composite particles can account for long-standing anomalies in SmB_{6}.

  4. Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire

    SciTech Connect

    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.

  5. Magnetic field effects on the DOS of a Kondo quantum dot coupled to LL leads

    NASA Astrophysics Data System (ADS)

    Yang, Kai-Hua; Qin, Chang-Dong; Wang, Huai-Yu; Wang, Xu

    2017-01-01

    We investigate the joint effects of a magnetic field and electron-electron interaction on the tunneling density of states (DOS) of a quantum dot coupled to the Luttinger liquid leads in the Kondo regime. We find that for intralead electron interaction, the DOS develops two peaks deviated from the origin by the Zeeman energy. With the increase of the intralead interaction, a phase transition occurs. For moderately strong interaction, the Zeeman splitting peaks develop into two dips. The splitting of the Kondo peak and dip is not symmetric with respect to up and down spins. In the limit of strong interaction the Zeeman splitting behavior disappears and there appears a power-law scaling behavior.

  6. Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire

    DOE PAGES

    Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A.; ...

    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.

  7. 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.

  8. Transport properties of a multichannel Kondo dot in a magnetic field

    NASA Astrophysics Data System (ADS)

    Hörig, Christoph B. M.; Schuricht, Dirk

    2012-04-01

    We study the nonequilibrium transport through a multichannel Kondo quantum dot in the presence of a magnetic field. We use the exact solution of the two-loop renormalization group equation to derive analytical results for the g factor, the spin relaxation rates, the magnetization, and the differential conductance. We show that the finite magnetization leads to a coupling between the conduction channels, which manifests itself in additional features in the differential conductance.

  9. Transport in a hybrid normal metal/topological superconductor Kondo model

    NASA Astrophysics Data System (ADS)

    Chirla, Razvan; Dinu, I. V.; Moldoveanu, V.; Moca, Cǎtǎlin Paşcu

    2014-11-01

    We investigate the equilibrium and nonequilibrium transport through a quantum dot in the Kondo regime, embedded between a normal metal and a topological superconductor supporting Majorana bound states at its end points. We find that the Kondo physics is significantly modified by the presence of the Majorana modes. When the Majorana modes are coupled, aside from the Kondo scale TK, a new energy scale T*≪TK emerges, that controls the low-energy physics of the system. At low temperatures, the ac conductance is suppressed for frequencies below T*, while the noise spectrum acquires a ˜ω3 dependence. At high temperatures, T ≫TK , the regular logarithmic dependence in the differential conductance is also affected. Under nonequilibrium conditions, and in particular in the {T ,B }→0 limit, the differential conductance becomes negative. These findings indicate that the changes in transport may serve as clues for detecting the Majorana bound states in such systems. In terms of methods used, we characterize the transport by using a combination of perturbative and renormalization-group approaches.

  10. Kondo physics of the Anderson impurity model by distributional exact diagonalization

    NASA Astrophysics Data System (ADS)

    Motahari, S.; Requist, R.; Jacob, D.

    2016-12-01

    The distributional exact diagonalization (DED) scheme is applied to the description of Kondo physics in the Anderson impurity model. DED maps Anderson's problem of an interacting impurity level coupled to an infinite bath onto an ensemble of finite Anderson models, each of which can be solved by exact diagonalization. An approximation to the self-energy of the original infinite model is then obtained from the ensemble-averaged self-energy. Using Friedel's sum rule, we show that the particle number constraint, a central ingredient of the DED scheme, ultimately imposes Fermi liquid behavior on the ensemble-averaged self-energy, and thus is essential for the description of Kondo physics within DED. Using the numerical renormalization group (NRG) method as a benchmark, we show that DED yields excellent spectra, both inside and outside the Kondo regime for a moderate number of bath sites. Only for very strong correlations (U /Γ ≫10 ) does the number of bath sites needed to achieve good quantitative agreement become too large to be computationally feasible.

  11. Controlling Kondo-like Scattering at the SrTiO3-based Interfaces

    PubMed Central

    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

  12. Anisotropy induced Kondo splitting in a mechanically stretched molecular junction: A first-principles based study

    SciTech Connect

    Wang, Xiaoli; Hou, Dong; Zheng, Xiao; Yan, YiJing

    2016-01-21

    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){sub 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.

  13. Anisotropy induced Kondo splitting in a mechanically stretched molecular junction: A first-principles based study

    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.

  14. 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).

  15. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

    NASA Astrophysics Data System (ADS)

    Morr, Dirk K.

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  16. Kondo screening in two-dimensional p -type transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Phillips, Michael; Aji, Vivek

    2017-02-01

    Systems with strong spin-orbit coupling support a number of new phases of matter and novel phenomena. This work focuses on the interplay of spin-orbit coupling and interactions in yielding correlated phenomena in two-dimensional transition-metal dichalcogenides. In particular we explore the physics of Kondo screening resulting from the lack of centrosymmetry, large spin splitting, and spin valley locking in hole-doped systems. The key ingredients are (i) valley-dependent spin-momentum locking perpendicular to the two-dimensional crystal, (ii) a single nondegenerate Fermi surface per valley, and (iii) nontrivial Berry curvature associated with the low-energy bands. The resulting Kondo resonance has a finite-triplet component and nontrivial momentum space structure which facilitates new approaches to both probing and manipulating the correlated state. Using a variational wave function and the numerical renormalization group approaches we study the nature of the Kondo resonance both in the absence and presence of circularly polarized light. The latter induces an imbalance in the population of the two valleys leading to novel magnetic phenomena in the correlated state.

  17. 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.

  18. Understanding Quantum Transport and the Kondo Effect in 2D Carbon Systems

    NASA Astrophysics Data System (ADS)

    McIntosh, Ross; Churochkin, Dmitry; Bhattacharyya, Somnath

    2013-03-01

    The rich physics surrounding correlations between conduction electrons and local spins in quantum dot systems is of significant interest towards the development of spintronic quantum information devices. In this study we establish the Kondo effect in reduced graphene oxide (RGO) films through a metal-insulator transition in resistance versus temperature interpreted within the Fermi liquid description of the Kondo effect and negative magnetoresistance which scales with a Kondo characteristic temperature. With a microstructure consisting of intact graphene nano-islands embedded within residual functionalized regions where local magnetic moments may form, RGO is effectively a disordered quantum dot system. This work is augmented with a theoretical study of transport through nano-scale multiple quantum dot devices. Solving within a Keldysh formalism we scrutinize quasi-bound state formation in a range of geometrical quantum dot configurations in order to interpret coherent quantum interference effects. We demonstrate negative differential conductance and control over device parameters such as the characteristic time. This tandem approach illustrates the promise of innovative low dimensional carbon spintronic devices.

  19. Kondo screening of Andreev bound states in a normal metal-quantum dot-superconductor system

    NASA Astrophysics Data System (ADS)

    Li, Lin; Cao, Zhan; Fang, Tie-Feng; Luo, Hong-Gang; Chen, Wei-Qiang

    2016-10-01

    Motivated by experimental observation of the Kondo-enhanced Andreev transport [R. S. Deacon et al., Phys. Rev. B 81, 121308(R) (2010), 10.1103/PhysRevB.81.121308] in a hybrid normal metal-quantum dot-superconductor (N-QD-S) device, we theoretically study the Kondo effect in such a device and clarify the different roles played by the normal and superconducting leads. Due to the Andreev reflection in a QD-S system, a pair of Andreev energy levels form in the superconducting gap, which is able to carry the magnetic moment if the ground state of the QD is a magnetic doublet. In this sense, the Andreev energy levels play a role of effective impurity levels. When the normal lead is coupled to the QD-S system, on the one hand, the Andreev energy levels broaden to form the so-called Andreev bound states (ABSs); on the other hand, it can screen the magnetic moment of the ABSs. By tuning the couplings between the QD and the normal (superconducting) leads, the ABSs can simulate the Kondo, mixed-valence, and even empty orbit regimes of the usual single-impurity Anderson model. The above picture is confirmed by the Green's function calculation of the hybrid N-QD-S Anderson model and is also able to explain qualitatively experimental phenomena observed by Deacon et al. These results can further stimulate related experimental study in the N-QD-S systems.

  20. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials.

    PubMed

    Morr, Dirk K

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments-the differential conductance and the quasi-particle interference spectrum-however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  1. Magnetic-field-induced mixed-level Kondo effect in two-level systems

    SciTech Connect

    Wong, Arturo; Ngo, Anh T.; Ulloa, Sergio E.

    2016-10-17

    We consider a two-orbital impurity system with intra-and interlevel Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local-singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite-spin states. We use the numerical renormalization group approach to fully characterize this mixed-level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature, and system parameters. Under suitable conditions, the total spectral function is shown to develop a Fermi-level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as a function of temperature. These features, as well as the local moment and entropy contribution of the impurity system, are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.

  2. Magnetic-field-induced mixed-level Kondo effect in two-level systems

    NASA Astrophysics Data System (ADS)

    Wong, Arturo; Ngo, Anh T.; Ulloa, Sergio E.

    2016-10-01

    We consider a two-orbital impurity system with intra- and interlevel Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local-singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite-spin states. We use the numerical renormalization group approach to fully characterize this mixed-level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature, and system parameters. Under suitable conditions, the total spectral function is shown to develop a Fermi-level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as a function of temperature. These features, as well as the local moment and entropy contribution of the impurity system, are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.

  3. Quantum phase transitions in the Kondo-necklace model: perturbative continuous unitary transformation approach.

    PubMed

    Hemmatiyan, S; Rahimi Movassagh, M; Ghassemi, N; Kargarian, M; Rezakhani, A T; Langari, A

    2015-04-22

    The Kondo-necklace model can describe 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 transition between the Kondo-singlet phase and the antiferromagnetic long-range ordered phase, and show the effect of anisotropies in terms of quantum information properties and vanishing energy gap. We employ the 'perturbative continuous unitary transformations' approach to calculate the energy gap and spin-spin correlations for the model in the thermodynamic limit of one, two, and three spatial dimensions as well as for spin ladders. In particular, we show that the method, although being perturbative, can predict the expected quantum critical point, where the gap of low-energy spectrum vanishes, which is in good agreement with results of other numerical and Green's function analyses. In addition, we employ concurrence, a bipartite entanglement measure, to study the criticality of the model. Absence of singularities in the derivative of concurrence in two and three dimensions in the Kondo-necklace model shows that this model features multipartite entanglement. We also discuss crossover from the one-dimensional to the two-dimensional model via the ladder structure.

  4. Photoelectrosynthesis at semiconductor electrodes

    SciTech Connect

    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)

  5. On the zero-bias anomaly and Kondo physics in quantum point contacts near pinch-off.

    PubMed

    Xiang, S; Xiao, S; Fuji, K; Shibuya, K; Endo, T; Yumoto, N; Morimoto, T; Aoki, N; Bird, J P; Ochiai, Y

    2014-03-26

    We investigate the linear and non-linear conductance of quantum point contacts (QPCs), in the region near pinch-off where Kondo physics has previously been connected to the appearance of the 0.7 feature. In studies of seven different QPCs, fabricated in the same high-mobility GaAs/AlGaAs heterojunction, the linear conductance is widely found to show the presence of the 0.7 feature. The differential conductance, on the other hand, does not generally exhibit the zero-bias anomaly (ZBA) that has been proposed to indicate the Kondo effect. Indeed, even in the small subset of QPCs found to exhibit such an anomaly, the linear conductance does not always follow the universal temperature-dependent scaling behavior expected for the Kondo effect. Taken collectively, our observations demonstrate that, unlike the 0.7 feature, the ZBA is not a generic feature of low-temperature QPC conduction. We furthermore conclude that the mere observation of the ZBA alone is insufficient evidence for concluding that Kondo physics is active. While we do not rule out the possibility that the Kondo effect may occur in QPCs, our results appear to indicate that its observation requires a very strict set of conditions to be satisfied. This should be contrasted with the case of the 0.7 feature, which has been apparent since the earliest experimental investigations of QPC transport.

  6. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    SciTech Connect

    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- to 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.

  7. Unexpected observation of spatially separated Kondo scattering and ferromagnetism in Ta alloyed anatase TiO2 thin films

    NASA Astrophysics Data System (ADS)

    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.

    2015-08-01

    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.

  8. Unitary lens semiconductor device

    DOEpatents

    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.

  9. Unitary lens semiconductor device

    DOEpatents

    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.

  10. Kondo Impurities in the Kitaev Spin Liquid: Numerical Renormalization Group Solution and Gauge-Flux-Driven Screening.

    PubMed

    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.

  11. The Ising-Anisotropic Kondo Lattice in a transverse field: EDMFT study and implications for the global phase diagram

    NASA Astrophysics Data System (ADS)

    Nica, Emilian Marius; Ingersent, Kevin; Si, Qimiao

    2015-03-01

    Heavy-fermion materials exhibit a rich variety of phase transitions. Of particular interest are quantum phase transitions and the associated breakdown of the Fermi liquid picture. A theoretical example of this is the Kondo destruction effect in the context of local quantum criticality. To capture this effect and others, a zero-temperature global phase diagram for heavy-fermion materials has been proposed. It incorporates the competition between the Kondo effect (promoted by exchange coupling JK) and the variable quantum fluctuations of the local-moment magnetism (parameterized by G). We investigate this competition in the Ising-anisotropic Kondo lattice with a transverse magnetic field, where the field serves to tune G. We determine a zero-temperature phase diagram of this model within the extended dynamical mean-field theory (EDMFT), and discuss the implications of our results for the global phase diagram of heavy-fermion systems.

  12. Microscopic resolution of the interplay of Kondo screening and superconducting pairing: Mn-phthalocyanine molecules adsorbed on superconducting Pb(111)

    NASA Astrophysics Data System (ADS)

    Bauer, Johannes; Pascual, Jose I.; Franke, Katharina J.

    2013-02-01

    Magnetic molecules adsorbed on a superconductor give rise to a local competition of Cooper pair and Kondo singlet formation inducing subgap bound states. For manganese-phthalocyanine molecules on a Pb(111) substrate, scanning tunneling spectroscopy resolves pairs of subgap bound states and two Kondo screening channels. We show in a combined approach of scaling and numerical renormalization group calculations that the intriguing relation between Kondo screening and superconducting pairing is solely determined by the hybridization strength with the substrate. We demonstrate that an effective one-channel Anderson impurity model with a sizable particle-hole asymmetry captures universal and nonuniversal observations in the system quantitatively. The model parameters and disentanglement of the two screening channels are elucidated by scaling arguments.

  13. Out-of-equilibrium Kondo effect in a quantum dot: Interplay of magnetic field and spin accumulation

    NASA Astrophysics Data System (ADS)

    Sahoo, Shaon; Crépieux, Adeline; Lavagna, Mireille

    2016-12-01

    We present a theoretical study of low-temperature nonequilibrium transport through an interacting quantum dot in the presence of Zeeman magnetic field and current injection into one of its leads. By using a self-consistent renormalized equation of motion approach, we show that the injection of a spin-polarized current leads to a modulation of the Zeeman splitting of the Kondo peak in the differential conductance. We find that an appropriate amount of spin accumulation in the lead can restore the Kondo peak by compensating the splitting due to magnetic field. By contrast when the injected current is spin-unpolarized, we establish that both Zeeman-split Kondo peaks are equally shifted and the splitting remains unchanged. Our results quantitatively explain the experimental findings reported in Kobayashi T. et al., Phys. Rev. Lett., 104 (2010) 036804. These features could be nicely exploited for the control and manipulation of spin in nanoelectronic and spintronic devices.

  14. Non-Kondo-like electronic structure in the correlated rare-earth hexaboride YbB(6).

    PubMed

    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

    2015-01-09

    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.

  15. Effect of the repulsion interaction on the ground-state of the Kondo lattice model with a superlattice potential

    NASA Astrophysics Data System (ADS)

    Silva-Valencia, J.; Franco, R.; Figueira, M. S.

    2014-04-01

    We investigate the ground-state of a new Kondo lattice model, where the free carriers interact repulsively between them and undergo an external superlattice potential. This model can be simulated with 171Yb atoms confined in optical lattices. We use the density matrix renormalization group method to evaluate the charge and spin gaps, and the structure factors. We found that the ground-state evolves from a Kondo spin liquid state to a charge-gapped antiferromagnetic state with zero spin gap, when the antiferromagnetic exchange increases. Also, we verify that the quantum critical point varies linearly with the repulsion and the exchange.

  16. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Kondo Resonance Splitting in a Quantum Dot with Perpendicular Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Peng, Ju; Yu, Hua-Ling; Wang, Xia-Ling; Chen, Zhi-Gao

    2009-12-01

    Using the nonequilibrium Green's function technique, we investigate the Kondo effect in the quantum dot with perpendicular magnetic fields, in which one is the Zeeman splitting lies in the z-direction and the other is the spin flip points at the x-direction. It is found whatever one or two magnetic fields are applied, the local density of states (LDOS) will split into two peaks. The positions of two Kondo resonance peaks are determined by Zeeman energy Δ when J = 0, and by when J ≠ 0.

  17. Extraordinary Hall effect in Kondo-type systems: Contributions from anomalous velocity

    NASA Astrophysics Data System (ADS)

    Levy, P. M.

    1988-10-01

    Kondo systems exhibit a relatively large extraordinary Hall effect which is due to asymmetric resonant scattering of conduction electrons. Theories based on the skew scattering mechanism account for data at high temperatures T>TK (the Kondo temperature) but are unable to explain the very-low-temperature variation of the Hall constant observed in heavy-fermion compounds. Aside from the ordinary Hall effect, caused by the Lorentz force and skew scattering (which makes the scattering probability antisymmetric with respect to interchange of scattering vectors), there exists an additional contribution to the Hall effect known as the anomalous-velocity contribution. This contribution is due to a change in the expression for the current operator in the presence of spin-orbit forces. We derive an expression for the anomalous velocity in terms of the T matrices describing conduction-electron scattering; it is not limited to weak spin-orbit scattering as were previous results. We use the Anderson model of local moments in metals to write this scattering in terms of the mixing interaction between local and conduction electrons, and the local state's Green's function. The transverse Hall current due to anomalous velocity is determined and evaluated in two limits. At high temperature, we use the weak-coupling form of the local state's Green's function; at T=0 K a phase-shift analysis is used, and we rely on the Friedel-Langreth sum rule to give us the phase shift at the Fermi surface. At high temperatures we find that the contribution from anomalous velocity to the Hall constant is quite small compared to that from skew scattering. On the contrary, at low temperatures the anomalous velocity makes the dominant contribution to the Hall constant in Kondo systems.

  18. Limit Cycle and Anomalous Capacitance in the Kondo Insulator SmB6

    NASA Astrophysics Data System (ADS)

    Kim, D. J.; Grant, T.; Fisk, Z.

    2012-08-01

    We report a frequency coding limit cycle and anomalous capacitance in the Kondo insulator SmB6 at low temperatures where the insulating gap becomes fully opened. The limit cycle appears to be associated with local activity and autocatalytic temporal pattern formation, as occurs in biological systems. The measured anomalous capacitance may indicate surface and bulk separation, suggesting the formation of a surface conducting state. The biological analogy suggests lossless information transport and complex information coding, and the surface state with a superconductor would provide a possible venue for quantum computing resources without decoherence.

  19. 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.

  20. Competition between Kondo Screening and Indirect Magnetic Exchange in a Quantum Box

    NASA Astrophysics Data System (ADS)

    Schwabe, Andrej; Gütersloh, Daniel; Potthoff, Michael

    2012-12-01

    Nanoscale systems of metal atoms antiferromagnetically exchange coupled to several magnetic impurities are shown to exhibit an unconventional reentrant competition between Kondo screening and indirect magnetic exchange interaction. Depending on the atomic positions of the magnetic moments, the total ground-state spin deviates from predictions of standard Ruderman-Kittel-Kasuya-Yosida perturbation theory. The effect shows up on an energy scale larger than the level width induced by the coupling to the environment and is experimentally accessible by studying magnetic field dependencies.

  1. Magnetically tunable Kondo-Aharonov-Bohm effect in a triangular quantum dot.

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2006-02-03

    The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.

  2. Vibration-induced Kondo tunneling through metal-organic complexes with even electron occupation number.

    PubMed

    Kikoin, K; Kiselev, M N; Wegewijs, M R

    2006-05-05

    We investigate transport through a mononuclear transition-metal complex with strong tunnel coupling to two electrodes. The ground state of this molecule is a singlet, while the first excited state is a triplet. We show that a modulation of the tunnel-barrier due to a molecular distortion which couples to the tunneling induces a Kondo-effect, provided the discrete vibrational energy compensates the singlet-triplet gap. We discuss the single-phonon and two-phonon-assisted cotunneling and possible experimental realization of the theory.

  3. 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.

  4. Coherent spectroscopy of semiconductors.

    PubMed

    Cundiff, Steven T

    2008-03-31

    The coherent optical response of semiconductors has been the subject of substantial research over the last couple of decades. The interest has been motivated by unique aspects of the interaction between light and semiconductors that are revealed by coherent techniques. The ability to probe the dynamics of charge carriers has been a significant driver. This paper presents a review of selected results in coherent optical spectroscopy of semiconductors.

  5. Semiconductor microcavity lasers

    SciTech Connect

    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.

  6. Semiconductor bridge (SCB) detonator

    DOEpatents

    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.

  7. Semiconductor bridge (SCB) detonator

    DOEpatents

    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.

  8. Interconnected semiconductor devices

    DOEpatents

    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.

  9. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Splitting and Restoration of Kondo Peak in a Deformed Molecule Quantum Dot Coupled to Ferromagnetic Electrodes

    NASA Astrophysics Data System (ADS)

    Wang, Rui-Qiang; Jiang, Kai-Ming

    2010-02-01

    We adopt the nonequilibrium Green's function method to theoretically study the Kondo effect in a deformed molecule, which is treated as an electron-phonon interaction (EPI) system. The self-energy for phonon part is calculated in the standard many-body diagrammatic expansion up to the second order in EPI strength. We find that the multiple phonon-assisted Kondo satellites arise besides the usual Kondo resonance. In the antiparallel magnetic configuration the splitting of main Kondo peak and phonon-assisted satellites only happen for asymmetrical dot-lead couplings, but it is free from the symmetry for the parallel magnetic configuration. The EPI strength and vibrational frequency can enhance the spin splitting of both main Kondo and satellites. It is shown that the suppressed zero-bias Kondo resonance can be restored by applying an external magnetic field, whose magnitude is dependent on the phononic effect remarkably. Although the asymmetry in tunnel coupling has no contribution to the restoration of spin splitting of Kondo peak, it can shrink the external field needed to switch tunneling magnetoresistance ratio between large negative dip and large positive peak.

  10. Phase diagram of the Kondo necklace model with planar and local anisotropies

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.

    2010-12-01

    We use the density matrix renormalization group to study the quantum critical behavior of a one-dimensional Kondo necklace model with two anisotropies: η in the XY interaction of conduction spins and Δ in the local exchange between localized and conduction spins (characterized by J). To do so, we calculate the gap between the ground and the first excited state for different values of η and Δ as a function of J, and fit it to a Kosterlitz-Thouless tendency; the point in which the gap vanishes is the quantum critical point Jc. To support our results, we calculate correlation functions and structure factors near the obtained critical points. The use of entanglement measures, specifically the von Neumann block entropy, to identify the quantum phase transition is also presented. Then we build the phase diagram of the model: for every Δ considered, any value of η > 0 generates a quantum phase transition from a Kondo singlet to an antiferromagnetic state at a finite value of J, and as η diminishes, so does Jc; when Δ diminishes for a fixed η, Jc increases, favoring the antiferromagnetic state.

  11. Kondo behavior and conductance through 3d impurities in gold chains doped with oxygen

    NASA Astrophysics Data System (ADS)

    Barral, M. A.; Di Napoli, S.; Blesio, G.; Roura-Bas, P.; Camjayi, A.; Manuel, L. O.; Aligia, A. A.

    2017-03-01

    Combining ab initio calculations and effective models derived from them, we discuss the electronic structure of oxygen doped gold chains when one Au atom is replaced by any transition-metal atom of the 3d series. The effect of O doping is to bring extended Au 5dxz and 5dyz states to the Fermi level, which together with the Au states of zero angular momentum projection leads to three possible channels for the screening of the magnetism of the impurity. For most 3d impurities the expected physics is similar to that of the underscreened Kondo model, with singular Fermi liquid behavior. For Fe and Co under a tetragonal crystal field introduced by leads, the system might display a non-Fermi liquid behavior. Ni and Cu impurities are described by a S = 1 two channel Kondo model and an SU(4) impurity Anderson model in the intermediate valence regime, respectively. In both cases, the system is a Fermi liquid, but the conductance shows some observable differences with the ordinary SU(2) Anderson model.

  12. Magnetic order and Kondo effect in the Anderson-lattice model

    NASA Astrophysics Data System (ADS)

    Bernhard, B. H.; Aguiar, C.; Kogoutiouk, I.; Coqblin, B.

    The Anderson-lattice model has been extensively developed to account for the properties of many anomalous rare-earth compounds and in particular for the competition between the Kondo effect and an antiferromagnetic (AF) phase in a cubic lattice. Here we apply the higher-order decoupling of the equations of motion for the Green Functions (GF) introduced in [H.G. Luo, S.J. Wang, Phys. Rev. B 62 (2000) 1485]. We obtain an improved description of the phase diagram, where the AF phase subsists in a smaller range of the model parameters. As higher-order GF are included in the chain of equations, we are able to calculate directly the local spin-flip correlation function . As a further improvement to the previous approximation of [B.H. Bernhard, C. Aguiar, B. Coqblin, Physica B 378-380 (2006) 712], we obtain a reduced range of existence for the AF phase for the symmetric half-filled case and then we discuss the competition between the AF order and the Kondo effect as a function of the band filling.

  13. 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.

  14. 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).

  15. Formation of metallic magnetic clusters in a Kondo-lattice metal: evidence from an optical study.

    PubMed

    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, Tb(2)PdSi(3). 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.

  16. Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study

    NASA Astrophysics Data System (ADS)

    Kovaleva, N. N.; Kugel, K. I.; Bazhenov, A. V.; Fursova, T. N.; Löser, W.; Xu, Y.; Behr, G.; Kusmartsev, F. V.

    2012-11-01

    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.

  17. Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study

    PubMed Central

    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

  18. Keldysh effective action theory for universal physics in spin-(1)/(2) Kondo dots

    NASA Astrophysics Data System (ADS)

    Smirnov, Sergey; Grifoni, Milena

    2013-03-01

    We present a theory for the Kondo spin-(1)/(2) effect in strongly correlated quantum dots. The theory is applicable at any temperature and voltage. It is based on a quadratic Keldysh effective action parametrized by a universal function. We provide a general analytical form for the tunneling density of states through this universal function for which we propose a simple microscopic model. We apply our theory to the highly asymmetric Anderson model with U=∞ and describe its strong-coupling limit, weak-coupling limit, and crossover region within a single analytical expression. We compare our results with a numerical renormalization group in equilibrium and with a real-time renormalization group out of equilibrium and show that the universal shapes of the linear and differential conductance obtained in our theory and in these theories are very close to each other in a wide range of temperatures and voltages. In particular, as in the real-time renormalization group, we predict that at the Kondo voltage the differential conductance is equal to 2/3 of its maximum.

  19. Thermoelectric response of a correlated impurity in the nonequilibrium Kondo regime

    NASA Astrophysics Data System (ADS)

    Dorda, Antonius; Ganahl, Martin; Andergassen, Sabine; von der Linden, Wolfgang; Arrigoni, Enrico

    2016-12-01

    We study nonequilibrium thermoelectric transport properties of a correlated impurity connected to two leads for temperatures below the Kondo scale. At finite bias, for which a current flows across the leads, we investigate the differential response of the current to a temperature gradient. In particular, we compare the influence of a bias voltage and of a finite temperature on this thermoelectric response. This is of interest from a fundamental point of view to better understand the two different decoherence mechanisms produced by a bias voltage and by temperature. Our results show that in this respect the thermoelectric response behaves differently from the electric conductance. In particular, while the latter displays a similar qualitative behavior as a function of voltage and temperature, both in theoretical and experimental investigations, qualitative differences occur in the case of the thermoelectric response. In order to understand this effect, we analyze the different contributions in connection to the behavior of the impurity spectral function versus temperature. Especially in the regime of strong interactions and large enough bias voltages, we obtain a simple picture based on the asymmetric suppression or enhancement of the split Kondo peaks as a function of the temperature gradient. Besides the academic interest, these studies could additionally provide valuable information to assess the applicability of quantum dot devices as responsive nanoscale temperature sensors.

  20. 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.

  1. Visualizing the formation of the Kondo lattice and the hidden order in URu2Si2

    PubMed Central

    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

  2. Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide.

    PubMed

    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.

  3. Heavy fermion and Kondo lattice behavior in the itinerant ferromagnet CeCrGe3.

    PubMed

    Das, Debarchan; Gruner, T; Pfau, H; Paramanik, U B; Burkhardt, U; Geibel, C; Hossain, Z

    2014-03-12

    Physical properties of polycrystalline CeCrGe3 and LaCrGe3 have been investigated by x-ray absorption spectroscopy, magnetic susceptibility χ(T), isothermal magnetization M(H), electrical resistivity ρ(T), specific heat C(T) and thermoelectric power S(T) measurements. These compounds are found to crystallize in the hexagonal perovskite structure (space group P63/mmc), as previously reported. The ρ(T), χ(T) and C(T) data confirm the bulk ferromagnetic ordering of itinerant Cr moments in LaCrGe3 and CeCrGe3 with TC = 90 K and 70 K respectively. In addition, a weak anomaly is also observed near 3 K in the C(T) data of CeCrGe3. The T dependences of ρ and finite values of Sommerfeld coefficient γ obtained from the specific heat measurements confirm that both the compounds are of metallic character. Further, the T dependence of ρ of CeCrGe3 reflects a Kondo lattice behavior. An enhanced γ of 130 mJ mol(-1) K(-2) together with the Kondo lattice behavior inferred from the ρ(T) establish CeCrGe3 as a moderate heavy fermion compound with a quasi-particle mass renormalization factor of ∼45.

  4. 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.

  5. A 1Ds ×1Dc Heisenberg-Kondo Lattice compound Nb12O29

    NASA Astrophysics Data System (ADS)

    Pickett, Warren; Lee, Kwan-Woo

    2015-03-01

    Local moments embedded in conducting systems form a rich platform for unusual phases, with phenomena including Kondo, heavy fermion, and non-Fermi liquid physics. Using first principles based methods and the refined crystal structure based on columns of 3 ×4 planar units of NbO6 octahedra, we determine that mixed valent Nb12O29 displays tightly bound local moments forming spin chains along one direction criss-crossed by conducting ``nanowires'' in the perpendicular direction. Just how local moments - very rare for Nb - emerge and coexist with itinerant electrons, an enigma for decades in this system, is elucidated based on the local structure of the NbO6 octahedra and orbital+spin ordering. The resulting 1Ds ×1Dc Heisenberg-Kondo lattice (s=spin, c=charge) picture will be discussed. NRF-2013R1A1A2A10008946 (K.W.L.), DOE DE-FG02-04ER46111 (W.E.P.).

  6. From bad metal to Kondo insulator: temperature evolution of the optical properties of SmB6

    NASA Astrophysics Data System (ADS)

    Tytarenko, A.; Nakatsukasa, K.; Huang, Y. K.; Johnston, S.; van Heumen, E.

    2016-12-01

    The recent rekindling of interest in the mixed valent Kondo insulator SmB6 as candidate for a first correlated topological insulator has resulted in a wealth of new experimental observations. In particular, angle-resolved photoemission experiments have provided completely new insights into the formation of the low temperature Kondo insulating state starting from the high temperature correlated metal. Here, we report detailed temperature and energy dependent measurements of the optical constants of SmB6 in order to provide a detailed study from the point of view of a bulk sensitive spectroscopic probe. We detect a previously unobserved infrared active optical phonon mode, involving the movement of the Sm ions against the boron cages. The changes taking place in the free carrier response with temperature and their connection to changes in optical transitions between different bands are discussed. We find that the free charge density starts to decrease rapidly below approximately 200 K. Below 60 K a small amount of spectral weight begins to accumulate in low lying interband transitions, indicating the formation of the Kondo insulating state; however, the total integrated spectral weight in our experimental window (∼4.35 eV) decreases. This indicates the involvement of a large Coulomb interaction (> 5 eV) in the formation of the Kondo insulator.

  7. Anomalous three-dimensional bulk ac conduction within the Kondo gap of SmB6 single crystals

    NASA Astrophysics Data System (ADS)

    Laurita, N. J.; Morris, C. M.; Koohpayeh, S. M.; Rosa, P. F. S.; Phelan, W. A.; Fisk, Z.; McQueen, T. M.; Armitage, N. P.

    2016-10-01

    The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures, T <5 K. In this temperatures range, a plateau is observed in the dc resistivity, contrary to the exponential divergence expected for a gapped system. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator (TKI) and propose that the residual conductivity is due to topological surface states which reside within the Kondo gap. Since the TKI prediction many experiments have claimed to observe high mobility surface states within a perfectly insulating hybridization gap. Here, we investigate the low energy optical conductivity within the hybridization gap of single crystals of SmB6 via time domain terahertz spectroscopy. Samples grown by both optical floating zone and aluminum flux methods are investigated to probe for differences originating from sample growth techniques. We find that both samples display significant three-dimensional bulk conduction originating within the Kondo gap. Although SmB6 may be a bulk dc insulator, it shows significant bulk ac conduction that is many orders of magnitude larger than any known impurity band conduction. The nature of these in-gap states and their coupling with the low energy spin excitons of SmB6 is discussed. Additionally, the well-defined conduction path geometry of our optical experiments allows us to show that any surface states, which lie below our detection threshold if present, must have a sheet resistance of R /square≥ 1000 Ω .

  8. Molecular Semiconductors: An Introduction

    NASA Astrophysics Data System (ADS)

    de Mello, John; Halls, Jonathan James Michael

    2005-10-01

    Introducing the fundamental ideas and concepts behind organic semiconductors, this book provides a clear impression of the broad range of research activities currently underway. Aimed specifically at new entrant doctoral students from a wide variety of backgrounds, including chemistry, physics, electrical engineering and materials science, it also represents an ideal companion text to undergraduate courses in organic semiconductors.

  9. 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.

  10. Screened spin-1 and -1/2 Kondo effect in a triangular quantum dot system with interdot Coulomb repulsion

    NASA Astrophysics Data System (ADS)

    Xiong, Yong-Chen; Wang, Wei-Zhong; Luo, Shi-Jun; Yang, Jun-Tao; Huang, Hai-Ming

    2017-03-01

    By means of the numerical renormalization group (NRG) technique, we study the low temperature transport property and the phase transition for a triangular triple quantum dot system, including two centered dots (dot 1 and 2) and one side dot (dot 3). We focus on the effect of interdot repulsion V between two centered dots in a wide range of the interdot hopping tij (i,j = 1,2,3). When the hoppings between the centered dot and the side dot are symmetric, i.e., t13 = t23, and that between two centered dots t12 is small, two centered dots form a spin triplet when V is absent, and a totally screened spin-1 Kondo effect is observed. In this case, one has a spin 1 that is partially screened by the leads as in the usual spin-1 Kondo model, and the remaining spin 1/2 degree of freedom forms a singlet with the side dot. As V is large enough, one of the centered dots is singly occupied, while the other one is empty. The spin-1/2 Kondo effect is found when t13 is small. For large t12, two centered dots form a spin singlet when V = 0, leading to zero conductance. As V is large enough, the spin-1/2 Kondo effect is recovered in the case of small t13. For asymmetric t13≠t23 and small t12, a crossover is found as V increases in comparison with a first order quantum phase transition for the symmetric case. In the regime of large V, the spin-1/2 Kondo effect could also be found when both t13 and t23 are small. We demonstrate the present model is similar to the side-coupled double dot system in some appropriate regimes, and it appears as a possible realization of side-controllable molecular electronics and spintronics devices.

  11. Semiconductor Solar Superabsorbers

    PubMed Central

    Yu, Yiling; Huang, Lujun; Cao, Linyou

    2014-01-01

    Understanding the maximal enhancement of solar absorption in semiconductor materials by light trapping promises the development of affordable solar cells. However, the conventional Lambertian limit is only valid for idealized material systems with weak absorption, and cannot hold for the typical semiconductor materials used in solar cells due to the substantial absorption of these materials. Herein we theoretically demonstrate the maximal solar absorption enhancement for semiconductor materials and elucidate the general design principle for light trapping structures to approach the theoretical maximum. By following the principles, we design a practical light trapping structure that can enable an ultrathin layer of semiconductor materials, for instance, 10 nm thick a-Si, absorb > 90% sunlight above the bandgap. The design has active materials with one order of magnitude less volume than any of the existing solar light trapping designs in literature. This work points towards the development of ultimate solar light trapping techniques. PMID:24531211

  12. Isotopically controlled semiconductors

    SciTech Connect

    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.

  13. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2–δAs2

    SciTech Connect

    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 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. 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.

  14. Quantum phase transition and protected ideal transport in a Kondo chain

    SciTech Connect

    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.

  15. Low energy properties of the Kondo chain in the RKKY regime

    SciTech Connect

    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 a 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.

  16. 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.

  17. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets.

    PubMed

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-02-08

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

  18. Kondo temperature when the Fermi level is near a step in the conduction density of states

    NASA Astrophysics Data System (ADS)

    Fernández, J.; Aligia, A. A.; Roura-Bas, P.; Andrade, J. A.

    2017-01-01

    The (111) surface of Cu, Ag, and Au is characterized by a band of surface Shockley states with a constant density of states beginning slightly below the Fermi energy. These states as well as bulk states hybridize with magnetic impurities which can be placed above the surface. We calculate the characteristic low-temperature energy scale, the Kondo temperature TK of the impurity Anderson model, as the bottom of the conduction band Ds crosses the Fermi energy ɛF. We find simple power laws TK≃|Ds-ɛF| η , where η depends on the sign of Ds-ɛF , the ratio between surface and bulk hybridizations with the impurity Δs/Δb , and the ratio between on-site and Coulomb energy Ed/U in the model.

  19. Low energy properties of the Kondo chain in the RKKY regime

    DOE PAGES

    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

  20. Kondo effect from a Lorentz-violating domain wall description of superconductivity

    NASA Astrophysics Data System (ADS)

    Bazeia, D.; Brito, F. A.; Mota-Silva, J. C.

    2016-11-01

    We extend recent results on domain wall description of superconductivity in an Abelian Higgs model by introducing a particular Lorentz-violating term. The temperature of the system is interpreted through the fact that the soliton following accelerating orbits is a Rindler observer experiencing a thermal bath. We show that this term can be associated with the Kondo effect, that is, the Lorentz-violating parameter is closely related to the concentration of magnetic impurities living on a superconducting domain wall. We also found that the critical temperature decreasing with the impurity concentration as a non-single-valued function, for the case TK

  1. Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6

    PubMed Central

    Hatnean, M. Ciomaga; Lees, M. R.; Paul, D. M. K.; Balakrishnan, G.

    2013-01-01

    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. PMID:24166216

  2. Suppression of magnetic excitations near the surface of the topological Kondo insulator SmB6

    NASA Astrophysics Data System (ADS)

    Biswas, P. K.; Legner, M.; Balakrishnan, G.; Hatnean, M. Ciomaga; Lees, M. R.; Paul, D. McK.; Pomjakushina, E.; Prokscha, T.; Suter, A.; Neupert, T.; Salman, Z.

    2017-01-01

    We present a detailed investigation of the temperature and depth dependence of the magnetic properties of the three-dimensional topological Kondo insulator SmB6, in particular, near its surface. We find that local magnetic field fluctuations detected in the bulk are suppressed rapidly with decreasing depths, disappearing almost completely at the surface. We attribute the magnetic excitations to spin excitons in bulk SmB6, which produce local magnetic fields of about ˜1.8 mT fluctuating on a time scale of ˜60 ns . We find that the excitonic fluctuations are suppressed when approaching the surface on a length scale of ˜40 -90 nm , accompanied by a small enhancement in static magnetic fields. We associate this length scale to the size of the excitonic state.

  3. 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.

  4. Unconventional bulk three-dimensional Fermi surface in Kondo insulating SmB6

    NASA Astrophysics Data System (ADS)

    Tan, Beng

    We report the observation of a paradoxical insulator with a bulk state which is electrically insulating and simultaneously yields quantum oscillations typical of good metals. We present high field measurements of conductivity and magnetic torque in high purity single crystals of the Kondo insulator SmB6 which reveal an activated behavior characteristics of an insulator with an energy gap at the Fermi energy in the former and quantum oscillation of frequencies characteristics of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6 in the latter. The quantum oscillations observed in the magnetic torque measurements are characteristic of an unconventional Fermi liquid - the amplitude strongly increases at low temperatures in a stark contrast to the saturating Lifshitz-Kosevich behavior in conventional metallic states.

  5. Magnetic excitations in the kondo liquid: superconductivity and hidden magnetic quantum critical fluctuations.

    PubMed

    Yang, Yi-Feng; Urbano, Ricardo; Curro, Nicholas J; Pines, David; Bauer, E D

    2009-11-06

    We report Knight-shift experiments on the superconducting heavy-electron material CeCoIn5 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 115In nuclear quadrupole resonance spin-lattice relaxation rate T1(-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 located at slightly negative pressure in CeCoIn5 and provide additional evidence for significant similarities between the heavy-electron materials and the high-T(c) cuprates.

  6. Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6

    DOE PAGES

    Fuhrman, W. T.; Leiner, Jonathan C.; Nikolić, P.; ...

    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

  7. Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6

    SciTech Connect

    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 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. Finally, we find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.

  8. Universal low-temperature crossover in two-channel Kondo models

    NASA Astrophysics Data System (ADS)

    Mitchell, Andrew K.; Sela, Eran

    2012-06-01

    An exact expression is derived for the electron Green function in two-channel Kondo models with one and two impurities, describing the crossover from non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi liquid (FL) physics at low temperatures. Symmetry-breaking perturbations generically present in experiment ensure the standard low-energy FL description, but the full crossover is wholly characteristic of the unstable NFL state. Distinctive conductance lineshapes in quantum dot devices should result. We exploit a connection between this crossover and one occurring in a classical boundary Ising model to calculate real-space electron densities at finite temperature. The single universal finite-temperature Green function is then extracted by inverting the integral transformation relating these Friedel oscillations to the t matrix. Excellent agreement is demonstrated between exact results and full numerical renormalization group calculations.

  9. Quantum phase transition and protected ideal transport in a Kondo chain

    DOE PAGES

    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

  10. Constructive influence of the induced electron pairing on the Kondo state

    PubMed Central

    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

  11. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    PubMed Central

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-01-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications. PMID:28176869

  12. Interacting topological phases in thin films of topological mirror Kondo insulators

    NASA Astrophysics Data System (ADS)

    Zhang, Rui-Xing; Xu, Cenke; Liu, Chao-Xing

    2016-12-01

    We study interaction effects on thin films of topological mirror Kondo insulators (TMKIs), where the strong interaction is expected to play an important role. Our study has led to the following results: (i) We identify a rich phase diagram of noninteracting TMKIs with different mirror Chern numbers in the monolayer and bilayer thin films; (ii) we obtain the phase diagram with interaction and identify the regimes of interaction parameters to mimic bosonic symmetry-protected topological phases with either gapless bosonic modes or spontaneous mirror symmetry breaking at the boundary; and (iii) for the spontaneous mirror symmetry-breaking boundary, we also study various domain-wall defects between different mirror symmetry-breaking order parameters at the boundary. Our results reveal that the thin-film TMKI serves as an intriguing platform for experimental studies of interacting topological phases.

  13. Interfacial phase competition induced Kondo-like effect in manganite-insulator composites

    NASA Astrophysics Data System (ADS)

    Lin, Ling-Fang; Wu, Ling-Zhi; Dong, Shuai

    2016-12-01

    A Kondo-like effect, namely, the upturn of resistivity at low temperatures, is observed in perovskite manganite when nonmagnetic insulators are doped as secondary phase. In this paper, the low-temperature resistivity upturn effect has been argued to originate from interfacial magnetic phase reconstruction. Heisenberg spin lattices have been simulated using the Monte Carlo method to reveal phase competition around secondary phase boundary, namely, manganite-insulator boundary that behaves with a weak antiferromagnetic tendency. Moreover, the resistor network model based on double-exchange conductive mechanism reproduces the low-temperature resistivity upturn effect. Our work provides a reasonable physical mechanism to understand the novel transport behaviors in microstructures of correlated electron systems.

  14. Kondo effect in CoxCu1-x granular alloys prepared by chemical reduction method

    NASA Astrophysics Data System (ADS)

    Dhara, Susmita; Chowdhury, Rajeswari Roy; Bandyopadhyay, Bilwadal

    2015-06-01

    Nanostructured CoCu granular alloys CoxCu1-x (x ≤ 0.3) have been prepared by chemical reduction method using NaBH4 as a reducing agent. Electronic transport properties are studied in the temperature range 4-300 K. Resistance exhibits a metallic behavior below room temperature and draws a minimum near 20 K in all the samples except in Co0.3Cu0.7. This low temperature resistivity minimum diminishes with applied magnetic field. There is also a logarithmic temperature dependence of resistivity at temperatures below 20 K. This phenomenon indicates a Kondo-like scattering mechanism involving magnetic Co impurity spin clusters in Cu host.

  15. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    NASA Astrophysics Data System (ADS)

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-02-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

  16. From tunneling to contact in a magnetic atom: The non-equilibrium Kondo effect

    NASA Astrophysics Data System (ADS)

    Choi, Deung-Jang; Abufager, Paula; Limot, Laurent; Lorente, Nicolás

    2017-03-01

    A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA.

  17. Semiconductor Nanocrystal Photonics

    DTIC Science & Technology

    2005-08-31

    D. Krauss, C. B. Poitras, and M. Lipson, " Energy transfer between colloidal semiconductor quantum dots in an optical microcavity," (submitted, 2006...Phys. Lett. 82, 4032 (2003). J. J. Peterson and T. D. Krauss, "Fluorescence Spectroscopy of Single Lead Sulfide Quantum Dots ," Nano Lett. (in press...Guo, Xiaowei Teng, Hong Yang, Todd D. Krauss, Carl B. Poitras, and Michal Lipson, "Enhanced Energy Transfer between Colloidal Semiconductor Quantum

  18. SILICON CARBIDE FOR SEMICONDUCTORS

    DTIC Science & Technology

    This state-of-the-art survey on silicon carbide for semiconductors includes a bibliography of the most important references published as of the end...of 1964. The various methods used for growing silicon carbide single crystals are reviewed, as well as their properties and devices fabricated from...them. The fact that the state of-the-art of silicon carbide semiconductors is not further advanced may be attributed to the difficulties of growing

  19. Majorana modes and Kondo effect in a quantum dot attached to a topological superconducting wire (Presentation Recording)

    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

  20. Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.

    PubMed

    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.

  1. 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.

  2. 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.

  3. Lateral Fano resonances and Kondo effect in the strong coupling regime of a T -coupled quantum dot

    NASA Astrophysics Data System (ADS)

    Franco, R.; Figueira, M. S.; Anda, E. V.

    2006-05-01

    We study the electronic transport through a quantum wire (QW), modeled by a tight-binding linear chain, with a side-coupled quantum dot (QD). We obtain the conductance with a strong Fano antiresonance. The calculated density of states shows that this behavior is associated to a many-body renormalized QD resonant level Ef˜ at the edge of the conduction band (CB) strongly hybridized with the Van Hove singularity of the one-dimensional density of states of the lead. Different from the Fano antiresonances experimentally found when this system is at the Kondo regime, this phenomenon appears above the Kondo temperature. It is due to the quantum interference between the ballistic channel and a thermal activated channel created by the QD resonance at the vicinity of the bottom of the CB.

  4. Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system

    NASA Astrophysics Data System (ADS)

    Seridonio, A. C.; Siqueira, E. C.; Franco, R.; Silva-Valencia, J.; Shelykh, I. A.; Figueira, M. S.

    2014-11-01

    We theoretically investigate the thermoelectric properties of a spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized with a STM tip. Such a setup is treated within the single-impurity Anderson model in combination with the atomic approach for the Green's functions. Due to the spin dependence of the Fermi wave numbers, the electrical and thermal conductances together with thermopower and Lorenz number reveal beating patterns as a function of the STM tip position in the Kondo regime. In particular, by tuning the lateral displacement of the tip with respect to the adatom vicinity, the temperature, and the position of the adatom level, one can change the sign of the Seebeck coefficient through charge and spin. This opens a possibility of the microscopic control of the heat flux analogously to that established for the electrical current.

  5. Fridel sum rules for one- and two-channel Kondo models and unitarity paradox via bosonization-refermionization approach

    NASA Astrophysics Data System (ADS)

    Kharitonov, Maxim; Andrei, Natan; Coleman, Piers

    2013-03-01

    We calculate the single-particle Green's functions and scattering amplitudes of the one-channel and channel-anisotropic two-channel Kondo models at the Toulouse and Emery-Kivelson lines, respectively, where exact solutions via the bosonization-refermionization approach are admitted. We demonstrate that in this approach the Friedel sum rules - the relations between the trapped spin and ``flavor'' moments and the scattering phase shifts in the Fermi-liquid regime - arise naturally and elucidate on their subtleties. We also recover the ``unitarity paradox'' - the vanishing of the single-particle scattering amplitude at the channel-symmetric point of the two-channel Kondo model - stemming from non-Fermi-liquid behavior. We discuss the implications of these results for the development of composite pairing in heavy fermion systems. This work was supported by National Science Foundation grants DMR 0907179 (MK, PC) and DMR 1006684 (NA).

  6. Kondo Resonance in a Mesoscopic Ring Coupled to a Quantum Dot: Exact Results for the Aharonov-Bohm-Casher Effects

    SciTech Connect

    Eckle, H.-P.; Johannesson, H.; Stafford, C. A.

    2001-07-02

    We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.

  7. Kondo resonance in a mesoscopic ring coupled to a quantum dot: exact results for the Aharonov-Bohm-Casher effects.

    PubMed

    Eckle, H P; Johannesson, H; Stafford, C A

    2001-07-02

    We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.

  8. GW approach to electron-electron interactions within the Anderson impurity model: Kondo correlated quantum transport through two coupled molecules

    NASA Astrophysics Data System (ADS)

    Aksu, H.; Goker, A.

    2017-03-01

    We invoke the nonequilibrium self-consistent GW method within the Anderson impurity model to investigate the dynamical effects occurring in a nanojunction comprised of two coupled molecules. Contrary to the previous single impurity model calculations based on the GW approximation, we observe that the density of states manages to capture both the Kondo resonance and the Breit-Wigner resonances associated with the HOMO and LUMO levels of the molecule. Moreover, the prominence of the Kondo resonance grows dramatically upon switching from the intermediate to the weak coupling regime involving large U / Γ values. The conductance is calculated as a function of the HOMO level and the applied bias across the molecular nanojunction. Calculated conductance curves deviate from the monotonic decay behaviour as a function of the bias when the half-filling condition is not met. The importance of the effect of the molecule-molecule coupling for the electron transport phenomena is also investigated.

  9. Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film

    PubMed Central

    Zhu, Lijun; Woltersdorf, Georg; Zhao, Jianhua

    2016-01-01

    The experimental existence and stability of the fixed point of the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics have been buried in persistent confusion despite the intensive theoretical and experimental efforts in past three decades. Here we report an experimental realization of the two-level system resonant scattering-induced orbital 2CK effect in a ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent resistivity upturn that has a logarithmic and a square-root temperature dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our results not only evidence the robust existence of orbital 2CK effect even in the presence of strong magnetic fields and long-range ferromagnetic ordering, but also extend the scope of 2CK host materials from nonmagnetic nanoscale point contacts to diffusive conductors of disordered alloys. PMID:27686323

  10. Quantum phases of the Shastry-Sutherland Kondo lattice: implications for the global phase diagram of heavy-fermion metals.

    PubMed

    Pixley, J H; Yu, Rong; Si, Qimiao

    2014-10-24

    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.

  11. Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film

    NASA Astrophysics Data System (ADS)

    Zhu, Lijun; Woltersdorf, Georg; Zhao, Jianhua

    2016-09-01

    The experimental existence and stability of the fixed point of the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics have been buried in persistent confusion despite the intensive theoretical and experimental efforts in past three decades. Here we report an experimental realization of the two-level system resonant scattering-induced orbital 2CK effect in a ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent resistivity upturn that has a logarithmic and a square-root temperature dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our results not only evidence the robust existence of orbital 2CK effect even in the presence of strong magnetic fields and long-range ferromagnetic ordering, but also extend the scope of 2CK host materials from nonmagnetic nanoscale point contacts to diffusive conductors of disordered alloys.

  12. Spin-Orbit-Coupled Correlated Metal Phase in Kondo Lattices: An Implementation with Alkaline-Earth Atoms

    NASA Astrophysics Data System (ADS)

    Isaev, L.; Schachenmayer, J.; Rey, A. M.

    2016-09-01

    We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.

  13. Kondo screening and beyond: An x-ray absorption and dichroism study of CePt5/Pt(111 )

    NASA Astrophysics Data System (ADS)

    Praetorius, C.; Fauth, K.

    2017-03-01

    We use x-ray absorption spectroscopy as well as its linear and circular magnetic dichroisms to characterize relevant interactions and energy scales in the surface intermetallic CePt5/Pt(111 ). The experiments provide insight into crystal field splitting, effective paramagnetic moments, their Kondo screening and mutual interactions, and thus into many aspects which typically determine the low-temperature behavior of correlated rare-earth compounds. Exploiting the tunability of Ce valence through the thickness-dependent epitaxial strain at the CePt5/Pt(111 ) interface, we are able to systematically investigate the impact of hybridization strength on these interactions. Considerable Kondo screening is indeed observed at all CePt5 thicknesses, and found to be strongest in case of strongest hybridization. While the magnetic response is commensurate with an impurity Kondo scale of TK≳102 K for specimen temperatures T ≳30 K, this is no longer the case at lower temperature. Its detailed study by x-ray circular magnetic dichroism (XMCD) at one specific thickness of CePt5 reveals an anomaly of the susceptibility at T*≈25 K instead, which we tentatively associate with the onset of lattice coherence. At lowest temperature we observe paramagnetic saturation with a small Ce 4 f saturation magnetization. Within the framework of itinerant 4 f electrons, saturation is due to a field-induced Lifshitz transition involving a very heavy band with correspondingly small degeneracy temperature of TF≈7 K. This small energy scale results in the persistence of Curie-Weiss behavior across the entire range of experimentally accessible temperatures (T ≳2 K). Our work highlights the potential of magnetic circular dichroism studies in particular for Kondo and heavy-fermion materials, which so far has remained largely unexplored.

  14. Method of doping a semiconductor

    DOEpatents

    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.

  15. Non-Kondo-like electronic structure in the correlated rare-earth hexaboride YbB6

    DOE PAGES

    Neupane, Madhab; Xu, Su -Yang; Alidoust, Nasser; ...

    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

  16. Effects of electron-phonon coupling in the Kondo regime of a two-orbital single-molecule junction

    NASA Astrophysics Data System (ADS)

    Vernek, Edson; Iorio, Gisele; Deng, Lili; Ingersent, Kevin; Anda, Enrique

    2012-02-01

    Single-molecule junctions (SMJs) are electronic devices formed by a molecule bridging the gap between two metallic contacts. Despite their apparent simplicity, such systems have attracted much attention for the rich variety of experimentally accessible physics that they display. The spatial confinement of electrons in molecules can lead to collective phenomena such as Coulomb blockade and the Kondo effect, as well as to strong coupling of electrons to molecular vibrations. We explore the interesting interplay of electron-electron and electron-phonon interactions in a model of an SMJ in which the central molecule has two active orbitals. The nonperturbative numerical renormalization group method is used to treat the many-body Kondo physics and electron-phonon coupling on equal footing. Electron-phonon coupling renormalizes the energies and Coulomb interactions of the molecular orbitals. The effects are most pronounced in cases where both molecular orbitals lie close to the Fermi energy of the contacts. Here, a sufficiently strong phonon-assisted inter-orbital tunneling can suppress the Kondo effect and cause a crossover to a phonon-dominated regime having very different electrical transport properties.

  17. Fine structure of the spectra of the Kondo lattice model: Two-site cellular dynamical mean-field theory study

    NASA Astrophysics Data System (ADS)

    Osolin, Žiga; Žitko, Rok

    2017-01-01

    We study the antiferromagnetic and paramagnetic Kondo insulator phases of the Kondo lattice model on the cubic lattice at half filling using the cellular dynamical mean-field theory (CDMFT) with the numerical renormalization group (NRG) as the impurity solver, focusing on the fine details of the spectral function and self-energy. We find that the nonlocal correlations increase the gap in both the antiferromagnetic and Kondo insulator phases and shrink the extent of the antiferromagnetic phase in the phase diagram but do not alter any properties qualitatively. The agreement between the numerical CDMFT results and those within a simple hybridization picture, which adequately describes the overall band structure of the system but neglects all effects on the inelastic-scattering processes, is similar to that of the single-site DMFT results; there are deviations that are responsible for the additional fine structure, in particular for the asymmetric spectral resonances or dips that become more pronounced in the strong-coupling regime close to the antiferromagnet-paramagnetic quantum phase transition. These features appear broader in the CDMFT mostly due to numerical artifacts linked to more aggressive state truncation required in the NRG.

  18. Revealing the Atomic Site-Dependent g Factor within a Single Magnetic Molecule via the Extended Kondo Effect

    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.

  19. ARPES view on surface and bulk hybridization phenomena in the antiferromagnetic Kondo lattice CeRh2Si2

    PubMed Central

    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

  20. Semiconductor surface protection material

    NASA Technical Reports Server (NTRS)

    Packard, R. D. (Inventor)

    1973-01-01

    A method and a product for protecting semiconductor surfaces is disclosed. The protective coating material is prepared by heating a suitable protective resin with an organic solvent which is solid at room temperature and converting the resulting solution into sheets by a conventional casting operation. Pieces of such sheets of suitable shape and thickness are placed on the semiconductor areas to be coated and heat and vacuum are then applied to melt the sheet and to drive off the solvent and cure the resin. A uniform adherent coating, free of bubbles and other defects, is thus obtained exactly where it is desired.

  1. Quantum Transport in Semiconductors

    DTIC Science & Technology

    1991-10-01

    SRS i 91 4. TITLE AND SUBTITLE Quantum Transport in Semiconductors 5. FUNDING NUMBER söMtos-rizk-ooss 6. AUTHOR(S) D. K. Ferry ©fte ELECTE...OF ABSTRACT UL NSN 7540-01-280-5500 O 1 9 Standard Form 298 (Rev. 2-89) Presented by ANSI Std «9-18 298-102 Final Report Quantum Transport in... Quantum Transport in Semiconductor Devices This final report describes a program of research investigating quantum effects which become important in

  2. GUARD RING SEMICONDUCTOR JUNCTION

    DOEpatents

    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)

  3. New unorthodox semiconductor devices

    NASA Astrophysics Data System (ADS)

    Board, K.

    1985-12-01

    A range of new semiconductor devices, including a number of structures which rely entirely upon new phenomena, are discussed. Unipolar two-terminal devices, including impurity-controlled barriers and graded composition barriers, are considered, as are new transistor structures, including the hot-electron camel transistor, the planar-doped barrier transistor, the thermionic emission transistor, and the permeable base transistor. Regenerative switching devices are addressed, including the metal-tunnel insulator-semiconductor switch, the polysilicon switch, MIS, and MISIM switching structures, and the triangular-barrier switch. Heterostructure devices are covered, including the heterojunction bipolar transistor, the selectively doped heterojunction transistor, heterojunction lasers, and quantum-well structures.

  4. 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

  5. Kansas Advanced Semiconductor Project

    SciTech Connect

    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.

  6. 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…

  7. 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.

  8. 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.

  9. Transport properties of the topological Kondo insulator SmB6 under the irradiation of light

    NASA Astrophysics Data System (ADS)

    Zhu, Guo-Bao; Yang, Hui-Min

    2016-10-01

    In this paper, we study transport properties of the X point in the Brillouin zone of the topological Kondo insulator SmB6 under the application of a circularly polarized light. The transport properties at high-frequency regime and low-frequency regime as a function of the ratio (κ) of the Dresselhaus-like and Rashba-like spin-orbit parameter are studied based on the Floquet theory and Boltzmann equation respectively. The sign of Hall conductivity at high-frequency regime can be reversed by the ratio κ and the amplitude of the light. The amplitude of the current can be enhanced by the ratio κ. Our findings provide a way to control the transport properties of the Dirac materials at low-frequency regime. Project supported by the National Natural Science Foundation of China (Grant Nos. 11504095 and 11447145), the Foundation of Heze University (Grant Nos. XY14B002 and XYPY01), and the Project funded by the Higher Educational Science and Technology Program of Shandong Province, China (Grant No. J15LJ55).

  10. Nonequilibrium spatiotemporal formation of the Kondo screening cloud on a lattice

    NASA Astrophysics Data System (ADS)

    Nuss, Martin; Ganahl, Martin; Arrigoni, Enrico; von der Linden, Wolfgang; Evertz, Hans Gerd

    2015-02-01

    We study the nonequilibrium formation of a spin screening cloud that accompanies the quenching of a local magnetic moment immersed in a Fermi sea at zero temperature. Based on high-precision density matrix renormalization-group results for the interacting single-impurity Anderson model, we discuss the real-time evolution after a quantum quench in the impurity-reservoir hybridization using time-evolving block decimation. We report emergent length and time scales in the spatiotemporal structure of nonlocal correlation functions in the spin and the charge density channel. At equilibrium, our data for the correlation functions and the extracted length scales show good agreement with existing results, as do local time-dependent observables at the impurity. In the time-dependent data, we identify a major signal which defines a "light cone" moving at the Fermi velocity and a ferromagnetic component in its wake. Inside the light cone we find that the structure of the nonequilibrium correlation functions emerges on two time scales. Initially, the qualitative structure of the correlation functions develops rapidly at the lattice Fermi velocity. Subsequently the spin correlations converge to the equilibrium results on a much larger time scale. This process sets a dynamic energy scale, which we identify to be proportional to the Kondo temperature. Outside the light cone we observe two different power-law decays of the correlation functions in space, with time- and interaction-strength-independent exponents.

  11. Kondo lattice heavy fermion behavior in CeRh2Ga2.

    PubMed

    Anand, V K; Adroja, D T; Bhattacharyya, A; Klemke, B; Lake, B

    2017-04-05

    The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility [Formula: see text], isothermal magnetization M(H), heat capacity [Formula: see text], electrical resistivity [Formula: see text], thermal conductivity [Formula: see text] and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The [Formula: see text] data show paramagnetic behavior with an effective moment [Formula: see text]/Ce indicating Ce(3+) valence state of Ce ions. The [Formula: see text] data exhibit Kondo lattice behavior with a metallic ground state. The low-T [Formula: see text] data yield an enhanced Sommerfeld coefficient [Formula: see text] mJ/mol K(2) characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T [Formula: see text] and [Formula: see text] show an anomaly near 255 K, reflecting a phase transition. The [Formula: see text] suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L 0.

  12. Nonequilibrium Kondo transport through a quantum dot in a magnetic field

    NASA Astrophysics Data System (ADS)

    Smirnov, Sergey; Grifoni, Milena

    2013-07-01

    We analyze the universal transport properties of a strongly interacting quantum dot in the Kondo regime when the quantum dot is placed in an external magnetic field. The quantum dot is described by the asymmetric Anderson model with the spin degeneracy removed by the magnetic field resulting in Zeeman splitting. Using an analytical expression for the tunneling density of states found from a Keldysh effective field theory, we obtain in the whole energy range the universal differential conductance and analytically demonstrate its Fermi-liquid and logarithmic behavior at low and high energies, respectively, as a function of the magnetic field. We also show results on the zero-temperature differential conductance as a function of the bias voltage at different magnetic fields as well as results on finite-temperature effects out of equilibrium and at a finite magnetic field. The modern nonequilibrium experimental issues of the critical magnetic field, at which the zero bias maximum of the differential conductance starts to split into two maxima, as well as the distance between these maxima as a function of the magnetic field, are also addressed.

  13. Kondo lattice heavy fermion behavior in CeRh2Ga2

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Adroja, D. T.; Bhattacharyya, A.; Klemke, B.; Lake, B.

    2017-04-01

    The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility χ (T) , isothermal magnetization M(H), heat capacity {{C}\\text{p}}(T) , electrical resistivity ρ (T) , thermal conductivity κ (T) and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The χ (T) data show paramagnetic behavior with an effective moment {μ\\text{eff}}≈ 2.5~{μ\\text{B}} /Ce indicating Ce3+ valence state of Ce ions. The ρ (T) data exhibit Kondo lattice behavior with a metallic ground state. The low-T {{C}\\text{p}}(T) data yield an enhanced Sommerfeld coefficient γ =130(2) mJ/mol K2 characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T {{C}\\text{p}}(T) and ρ (T) show an anomaly near 255 K, reflecting a phase transition. The κ (T) suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L 0.

  14. Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites.

    PubMed

    Meyers, D; Middey, S; Cheng, J-G; Mukherjee, Swarnakamal; Gray, B A; Cao, Yanwei; Zhou, J-S; Goodenough, J B; Choi, Yongseong; Haskel, D; Freeland, J W; Saha-Dasgupta, T; Chakhalian, J

    2014-12-17

    With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on A-site-ordered perovskites with Cu in the A-site and the B-sites descending along the ninth group of the periodic table to elucidate the emerging properties as d-orbitals change from partially filled 3d to 4d to 5d. The results show that when descending from Co to Ir, the charge transfers from the cuprate-like Zhang-Rice state on Cu to the t(2g) orbital of the B site. As the Cu d-orbital occupation approaches the Cu(2+) limit, a mixed valence state in CaCu(3)Rh(4)O(12) and heavy fermion state in CaCu(3)Ir(4)O(12) are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for the f-electron systems.

  15. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Anomalous Kondo-Switching Effect of a Spin-Flip Quantum Dot Embedded in an Aharonov-Bohm Ring

    NASA Astrophysics Data System (ADS)

    Chen, Xiong-Wen; Shi, Zhen-Gang; Song, Ke-Hui

    2009-11-01

    We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov-Bohm (AB) ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on the slave-boson mean-field theory, we find that in this system the persistent current (PC) sensitively depends on the parity and size of the AB ring and can be tuned by the spin-flip scattering (R). In the small AB ring, the PC is suppressed due to the enhancing R weakening the Kondo resonance. On the contrary, in the large AB ring, with R increasing, the peak of PC firstly moves up to max-peak and then down. Especially, the PC phase shift of π appears suddenly with the proper value of R, implying the existence of the anomalous Kondo effect in this system. Thus this system may be a candidate for quantum switch.

  16. Kondo interactions from band reconstruction in YbInCu4

    SciTech Connect

    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.

  17. Semiconductor radiation detector

    DOEpatents

    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.

  18. Three dimensional strained semiconductors

    DOEpatents

    Voss, Lars; Conway, Adam; Nikolic, Rebecca J.; Leao, Cedric Rocha; Shao, Qinghui

    2016-11-08

    In one embodiment, an apparatus includes a three dimensional structure comprising a semiconductor material, and at least one thin film in contact with at least one exterior surface of the three dimensional structure for inducing a strain in the structure, the thin film being characterized as providing at least one of: an induced strain of at least 0.05%, and an induced strain in at least 5% of a volume of the three dimensional structure. In another embodiment, a method includes forming a three dimensional structure comprising a semiconductor material, and depositing at least one thin film on at least one surface of the three dimensional structure for inducing a strain in the structure, the thin film being characterized as providing at least one of: an induced strain of at least 0.05%, and an induced strain in at least 5% of a volume of the structure.

  19. Stretchable Organic Semiconductor Devices.

    PubMed

    Qian, Yan; Zhang, Xinwen; Xie, Linghai; Qi, Dianpeng; Chandran, Bevita K; Chen, Xiaodong; Huang, Wei

    2016-11-01

    Stretchable electronics are essential for the development of intensely packed collapsible and portable electronics, wearable electronics, epidermal and bioimplanted electronics, 3D surface compliable devices, bionics, prosthesis, and robotics. However, most stretchable devices are currently based on inorganic electronics, whose high cost of fabrication and limited processing area make it difficult to produce inexpensive, large-area devices. Therefore, organic stretchable electronics are highly attractive due to many advantages over their inorganic counterparts, such as their light weight, flexibility, low cost and large-area solution-processing, the reproducible semiconductor resources, and the easy tuning of their properties via molecular tailoring. Among them, stretchable organic semiconductor devices have become a hot and fast-growing research field, in which great advances have been made in recent years. These fantastic advances are summarized here, focusing on stretchable organic field-effect transistors, light-emitting devices, solar cells, and memory devices.

  20. Isotopically controlled semiconductors

    SciTech Connect

    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.

  1. Metal Contacts in Semiconductors.

    DTIC Science & Technology

    1983-11-01

    surfaces, Pnotoelectron spe troscopy, Auger electron spectro- I scopy, Schottky barriers, ohmic contacts, Defects in semiconductors, Cadmium * telluride...Indium phosphide, Gallium arsenide, Gallium Selenide . j 20. ABSTR ACT (roothat ow rees esh " neceay and td..ity by block -. b*w) SThe application of...angstroms. Also, provided one eliminates the systems where cadmium outdiffusion into high work function metals occurs then good agreement between the

  2. Tunable semiconductor lasers

    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.

  3. Semiconductor Ion Implanters

    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.

  4. Semiconductor Ion Implanters

    SciTech Connect

    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.

  5. New Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Balestra, F.

    2008-11-01

    A review of recently emerging semiconductor devices for nanoelectronic applications is given. For the end of the international technology roadmap for semiconductors, very innovative materials, technologies and nanodevice architectures will be needed. Silicon on insulator-based devices seem to be the best candidates for the ultimate integration of integrated circuits on silicon. The flexibility of the silicon on insulator-based structure and the possibility to realize new device architectures allow to obtain optimum electrical properties for low power and high performance circuits. These transistors are also very interesting for high frequency and memory applications. The performance and physical mechanisms are addressed in single- and multi-gate thin film Si, SiGe and Ge metal-oxide-semiconductor field-effect-transistors. The impact of tensile or compressive uniaxial and biaxial strains in the channel, of high k materials and metal gates as well as metallic Schottky source-drain architectures are discussed. Finally, the interest of advanced beyond-CMOS (complementary MOS) nanodevices for long term applications, based on nanowires, carbon electronics or small slope switch structures are presented.

  6. Theory of the orbital Kondo effect with assisted hopping in strongly correlated electron systems: Parquet equations, superconductivity, and mass enhancement

    NASA Astrophysics Data System (ADS)

    Penc, K.; Zawadowski, A.

    1994-10-01

    The orbital Kondo effect is treated in a model where, additional to the conduction band, there are localized orbitals close to the Fermi energy. If the hopping between the conduction band and the localized heavy orbitals depends on the occupation of the atomic orbitals in the conduction band, then orbital Kondo correlation occurs. The noncommutative nature of the coupling required for the Kondo effect is formally due to the form factors associated with the assisted hopping, which in the momentum representation depends on the momenta of the conduction electrons involved. The leading logarithmic vertex corrections are due to the local Coulomb interaction between the electrons on the heavy orbital and in the conduction band. The renormalized vertex functions are obtained as a solution of a closed set of differential equations and they show power behavior. The amplitude of large renormalization is determined by an infrared cutoff due to finite energy and dispersion of the heavy particles. The enhanced assisted hopping rate results in mass enhancement and attractive interaction in the conduction band. The superconductivity transition temperature calculated is largest for the intermediate mass enhancement, m*/m~=2-3. For larger mass enhancement the small one-particle weight (Z) in the Green's function reduces the transition temperature, which may be characteristic for other models as well. The theory is developed for different one-dimensional and square-lattice models, but the applicability is not limited to them. In the one-dimensional case charge- and spin-density susceptibilities are also discussed. Good candidates for the heavy orbital are f bands in the heavy fermionic systems and nonbonding oxygen orbitals in high-temperature superconductors and different flatbands in the quasi-one-dimensional organic conductors.

  7. 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.

  8. Mesoscopic features in the transport properties of a Kondo-correlated quantum dot in a magnetic field.

    PubMed

    Camjayi, Alberto; Arrachea, Liliana

    2014-01-22

    We study the transport behavior induced by a small bias voltage through a quantum dot connected to one-channel finite-size wires. We describe the quantum dot using the Hubbard-Anderson impurity model and we obtain solutions by means of a quantum Monte Carlo method. We investigate the effect of a magnetic field applied at the quantum dot in the Kondo regime. We identify mesoscopic oscillations in the conductance, which are introduced by the magnetic field. This behavior is analogous to that observed as a function of the temperature.

  9. Complex magnetic behavior in the novel Kondo lattice compound CeRhSn₃.

    PubMed

    Anand, V K; Adroja, D T; Hillier, A D; Kockelmann, W; Fraile, A; Strydom, A M

    2011-07-13

    We report the magnetic and transport properties of a new ternary intermetallic compound, CeRhSn₃, using magnetic susceptibility, magnetization, specific heat, electrical resistivity, muon-spin relaxation (μSR) and neutron diffraction investigations. The dc magnetic susceptibility data reveal two magnetic phase transitions at 0.9 and 4 K. The overall behavior of dc susceptibility and magnetization indicates a ferrimagnetic-type phase transition near 4 K. The specific heat data also exhibit sharp λ-type anomalies at 1 and 4 K. The behavior of the specific heat anomaly under the application of a magnetic field suggests that the 1 K transition is probably related to a transition from a ferri- to a ferromagnetic state. The low temperature specific heat exhibits an enhanced Sommerfeld coefficient γ (~100 mJ mol⁻¹ K⁻²) due to the formation of a moderate heavy fermion state. The resistivity of CeRhSn₃ demonstrates an interplay between the RKKY and Kondo interactions which is further modified by the presence of the crystal electric field. Interestingly, the resistivity of the nonmagnetic reference compound, LaRhSn₃, is found to increase with decreasing temperature. Further, the onset of long-range magnetic order below 1 K is confirmed from our μSR study on CeRhSn₃. However, the 4 K transition is not detected in the μSR and low temperature neutron diffraction data. Analysis of the dc magnetic susceptibility data within the framework of a two-sublattice model of ferrimagnetism supports the ferrimagnetic-type transition at 4 K in CeRhSn₃. We have observed an unusual frequency dependence of the peak near 4 K in the ac susceptibility, which shows that the transition temperature shifts toward the lower temperature side with increasing frequency.

  10. Tunable High Brightness Semiconductor Sources

    DTIC Science & Technology

    2015-05-01

    AFRL-RY-WP-TR-2015-0066 TUNABLE HIGH BRIGHTNESS SEMICONDUCTOR SOURCES Robert Bedford, Saima Husaini, Charles Reyner, and Tuoc Dang...3. DATES COVERED (From - To) May 2015 Final 5 November 2010 – 1 February 2015 4. TITLE AND SUBTITLE TUNABLE HIGH BRIGHTNESS SEMICONDUCTOR SOURCES 5a...included within the Tunable High Brightness Semiconductor Sources work unit includes several technology advancements. First, theoretical advances in mid

  11. 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.

  12. Method of passivating semiconductor surfaces

    DOEpatents

    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.

  13. Electrodes for Semiconductor Gas Sensors.

    PubMed

    Lee, Sung Pil

    2017-03-25

    The electrodes of semiconductor gas sensors are important in characterizing sensors based on their sensitivity, selectivity, reversibility, response time, and long-term stability. The types and materials of electrodes used for semiconductor gas sensors are analyzed. In addition, the effect of interfacial zones and surface states of electrode-semiconductor interfaces on their characteristics is studied. This study describes that the gas interaction mechanism of the electrode-semiconductor interfaces should take into account the interfacial zone, surface states, image force, and tunneling effect.

  14. Method of passivating semiconductor surfaces

    DOEpatents

    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.

  15. Nanoscale Semiconductor Electronics

    DTIC Science & Technology

    2015-02-25

    MONITOR’S REPORT Kirtland AFB, NM 87117-5776 NUMBER(S) AFRL -RV-PS-TR-2014-0202 12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release...Kingman Rd, Suite 0944 Ft Belvoir, VA 22060-6218 1 cy AFRL /RVIL Kirtland AFB, NM 87117-5776 2 cys Official Record Copy AFRL /RVSE/Jesse Mee 1 cy ... AFRL -RV-PS- AFRL -RV-PS- TR-2014-0202 TR-2014-0202 NANOSCALE SEMICONDUCTOR ELECTRONICS Steven R. J. Brueck and Ganesh Balakrishnan University of New

  16. Electrowetting on semiconductors

    NASA Astrophysics Data System (ADS)

    Palma, Cesar; Deegan, Robert

    2015-01-01

    Applying a voltage difference between a conductor and a sessile droplet sitting on a thin dielectric film separating it from the conductor will cause the drop to spread. When the conductor is a good metal, the change of the drop's contact angle due to the voltage is given by the Young-Lippmann (YL) equation. Here, we report experiments with lightly doped, single crystal silicon as the conductive electrode. We derive a modified YL equation that includes effects due to the semiconductor and contact line pinning. We show that light induces a non-reversible wetting transition, and that our model agrees well with our experimental results.

  17. 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.

  18. Microwave semiconductor devices

    NASA Astrophysics Data System (ADS)

    Sitch, J. E.

    1985-03-01

    The state of the art of microwave semiconductor design is reviewed, with emphasis on developments of the past 10-12 years. Consideration is given to: varistor diodes; varactor diodes; and transit time negative diodes. The design principles of bipolar and unipolar transistors are discussed, with reference to power FETs, traveling-wave FETs, and camel or planar-doped barrier transistors. Recent innovations in the field of fabrication technology are also considered, including: crystal growth; doping; and packaging. Several schematic drawings and photographs of the different devices are provided.

  19. Semiconductor Terahertz Technology

    DTIC Science & Technology

    2009-06-15

    COVERED (From - To) 15-June-2009 Final Report 12 Apr 07 - 15 Apr 09 4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER FA8718-07-C-0030 Semiconductor Terahertz ...and the other for the phononic waveguides. 15. SUBJECT TERMS Quantum cascade laser, gennanium, gennanium-tin, terahertz 16. SECURITY CLASStFICATION OF...7 Figure 7 lllustration of a GaAs-based active region waveguide with either Ga or Au as cladding operating in the Restrahlen band of GaN . 10 Figure 8

  20. Chemically Derivatized Semiconductor Photoelectrodes.

    DTIC Science & Technology

    1982-01-04

    as Si, Ge, and GaAs derivatized with reagents based on ferrocene such as those represented by I and II. Work with p-type semiconductor photoelectrode...Concerning n-type Si it was found that EtOH/0.1 M En-Bu4N)C104 solutions containing A = ferrocene and A+ = ferri-- cinium result in a constant output of...electrical energy from an illuminated photoelectrochemical device configured as in Scheme II.(20) The ferrocene captures the photogenerated h+ at a rate -4

  1. Layered semiconductor neutron detectors

    DOEpatents

    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.

  2. Power semiconductor controlled drives

    NASA Astrophysics Data System (ADS)

    Dubey, Gopal K.

    This book presents power semiconductor controlled drives employing dc motors, induction motors, and synchronous motors. The dynamics of motor and load systems are covered. Open-loop and closed-loop drives are considered, and thyristor, power transistor, and GTO converters are discussed. In-depth coverage is given to ac drives, particularly those fed by voltage and current source inverters and cycloconverters. Full coverage is given to brushless and commutatorless dc drives, including load-commuted synchronous motor drives. Rectifier-controlled dc drives are presented in detail.

  3. 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.

  4. The effect of Ce dilution on the ferromagnetic ordering and Kondo behavior of CeRuPO

    NASA Astrophysics Data System (ADS)

    Noorafshan, M.; Nourbakhsh, Z.

    2017-03-01

    The structural, electronic and magnetic properties and Kondo behavior of Ce1-xLax RuPO (x=0, 0.25, 0.5, 0.75 and 1) alloys are investigated using density functional theory by utilizing Wien2k package. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approach (where U is the Hubbard correlation term) is employed to treat the f-electrons properly. We also present a comparative study between the electronic structure and magnetic properties of these alloys within GGA and GGA+U approaches. The calculated lattice parameters and bulk moduli of these alloys as a function of x are in the best agreement with Vegard's linear rule. The total and partial electron density of states and linear coefficient of electronic specific heat of these alloy within GGA and GGA+U are investigated and compared. The effect of La substitution on the Kondo behavior of CeRuPO compound is investigated.

  5. The effect of Th substitution and of magnetic field on Kondo semiconducting behaviour in U2Ru2Sn

    NASA Astrophysics Data System (ADS)

    du Plessis, P. de V.; Strydom, A. M.; Troc, R.; Menon, L.

    2001-09-01

    Electrical resistivity, ρ(T), measurements on U2Ru2Sn show typical Kondo semiconducting behaviour, namely a ρ(T)~ln T behaviour at higher temperatures and an activation-like increase in ρ(T) below 20 K which indicates the opening of a small gap in the electronic density of states. The magnetic susceptibility, χ(T), of U2Ru2Sn has a maximum around 180 K which is characteristic of intermediate-valence behaviour. The χ(T) data for U2Ru2Sn have been fitted to the interconfigurational fluctuation model of Sales and Wohlleben giving a value of Tsf* = 155(2) K for the characteristic fluctuation temperature. Substituting as little as 5% Th for U leads to a ρ(T) variation reminiscent of that of a single-ion Kondo metal ρ(T) = ρ(0)[1- (π2/16)(T2/TK2)]. Values of TK = 79(1) and 113(1) K are respectively obtained for alloys with 5% and 10% Th substitution.

  6. Magnetic susceptibility of Dirac fermions, Bi-Sb alloys, interacting Bloch fermions, dilute nonmagnetic alloys, and Kondo alloys

    NASA Astrophysics Data System (ADS)

    Buot, Felix A.; Otadoy, Roland E. S.; Rivero, Karla B.

    2017-03-01

    Wide ranging interest in Dirac Hamiltonian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. The unified treatment of all the above calculations is based on the lattice Weyl-Wigner formulation of discrete phase-space quantum mechanics. For completeness, the magnetic susceptibility of Kondo alloys is also given since Dirac fermions in conduction band and magnetic impurities exhibit Kondo effect.

  7. 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.

  8. Topological surface states interacting with bulk excitations in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy

    PubMed Central

    Park, Wan Kyu; Sun, Lunan; Noddings, Alexander; Kim, Dae-Jeong; Fisk, Zachary; Greene, Laura H.

    2016-01-01

    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

  9. Enhanced superconductivity, Kondo behavior, and negative-curvature resistivity of oxygen-irradiated thin films of aluminium

    NASA Astrophysics Data System (ADS)

    Sinnecker, E. H. C. P.; Sant'Anna, M. M.; ElMassalami, M.

    2017-02-01

    We followed the evolution of the normal and superconducting properties of Al thin films after each session of various successive oxygen irradiations at ambient temperature. Such irradiated films, similar to the granular ones, exhibit enhanced superconductivity, Kondo behavior, and negative-curvature resistivity. Two distinct roles of oxygen are identified: as a damage-causing projectile and as an implanted oxidizing agent. The former gives rise to the processes involved in the conventional recovery stages. The latter, considered within the context of the Cabrera-Mott model, gives rise to a multistep process which involves charges transfer and creation of stabilized vacancies and charged defects. Based on the outcome of this multistep process, we consider (i) the negative-curvature resistivity as a manifestation of a thermally assisted liberation of trapped electric charges, (ii) the Kondo contribution as a spin-flip scattering from paramagnetic, color-center-type defects, and (iii) the enhancement of Tc as being due to a lattice softening facilitated by the stabilized defects and vacancies. The similarity in the phase diagrams of granular and irradiated films as well as the aging effects are discussed along the same line of reasoning.

  10. Semiconductor devices incorporating multilayer interference regions

    DOEpatents

    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.

  11. Semiconductor devices incorporating multilayer interference regions

    DOEpatents

    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.

  12. Fibre ring cavity semiconductor laser

    SciTech Connect

    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)

  13. Process for producing chalcogenide semiconductors

    DOEpatents

    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.

  14. Process for producing chalcogenide semiconductors

    DOEpatents

    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.

  15. Variable temperature semiconductor film deposition

    DOEpatents

    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.

  16. Variable temperature semiconductor film deposition

    DOEpatents

    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.

  17. Progress in semiconductor drift detectors

    SciTech Connect

    Rehak, P.; Walton, J.; Gatti, E.; Longoni, A.; Sanpietro, M.; Kemmer, J.; Dietl, H.; Holl, P.; Klanner, R.; Lutz, G.

    1985-01-01

    Progress in testing semiconductor drift detectors is reported. Generally better position and energy resolutions were obtained than resolutions published previously. The improvement is mostly due to new electronics better matched to different detectors. It is shown that semiconductor drift detectors are becoming versatile and reliable detectors for position and energy measurements.

  18. Physics with isotopically controlled semiconductors

    SciTech Connect

    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.

  19. Semiconductor nanowire lasers

    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.

  20. Photocatalysis Using Semiconductor Nanoclusters

    SciTech Connect

    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.

  1. Semiconductor adiabatic qubits

    DOEpatents

    Carroll, Malcolm S.; Witzel, Wayne; Jacobson, Noah Tobias; Ganti, Anand; Landahl, Andrew J.; Lilly, Michael; Nguyen, Khoi Thi; Bishop, Nathaniel; Carr, Stephen M.; Bussmann, Ezra; Nielsen, Erik; Levy, James Ewers; Blume-Kohout, Robin J.; Rahman, Rajib

    2016-12-27

    A quantum computing device that includes a plurality of semiconductor adiabatic qubits is described herein. The qubits are programmed with local biases and coupling terms between qubits that represent a problem of interest. The qubits are initialized by way of a tuneable parameter, a local tunnel coupling within each qubit, such that the qubits remain in a ground energy state, and that initial state is represented by the qubits being in a superposition of |0> and |1> states. The parameter is altered over time adiabatically or such that relaxation mechanisms maintain a large fraction of ground state occupation through decreasing the tunnel coupling barrier within each qubit with the appropriate schedule. The final state when tunnel coupling is effectively zero represents the solution state to the problem represented in the |0> and |1> basis, which can be accurately read at each qubit location.

  2. Semiconductor radiation detector

    DOEpatents

    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.

  3. Semiconductor Nanocrystals for Biological Imaging

    SciTech Connect

    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.

  4. Semiconductor device PN junction fabrication using optical processing of amorphous semiconductor material

    SciTech Connect

    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.

  5. State of the art in semiconductor detectors

    SciTech Connect

    Rehak, P. ); Gatti, E. )

    1989-01-01

    The state of the art in semiconductor detectors for elementary particle physics and x-ray astronomy is briefly reviewed. Semiconductor detectors are divided into two groups; classical semiconductor diode detectors; and semiconductor memory detectors. Principles of signal formation for both groups of detectors are described and their performance is compared. New developments of silicon detectors are reported here. 13 refs., 8 figs.

  6. Heavy surface state in a possible topological Kondo insulator: Magnetothermoelectric transport on the (011) plane of SmB6

    DOE PAGES

    Luo, Yongkang; Chen, Hua; Dai, Jianhui; ...

    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

  7. 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.

  8. Carrier-mediated Kondo effect and Hall mobility by electrolyte gating in slightly doped anatase TiO2 films

    NASA Astrophysics Data System (ADS)

    Han, Yin-Long; Luo, Zhong-Zhong; Li, Cheng-Jian; Shen, Sheng-Chun; Qu, Guo-Liang; Xiong, Chang-Min; Dou, Rui-Fen; He, Lin; Nie, Jia-Cai

    2014-11-01

    Carrier density (ns) is a crucial parameter that governs the properties of correlated oxides, so the field-effect approach is an ideal tool to investigate the novel physics of the system. Here, the carrier-mediated transport of slightly doped anatase TiO2 epitaxial films were studied by electric double layer transistor (EDLT) gating. The ns has been increased hugely, and concomitantly, the channels of anatase TiO2 films undergo an insulator-metal transition with a decrease in resistivity by almost three orders of magnitude. More fascinating, the Kondo effect depends very strongly on ns, and the Hall mobility could be enhanced about one order of magnitude with increasing ns. This study shows that EDLT gating is a powerful method to stimulate and mediate novel phenomena of correlated oxides.

  9. Kondo effect in Co{sub x}Cu{sub 1-x} granular alloys prepared by chemical reduction method

    SciTech Connect

    Dhara, Susmita Chowdhury, Rajeswari Roy; Bandyopadhyay, Bilwadal

    2015-06-24

    Nanostructured CoCu granular alloys Co{sub x}Cu{sub 1-x} (x ≤ 0.3) have been prepared by chemical reduction method using NaBH{sub 4} as a reducing agent. Electronic transport properties are studied in the temperature range 4-300 K. Resistance exhibits a metallic behavior below room temperature and draws a minimum near 20 K in all the samples except in Co{sub 0.3}Cu{sub 0.7}. This low temperature resistivity minimum diminishes with applied magnetic field. There is also a logarithmic temperature dependence of resistivity at temperatures below 20 K. This phenomenon indicates a Kondo-like scattering mechanism involving magnetic Co impurity spin clusters in Cu host.

  10. Crystal structure and anisotropic magnetic properties of new ferromagnetic Kondo lattice compound Ce(Cu,Al,Si)2

    NASA Astrophysics Data System (ADS)

    Maurya, A.; Thamizhavel, A.; Dhar, S. K.; Provino, A.; Pani, M.; Costa, G. A.

    2017-03-01

    Single crystals of the new compound CeCu0.18Al0.24Si1.58 have been grown by high-temperature solution growth method using a eutectic Al-Si mixture as flux. This compound is derived from the binary CeSi2 (tetragonal α-ThSi2-type, Pearson symbol tI12, space group I41/amd) obtained by partial substitution of Si by Cu and Al atoms but showing full occupation of the Si crystal site (8e). While CeSi2 is a well-known valence-fluctuating paramagnetic compound, the CeCu0.18Al0.24Si1.58 phase orders ferromagnetically at TC=9.3 K. At low temperatures the easy-axis of magnetization is along the a-axis, which re-orients itself along the c-axis above 30 K. The presence of hysteresis in the magnetization curve, negative temperature coefficient of resistivity at high temperatures, reduced jump in the heat capacity and a relatively lower entropy released up to the ordering temperature, and enhanced Sommerfeld coefficient (≈100 mJ/mol K2) show that CeCu0.18Al0.24Si1.58 is a Kondo lattice ferromagnetic, moderate heavy fermion compound. Analysis of the high temperature heat capacity data in the paramagnetic region lets us infer that the crystal electric field split doublet levels are located at 178 and 357 K, respectively, and Kondo temperature (8.4 K) is of the order of TC in CeCu0.18Al0.24Si1.58.

  11. Anderson lattice with explicit Kondo coupling revisited: metamagnetism and the field-induced suppression of the heavy fermion state.

    PubMed

    Howczak, Olga; Spałek, Jozef

    2012-05-23

    We apply the extended (statistically consistent, SCA) Gutzwiller-type approach to the periodic Anderson model (PAM) in an applied magnetic field and in the strong-correlation limit. The finite-U corrections are included systematically by transforming the PAM into the form with the Kondo-type interaction and the residual hybridization, both appearing at the same time and on equal footing. This effective Hamiltonian represents the essence of our Anderson-Kondo lattice model. We show that in ferromagnetic phases the low-energy single-particle states are strongly affected by the presence of the applied magnetic field. We also find that for large values of hybridization strength the system enters the so-called locked heavy fermion state introduced earlier. In this state the chemical potential lies in the majority-spin hybridization gap and, as a consequence, the system evolution is insensitive to further increase of the applied field. However, for a sufficiently strong magnetic field, the system transforms from the locked state to the fully spin-polarized phase. This is accompanied by a metamagnetic transition, as well as by a drastic reduction of the effective mass of the quasiparticles. In particular, we observe no effective mass enhancement in the fully polarized state. The findings are in overall agreement with experimental results for the Ce compounds in high magnetic fields. The mass enhancement for the spin-minority electrons may also diminish with the increasing field, unlike for the quasiparticle states in a single narrow band in the same limit of strong correlations.

  12. 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.

  13. Metal-Insulator-Semiconductor Photodetectors

    PubMed Central

    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

  14. Signal processing for semiconductor detectors

    SciTech Connect

    Goulding, F.S.; Landis, D.A.

    1982-02-01

    A balanced perspective is provided on the processing of signals produced by semiconductor detectors. The general problems of pulse shaping to optimize resolution with constraints imposed by noise, counting rate and rise time fluctuations are discussed.

  15. Optical properties of semiconductor microcavities

    NASA Astrophysics Data System (ADS)

    Son, Joong-Kon

    Thanks to the difference in energy gap between two semiconductors and to their different indices of refraction, semiconductor heterostructures can confine electrons as well as photons. This property makes it possible to build semiconductor-based optical resonators (microcavities) with a radiation dipole (a quantum well) in its midst to investigate the coupling between the optical modes of the microcavity with the exciton modes of the quantum well. Such an interaction, besides its intrinsic interest, is relevant to vertically-emitting semiconductor lasers, based on the quantum well- microcavity system. In this thesis, we will present experimental evidence of temperature and electric-field dependent exciton-cavity coupling in GaAs-GaAlAs microcavities.

  16. Dye Sensitization of Semiconductor Particles

    SciTech Connect

    Hartland, G. V.

    2003-01-13

    In this project electron transfer at semiconductor liquid interfaces was examined by ultrafast time-resolved and steady-state optical techniques. The experiments primarily yielded information about the electron transfer from titanium dioxide semiconductor particles to absorbed molecules. The results show that the rate of electron transfer depends on the structure of the molecule, and the crystalline phase of the particle. These results can be qualitatively explained by Marcus theory for electron transfer.

  17. 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).

  18. Laser Assisted Semiconductor Device Processing

    DTIC Science & Technology

    1980-11-30

    In strongly absorbing semiconductors, the dominant absorption mechanism at frequencies higher than the bandgap frequency is interband transitions. The...current). The solution for miconductors. In strongly absorbing semiconductors, the n(x,t ) is a closed-form expression consisting of complemen- dominant 0...representative profles are shown in Fis. $-12. o -- For Nd: YAG in silicon. E, _0.99hv and the profiks are therefore and-gap recombination dominated

  19. Survey of cryogenic semiconductor devices

    SciTech Connect

    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.

  20. Impurity gettering in semiconductors

    DOEpatents

    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.

  1. Impurity gettering in semiconductors

    DOEpatents

    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.

  2. 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

  3. 75 FR 49526 - Freescale Semiconductor, Inc., Technical Information Center, Tempe, AZ; Freescale Semiconductor...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-13

    ... Employment and Training Administration Freescale Semiconductor, Inc., Technical Information Center, Tempe, AZ; Freescale Semiconductor, Inc., Technical Information Center, Woburn, MA; Amended Certification Regarding... Semiconductor, Inc., Technical Information Center, Tempe, Arizona. The notice was published in the...

  4. Upper critical field and Kondo effects in Fe(Te0.9Se0.1) thin films by pulsed field measurements

    DOE PAGES

    Salamon, Myron B.; Cornell, Nicholas; Jaime, Marcelo; ...

    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

  5. Wide-Bandgap Semiconductors

    SciTech Connect

    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

  6. Dielectric screening in semiconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Walter A.; Klepeis, John E.

    1988-01-01

    Intra-atomic and interatomic Coulomb interactions are incorporated into bond-orbital theory, based upon universal tight-binding parameters, in order to treat the effects of charge redistribution in semiconductor bonds. The dielectric function ɛ(q) is obtained for wave numbers in a [100] direction. The screening of differences in average hybrid energy across a heterojunction is calculated in detail, indicating that the decay length for the potential depends upon the relative values of Madelung and intra-atomic Coulomb terms. The parameters used here predict an imaginary decay length and thus an oscillating potential near the interface. The same theory is applied to point defects by imbedding a cluster in a matrix lattice, taking charges in that lattice to be consistent with continuum theory. Illustrating the theory with a phosphorus impurity in silicon, it is seen that the impurity and its neighboring atoms have charges on the order of only one-tenth of an electronic charge, alternating in sign from neighbor to neighbor as for planar defects. Although there are shifts in the term values on the order of a volt, the difference in these shifts for neighboring atoms is much smaller so that the effect on the bonds is quite small. This behavior is analogous to the response of a dielectric continuum to a point charge: The medium is locally neutral except at the center of the cluster and there are slowly varying potentials e2/ɛr. Because of this slow variation, free-atom term values should ordinarily suffice for the calculation of bond properties and bond lengths at impurities. Corrections are larger for homovalent substitutions such as carbon in silicon.

  7. Observation of a non-Kondo-like topological insulator state in the correlated rare-earth hexaboride YbB6

    NASA Astrophysics Data System (ADS)

    Neupane, Madhab; Xu, S.-Y.; Alidoust, N.; Bian, G.; Liu, C.; Belopolski, I.; Chang, T.-R.; Jeng, H. T.; Durakiewicz, T.; Lin, H.; Bansil, A.; Kim, D. J.; Fisk, Z.; Hasan, M. Z.

    2015-03-01

    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 surface states enclosing the Kramers' points, while the f - orbital which would be relevant for the Kondo mechanism is about 1 eV below the Fermi level. Our first-principles calculation shows that the topological state which we observe in YbB6 is due to an inversion between Yb d and B p bands. I will also present some of our recent results on other member of hexaborides. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials. The work at Princeton and Princeton-led synchrotron-based ARPES measurements is supported by U.S. DOE DE-FG-02-05ER46200.

  8. Kondo screening and spin excitation in few-layer CoPc molecular assembly stacking on Pb(111) surface: A DFT+HEOM study

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zheng, Xiao; Yang, Jinlong

    2016-10-01

    Transition metal phthalocyanine molecules adsorbed on a metal substrate exhibit rich spin-related phenomena such as magnetic anisotropy, spin excitation, and Kondo effect. In this work, we investigate theoretically few-layer cobalt phthalocyanine (CoPc) molecular assembly stacking on Pb(111) surface with the use of a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. Calculation results indicate that the local spin properties of CoPc/Pb(111) composites depend critically on the number of adsorption layers. The first layer of CoPc on the Pb(111) surface serves as a spin-insulating buffer, while the CoPc molecules in the second layer exhibit spin-1/2 Kondo effect with a Kondo temperature of about 22 K. In a triple-layer CoPc assembly stacking on Pb(111), the antiferromagnetic coupling between the second and third layers leads to local spin-flip excitations under finite bias voltages, which gives rise to characteristic signatures in the differential conductance spectra. The DFT+HEOM approach thus provides a practical means for investigating the local electronic and spin properties of two-dimensional molecular assemblies adsorbed on the metal surface. The insights obtained from the first-principles based simulations could be useful for experimental manipulation or design of magnetic composite systems.

  9. Indications of a Quantum Critical Point in Bi2Sr2CaCu2O8+δ Using a Local Kondo Effect

    NASA Astrophysics Data System (ADS)

    Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle

    2014-03-01

    A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By substituting Fe atoms for Cu atoms in the CuO plane of Bi2Sr2CaCu2O8+δ (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.

  10. Thienoacene-based organic semiconductors.

    PubMed

    Takimiya, Kazuo; Shinamura, Shoji; Osaka, Itaru; Miyazaki, Eigo

    2011-10-11

    Thienoacenes consist of fused thiophene rings in a ladder-type molecular structure and have been intensively studied as potential organic semiconductors for organic field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar molecular structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chemical structures, and elucidates the molecular electronic structure of each class. The packing structures of thienoacenes and the thus-estimated solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the molecular structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relationships in thienoacene-based organic semiconductors are discussed. The discussion provides insight into new molecular design strategies for the development of superior organic semiconductors.

  11. Diamagnetic excitons in semiconductors (Review)

    NASA Astrophysics Data System (ADS)

    Seisyan, R. P.

    2016-05-01

    Optical properties of semiconductor crystals in the presence of a high magnetic field have been considered. The field turn-on gives rise to oscillations of the optical-absorption edge or, more specifically, the formation of a complex absorption spectrum with a periodic structure, referred to as the spectrum of "diamagnetic excitons." Such spectra appear a source of the most accurate knowledge about the band structure of semiconductors. Moreover, these spectra can be used for simulating the low-dimensional state in semiconductors and possible interpretation of the emission spectra of neutron stars. The proposed analytical review is based on extensive experimental and theoretical data contained mostly in cited original works of the author with colleagues.

  12. Selenium semiconductor core optical fibers

    SciTech Connect

    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.

  13. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

    Part I: 1. Introduction E. F. Schubert; Part II: 2. Electronic structure of delta-doped semiconductors C. R. Proetto; Part III: 3. Recent progress in delta-like confinement of impurities in GaAs K. H. Ploog; 4. Flow-rate modulation epitaxy (FME) of III-V semiconductors T. Makimoto and Y. Horikoshi; 5. Gas source molecular beam epitaxy (MBE) of delta-doped III-V semiconductors D. Ritter; 6. Solid phase epitaxy for delta-doping in silicon I. Eisele; 7. Low temperature MBE of silicon H.-J. Gossmann; Part IV: 8. Secondary ion mass spectrometry of delta-doped semiconductors H. S. Luftmann; 9. Capacitance-voltage profiling E. F. Schubert; 10. Redistribution of impurities in III-V semiconductors E. F. Schubert; 11. Dopant diffusion and segregation in delta-doped silicon films H.-J. Gossmann; 12. Characterisation of silicon and delta-doped structures in GaAs R. C. Newman; 13. The DX-center in silicon delta-doped GaAs and AlxGa1-xAs P. M. Koenraad; Part V: 14. Luminescence and ellipsometry spectroscopy H. Yao and E. F. Schubert; 15. Photoluminescence and Raman spectroscopy of single delta-doped III-V semiconductor heterostructures J. Wagner and D. Richards; 16. Electron transport in delta-doped quantum wells W. T. Masselink; 17. Electron mobility in delta-doped layers P. M. Koenraad; 18. Hot electrons in delta-doped GaAs M. Asche; 19. Ordered delta-doping R. L. Headrick, L. C. Feldman and B. E. Weir; Part IV: 20. Delta-doped channel III-V field effect transistors (FETs) W.-P. Hong; 21. Selectively doped heterostructure devices E. F. Schubert; 22. Silicon atomic layer doping FET K. Nakagawa and K. Yamaguchi; 23. Planar doped barrier devices R. J. Malik; 24. Silicon interband and intersubband photodetectors I. Eisele; 25. Doping superlattice devices E. F. Schubert.

  14. Quantum Transport in Semiconductor Devices

    DTIC Science & Technology

    1994-06-30

    TITLE AND SUBTITLE S. FUNDING NUMBERS " Quantum Transport in Semiconductor Devices" 6. AUTHOR(S) ,DftftLo3-91-6-oo 7 David K. Ferry 7. PERFORMING...OF ABSTRACT UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL NZIN 1540-01-280-5500 Standard Form 298 (Rev 2-89) PrinCrlt>• oy ANSI SIC Z39-18 QUANTUM ... TRANSPORT IN SEMICONDUCTOR DEVICES Final Report on DAAL03-91-G-0067 (28461-EL) David K. Ferry, Principal Investigator Department of Electrical Engineering

  15. 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.

  16. 3D Nanostructuring of Semiconductors

    NASA Astrophysics Data System (ADS)

    Blick, Robert

    2000-03-01

    Modern semiconductor technology allows to machine devices on the nanometer scale. I will discuss the current limits of the fabrication processes, which enable the definition of single electron transistors with dimensions down to 8 nm. In addition to the conventional 2D patterning and structuring of semiconductors, I will demonstrate how to apply 3D nanostructuring techniques to build freely suspended single-crystal beams with lateral dimension down to 20 nm. In transport measurements in the temperature range from 30 mK up to 100 K these nano-crystals are characterized regarding their electronic as well as their mechanical properties. Moreover, I will present possible applications of these devices.

  17. Wide band gap semiconductor templates

    DOEpatents

    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.

  18. Nonlinear Peltier effect in semiconductors

    NASA Astrophysics Data System (ADS)

    Zebarjadi, Mona; Esfarjani, Keivan; Shakouri, Ali

    2007-09-01

    Nonlinear Peltier coefficient of a doped InGaAs semiconductor is calculated numerically using the Monte Carlo technique. The Peltier coefficient is also obtained analytically for single parabolic band semiconductors assuming a shifted Fermi-Dirac electronic distribution under an applied bias. Analytical results are in agreement with numerical simulations. Key material parameters affecting the nonlinear behavior are doping concentration, effective mass, and electron-phonon coupling. Current density thresholds at which nonlinear behavior is observable are extracted from numerical data. It is shown that the nonlinear Peltier effect can be used to enhance cooling of thin film microrefrigerator devices especially at low temperatures.

  19. Optical Processing With Photorefractive Semiconductors

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory

    1989-01-01

    Experimental phase-conjugate four-wave-mixing apparatus used to demonstrate capabilities of GaAs (and potentially of other photorefractive semiconductors like InP and CdTe) for optical processing of information. With modifications, performs any of three basic image-processing functions: transfer to different light beam, enhancement of edges, and autocorrelation. Includes crystal of GaAs of 5 by 9 by 9 mm with cubic crystalline axes. Advantages include high speed and compatibilty with other semiconductor devices.

  20. Method of preparing nitrogen containing semiconductor material

    DOEpatents

    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.

  1. 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)

  2. Method and structure for passivating semiconductor material

    DOEpatents

    Pankove, Jacques I.

    1981-01-01

    A structure for passivating semiconductor material comprises a substrate of crystalline semiconductor material, a relatively thin film of carbon disposed on a surface of the crystalline material, and a layer of hydrogenated amorphous silicon deposited on the carbon film.

  3. Semiconductor structure and recess formation etch technique

    DOEpatents

    Lu, Bin; Sun, Min; Palacios, Tomas Apostol

    2017-02-14

    A semiconductor structure has a first layer that includes a first semiconductor material and a second layer that includes a second semiconductor material. The first semiconductor material is selectively etchable over the second semiconductor material using a first etching process. The first layer is disposed over the second layer. A recess is disposed at least in the first layer. Also described is a method of forming a semiconductor structure that includes a recess. The method includes etching a region in a first layer using a first etching process. The first layer includes a first semiconductor material. The first etching process stops at a second layer beneath the first layer. The second layer includes a second semiconductor material.

  4. Model of coherent transport in metal-insulator-midband gap semiconductor-insulator-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Abramov, I. I.; Danilyuk, A. L.

    1997-08-01

    A kinetic model of coherent transport with self-organized carrier transfer via midband gap semiconductor states in metal-insulator-midband gap semiconductor-insulator-semiconductor structure at room temperature is proposed. The coherent transport at room temperature can be a result of continuous oscillations of charge carriers at midband gap semiconductor states.

  5. Semiconductor electrode with improved photostability characteristics

    DOEpatents

    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.

  6. Semiconductor electrode with improved photostability characteristics

    DOEpatents

    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.

  7. Diode having trenches in a semiconductor region

    DOEpatents

    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.

  8. Semiconductor nanocrystal-based phagokinetic tracking

    SciTech Connect

    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.

  9. Semiconductor devices having a recessed electrode structure

    DOEpatents

    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.

  10. Semiconductor assisted metal deposition for nanolithography applications

    DOEpatents

    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.

  11. Semiconductor assisted metal deposition for nanolithography applications

    DOEpatents

    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.

  12. Semiconductor films on flexible iridium substrates

    DOEpatents

    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.

  13. Probing many body effects in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Potok, Ron M.

    This thesis describes two sets of experiments performed in quantum dots and quantum point contacts fabricated in GaAs/AlGaAs 2D electron gases. First, we investigate the role of interactions in determining the ground state of a quantum dot. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states. We then compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current by developing the first mesoscopic spin polarizer/analyzer system using spin-selective transverse electron focusing. A transverse electron focusing geometry is used to couple current from an emitter (either a quantum point contact or quantum dot) into a collector point contact. In a magnetic field, the collector point contact can be biased to transmit only a single spin, which allows a direct measure of spin polarization of the current incident on it. Spin polarization of >70% is found for a quantum point contact, while the spin of emitted current in the Coulomb blockade regime of a quantum dot is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition. In the second set of experiments, we realize a highly correlated electron system, the two channel Kondo system, in a specific geometry of coupled quantum dots. The two channel Kondo model, in which a local magnetic moment is screened by two independent conduction reservoirs, is created in a double quantum dot system based on a proposal by Oreg and Goldhaber-Gordon [1]. Using electrostatic gates we demonstrate in situ control of the parameters of the two channel Kondo model. We tune continuously between two distinct Fermi-liquid regimes, which are characterized by different values of conductance through the nanostructure. We investigate the properties of this quantum phase transition and the associated two channel Kondo quantum critical point. [1]Y. Oreg and D

  14. Chemical modification of semiconductor surfaces

    NASA Technical Reports Server (NTRS)

    Finklea, H. O.

    1981-01-01

    Results of research on the chemical modification of TiO2 powders in the gas phase and the examination of the modified powders by infrared absorption spectroscopy are comprehensively summarized. The range of information obtainable by IR spectroscopy of chemically modified semiconductors, and a definition of the optimum reaction conditions for synthesizing a monolayer of methylsilanes using vapor phase reaction conditions were considered.

  15. 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.

  16. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    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.

  17. 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…

  18. Electronic Properties of Semiconductor Interfaces.

    DTIC Science & Technology

    1983-02-01

    AD-A130 745 ELECTRONIC PROPERTIES OF SEMICONDUCTOR INTERFACES(U) /; UNIVERSIDAD AUfONOMA DE MADRID (SPAIN) DEPT DE FISICA DEL ESTADO SOLIDO F FLORES...J.Sfinchez-Dehesa 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK AREA & WORK UNIT NUMBERS Departamento de Fisica del Estado Solido 6.11.02A

  19. 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.

  20. (Magnetic properties of doped semiconductors)

    SciTech Connect

    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)

  1. Mechanical scriber for semiconductor devices

    DOEpatents

    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.

  2. Mechanical scriber for semiconductor devices

    DOEpatents

    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.

  3. 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.

  4. Hopping conduction in polycrystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Sharma, R. P.; Shukla, A. K.; Kapoor, A. K.; Srivastava, R.; Mathur, P. C.

    1985-03-01

    Measurements of dc conductivity (sigma) on polycrystalline semiconductors, viz., InSb, Si, and CdTe, have been reported in the temperature range 77-300 K. The conduction mechanism near liquid-nitrogen temperature has been identified as the hopping of charge carriers from the charged trap centers to empty traps near the Fermi level.

  5. Optical bistability in semiconductor microcavities

    SciTech Connect

    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.

  6. Semiconductor-based optical refrigerator

    DOEpatents

    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.

  7. 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.

  8. First-principles study of the Kondo physics of a single Pu impurity in a Th host

    SciTech Connect

    Zhu, Jian -Xin; Albers, R. C.; Haule, K.; Wills, J. M.

    2015-04-23

    Based on its condensed-matter properties, crystal structure, and metallurgy, which includes a phase diagram with six allotropic phases, plutonium is one of the most complicated pure elements in its solid state. Its anomalous properties, which are indicative of a very strongly correlated state, are related to its special position in the periodic table, which is at the boundary between the light actinides that have itinerant 5f electrons and the heavy actinides that have localized 5f electrons. As a foundational study to probe the role of local electronic correlations in Pu, we use the local-density approximation together with a continuous-time quantum Monte Carlo simulation to investigate the electronic structure of a single Pu atom that is either substitutionally embedded in the bulk and or adsorbed on the surface of a Th host. This is a simpler case than the solid phases of Pu metal. With the Pu impurity atom we have found a Kondo resonance peak, which is an important signature of electronic correlations, in the local density of states around the Fermi energy. We show that the peak width of this resonance is narrower for Pu atoms at the surface of Th than for those in the bulk due to a weakened Pu - 5f hybridization with the ligands at the surface.

  9. First-principles study of the Kondo physics of a single Pu impurity in a Th host

    DOE PAGES

    Zhu, Jian -Xin; Albers, R. C.; Haule, K.; ...

    2015-04-23

    Based on its condensed-matter properties, crystal structure, and metallurgy, which includes a phase diagram with six allotropic phases, plutonium is one of the most complicated pure elements in its solid state. Its anomalous properties, which are indicative of a very strongly correlated state, are related to its special position in the periodic table, which is at the boundary between the light actinides that have itinerant 5f electrons and the heavy actinides that have localized 5f electrons. As a foundational study to probe the role of local electronic correlations in Pu, we use the local-density approximation together with a continuous-time quantummore » Monte Carlo simulation to investigate the electronic structure of a single Pu atom that is either substitutionally embedded in the bulk and or adsorbed on the surface of a Th host. This is a simpler case than the solid phases of Pu metal. With the Pu impurity atom we have found a Kondo resonance peak, which is an important signature of electronic correlations, in the local density of states around the Fermi energy. We show that the peak width of this resonance is narrower for Pu atoms at the surface of Th than for those in the bulk due to a weakened Pu - 5f hybridization with the ligands at the surface.« less

  10. Unusual Kondo-hole effect and crystal-field frustration in Nd-doped CeRhIn5

    DOE PAGES

    Rosa, Priscila Ferrari Silveira; Oostra, Aaron; Thompson, Joe David; ...

    2016-07-05

    In this research, we investigate single crystals of Ce1₋xNdxRhIn5 by means of x-ray-diffraction, microprobe, magnetic susceptibility, heat capacity, and electrical resistivity measurements. Our data reveal that the antiferromagnetic transition of CeRhIn5, at Tmore » $$Ce\\atop{N}$$=3.8 K, is linearly suppressed with xNd. We associate this effect with the presence of a “Kondo hole” created by Nd substitution. The extrapolation of T$$Ce\\atop{N}$$ to zero temperature, however, occurs at xc~0.3, which is below the two-dimensional percolation limit found in Ce1₋xLaxRhIn5. This result strongly suggests the presence of a crystal-field induced magnetic frustration. Near xNd~0.2, the Ising antiferromagnetic order from Nd3+ ions is stabilized and T$$Nd\\atop{N}$$ increases up to 11 K in NdRhIn5. Finally, our results shed light on the effects of magnetic doping in heavy-fermion antiferromagnets and stimulate the study of such systems under applied pressure.« less

  11. The Effect of the Berry Phase on the Quantum Critical Properties of the Bose-Fermi Kondo model

    NASA Astrophysics Data System (ADS)

    Kirchner, Stefan; Si, Qimiao

    2006-03-01

    The theory of the quantum critical point of a T=0 transition is traditionally formulated in terms of a quantum-to-classical mapping, leading to a theory of its classical counterpart in elevated dimensions. Recently, it has been shown that this mapping breaks down in an SU(N)xSU(N/2) Bose-Fermi Kondo model (BFKM) [1], a BFKM with Ising anisotropy [2] and the spin-boson model [3]. Here we report the Quantum Monte Carlo results for the scaling properties of the quantum critical point of the BFKM with Ising anisotropy. In addition, using the Lagrangian formulation of the BFKM, we study the critical properties in the presence and absence of the spin Berry phase term. The results of the two cases are compared with the numerical results.[1] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett. 93,267201 (2004). [2] M. Glossop and K. Ingersent, Phys. Rev. Lett. 95, 067202 (2005). [3] M. Vojta, N-H Tong, and R. Bulla, Phys. Rev. Lett. 94, 070604 (2005).

  12. Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6.

    PubMed

    Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X C; Zhang, Chi; Shi, Jing; Han, Wei

    2016-11-11

    There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin-momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin-momentum locking property of surface states of SmB6.

  13. Thermodynamic Investigation of Metamagnetic Transitions and Partial Disorder in the Quasi-Kagome Kondo Lattice CePdAl

    NASA Astrophysics Data System (ADS)

    Mochidzuki, Kenji; Shimizu, Yusei; Kondo, Akihiro; Nakamura, Shota; Kittaka, Shunichiro; Kono, Yohei; Sakakibara, Toshiro; Ikeda, Yoichi; Isikawa, Yosikazu; Kindo, Koichi

    2017-03-01

    Low-temperature (T) thermodynamic properties of the quasi-Kagome antiferromagnet CePdAl (TN ˜ 2.7 K) in magnetic fields (B) were studied by magnetization and specific-heat C(T, B) measurements. The unusual magnetic phase diagram, including three thermodynamic phases I-III and crossover anomalies, has been obtained. In the low-field phase I, the existence of the partial Kondo screening state on one-third of the Ce sites is supported from the following thermodynamic view points: (i) the appearance of a paramagnetic moment with one-third of the full moment around 3 T and (ii) the occurrence of an entropy release of ˜0.3R ln 2 around the observed crossover. On the other hand, a strong enhancement of C/T was found around the point where TN(B) meets the boundary of phase III, indicating the possible presence of a tricritical point. Furthermore, it is suggested that the three metamagnetic transitions at Bmi (i = 1,2,3) originate from successive increments of the Ising-type magnetic moment along the c-axis. In the high-field region above 20 T, the behavior of f electrons can be roughly described by the crystal-electric-field model.

  14. Strongly correlated electron physics: From Kondo and spin glasses to heavy fermions, hidden order and quantum phase transitions

    NASA Astrophysics Data System (ADS)

    Bennett, Edmund; Mydosh, J. A.

    2012-09-01

    We summarize the development of strongly correlated electron physics (SCEP) stimu-lated from the 1930's when a strange upturn was found in the electrical resistivity at low temper-atures. It was only in 1965 that this effect was explained as a many-body, spin-flip, scattering of electrons from a magnetic impurity, i.e., the Kondo effect. This marked the beginning of SCEP. When the concentration of these impurities is increased so that they can randomly interact we have the spin glasses and their unconventional, yet classical phase transition. Spin glass physics formed the background know-how for the combination of two ferromagnetic layers separated by a non-magnetic spacer which generated the the giant magnetic resistance and it many applications in com-puter hardware. By fabricating a lattice of the magnetic species, viz., an intermetallic compound based upon certain rare-earth and actinide elements, we then create a heavy Fermi liquid that can support most unusual ground-state behavior, e.g., unconventional superconductivity. This leads to the mysterious and still unexplained "hidden order" phase transition of URu2Si2. Finally, since the heavy fermions commonly exhibit zero temperature phase transitions, aka, quantum phase transitions when tuned with pressure, magnetic field or doping, we are at the summit of today's SCEP - the prime topic of 2012 condensed matter physics.

  15. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

    PubMed Central

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-01-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds. PMID:27641364

  16. Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals

    DOE PAGES

    Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; ...

    2016-02-26

    Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materialsmore » as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.« less

  17. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

    NASA Astrophysics Data System (ADS)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-09-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.

  18. Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6

    NASA Astrophysics Data System (ADS)

    Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X. C.; Zhang, Chi; Shi, Jing; Han, Wei

    2016-11-01

    There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin-momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin-momentum locking property of surface states of SmB6.

  19. Interplay of atomic randomness and Kondo effect in disordered metallic conductor La2NiSi3

    NASA Astrophysics Data System (ADS)

    Gnida, Daniel; Szlawska, Maria; Swatek, Przemysław; Kaczorowski, Dariusz

    2016-11-01

    A polycrystalline sample of La2NiSi3 was investigated by means of heat capacity, magnetic susceptibility, magnetization, electrical resistivity and magnetoresistivity measurements. The compound was basically characterized as a Pauli paramagnet with metallic-like electrical conductivity, notably reduced in magnitude and weakly temperature dependent, as is usually observed for atomically disordered systems. Furthermore, the experimental data revealed the presence of a small amount of paramagnetic impurities. As a result, the low-temperature electrical resistivity in La2NiSi3 was found to be governed by both quantum corrections due to electron-electron interactions (ρ ˜ {{T}1/2} contribution) and spin-flip Kondo scattering (ρ ˜ log T contribution). The presence of paramagnetic impurities led to an increase in s-electron spin splitting due to the s-d interactions, manifested by a B 1/2 dependence of the magnetoresistivity, anomalously observed in the present study for thermal energy being larger than the Zeeman splitting energy {{k}\\text{B}}T>g{μ\\text{B}}B .

  20. Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6

    PubMed Central

    Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X. C.; Zhang, Chi; Shi, Jing; Han, Wei

    2016-01-01

    There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6. PMID:27834378

  1. Controlled growth of semiconductor crystals

    DOEpatents

    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.

  2. Controlled growth of semiconductor crystals

    DOEpatents

    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.

  3. 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

  4. Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

    SciTech Connect

    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.

  5. Back-side readout semiconductor photomultiplier

    DOEpatents

    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.

  6. Semiconductor detectors in nuclear and particle physics

    SciTech Connect

    Rehak, P.; Gatti, E.

    1992-12-31

    Semiconductor detectors for elementary particle physics and nuclear physics in the energy range above 1 GeV are briefly reviewed. In these two fields semiconductor detectors are used mainly for the precise position sensing. In a typical experiment, the position of a fast charged particle crossing a relatively thin semiconductor detector is measured. The position resolution achievable by semiconductor detectors is compared with the resolution achievable by gas filled position sensing detectors. Semiconductor detectors are divided into two groups: Classical semiconductor diode detectors and semiconductor memory detectors. Principles of the signal formation and the signal read-out for both groups of detectors are described. New developments of silicon detectors of both groups are reported.

  7. Dimensional crossover in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    McDonald, Matthew P.; Chatterjee, Rusha; Si, Jixin; Jankó, Boldizsár; Kuno, Masaru

    2016-08-01

    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.

  8. Dimensional crossover in semiconductor nanostructures

    PubMed Central

    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

  9. 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.

  10. 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.

  11. Squeezing of phonoritons in semiconductors

    NASA Astrophysics Data System (ADS)

    Huong, N. Q.; Hau, N. N.; Birman, J. L.

    2007-12-01

    If a semiconductor sample is illuminated by hight-intensity electro-magnetic radiation near the resonance, the occupation number of polaritons in the same mode is large and the interaction between polaritons and phonons become very important. This interaction leads to the formation of a new kind of elementary excitation called phonoriton, which actually is a coherent superposition of excitons, photons, and longitudinal acoustic phonons under Brillouin scattering of an intense polariton. The phonoritons have been studied theoretically and experimentally and have been found in Cu2O. In this work we discuss the squeezing of phonoritons inside semiconductors from a theoretical point of view. We found the squeezed states, or so called 'low-noise' states- the states of reduced quantum noise with reducing effect of vacuum fluctuation, for phonoritons. It shows that the phonoritons are intrinsically squeezed. From our results we also have the possibility to tune the squeeze amplitude, what is important both theoretically and experimentally.

  12. Semiconductor metafilms devices (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Brongersma, Mark L.

    2016-09-01

    Many conventional optoelectronic devices consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-structuring the constituent layers at length scales below the wavelength of light. The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical transmission, absorption, reflection, and refraction properties of device layers. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers may be used to enhance the performance of solar cells, photodetectors, and enable new imaging technologies. I will also demonstrate how the use of active nanoscale building blocks can facilitate the creation of active metafilm devices.

  13. Compound semiconductor optical waveguide switch

    DOEpatents

    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.

  14. Etching Of Semiconductor Wafer Edges

    DOEpatents

    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.

  15. Lasing in subwavelength semiconductor nanopatches

    NASA Astrophysics Data System (ADS)

    Lakhani, Amit M.; Yu, Kyoungsik; Wu, Ming C.

    2011-01-01

    Subwavelength semiconductor nanopatch lasers were analyzed, fabricated and characterized. Lasing was achieved in cylindrical and rectangular metallodielectric nanopatch geometries. The two smallest moderate quality factor modes of cylindrical cavities, the 'electric-' and 'magnetic-' dipole-like modes, successfully lased with physical volumes as small as 0.75 (λ0/n)3. Polarization control in nanopatch geometries is successfully demonstrated in anisotropic rectangular nanopatch structures.

  16. Cooling and mounting power semiconductors

    NASA Astrophysics Data System (ADS)

    Wetzel, P.

    1980-04-01

    The article examines the process of heat dissipation from power semiconductors. It is shown that for the relationship between temperature loading and dissipation it is possible to take an 'Ohm's law of heat abduction' to define the thermal impedance. The computation of the optimal size for a heatsink is demonstrated in detail. Discussion covers the types of heat dissipation such as heat radiation, heat conduction, and convection. Finally, some factors to consider during installation are examined.

  17. Optoelectronics with 2D semiconductors

    NASA Astrophysics Data System (ADS)

    Mueller, Thomas

    2015-03-01

    Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies.

  18. Technology Roadmaps for Compound Semiconductors

    PubMed Central

    Bennett, Herbert S.

    2000-01-01

    The roles cited for compound semiconductors in public versions of existing technology roadmaps from the National Electronics Manufacturing Initiative, Inc., Optoelectronics Industry Development Association, Microelectronics Advanced Research Initiative on Optoelectronic Interconnects, and Optoelectronics Industry and Technology Development Association (OITDA) are discussed and compared within the context of trends in the Si CMOS industry. In particular, the extent to which these technology roadmaps treat compound semiconductors at the materials processing and device levels will be presented for specific applications. For example, OITDA’s Optical Communications Technology Roadmap directly connects the information demand of delivering 100 Mbit/s to the home to the requirement of producing 200 GHz heterojunction bipolar transistors with 30 nm bases and InP high electron mobility transistors with 100 nm gates. Some general actions for progress towards the proposed International Technology Roadmap for Compound Semiconductors (ITRCS) and methods for determining the value of an ITRCS will be suggested. But, in the final analysis, the value added by an ITRCS will depend on how industry leaders respond. The technical challenges and economic opportunities of delivering high quality digital video to consumers provide concrete examples of where the above actions and methods could be applied. PMID:27551615

  19. Conductivity in transparent oxide semiconductors.

    PubMed

    King, P D C; Veal, T D

    2011-08-24

    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

  20. Stretchable semiconductor elements and stretchable electrical circuits

    DOEpatents

    Rogers, John A.; Khang, Dahl-Young; Menard, Etienne

    2009-07-07

    The invention provides methods and devices for fabricating printable semiconductor elements and assembling printable semiconductor elements onto substrate surfaces. Methods, devices and device components of the present invention are capable of generating a wide range of flexible electronic and optoelectronic devices and arrays of devices on substrates comprising polymeric materials. The present invention also provides stretchable semiconductor structures and stretchable electronic devices capable of good performance in stretched configurations.

  1. Surface Flashover of Semiconductors: A Fundamental Study

    DTIC Science & Technology

    1993-06-16

    mechanisms responsible for inducing surface flashover in semiconductors , par- ticularly silicon. In order to achieve this...of semiconductors . 2.9.2 Our Modelfor the Surface Flashover Mechanism We have developed a model in which the flashover initiation process occurs on...is described in detail in the following pages. 3-1 4. CUMULATIVE LIST OF PUBLICATIONS 1. "A Mechanism for Surface Flashover of Semiconductors ,"

  2. Optical devices featuring textured semiconductor layers

    DOEpatents

    Moustakas, Theodore D [Dover, MA; Cabalu, Jasper S [Cary, NC

    2012-08-07

    A semiconductor sensor, solar cell or emitter, or a precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate. The textured layers enhance light extraction or absorption. Texturing in the region of multiple quantum wells greatly enhances internal quantum efficiency if the semiconductor is polar and the quantum wells are grown along the polar direction. Electroluminescence of LEDs of the invention is dichromatic, and results in variable color LEDs, including white LEDs, without the use of phosphor.

  3. Optical devices featuring textured semiconductor layers

    DOEpatents

    Moustakas, Theodore D [Dover, MA; Cabalu, Jasper S [Cary, NC

    2011-10-11

    A semiconductor sensor, solar cell or emitter, or a precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate. The textured layers enhance light extraction or absorption. Texturing in the region of multiple quantum wells greatly enhances internal quantum efficiency if the semiconductor is polar and the quantum wells are grown along the polar direction. Electroluminescence of LEDs of the invention is dichromatic, and results in variable color LEDs, including white LEDs, without the use of phosphor.

  4. High performance compound semiconductor SPAD arrays

    NASA Astrophysics Data System (ADS)

    Harmon, Eric S.; Naydenkov, Mikhail; Bowling, Jared

    2016-05-01

    Aggregated compound semiconductor single photon avalanche diode (SPAD) arrays are emerging as a viable alternative to the silicon photomultiplier (SiPM). Compound semiconductors have the potential to surpass SiPM performance, potentially achieving orders of magnitude lower dark count rates and improved radiation hardness. New planar processing techniques have been developed to enable compound semiconductor SPAD devices to be produced with pixel pitches of 11 - 25 microns, with thousands of SPADs per array.

  5. Wafer-fused semiconductor radiation detector

    DOEpatents

    Lee, Edwin Y.; James, Ralph B.

    2002-01-01

    Wafer-fused semiconductor radiation detector useful for gamma-ray and x-ray spectrometers and imaging systems. The detector is fabricated using wafer fusion to insert an electrically conductive grid, typically comprising a metal, between two solid semiconductor pieces, one having a cathode (negative electrode) and the other having an anode (positive electrode). The wafer fused semiconductor radiation detector functions like the commonly used Frisch grid radiation detector, in which an electrically conductive grid is inserted in high vacuum between the cathode and the anode. The wafer-fused semiconductor radiation detector can be fabricated using the same or two different semiconductor materials of different sizes and of the same or different thicknesses; and it may utilize a wide range of metals, or other electrically conducting materials, to form the grid, to optimize the detector performance, without being constrained by structural dissimilarity of the individual parts. The wafer-fused detector is basically formed, for example, by etching spaced grooves across one end of one of two pieces of semiconductor materials, partially filling the grooves with a selected electrical conductor which forms a grid electrode, and then fusing the grooved end of the one semiconductor piece to an end of the other semiconductor piece with a cathode and an anode being formed on opposite ends of the semiconductor pieces.

  6. Transient Transport in Binary and Ternary Semiconductors.

    DTIC Science & Technology

    1986-02-27

    transport; Semiconductors, Microelectronics, Quantum transport , Boltzmann transport, Drift and diffusion, Gallium arsende, Aluminum gallium arsenide, Indium gallium arsenide, and Transient transport.

  7. Reflection technique for thermal mapping of semiconductors

    DOEpatents

    Walter, Martin J.

    1989-06-20

    Semiconductors may be optically tested for their temperatures by illuminating them with tunable monochromatic electromagnetic radiation and observing the light reflected off of them. A transition point will occur when the wavelength of the light corresponds with the actual band gap energy of the semiconductor. At the transition point, the image of the semiconductor will appreciably darken as the light is transmitted through it, rather than being reflected off of it. The wavelength of the light at the transition point corresponds to the actual band gap energy and the actual temperature of the semiconductor.

  8. Toward a national semiconductor strategy, volume 1

    NASA Astrophysics Data System (ADS)

    1991-02-01

    Updated here are key market data showing trends in the U.S. semiconductor industry's world market position. New information is given on three emerging semiconductor-based technologies: broadband communications, advanced display systems, and intelligent vehicles and highways. These are examples of important, high-volume markets that will consume significant numbers of semiconductor components and that must be addressed in a national semiconductor strategy. New recommendations and a summary of all Committee recommendations to date are given as well as a summary of comments received at a public forum held in Silicon Valley in may 1990.

  9. Sensor Detects Semiconductor Escaping From Ampoule

    NASA Technical Reports Server (NTRS)

    Watring, Dale A.; Johnson, Martin L.

    1994-01-01

    Electrical resistance and temperature change upon exposure to semiconductors. Sensor detects breakage of ampoule containing molten semiconductor. Chemical reaction between hot semiconductor material and wire causes step increase in electrical resistance and temperature of wire. Step increase in temperature and resistance of sensor indicates presence of hot GaAs. Sensor used to shut down furnace automatically if ampoule breaks and prevents further release of molton semiconductor, which could quickly breach surrounding thin wall of cartridge, damage furnace, and/or release toxic vapors into surrounding area.

  10. Study of the magnetic properties of the Cex La1-x Pt alloy system: Which interaction establishes ferromagnetism in Kondo systems?

    NASA Astrophysics Data System (ADS)

    Očko, M.; Zadro, K.; Drobac, Đ.; Aviani, I.; Salamon, K.; Mixson, D.; Bauer, E. D.; Sarrao, J. L.

    2016-11-01

    In order to study Kondo ferromagnetism, particularly of the CePt compound, we investigate the magnetic properties of the CexLa1-xPt alloy system in the temperature range from 1.8 K to 320 K. The results of these investigations can be summarized as follows: dc-susceptibility can be described by the Curie-Weiss law at higher temperatures down to about 100 K, but also at the low temperatures above the phase transition. At higher temperatures, the extracted Curie-Weiss constant, θp, is negative in contrast to the low temperatures, where θC is positive. The extracted effective magnetic moment from the higher temperatures is the same for all the alloys and is close to the theoretical value of the isolated Ce3+ ion, μ=2.54 μB, indicating the hybridization is weak and, and consequently, Kondo interaction is weak. These observations confirm the main important conclusions inferred from an earlier transport properties investigation of this alloy system. The Curie temperature extracted by various approaches was compared to the extraction from the ac-susceptibility measurements. We show that its concentration dependence is not consistent with Doniach's diagram. Hence, RKKY interaction is not responsible for the ferromagnetism in this alloy system.

  11. Antiferromagnetic Kondo lattice in the layered compound CePd1–xBi₂ and comparison to the superconductor LaPd1–xBi₂

    DOE PAGES

    Han, Fei; Wan, Xiangang; Phelan, Daniel; ...

    2015-07-13

    The layered compound CePd1–xBi₂ with the tetragonal ZrCuSi₂-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd1–xBi₂ show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the ab plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of 0.191 J mol Ce⁻¹ K⁻² obtained from specific-heat measurement suggests a moderate Kondo effect in CePd1–xBi₂. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulderlike behavior around 75 Kmore » which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd1–xBi₂ around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures.« less

  12. Upper critical field and Kondo effects in Fe(Te0.9Se0.1) thin films by pulsed field measurements

    SciTech Connect

    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 an 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.

  13. Polynomial expansion Monte Carlo study of frustrated itinerant electron systems: Application to a spin-ice type Kondo lattice model on a pyrochlore lattice

    NASA Astrophysics Data System (ADS)

    Ishizuka, Hiroaki; Udagawa, Masafumi; Motome, Yukitoshi

    2013-12-01

    We present the benchmark of the polynomial expansion Monte Carlo method to a Kondo lattice model with classical localized spins on a geometrically frustrated lattice. The method enables us to reduce the calculation amount by using the Chebyshev polynomial expansion of the density of states compared to a conventional Monte Carlo technique based on the exact diagonalization of the fermion Hamiltonian matrix. Further reduction is brought about by a real-space truncation of the vector-matrix operations. We apply the method to the model with spin-ice type Ising spins on a three-dimensional pyrochlore lattice and carefully examine the convergence in terms of the order of polynomials and the truncation distance. We find that, in a wide range of electron density at a relatively weak Kondo coupling compared to the noninteracting bandwidth, the results by the polynomial expansion method show good convergence to those by the conventional method within reasonable numbers of polynomials. This enables us to study the systems up to 4×83=2048 sites, while the previous study by the conventional method was limited to 4×43=256 sites. On the other hand, the real-space truncation is not helpful in reducing the calculation amount for the system sizes that we reached, as the sufficient convergence is obtained when most of the sites are involved within the truncation distance. The necessary truncation distance, however, appears not to show significant system size dependence, suggesting that the truncation method becomes efficient for larger system sizes.

  14. Semiconductor technology program. Progress briefs

    NASA Technical Reports Server (NTRS)

    Bullis, W. M. (Editor)

    1979-01-01

    The current status of NBS work on measurement technology for semiconductor materials, process control, and devices is reported. Results of both in-house and contract research are covered. Highlighted activities include modeling of diffusion processes, analysis of model spreading resistance data, and studies of resonance ionization spectroscopy, resistivity-dopant density relationships in p-type silicon, deep level measurements, photoresist sensitometry, random fault measurements, power MOSFET thermal characteristics, power transistor switching characteristics, and gross leak testing. New and selected on-going projects are described. Compilations of recent publications and publications in press are included.

  15. Multivalley engineering in semiconductor microcavities.

    PubMed

    Sun, M; Savenko, I G; Flayac, H; Liew, T C H

    2017-04-03

    We consider exciton-photon coupling in semiconductor microcavities in which separate periodic potentials have been embedded for excitons and photons. We show theoretically that this system supports degenerate ground-states appearing at non-zero inplane momenta, corresponding to multiple valleys in reciprocal space, which are further separated in polarization corresponding to a polarization-valley coupling in the system. Aside forming a basis for valleytronics, the multivalley dispersion is predicted to allow for spontaneous momentum symmetry breaking and two-mode squeezing under non-resonant and resonant excitation, respectively.

  16. Conduction in short semiconductor structures

    NASA Astrophysics Data System (ADS)

    Sinkkonen, J.

    1983-12-01

    Low field mobility in short semiconductor structures decreases as a result of finite sample length. According to Kastalsky and Shur [1] the mobility scales down by a factor 1 - exp ( {-3η}/{2}) where η is the sample length divided by the mean free path. From a solution of Boltzmann equation we show that the scaling factor is more accurately given by {η}/{(η + α)} where α is between {4}/{3} and 2. Mobility decrease can be simply interpreted in terms of a finite contact resistance.

  17. Hot Electron Emission in Semiconductors.

    DTIC Science & Technology

    2014-09-26

    Second Interim Report Hot Electron Emission in Semiconductors Jan. 85 - June 85 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(s) 6. CONTRACT OR GRANT NUMBER(a...KEY WORDS (Continue on reverse side Jf necessary and identify by block number) " -novel tunable FIR sources) • hot electron emission in GaAs/GaAlAs...heterostructures)" -,/ " streaming of hot carriers in crossed electric and magnetic fields ABST’AACr C-rrhmus- m .wr. efe it rewo-- .rv d identify by

  18. Processing of insulators and semiconductors

    DOEpatents

    Quick, Nathaniel R.; Joshi, Pooran C.; Duty, Chad Edward; Jellison, Jr., Gerald Earle; Angelini, Joseph Attilio

    2015-06-16

    A method is disclosed for processing an insulator material or a semiconductor material. The method includes pulsing a plasma lamp onto the material to diffuse a doping substance into the material, to activate the doping substance in the material or to metallize a large area region of the material. The method may further include pulsing a laser onto a selected region of the material to diffuse a doping substance into the material, to activate the doping substance in the material or to metallize a selected region of the material.

  19. Multivalley engineering in semiconductor microcavities

    PubMed Central

    Sun, M.; Savenko, I. G.; Flayac, H.; Liew, T. C. H.

    2017-01-01

    We consider exciton-photon coupling in semiconductor microcavities in which separate periodic potentials have been embedded for excitons and photons. We show theoretically that this system supports degenerate ground-states appearing at non-zero inplane momenta, corresponding to multiple valleys in reciprocal space, which are further separated in polarization corresponding to a polarization-valley coupling in the system. Aside forming a basis for valleytronics, the multivalley dispersion is predicted to allow for spontaneous momentum symmetry breaking and two-mode squeezing under non-resonant and resonant excitation, respectively. PMID:28367953

  20. The genetic diversity,relationships,and potential for biological control of the lobate lac scale,Paratachardina pseudolobata Kondo&Gullan(Hemiptera:Coccoidea:Kerriidae),a pest in Florida,the Bahamas,Cuba and Christmas Island

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The lobate lac scale Paratachardina pseudolobata Kondo & Gullan (Kerriidae) is a polyphagous pest of woody plants in Florida (U.S.A), the Bahamas, Cuba, and Christmas Island (Australia). Its recent appearance as a pest in these places indicates that this scale is introduced; however, its native rang...

  1. Recent developments in semiconductor research

    NASA Technical Reports Server (NTRS)

    Yoder, M. N.

    1984-01-01

    Recent findings drawn from various laboratories focused toward a new understanding of the nature of crystal growth and how impurities are incorporated or excluded from the lattice were considered. From these findings a heuristic approach is given for improving the uniformity and charge carrier concentration of thin semiconductor films. Such improvement is considered essential to achieve respectable yield on large scale integrated circuits. A tentative conclusion is drawn which indicates that if the host compound crystal reactants are provided to the growing crystal surface in a reasonably stoichiometric manner, it is virtually impossible to include impurities into a growing crystal surface held at a sufficiently low temperature; impurities are incorporated into the crystal by gettering action of crystal defects located one and two monlayers beneath the growing surface. Devices in 3-5 semiconductors based on heterojunctions and two dimensional electron gases are noted and reliability concerns are voiced. Alternatives and novel device structures such as truly single crystal high quality silicon on insulator and beta silicon carbide devices are presented.

  2. Nitride semiconductors for ultraviolet detection

    NASA Astrophysics Data System (ADS)

    Davis, R. F.; Bremser, M. D.; Gruss, K.; Linthicum, K.; Ferry, B.

    1995-06-01

    Continued development and commercialization of optoelectronic devices, including light emitting diodes and semiconductor lasers produced from 3-5 gallium arsenide-based materials, has also generated interest in the much wider bandgap semiconductor mononitride materials containing aluminum, gallium, and indium. The majority of the studies have been conducted on pure gallium nitride thin films having the wurtzite structure, and this emphasis continues to the present day. The program objectives achieved in this reporting period have been (1) the growth of undoped, high resistivity and n- and p-type doped monocrystalline, GaN thin films on alpha(6H)-SiC(000l) wafers via organometallic vapor phase epitaxy (OMVPE), and their characterization via photoluminescence; (2) the growth and cathodoluminescence characterization of Al(x)Ga(1-x)N alloys and abrupt heterojunctions of these alloys; (3) the development and application of a novel NH3 cracker cell for gas source MBE to reduce film damage; and (4) the reactive ion etching of undoped GaN films via use of Cl-containing compounds.

  3. Semiconductor nanostructures for artificial photosynthesis

    NASA Astrophysics Data System (ADS)

    Yang, Peidong

    2012-02-01

    Nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have already been demonstrated as important materials for different energy conversion. One emerging and exciting direction is their application for solar to fuel conversion. The generation of fuels by the direct conversion of solar energy in a fully integrated system is an attractive goal, but no such system has been demonstrated that shows the required efficiency, is sufficiently durable, or can be manufactured at reasonable cost. One of the most critical issues in solar water splitting is the development of a suitable photoanode with high efficiency and long-term durability in an aqueous environment. Semiconductor nanowires represent an important class of nanostructure building block for direct solar-to-fuel application because of their high surface area, tunable bandgap and efficient charge transport and collection. Nanowires can be readily designed and synthesized to deterministically incorporate heterojunctions with improved light absorption, charge separation and vectorial transport. Meanwhile, it is also possible to selectively decorate different oxidation or reduction catalysts onto specific segments of the nanowires to mimic the compartmentalized reactions in natural photosynthesis. In this talk, I will highlight several recent examples in this lab using semiconductor nanowires and their heterostructures for the purpose of direct solar water splitting.

  4. Polaronic trapping in magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Raebiger, Hannes

    2012-02-01

    GaN doped with iron is an interesting candidate material for magnetic semiconductors, as p-d coupling between the localized Fe-d and extended N-p hole states is expected to facilitate long-range ferromagnetic alignment of the Fe spins [1]. This picture of extended states in GaN:Fe, however, falls apart due to a polaronic localization of the hole carriers nearby the Fe impurities. To elucidate the carrier localization in GaN:Fe and related iron doped III-V semiconductors, I present a systematic study using self-interaction corrected density-functional calculations [2]. These calculations predict three distinct scenarios. (i) Some systems do sustain extended host-like hole states, (ii) some exhibit polaronic trapping, (iii) and some exhibit carrier trapping at Fe-d orbitals. These behaviors are described in detail to give an insight as to how to distinguish them experimentally. I thank T. Fujita, C. Echeverria-Arrondo, and A. Ayuela for their collaboration.[4pt] [1] T. Dietl et al, Science, 287, 1019 (2000).[0pt] [2] S. Lany and A. Zunger, Phys. Rev. B, 80, 085202 (2009).

  5. Zener tunneling in semiconductor superlattices.

    PubMed

    Romanova, J Yu; Demidov, E V; Mourokh, L G; Romanov, Yu A

    2011-08-03

    Characteristics of miniband tunneling and Wannier-Stark levels in semiconductor superlattices are studied as regards their dependence on the symmetry of the unit cells and the type of miniband structure. We modify the k ⋅ p method into a k ⋅ v form and on this basis generalize the Zener formula for the inter-band tunneling in homogeneous semiconductors to the case of inter-miniband tunneling in superlattices, account being taken of the inhomogeneity of the electron effective mass. The corresponding sum rule for the effective masses in such structures is obtained. We develop a unified matrix approach for the calculation of the inter-miniband tunneling and Wannier-Stark levels in the case of an arbitrary number of minibands. We study the electric field dependence of the probability of inter-miniband tunneling for an electron transferred through the Brillouin minizone only once. The peculiarities of the inter-miniband transitions for the case where this transfer is repeated are also examined for various unit cells and miniband structures of the superlattice. In addition, we discuss mechanisms and specific features of the resonant Zener tunneling and its manifestations in electron transport.

  6. Charge transport in organic semiconductors.

    PubMed

    Bässler, Heinz; Köhler, Anna

    2012-01-01

    Modern optoelectronic devices, such as light-emitting diodes, field-effect transistors and organic solar cells require well controlled motion of charges for their efficient operation. The understanding of the processes that determine charge transport is therefore of paramount importance for designing materials with improved structure-property relationships. Before discussing different regimes of charge transport in organic semiconductors, we present a brief introduction into the conceptual framework in which we interpret the relevant photophysical processes. That is, we compare a molecular picture of electronic excitations against the Su-Schrieffer-Heeger semiconductor band model. After a brief description of experimental techniques needed to measure charge mobilities, we then elaborate on the parameters controlling charge transport in technologically relevant materials. Thus, we consider the influences of electronic coupling between molecular units, disorder, polaronic effects and space charge. A particular focus is given to the recent progress made in understanding charge transport on short time scales and short length scales. The mechanism for charge injection is briefly addressed towards the end of this chapter.

  7. Negative refraction in semiconductor metamaterials.

    PubMed

    Hoffman, Anthony J; Alekseyev, Leonid; Howard, Scott S; Franz, Kale J; Wasserman, Dan; Podolskiy, Viktor A; Narimanov, Evgenii E; Sivco, Deborah L; Gmachl, Claire

    2007-12-01

    An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity, epsilon, and permeability, mu, to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment. This work will influence future metamaterial designs and their incorporation into optical semiconductor devices.

  8. Heterogeneous Integration of Compound Semiconductors

    NASA Astrophysics Data System (ADS)

    Moutanabbir, Oussama; Gösele, Ulrich

    2010-08-01

    The ability to tailor compound semiconductors and to integrate them onto foreign substrates can lead to superior or novel functionalities with a potential impact on various areas in electronics, optoelectronics, spintronics, biosensing, and photovoltaics. This review provides a brief description of different approaches to achieve this heterogeneous integration, with an emphasis on the ion-cut process, also known commercially as the Smart-Cut™ process. This process combines semiconductor wafer bonding and undercutting using defect engineering by light ion implantation. Bulk-quality heterostructures frequently unattainable by direct epitaxial growth can be produced, provided that a list of technical criteria is fulfilled, thus offering an additional degree of freedom in the design and fabrication of heterogeneous and flexible devices. Ion cutting is a generic process that can be employed to split and transfer fine monocrystalline layers from various crystals. Materials and engineering issues as well as our current understanding of the underlying physics involved in its application to cleaving thin layers from freestanding GaN, InP, and GaAs wafers are presented.

  9. Method for fabricating semiconductor devices

    NASA Technical Reports Server (NTRS)

    Kaiser, William J. (Inventor); Grunthaner, Frank J. (Inventor); Hecht, Michael H. (Inventor); Bell, Lloyd D. (Inventor)

    1995-01-01

    A process for fabricating gold/gallium arsenide structures, in situ, on molecular beam epitaxially grown gallium arsenide. The resulting interface proves to be Ohmic, an unexpected result which is interpreted in terms of increased electrode interdiffusion. More importantly, the present invention surprisingly permits the fabrication of Ohmic contacts in a III-V semiconductor material at room temperature. Although it may be desireable to heat the Ohmic contact to a temperature of, for example, 200 degrees Centigrade if one wishes to further decrease the resistance of the contact, such low temperature annealing is much less likely to have any deleterious affect on the underlying substrate. The use of the term in situ herein, contemplates continuously maintaining an ultra-high vacuum, that is a vacuum which is at least 10.sup.-8 Torr, until after the metallization has been completed. An alternative embodiment of the present invention comprising an additional step, namely the termination of the gallium arsenide by a two monolayer thickness of epitaxial aluminum arsenide as a diffusion barrier, enables the recovery of Schottky barrier behavior, namely a rectified I-V characteristic. The present invention provides a significant breakthrough in the fabrication of III-V semiconductor devices wherein excellent Ohmic contact and Schottky barrier interfaces to such devices can be achieved simply and inexpensively and without requiring the high temperature processing of the prior art and also without requiring the use of exotic high temperature refractory materials as substitutes for those preferred contact metals such as gold, aluminum and the like.

  10. Novel room temperature ferromagnetic semiconductors

    SciTech Connect

    Gupta, Amita

    2004-06-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous distribution of Mn substituting

  11. Energetics of the Semiconductor-Electrolyte Interface.

    ERIC Educational Resources Information Center

    Turner, John A.

    1983-01-01

    The use of semiconductors as electrodes for electrochemistry requires an understanding of both solid-state physics and electrochemistry, since phenomena associated with both disciplines are seen in semiconductor/electrolyte systems. The interfacial energetics of these systems are discussed. (JN)

  12. Photoelectroconversion by Semiconductors: A Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Fan, Qinbai; And Others

    1995-01-01

    Presents an experiment designed to give students some experience with photochemistry, electrochemistry, and basic theories about semiconductors. Uses a liquid-junction solar cell and illustrates some fundamental physical and chemical principles related to light and electricity interconversion as well as the properties of semiconductors. (JRH)

  13. Silicon Carbide Semiconductor Device Fabrication and Characterization

    DTIC Science & Technology

    1990-02-08

    SPACE ADMINISTRATION For Grant NAG 3-782 S- 1 entitled SILICON CARBIDE SEMICONDUCTOR DEVICE FABRICATION AND CHARACTERIZATION For the Period 10 February...NUMBERS Silicon Carbide ..Semiconductor Device Fabrication and PR# 335820 Characterization __________________________________________________ APP# 505-62-01...also been demonstrated. _________ 14. SUBJECT TERMS 15. NuMBER OF PACiES -~- Silicon carbide , Ysemiconductor devices, ion implantation aseeI4i

  14. Hybrid anode for semiconductor radiation detectors

    DOEpatents

    Yang, Ge; Bolotnikov, Aleksey E; Camarda, Guiseppe; Cui, Yonggang; Hossain, Anwar; Kim, Ki Hyun; James, Ralph B

    2013-11-19

    The present invention relates to a novel hybrid anode configuration for a radiation detector that effectively reduces the edge effect of surface defects on the internal electric field in compound semiconductor detectors by focusing the internal electric field of the detector and redirecting drifting carriers away from the side surfaces of the semiconductor toward the collection electrode(s).

  15. Preparation of a semiconductor thin film

    DOEpatents

    Pehnt, M.; Schulz, D.L.; Curtis, C.J.; Ginley, D.S.

    1998-01-27

    A process is disclosed for the preparation of a semiconductor film. The process comprises depositing nanoparticles of a semiconductor material onto a substrate whose surface temperature during nanoparticle deposition thereon is sufficient to cause substantially simultaneous fusion of the nanoparticles to thereby coalesce with each other and effectuate film growth.

  16. Preparation of a semiconductor thin film

    DOEpatents

    Pehnt, Martin; Schulz, Douglas L.; Curtis, Calvin J.; Ginley, David S.

    1998-01-01

    A process for the preparation of a semiconductor film. The process comprises depositing nanoparticles of a semiconductor material onto a substrate whose surface temperature during nanoparticle deposition thereon is sufficient to cause substantially simultaneous fusion of the nanoparticles to thereby coalesce with each other and effectuate film growth.

  17. Stable surface passivation process for compound semiconductors

    DOEpatents

    Ashby, Carol I. H.

    2001-01-01

    A passivation process for a previously sulfided, selenided or tellurated III-V compound semiconductor surface. The concentration of undesired mid-gap surface states on a compound semiconductor surface is reduced by the formation of a near-monolayer of metal-(sulfur and/or selenium and/or tellurium)-semiconductor that is effective for long term passivation of the underlying semiconductor surface. Starting with the III-V compound semiconductor surface, any oxidation present thereon is substantially removed and the surface is then treated with sulfur, selenium or tellurium to form a near-monolayer of chalcogen-semiconductor of the surface in an oxygen-free atmosphere. This chalcogenated surface is then contacted with a solution of a metal that will form a low solubility chalcogenide to form a near-monolayer of metal-chalcogen-semiconductor. The resulting passivating layer provides long term protection for the underlying surface at or above the level achieved by a freshly chalcogenated compound semiconductor surface in an oxygen free atmosphere.

  18. Semiconductor switch geometry with electric field shaping

    DOEpatents

    Booth, R.; Pocha, M.D.

    1994-08-23

    An optoelectric switch is disclosed that utilizes a cylindrically shaped and contoured GaAs medium or other optically active semiconductor medium to couple two cylindrically shaped metal conductors with flat and flared termination points each having an ovoid prominence centrally extending there from. Coupling the truncated ovoid prominence of each conductor with the cylindrically shaped optically active semiconductor causes the semiconductor to cylindrically taper to a triple junction circular line at the base of each prominence where the metal conductor conjoins with the semiconductor and a third medium such as epoxy or air. Tapering the semiconductor at the triple junction inhibits carrier formation and injection at the triple junction and thereby enables greater current carrying capacity through and greater sensitivity of the bulk area of the optically active medium. 10 figs.

  19. Semiconductor switch geometry with electric field shaping

    DOEpatents

    Booth, Rex; Pocha, Michael D.

    1994-01-01

    An optoelectric switch is disclosed that utilizes a cylindrically shaped and contoured GaAs medium or other optically active semiconductor medium to couple two cylindrically shaped metal conductors with flat and flared termination points each having an ovoid prominence centrally extending there from. Coupling the truncated ovoid prominence of each conductor with the cylindrically shaped optically active semiconductor causes the semiconductor to cylindrically taper to a triple junction circular line at the base of each prominence where the metal conductor conjoins with the semiconductor and a third medium such as epoxy or air. Tapering the semiconductor at the triple junction inhibits carrier formation and injection at the triple junction and thereby enables greater current carrying capacity through and greater sensitivity of the bulk area of the optically active medium.

  20. Semiconductor Laser Low Frequency Noise Characterization

    NASA Technical Reports Server (NTRS)

    Maleki, Lute; Logan, Ronald T.

    1996-01-01

    This work summarizes the efforts in identifying the fundamental noise limit in semiconductor optical sources (lasers) to determine the source of 1/F noise and it's associated behavior. In addition, the study also addresses the effects of this 1/F noise on RF phased arrays. The study showed that the 1/F noise in semiconductor lasers has an ultimate physical limit based upon similar factors to fundamental noise generated in other semiconductor and solid state devices. The study also showed that both additive and multiplicative noise can be a significant detriment to the performance of RF phased arrays especially in regard to very low sidelobe performance and ultimate beam steering accuracy. The final result is that a noise power related term must be included in a complete analysis of the noise spectrum of any semiconductor device including semiconductor lasers.