Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system
Ren, Jindong; Wu, Xu; Guo, Haiming Pan, Jinbo; Du, Shixuan; Gao, Hong-Jun; Luo, Hong-Gang
2015-08-17
The atomic-scale spatial relationship of a two-impurity Kondo system has been determined at varying lateral distance by scanning tunneling microscopy (STM) and spectroscopy. The localized spins of two cobalt magnetic adatoms that are placed on different electrodes of an STM form two individual Kondo singlet states, each showing quite different Kondo coupling, i.e., the tip-Kondo with low Kondo temperature and the sample-Kondo with high Kondo temperature. The differential conductance dI/dV spectra show the continuous changes of the resonance peak feature when approaching the Kondo tip laterally to the local sample-Kondo impurity on the surface. The result indicates a notable interplay between these two Kondo systems. We propose a convolution model based on the q factor of the sample-Kondo (q{sub s}) and tip-Kondo (q{sub t}) to interpret the change of various tunneling channels and the evolution of the experimental spectra.
Nuclear magnetic resonance in Kondo lattice systems
NASA Astrophysics Data System (ADS)
Curro, Nicholas J.
2016-06-01
Nuclear magnetic resonance has emerged as a vital tool to explore the fundamental physics of Kondo lattice systems. Because nuclear spins experience two different hyperfine couplings to the itinerant conduction electrons and to the local f moments, the Knight shift can probe multiple types of spin correlations that are not accessible via other techniques. The Knight shift provides direct information about the onset of heavy electron coherence and the emergence of the heavy electron fluid.
Influence of organic ligands on the line shape of the Kondo resonance
NASA Astrophysics Data System (ADS)
Meyer, Jörg; Ohmann, Robin; Nickel, Anja; Toher, Cormac; Gresser, Roland; Leo, Karl; Ryndyk, Dmitry A.; Moresco, Francesca; Cuniberti, Gianaurelio
2016-04-01
The Kondo resonance of an organic molecule containing a Co atom is investigated by scanning tunneling spectroscopy and ab initio calculations on a Ag(100) surface. High resolution mapping of the line shape shows evidence of local nonradially symmetric variations of the Fano factor and the Kondo amplitude, revealing a strong influence of the molecular ligand. We show that the decay of the amplitude of the Kondo resonance is determined by the spatial distribution of the ligand's orbital being hybridized with the singly occupied Co dz2 orbital, forming together the singly occupied Kondo-active orbital.
Kondo effect and non-Fermi-liquid behavior in Dirac and Weyl semimetals
NASA Astrophysics Data System (ADS)
Principi, Alessandro; Vignale, Giovanni; Rossi, E.
2015-07-01
We study the Kondo effect in three-dimensional (3D) Dirac materials and Weyl semimetals. We find the scaling of the Kondo temperature with respect to the doping n and the coupling J between the moment of the magnetic impurity and the carriers of the semimetal. We consider the interplay of long-range scalar disorder and Kondo screening and find that it causes the Kondo effect to be characterized not by a Kondo temperature, but by a distribution of Kondo temperatures with features that cause the appearance of strong non-Fermi-liquid behavior. We then consider the effect of Kondo screening, and of the interplay of Kondo screening and long-range scalar disorder, on the transport properties of Weyl semimetals. Finally, we compare the properties of the Kondo effect in 3D and 2D Dirac materials such as graphene and topological insulators.
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.
Kondo effect in alkaline-earth-metal atomic gases with confinement-induced resonances
NASA Astrophysics Data System (ADS)
Zhang, Ren; Zhang, Deping; Cheng, Yanting; Chen, Wei; Zhang, Peng; Zhai, Hui
2016-04-01
Alkaline-earth-metal atoms have a long-lived electronic excited state, and when atoms in this excited state are localized in the Fermi sea of ground-state atoms by an external potential, they serve as magnetic impurities, due to the spin-exchange interaction between the excited- and the ground-state atoms. This can give rise to the Kondo effect. However, in order to achieve this effect in current atomic gas experiments, it requires the Kondo temperature to be increased to a sizable portion of the Fermi temperature. In this paper we calculate the confinement-induced resonance (CIR) for the spin-exchanging interaction between the ground and the excited states of the alkaline-earth-metal atoms and propose that the spin-exchange interaction can be strongly enhanced by utilizing the CIR. We analyze this system by the renormalization-group approach and show that near a CIR, the Kondo temperature can be significantly enhanced.
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system.
Wang, Yu; Zheng, Xiao; Li, Bin; Yang, Jinlong
2014-08-28
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied dz(2) orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems. PMID:25173036
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system
Wang, Yu; Zheng, Xiao Li, Bin; Yang, Jinlong
2014-08-28
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied d{sub z{sup 2}} orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems.
Understanding the Kondo resonance in the d-CoPc/Au(111) adsorption system
NASA Astrophysics Data System (ADS)
Wang, Yu; Zheng, Xiao; Li, Bin; Yang, Jinlong
2014-08-01
By combining the density functional theory (DFT) and a hierarchical equations of motion (HEOM) approach, we investigate the Kondo phenomena in a composite system consisting of a dehydrogenated cobalt phthalocyanine molecule (d-CoPc) adsorbed on an Au(111) surface. DFT calculations are performed to determine the ground-state geometric and electronic structures of the adsorption system. It is found that the singly occupied d_{z^2} orbital of Co forms a localized spin, which could be screened by the substrate conduction electrons. This screening leads to the prominent Kondo features as observed in the scanning tunneling microscopy experiments. We then employ the HEOM approach to characterize the Kondo correlations of the adsorption system. The calculated temperature-dependent differential conductance spectra and the predicted Kondo temperature agree well with the experiments, and the universal Kondo scaling behavior is correctly reproduced. This work thus provides important insights into the relevant experiments, and it also highlights the applicability of the combined DFT+HEOM approach to the studies of strongly correlated condensed matter systems.
Sub-molecular modulation of a 4f driven Kondo resonance by surface-induced asymmetry
NASA Astrophysics Data System (ADS)
Warner, Ben; El Hallak, Fadi; Atodiresei, Nicolae; Seibt, Philipp; Pruser, Henning; Caciuc, Vasile; Waters, Michael; Fisher, Andrew J.; Blugel, Stefan; van Slageren, Joris; Hirjibehedin, Cyrus F.
Coupling between a magnetic impurity and an external bath can give rise to many-body quantum phenomena, including Kondo and Hund's Impurity states in metals, and Yu-Shiba-Rusinov states in superconductors. While advances have been made in probing the magnetic properties of d-shell impurities on surfaces, the confinement of f orbitals makes them much more difficult to access directly. Here we show that a 4f driven Kondo resonance can be modulated spatially by asymmetric coupling between a metallic surface and a molecule containing a 4f-like moment. Strong hybridisation of dysprosium double-decker phthalocyanine (DyPc2) with Cu(001) induces Kondo screening of the central magnetic moment. Misalignment between the symmetry axes of the molecule and the surface induces asymmetry in the molecule's electronic structure, spatially mediating electronic access to the magnetic moment through the Kondo resonance. This work demonstrates the important role that molecular ligands play in mediating electronic and magnetic coupling and in accessing many-body quantum states.
Blocking transport resonances via Kondo many-body entanglement in quantum dots
Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena
2016-01-01
Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) ⊗ SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin. PMID:27526870
Blocking transport resonances via Kondo many-body entanglement in quantum dots.
Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena
2016-01-01
Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) ⊗ SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin. PMID:27526870
Rakhmilevitch, D; Korytár, R; Bagrets, A; Evers, F; Tal, O
2014-12-01
The interaction of individual electrons with vibrations has been extensively studied. However, the nature of electron-vibration interaction in the presence of many-body electron correlations such as a Kondo state has not been fully investigated. Here, we present transport measurements on a Copper-phthalocyanine molecule, suspended between two silver electrodes in a break-junction setup. Our measurements reveal both zero bias and satellite conductance peaks, which are identified as Kondo resonances with a similar Kondo temperature. The relation of the satellite peaks to electron-vibration interaction is corroborated using several independent spectroscopic indications, as well as ab initio calculations. Further analysis reveals that the contribution of vibration-induced inelastic current is significant in the presence of a Kondo resonance. PMID:25526145
NASA Astrophysics Data System (ADS)
Huo, Dong-Ming
2015-10-01
We present nonequilibrium Green function calculations for electronic transport through a laterally coupled carbon-nanotube quantum-dot system. In this system, a one-dimensional double carbon nanotube quantum dot attached to polarised electrodes forms a main channel for electronic tunnelling. Each carbon nanotube quantum dot in the main channel couples to a dangling carbon nanotube quantum dot. Then, the conductance spectrum is calculated. The insulating band and resonance peak in this spectrum, due to Fano antiresonance and Kondo resonance, are discussed. The intradot electron's Coulomb interaction effect on the insulating band is also investigated. By controlling the coupling coefficient between the quantum dots, we can realise mutual transformation between Kondo resonance and Fano antiresonance at the Fermi level. The spin-orbit coupling and magnetic field's influence on the Kondo resonance peak are discussed in detail. Finally, spin magnetic moment and orbital magnetic moment of electrons in the quantum dot by applying parallel magnetic field are also predicted.
Mapping itinerant electrons around Kondo impurities.
Prüser, H; Wenderoth, M; Weismann, A; Ulbrich, R G
2012-04-20
We investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic. PMID:22680744
NASA Astrophysics Data System (ADS)
Bernal, Oscar Orlando
The intermetallic Kondo alloy system UCu _{5-x}Pd_{x } is one of a number of recently-discovered Kondo materials which exhibit deviations from Fermi liquid behavior in their thermodynamic and transport properties down to micro-Kelvin temperatures. Studying local electronic structure by nuclear magnetic resonance techniques (NMR) in this unconventional system, we find anomalous behavior of NMR parameters versus magnetic susceptibility chi in UCu_4Pd and UCu_{3.5}Pd_ {1.5}. Metallic alloys containing magnetic impurities usually display a linear relation between the susceptibility and the Knight shift and its distribution, the magnetic broadening. In UCu_{5 -x}Pd_{x}, as the temperature is lowered, it is found that for both concentrations the magnetic broadening of the ^{63}Cu NMR spectra grows non-linearly with respect to chi, reaching enhancements at the lowest temperatures of ~100% over the values expected from a high-temperature linear relation. Enhancement of the linewidth over the susceptibility might indicate the possibility of U-spin freezing, as observed in some dilute Kondo alloys. The absence of any anomalies in either the specific heat or the magnetic susceptibility of these samples suggests, however, that spin freezing does not account for the observations, and that the enhancement is related to intrinsic behavior of the paramagnetic alloys. Smaller but similar anomalies are found for the isotropic and axial components of the Knight shift {cal K} as functions chi in the two materials. {cal K} presents a linear relation with chi only down to ~30 K. Below this temperature, the absolute value of the Knight-shift components grows more slowly than would be expected from extrapolating their high temperature behavior, suggesting temperature-dependent transferred-hyperfine fields at the Cu sites or a temperature-dependent lineshape asymmetry. We interpret these observations in terms of disorder of the density of conduction-electron states (DOS). A simple model of
Emergent Kondo Lattice Behavior in Iron-Based Superconductors AFe_{2}As_{2} (A=K, Rb, Cs).
Wu, Y P; Zhao, D; Wang, A F; Wang, N Z; Xiang, Z J; Luo, X G; Wu, T; Chen, X H
2016-04-01
Here, we experimentally study the origin of d-electron heavy fermion (HF) behavior in iron-based superconductors (FeSCs) AFe_{2}As_{2} (A=K, Rb, Cs). Nuclear magnetic resonance on ^{75}As reveals a universal coherent-incoherent crossover with a characteristic temperature T^{*}. Below T^{*}, a so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling behavior similar to f-electron HF materials. Furthermore, the scaling rule also regulates the manifestation of magnetic fluctuation. These results undoubtedly support an emergent Kondo lattice scenario for the d-electron HF behavior, which qualifies the AFe_{2}As_{2} (A=K, Rb, Cs) as d-electron HF superconductors. PMID:27104721
Emergent Kondo Lattice Behavior in Iron-Based Superconductors A Fe2As2 (A =K , Rb, Cs)
NASA Astrophysics Data System (ADS)
Wu, Y. P.; Zhao, D.; Wang, A. F.; Wang, N. Z.; Xiang, Z. J.; Luo, X. G.; Wu, T.; Chen, X. H.
2016-04-01
Here, we experimentally study the origin of d -electron heavy fermion (HF) behavior in iron-based superconductors (FeSCs) A Fe2As2 (A =K , Rb, Cs). Nuclear magnetic resonance on 75As reveals a universal coherent-incoherent crossover with a characteristic temperature T*. Below T*, a so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling behavior similar to f -electron HF materials. Furthermore, the scaling rule also regulates the manifestation of magnetic fluctuation. These results undoubtedly support an emergent Kondo lattice scenario for the d -electron HF behavior, which qualifies the A Fe2As2 (A =K , Rb, Cs) as d -electron HF superconductors.
4 f excitations in Ce Kondo lattices studied by resonant inelastic x-ray scattering
NASA Astrophysics Data System (ADS)
Amorese, A.; Dellea, G.; Fanciulli, M.; Seiro, S.; Geibel, C.; Krellner, C.; Makarova, I. P.; Braicovich, L.; Ghiringhelli, G.; Vyalikh, D. V.; Brookes, N. B.; Kummer, K.
2016-04-01
The potential of resonant inelastic soft x-ray scattering to measure 4 f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4 ,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.
Goker, A
2015-05-01
We study the optical absorption of a system consisting of a diatomic molecule that exhibits strong electron correlations coupled to metal nanoparticles possessing plasmon resonances by invoking the time-dependent non-crossing approximation. We investigate the evolution of the Fano resonance arising from the plasmon-exciton coupling when both atoms are Coulomb blockaded. We found that the Fano resonance rapidly dwindles as the ambient temperature exceeds the Kondo temperature of the singly occupied discrete state with higher energy and vanishes entirely at elevated temperatures. Our results show that even boosting the plasmon-exciton coupling above this temperature scale fails to revive the Fano resonance. We propose a microscopic model that accounts for these results. We suggest that a possible remedy for observation of the Fano resonance at high ambient temperatures is to position the singly occupied discrete state with the higher energy as close as possible to the Fermi level of the contacts while keeping the emitter resonance constant to prevent the merger of the Fano and plasmon resonances. PMID:25858207
Surface-Supported Hydrocarbon π Radicals Show Kondo Behavior
2013-01-01
Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7–50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support. PMID:23539333
Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model
NASA Astrophysics Data System (ADS)
Irkhin, Valentin Yu.
2016-05-01
Scaling equations for the Kondo lattice in the paramagnetic and magnetically ordered phases are derived to next-leading order with account of spin dynamics. The results are applied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in the multichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region. The corresponding temperature dependences of electronic and magnetic properties are discussed. The model describes naturally formation of a magnetic state with soft boson mode and small moment value. An important role of Van Hove singularities in the magnon spectral function is demonstrated. The results are rather sensitive to the type of magnetic ordering and space dimensionality, the conditions for NFL behavior being more favorable in the antiferromagnetic and 2D cases.
Kondo-type behavior of the Ru4 + lattice in LaCu3Ru4O12
NASA Astrophysics Data System (ADS)
Riegg, S.; Widmann, S.; Meir, B.; Sterz, S.; Günther, A.; Büttgen, N.; Ebbinghaus, S. G.; Reller, A.; von Nidda, H.-A. Krug; Loidl, A.
2016-03-01
Rare d -electron-derived heavy-fermion properties of the solid-solution series LaCu3RuxTi4 -xO12 were studied for 1 ≤x ≤4 by resistivity, susceptibility, specific-heat measurements, and magnetic-resonance techniques. Our results suggest the existence of a coherent Kondo lattice formed by localized Ru 4 d electrons leading to strongly enhanced effective electron masses. Pure ruthenate (x =4 ) is a heavy-fermion metal characterized by a resistivity proportional to T2 at low temperatures T . By increasing titanium substitution the coherent Fermi-liquid state is disturbed, yielding single-ion Kondo-type properties as in the paradigm 4 f -based heavy-fermion compound CexLa1 -xCu2.05Si2 [M. Ocko et al., Phys. Rev. B 64, 195106 (2001), 10.1103/PhysRevB.64.195106]. In LaCu3RuxTi4 -xO12 the heavy-fermion behavior finally breaks down upon crossing the metal-to-insulator transition close to x =2 .
Interplay of localized and itinerant behavior in the one-dimensional Kondo-Heisenberg model
NASA Astrophysics Data System (ADS)
Xie, Neng; Yang, Yi-feng
2015-05-01
We use the density matrix renormalization group method to study the interplay of the localized and itinerant behaviors in the one-dimensional Kondo-Heisenberg model. We find signatures of simultaneously localized and itinerant behaviors of the local spins and attribute this duality to their simultaneous entanglement within the spin chain and with conduction electrons due to incomplete hybridization. We propose a microscopic definition of the hybridization parameter that measures this "partial" itinerancy. Our results provide a microscopic support for the dual nature of f electrons and the resulting two-fluid behavior widely observed in heavy electron materials.
Ferromagnetic Kondo lattice CeRuSi{sub 2} with non-Fermi-liquid behavior
Nikiforov, V. N.; Baran, M.; Irkhin, V. Yu.
2013-05-15
The structure, electronic, thermodynamic, and magnetic properties of the CeRuSi{sub 2} Kondo lattice with ferromagnetic ordering characterized by a small moment of the ground state are investigated. Anomalies in the temperature dependences of heat capacity and resistivity (unusual power or logarithmic behavior) observed in the low-temperature range indicate a non-Fermi-liquid behavior. The results are compared with those for other Ce{sub l}Ru{sub n}X{sub m} compounds and anomalous systems based on rare-earth elements and actinides that had been studied earlier.
Spin Relaxation in Kondo Lattice Systems with Anisotropic Kondo Interaction
NASA Astrophysics Data System (ADS)
Belov, S. I.; Kutuzov, A. S.
2016-04-01
We study the influence of the Kondo effect on the spin relaxation in systems with anisotropic Kondo interaction at temperatures both high and low as compared with the static magnetic field. In the absence of the Kondo effect, the electron spin resonance linewidth is not narrowed in the whole temperature range due to the high anisotropy of the Kondo interaction. The Kondo effect leads to the universal energy scale, which regulates the temperature and magnetic field dependence of different kinetic coefficients and results in a mutual cancelation of their singular parts in a collective spin mode.
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.
Resonant behavior of dielectric objects (electrostatic resonances).
Fredkin, D R; Mayergoyz, I D
2003-12-19
Resonant behavior of dielectric objects occurs at certain frequencies for which the object permittivity is negative and the free-space wavelength is large in comparison with the object dimensions. Unique physical features of these resonances are studied and a novel technique for the calculation of resonance values of permittivity, and hence resonance frequencies, is proposed. Scale invariance of resonance frequencies, unusually strong orthogonality properties of resonance modes, and a two-dimensional phenomenon of "twin" spectra are reported. The paper concludes with brief discussions of optical controllability of these resonances in semiconductor nanoparticles and a plausible, electrostatic resonance based, mechanism for nucleation and formation of ball lightning. PMID:14754117
Renormalization group theory for Kondo breakdown in Kondo lattice systems
NASA Astrophysics Data System (ADS)
Ballmann, K.; Nejati, A.; Kroha, J.
2015-03-01
We present a renormalization group (RG) theory for the breakdown of Kondo screening in the Kondo lattice model (KLM) without pre-assumptions about the competition between Kondo effect and magnetic ordering or Fermi surface criticality. We show that the vertex between a single, local Kondo spin and the extended conduction electrons obtains RKKY- induced, non-local contributions in the in-and out-going coordinates of scattering electrons due to scattering at surrounding Kondo sites, but it remains local in the Kondo spin position. This enables the existence of a local Kondo screening scale TK(y) in the KLM, controlled by the effective RKKY coupling parameter y. TK(y) is determined by the RG flow of the local spin exchange coupling in the presence of the self-consistent spin response on surrounding Kondo sites. We show that TK(y) exhibits universal behavior and is suppressed by the antiferromagnetic RKKY coupling. Beyond a maximal RKKY parameter value ymax Kondo screening ceases to exist even without magnetic ordering. The theory opens up the possibility of describing quantum critical scenarios involving spin wave instabilities or local Kondo breakdown on the same footing.
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
NASA Astrophysics Data System (ADS)
Barzykin, Victor
2006-03-01
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D. Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that thermodynamic and transport properties of Kondo lattices below coherence temperature can be very successfully described in terms of a two-fluid model, with Kondo impurity and heavy electron Fermi liquid contributions. We analyze thermodynamic properties of Kondo lattices using 1/N slave boson treatment of the periodic Anderson model and show that these two contributions indeed arise below the coherence temperature. We find that the Kondo impurity contribution to thermodynamics corresponds to thermal excitations into the flat portion of the energy spectrum.
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).
Fisk, Z.; Sarrao, J.L.; Thompson, J.D.
1994-10-01
The Kondo insulating materials present a particularly simple limiting case of the strongly correlated electron lattice problem: one occupied f-state interacting with a single half-filled conduction band. Experiment shows that the solution to this problem has some remarkably simple aspects. Optical conductivity data display the strong coupling nature of this physics.
NASA Astrophysics Data System (ADS)
Dzero, Maxim; Xia, Jing; Galitski, Victor; Coleman, Piers
2016-03-01
This article reviews recent theoretical and experimental work on a new class of topological material -- topological Kondo insulators, which develop through the interplay of strong correlations and spin-orbit interactions. The history of Kondo insulators is reviewed along with the theoretical models used to describe these heavy fermion compounds. The Fu-Kane method of topological classification of insulators is used to show that hybridization between the conduction electrons and localized f electrons in these systems gives rise to interaction-induced topological insulating behavior. Finally, some recent experimental results are discussed, which appear to confirm the theoretical prediction of the topological insulating behavior in samarium hexaboride, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from robust surface states.
Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals
Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar
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
Probing the Kondo State using Terahertz Radiation
NASA Astrophysics Data System (ADS)
Wetli, Christoph; Kroha, Johann; Krellner, Cornelius; Kliemt, Kristin; Stockert, Oliver; v. Loehneysen, Hilbert; Fiebig, Manfred
The appearance of quantum critical phase transitions is boosting the interest in the field of Kondo-lattice systems. After intense research over the last decades, experimental insights have been mainly gained by measuring the specific heat capacity or the magnetic susceptibility and relating them to the increase of the effective mass. Lately, it has been demonstrated that ARPES experiments allow direct access to the electrons contributing to the Kondo-lattice effect, but with some experimental restrictions. We will show that THz radiation is a powerful and highly accurate alternative for investigating the approach to the coherent Kondo-state of heavy-fermion systems. Photons in the THz range directly couple to the electronic heavy quasiparticles causing the Kondo-singlet behavior. Additionally, this technique allows studying Kondo-state dynamics on the picosecond time scale. We report lifetime measurements of excited Kondo singlets for the two crystalline rare earth heavy-fermion systems CeCu6 and YbRh2Si2, where the lifetimes scale inversely proportional to the Kondo-temperature. THz spectroscopy thus gives a very different perspective towards the Kondo-lattice effect, with the unique ability to combine temporal resolution and possible measurements in magnetic field.
A holographic model of the Kondo effect
NASA Astrophysics Data System (ADS)
Erdmenger, Johanna; Hoyos, Carlos; O'Bannon, Andy; Wu, Jackson
2013-12-01
We propose a model of the Kondo effect based on the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, also known as holography. The Kondo effect is the screening of a magnetic impurity coupled anti-ferromagnetically to a bath of conduction electrons at low temperatures. In a (1+1)-dimensional CFT description, the Kondo effect is a renormalization group flow triggered by a marginally relevant (0+1)-dimensional operator between two fixed points with the same Kac-Moody current algebra. In the large- N limit, with spin SU( N) and charge U(1) symmetries, the Kondo effect appears as a (0+1)-dimensional second-order mean-field transition in which the U(1) charge symmetry is spontaneously broken. Our holographic model, which combines the CFT and large- N descriptions, is a Chern-Simons gauge field in (2+1)-dimensional AdS space, AdS 3, dual to the Kac-Moody current, coupled to a holographic superconductor along an AdS 2 sub-space. Our model exhibits several characteristic features of the Kondo effect, including a dynamically generated scale, a resistivity with power-law behavior in temperature at low temperatures, and a spectral flow producing a phase shift. Our holographic Kondo model may be useful for studying many open problems involving impurities, including for example the Kondo lattice problem.
Kondo peak splitting and Kondo dip induced by a local moment
Niu, Pengbin; Shi, Yun-Long; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang
2015-01-01
Many features like spin-orbit coupling, bias and magnetic fields applied, and so on, can strongly influence the Kondo effect. One of the consequences is Kondo peak splitting. However, Kondo peak splitting led by a local moment has not been investigated systematically. In this research we study theoretically electronic transport through a single-level quantum dot exchange coupled to a local magnetic moment in the Kondo regime. We focus on the Kondo peak splitting induced by an anisotropic exchange coupling between the quantum dot and the local moment, which shows rich splitting behavior. We consider the cases of a local moment with S = 1/2 and S = 1. The longitudinal (z-component) coupling plays a role of multivalued magnetic fields and the transverse (x, y-components) coupling lifts the degeneracy of the quantum dot, both of which account for the fine Kondo peak splitting structures. The inter-level or intra-level transition processes are identified in detail. Moreover, we find a Kondo dip at the Fermi level under the proper parameters. The possible experimental observations of these theoretical results should deepen our understanding of Kondo physics. PMID:26658128
Kondo peak splitting and Kondo dip induced by a local moment.
Niu, Pengbin; Shi, Yun-Long; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang
2015-01-01
Many features like spin-orbit coupling, bias and magnetic fields applied, and so on, can strongly influence the Kondo effect. One of the consequences is Kondo peak splitting. However, Kondo peak splitting led by a local moment has not been investigated systematically. In this research we study theoretically electronic transport through a single-level quantum dot exchange coupled to a local magnetic moment in the Kondo regime. We focus on the Kondo peak splitting induced by an anisotropic exchange coupling between the quantum dot and the local moment, which shows rich splitting behavior. We consider the cases of a local moment with S = 1/2 and S = 1. The longitudinal (z-component) coupling plays a role of multivalued magnetic fields and the transverse (x, y-components) coupling lifts the degeneracy of the quantum dot, both of which account for the fine Kondo peak splitting structures. The inter-level or intra-level transition processes are identified in detail. Moreover, we find a Kondo dip at the Fermi level under the proper parameters. The possible experimental observations of these theoretical results should deepen our understanding of Kondo physics. PMID:26658128
The Kondo effect in ferromagnetic atomic contacts.
Calvo, M Reyes; Fernández-Rossier, Joaquín; Palacios, Juan José; Jacob, David; Natelson, Douglas; Untiedt, Carlos
2009-04-30
Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system; this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent log-normal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures. PMID:19407797
Antiferromagnetic order and Kondo-lattice behavior in single-crystalline Ce2RhSi3
NASA Astrophysics Data System (ADS)
Szlawska, M.; Kaczorowski, D.; Ślebarski, A.; Gulay, L.; Stępień-Damm, J.
2009-04-01
Single crystal of Ce2RhSi3 was investigated by means of x-ray diffraction, magnetization, electrical resistivity, and heat-capacity measurements. Moreover, its electronic structure was studied by cerium core-level x-ray photoemission spectroscopy. The results revealed that Ce2RhSi3 is an antiferromagnetic Kondo lattice due to the presence of stable trivalent Ce ions.
From Kondo behavior to high temperature superconductivity in Sr(Ni1-xFex)2As2
NASA Astrophysics Data System (ADS)
Wakeham, Nicholas; Ni, Ni; Bauer, Eric; Thompson, Joe; Ronning, Filip
SrFe2As2 has an antiferromagnetic groundstate at ambient pressure that can be suppressed by chemical doping or pressure to produce unconventional superconductivity. SrNi2As2 is a non-magnetic conventional superconductor with Tc of 0.6 K. It has been shown that in Sr(Ni1-xFex)2As2 there is a dome of superconductivity between x = 0 . 95 and x = 0 . 9 . However, little is known about this doping series for small x values. We will present the study of the thermodynamic and transport properties of the doping series of Sr(Ni(1-x)Fex)2As2 for x <= 0 . 6 . In the dilute Fe limit (x <= 0 . 01) we find strong evidence for single-ion Kondo behaviour. As the concentration of Fe is increased, Fe-Fe interaction effects become significant and the Kondo scale increases. For 0 . 2 <= x <= 0 . 6 magnetic susceptibility measurements show the presence of a spin glass transition. The presence of Kondo behaviour in Sr(Ni(1-x)Fex)2As2 indicates the formation of local moments interacting with conduction electrons. Therefore, we will address the relevance of this result to the discussion of the itineracy of the magnetism in SrFe2As2, as well as the observed enhancement of the effective mass seen in many pnictide compounds.
Fano-Kondo and the Kondo box regimes crossover in a quantum dot coupled to a quantum box.
Apel, Victor M; Orellana, Pedro A; Pacheco, Monica; Anda, Enrique V
2013-12-18
In this work, we study the Kondo effect of a quantum dot (QD) connected to leads and to a discrete set of one-particle states provided by a quantum box represented by a quantum ring (QR) pierced by a magnetic flux side attached to the QD. The interplay between the bulk Kondo effect and the so-called Kondo box regime is studied. In this system the QR energies can be continuously modified by the application of the magnetic field. The crossover between these two regimes is analyzed by changing the connection of the QD to the QR from the weak to the strong coupling regime. In the weak coupling regime, the differential conductance develops a sequence of Fano-Kondo anti-resonances due to destructive interference between the discrete quantum ring levels and the conducting Kondo channel provided by the leads. In the strong coupling regime the differential conductance has very sharp resonances when one of the Kondo discrete sub-levels characterizing the Kondo box is tuned by the applied potential. The conductance, the current fluctuations and the Fano coefficient result as being the relevant physical magnitudes to be analyzed to reveal the physical properties of these two Kondo regimes and the crossover region between them. The results were obtained by using the slave boson mean field theory (SBMFT). PMID:24275637
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.
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.
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.
Thermoelectric effect in the Kondo dot side-coupled to a Majorana mode
NASA Astrophysics Data System (ADS)
Khim, Heunghwan; López, Rosa; Lim, Jong Soo; Lee, Minchul
2015-06-01
We investigate the linear thermoelectric response of an interacting quantum dot side-coupled by one of two Majorana modes hosted by a topological superconducting wire. We employ the numerical renormalization group technique to obtain the thermoelectrical conductance L in the Kondo regime while the background temperature T, the Majorana-dot coupling Γm, and the overlap ɛm between the two Majorana modes are tuned. We distinguish two transport regimes in which L displays different features: the weak- (Γm
Colossal magnetoresistance in topological Kondo insulator
NASA Astrophysics Data System (ADS)
Slieptsov, Igor O.; Karnaukhov, Igor N.
2016-04-01
Abnormal electronic properties of complex systems require new ideas concerning explanation of their behavior and possibility of realization. In this acticle we show that a colossal magnetoresistance is realized in the state of the topological Kondo insulator, that is similar to the Kondo insulator state in the Kondo lattice. The mechanism of the phenomenon is the following: in the spin gapless phase an external magnetic field induces the gap in the spectrum of spin excitations, the gap in the spectrum of fermions is opened due to a hybridization between spin and fermion subsystems at half-filling, as the result the magnetic field leads to metal–insulator (or bad metal–insulator) phase transition. A model of the topological Kondo lattice defined on a honeycomb lattice is studied for the case when spinless fermion bands are half-filled. It is shown that the hybridization between local moments and itinerant fermions should be understood as the hybridization between corresponding Majorana fermions of the spin and charge sectors. The system is a topological insulator, single fermion and spin excitations at low energies are massive. We will show that a spin gap induces a gap in the charge channel, it leads to an appearance of a topological insulator state with chiral gapless edge modes and the Chern number one or two depending on the exchange integrals’ values. The relevance of this to the traditional Kondo insulator state is discussed.
From Kondo lattices to Kondo superlattices.
Shimozawa, Masaaki; Goh, Swee K; Shibauchi, Takasada; Matsuda, Yuji
2016-07-01
The realization of new classes of ground states in strongly correlated electron systems continues to be a major issue in condensed matter physics. Heavy fermion materials, whose electronic structure is essentially three-dimensional, are one of the most suitable systems for obtaining novel electronic states because of their intriguing properties associated with many-body effects. Recently, a state-of-the-art molecular beam epitaxy technique was developed to reduce the dimensionality of heavy electron systems by fabricating artificial superlattices that include heavy fermion compounds; this approach can produce a new type of electronic state in two-dimensional (2D) heavy fermion systems. In artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3, the magnetic order is suppressed by a reduction in the thickness of the CeIn3 layers. In addition, the 2D confinement of heavy fermions leads to enhancement of the effective electron mass and deviation from the standard Fermi liquid electronic properties, which are both associated with the dimensional tuning of quantum criticality. In the superconducting superlattices of the heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, signatures of superconductivity are observed even at the thickness of one unit-cell layer of CeCoIn5. The most remarkable feature of this 2D heavy fermion superconductor is that the thickness reduction of the CeCoIn5 layers changes the temperature and angular dependencies of the upper critical field significantly. This result is attributed to a substantial suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking at the interfaces of CeCoIn5 block layers. The importance of the inversion symmetry breaking in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy, which can resolve spectroscopic information from each layer separately, even within the same CeCoIn5
From Kondo lattices to Kondo superlattices
NASA Astrophysics Data System (ADS)
Shimozawa, Masaaki; Goh, Swee K.; Shibauchi, Takasada; Matsuda, Yuji
2016-07-01
The realization of new classes of ground states in strongly correlated electron systems continues to be a major issue in condensed matter physics. Heavy fermion materials, whose electronic structure is essentially three-dimensional, are one of the most suitable systems for obtaining novel electronic states because of their intriguing properties associated with many-body effects. Recently, a state-of-the-art molecular beam epitaxy technique was developed to reduce the dimensionality of heavy electron systems by fabricating artificial superlattices that include heavy fermion compounds; this approach can produce a new type of electronic state in two-dimensional (2D) heavy fermion systems. In artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3, the magnetic order is suppressed by a reduction in the thickness of the CeIn3 layers. In addition, the 2D confinement of heavy fermions leads to enhancement of the effective electron mass and deviation from the standard Fermi liquid electronic properties, which are both associated with the dimensional tuning of quantum criticality. In the superconducting superlattices of the heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, signatures of superconductivity are observed even at the thickness of one unit-cell layer of CeCoIn5. The most remarkable feature of this 2D heavy fermion superconductor is that the thickness reduction of the CeCoIn5 layers changes the temperature and angular dependencies of the upper critical field significantly. This result is attributed to a substantial suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking at the interfaces of CeCoIn5 block layers. The importance of the inversion symmetry breaking in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy, which can resolve spectroscopic information from each layer separately, even within the same CeCoIn5
Voltage Quench Dynamics of a Kondo System.
Antipov, Andrey E; Dong, Qiaoyuan; Gull, Emanuel
2016-01-22
We examine the dynamics of a correlated quantum dot in the mixed valence regime. We perform numerically exact calculations of the current after a quantum quench from equilibrium by rapidly applying a bias voltage in a wide range of initial temperatures. The current exhibits short equilibration times and saturates upon the decrease of temperature at all times, indicating Kondo behavior both in the transient regime and in the steady state. The time-dependent current saturation temperature connects the equilibrium Kondo temperature to a substantially increased value at voltages outside of the linear response. These signatures are directly observable by experiments in the time domain. PMID:26849606
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.
Kondo Force in Shuttling Devices: Dynamical Probe for a Kondo Cloud
NASA Astrophysics Data System (ADS)
Kiselev, M. N.; Kikoin, K. A.; Gorelik, L. Y.; Shekhter, R. I.
2013-02-01
We consider the electromechanical properties of a single-electronic device consisting of a movable quantum dot attached to a vibrating cantilever, forming a tunnel contact with a nonmovable source electrode. We show that the resonance Kondo tunneling of electrons amplifies exponentially the strength of nanoelectromechanical (NEM) coupling in such a device and make the latter insensitive to mesoscopic fluctuations of electronic levels in a nanodot. It is also shown that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a nonmechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.
NASA Astrophysics Data System (ADS)
Nakatsuji, Satoru
2008-03-01
Among metallic magnets on geometrical frustrated lattices, the pyrochlore oxide Pr2Ir2O7 is unique for its metallic spin liquid behavior ootnotetextS. Nakatsuji, Y. Machida, Y. Maeno, T. Tayama, T. Sakakibara, J. v. Duijn, L. Balicas, J. N. Millican, R. T. Macaluso, and Julia Y. Chan, Phys. Rev. Lett. 96, 087204 (2006)., and unconventional Hall transport phenomena ootnotetextY. Machida, S. Nakatsuji, Y. Maeno, T. Tayama, T. Sakakibara, and S. Onoda, Phys. Rev. Lett. 98, 057203 (2007).. Despite the Weiss temperature T^* = 20 K deu to the RKKY interaction, Pr2Ir2O7 exhibits no magnetic long range order, but spin freezing at a very low temperature ˜120 mK. Instead, the Kondo effect, including lnT dependence in the resistivity, emerges and leads to partial screening of the 4f-moments below T^*. Moreover, the underscreened 4f- moments show spin-liquid behavior below a renormalized energy scale of θw˜1.7 K. Interestingly, in this spin-liquidlike paramagnetic regime, the Hall resistivity ρxy becomes largely enhanced, and shows behavior far different from anomalous Hall effects (AHE) due to the spin- orbit coupling observed in ordinary magnetic conductors. We discuss the origin of the metallic spin liquid behavior and unconventional AHE in terms of the spin chirality due to the non-coplanar texture of the <111> Ising-like Pr moments. This work is based on the collaboration with Y. Machida, T. Tayama, T. Sakakibara (ISSP, Univ.of Tokyo), Y. Maeno (Kyoto Univ.), S. Onoda (RIKEN, Tokyo), C. Broholm (Johns Hopkins Univ.), C. Stock and J. van Duijn (ISIS), L. Balicas (NHMFL), Jung Young Cho, and Julia Y. Chan (Louisiana State Univ.).
Tunable unconventional Kondo effect on topological insulator surfaces
NASA Astrophysics Data System (ADS)
Isaev, L.; Ortiz, G.; Vekhter, I.
2015-11-01
We study Kondo physics of a spin-1/2 impurity in electronic matter with strong spin-orbit interaction, which can be realized by depositing magnetic adatoms on the surface of a three-dimensional topological insulator. We show that magnetic properties of topological surface states and the very existence of Kondo screening strongly depend on details of the bulk material, and specifics of surface preparation encoded in time-reversal preserving boundary conditions for electronic wavefunctions. When this tunable Kondo effect occurs, the impurity spin is screened by purely orbital motion of surface electrons. This mechanism gives rise to a transverse magnetic response of the surface metal, and to spin textures that can be used to experimentally probe signatures of a Kondo resonance. Our predictions are particularly relevant for STM measurements in Pb Te -class crystalline topological insulators, but we also discuss implications for other classes of topological materials.
Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes
NASA Astrophysics Data System (ADS)
Hamaya, K.; Kitabatake, M.; Shibata, K.; Jung, M.; Kawamura, M.; Hirakawa, K.; Machida, T.; Taniyama, T.; Ishida, S.; Arakawa, Y.
2007-12-01
Using a laterally fabricated quantum-dot (QD) spin-valve device, we experimentally study the Kondo effect in the electron transport through a semiconductor QD with an odd number of electrons (N). In a parallel magnetic configuration of the ferromagnetic electrodes, the Kondo resonance at N =3 splits clearly without external magnetic fields. With applying magnetic fields (B), the splitting is gradually reduced, and then the Kondo effect is almost restored at B =1.2T. This means that, in the Kondo regime, an inverse effective magnetic field of B ˜1.2T can be applied to the QD in the parallel magnetic configuration of the ferromagnetic electrodes.
Panel resonant behavior of wind turbine blades.
Paquette, Joshua A.; Griffith, Daniel Todd
2010-03-01
The principal design drivers in the certification of wind turbine blades are ultimate strength, fatigue resistance, adequate tip-tower clearance, and buckling resistance. Buckling resistance is typically strongly correlated to both ultimate strength and fatigue resistance. A composite shell with spar caps forms the airfoil shape of a blade and reinforcing shear webs are placed inside the blade to stiffen the blade in the flap-wise direction. The spar caps are dimensioned and the shear webs are placed so as to add stiffness to unsupported panel regions and reduce their length. The panels are not the major flap-wise load carrying element of a blade; however, they must be designed carefully to avoid buckling while minimizing blade weight. Typically, buckling resistance is evaluated by consideration of the load-deflection behavior of a blade using finite element analysis (FEA) or full-scale static testing of blades under a simulated extreme loading condition. The focus of this paper is on the use of experimental modal analysis to measure localized resonances of the blade panels. It can be shown that the resonant behavior of these panels can also provide a means to evaluate buckling resistance by means of analytical or experimental modal analysis. Further, panel resonances have use in structural health monitoring by observing changes in modal parameters associated with panel resonances, and use in improving panel laminate model parameters by correlation with test data. In recent modal testing of wind turbine blades, a set of panel modes were measured. This paper will report on the findings of these tests and accompanying numerical and analytical modeling efforts aimed at investigating the potential uses of panel resonances for blade evaluation, health monitoring, and design.
Competition between Kondo Screening and Quantum Hall Edge Reconstruction.
Heine, A W; Tutuc, D; Zwicknagl, G; Haug, R J
2016-03-01
We report on a Kondo correlated quantum dot connected to two-dimensional leads where we demonstrate the renormalization of the g factor in the pure Zeeman case. i.e., for magnetic fields parallel to the plane of the quantum dot. For the same system, we study the influence of orbital effects by investigating the quantum Hall regime; i.e., a perpendicular magnetic field is applied. In this case an unusual behavior of the suppression of the Kondo effect and of the split zero-bias anomaly is observed. The splitting decreases with magnetic field and shows discontinuous changes that are attributed to the intricate interplay between Kondo screening and the quantum Hall edge structure originating from electrostatic screening. This edge structure, made up of compressible and incompressible stripes, strongly affects the Kondo temperature of the quantum dot and thereby influences the renormalized g factor. PMID:26991192
Competition between Kondo Screening and Quantum Hall Edge Reconstruction
NASA Astrophysics Data System (ADS)
Heine, A. W.; Tutuc, D.; Zwicknagl, G.; Haug, R. J.
2016-03-01
We report on a Kondo correlated quantum dot connected to two-dimensional leads where we demonstrate the renormalization of the g factor in the pure Zeeman case. i.e., for magnetic fields parallel to the plane of the quantum dot. For the same system, we study the influence of orbital effects by investigating the quantum Hall regime; i.e., a perpendicular magnetic field is applied. In this case an unusual behavior of the suppression of the Kondo effect and of the split zero-bias anomaly is observed. The splitting decreases with magnetic field and shows discontinuous changes that are attributed to the intricate interplay between Kondo screening and the quantum Hall edge structure originating from electrostatic screening. This edge structure, made up of compressible and incompressible stripes, strongly affects the Kondo temperature of the quantum dot and thereby influences the renormalized g factor.
Tunable Kondo effect and spin textures on topological insulators surfaces
NASA Astrophysics Data System (ADS)
Vekhter, Ilya; Ortiz, Gerardo; Isaev, Leonid
We consider screening of a spin- 1 / 2 impurity at the surface of a topological insulator, and show that the very existence of Kondo screening strongly depend on details of the bulk material and surface preparation whose details are encoded in time-reversal preserving boundary conditions for electronic wavefunctions. We investigate in detail the formation of the Kondo resonance by studying the ''orbital-flip'' processes that screen the impurity spin in the resulting strongly spin-orbit coupled system. This mechanism gives rise to spin textures that can be used to experimentally probe signatures of a Kondo resonance in topological insulators, and we give examples relevant to specific materials. L.I. was supported by the NSF (PIF-1211914 and PFC-1125844), AFOSR, AFOSR-MURI, NIST and ARO individual investigator awards, and also in part by ICAM. I.V. acknowledges support from NSF Grant DMR-1105339.
Quantitative Calculation of the Spatial Extension of the Kondo Cloud
NASA Astrophysics Data System (ADS)
Gerd, Bergmann
2008-03-01
A recently developed compact solution for the singlet state of the Friedel-Anderson and the Kondo impurity is applied to investigate the old question of a Kondo cloud in the Kondo ground state. Wilson's states with an exponentially decreasing frame of energy cells towards the Fermi level are used. The Wilson states are expressed as free electron waves with a linear dispersion and integrated over the width of their energy cells. For the magnetic state of the Friedel-Anderson impurity one finds essentially no spin polarization in the vicinity of the d-impurity. However, for the magnetic component of the singlet state a spin polarization cloud is observed which screens the spin (magnetic moment) of the d-electron. The range ξK of this polarization cloud is investigated in detail for the Kondo impurity. The range is inversely proportional to the Kondo energy δK. The extent of the electron density in real space is a detector for a resonance in energy. The spatial extension ξ and the resonance width δ are reciprocal and given by the relation ξδ vF.
Quantitative calculation of the spatial extension of the Kondo cloud
NASA Astrophysics Data System (ADS)
Bergmann, Gerd
2008-03-01
A recently developed compact solution for the singlet state of the Friedel-Anderson and the Kondo impurity is applied to investigate the old question of a Kondo cloud in the Kondo ground state. Wilson’s states with an exponentially decreasing frame of energy cells toward the Fermi level are used. The Wilson states are expressed as free electron waves with a linear dispersion and integrated over the width of their energy cells. For the magnetic state of the Friedel-Anderson impurity, one finds essentially no spin polarization in the vicinity of the d impurity. However, for the magnetic component of the singlet state, a spin polarization cloud is observed which screens the spin (magnetic moment) of the d electron. The range ξK of this polarization cloud is investigated in detail for the Kondo impurity. The range is inversely proportional to the Kondo energy ΔK . The extent of the electron density in real space is a detector for a resonance in energy. The spatial extension ξ and the resonance width Δ are reciprocal and given by the relation ξΔ≈ℏvF .
Measurement of Valley Kondo Effect in a Si/SiGe Quantum Dot
NASA Astrophysics Data System (ADS)
Yuan, Mingyun; Yang, Zhen; Tang, Chunyang; Rimberg, A. J.; Joynt, R.; Savage, D. E.; Lagally, M. G.; Eriksson, M. A.
2013-03-01
The Kondo effect in Si/SiGe QDs can be enriched by the valley degree of freedom in Si. We have observed resonances showing temperature dependence characteristic of the Kondo effect in two consecutive Coulomb diamonds. These resonances exhibit unusual magnetic field dependence that we interpret as arising from Kondo screening of the valley degree of freedom. In one diamond two Kondo peaks due to screening of the valley index exist at zero magnetic field, revealing a zero-field valley splitting of Δ ~ 0.28 meV. In a non-zero magnetic field the peaks broaden and coalesce due to Zeeman splitting. In the other diamond, a single resonance at zero bias persists without Zeeman splitting for non-zero magnetic field, a phenomenon characteristic of valley non-conservation in tunneling. This research is supported by the NSA and ARO.
NASA Astrophysics Data System (ADS)
Kettemann, S.; Mucciolo, E. R.; Varga, I.; Slevin, K.
2012-03-01
Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature TK is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.
Gate-tunable split Kondo effect in a carbon nanotube quantum dot
NASA Astrophysics Data System (ADS)
Eichler, A.; Weiss, M.; Schönenberger, C.
2011-07-01
We show a detailed investigation of the split Kondo effect in a carbon nanotube quantum dot with multiple gate electrodes. Two conductance peaks, observed at finite bias in nonlinear transport measurements, are found to approach each other for increasing magnetic field, to result in a recovered zero bias Kondo resonance at finite magnetic field. Surprisingly, in the same charge state, but under different gate configurations, the splitting does not disappear for any value of the magnetic field, but we observe an avoided crossing. We think that our observations can be understood in terms of a two-impurity Kondo effect with two spins coupled antiferromagnetically. The exchange coupling between the two spins can be influenced by a local gate, and the non-recovery of the Kondo resonance for certain gate configurations is explained by the existence of a small antisymmetric contribution to the exchange interaction between the two spins.
Kondo effect in triple quantum dots
NASA Astrophysics Data System (ADS)
Žitko, R.; Bonča, J.; Ramšak, A.; Rejec, T.
2006-04-01
Numerical analysis of the simplest odd-numbered system of coupled quantum dots reveals an interplay between magnetic ordering, charge fluctuations, and the tendency of itinerant electrons in the leads to screen magnetic moments. The transition from local-moment to molecular-orbital behavior is visible in the evolution of correlation functions as the interdot coupling is increased. Resulting Kondo phases are presented in a phase diagram which can be sampled by measuring the zero-bias conductance. We discuss the origin of the even-odd effects by comparing with the double quantum dot.
Universal Symmetry-Protected Resonances in a Spinful Luttinger Liquid
NASA Astrophysics Data System (ADS)
Hu, Yichen; Kane, Charles
We study the problem of resonant tunneling through a quantum dot in a spinful Luttinger liquid. It provides the simplest example of a (0 + 1) d system with symmetry-protected topological phases. Transitions between different symmetry-protected topological phases separated by fixed points are achieved by tuning the system through resonance. For a particular interaction strength (Luttinger parameter gρ =1/3 , gσ = 1), we show that the problem is equivalent to a two channel SU (3) Kondo problem. Both problems can be mapped to a quantum Brownian motion model on a Kagome lattice, which in turn is related to quantum Brownian motion on a honeycomb lattice and the three channel SU (2) Kondo problem. Utilizing boundary conformal field theory, we find the universal peak conductance g*e2/h as well as dimensions of the leading relevant operators of the problem. This allows us to compute the scaling behavior of the resonance line-shape as a function of temperature. We also established the fact that the fixed point quantum Brownian motion on both generalized honeycomb lattice(SU(2)k Kondo) and generalized Kagome lattice(SU(k)2 Kondo) flow into are the same (with k = 3 our original resonant tunneling problem).
Spin polarization of the split Kondo state.
von Bergmann, Kirsten; Ternes, Markus; Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J
2015-02-20
Spin-resolved scanning tunneling microscopy is employed to quantitatively determine the spin polarization of the magnetic field-split Kondo state. Tunneling conductance spectra of a Kondo-screened magnetic atom are evaluated within a simple model taking into account inelastic tunneling due to spin excitations and two Kondo peaks positioned symmetrically around the Fermi energy. We fit the spin state of the Kondo-screened atom with a spin Hamiltonian independent of the Kondo effect and account for Zeeman splitting of the Kondo peak in the magnetic field. We find that the width and the height of the Kondo peaks scales with the Zeeman energy. Our observations are consistent with full spin polarization of the Kondo peaks, i.e., a majority spin peak below the Fermi energy and a minority spin peak above. PMID:25763966
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).
Entanglement probe of two-impurity Kondo physics in a spin chain.
Bayat, Abolfazl; Bose, Sougato; Sodano, Pasquale; Johannesson, Henrik
2012-08-10
We propose that real-space properties of the two-impurity Kondo model can be obtained from an effective spin model where two single-impurity Kondo spin chains are joined via an Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the two impurity spins. We then use a density matrix renormalization group approach, valid in all ranges of parameters, to study its features using two complementary quantum-entanglement measures, the negativity and the von Neumann entropy. This nonperturbative approach enables us to uncover the precise dependence of the spatial extent ξ(K) of the Kondo screening cloud with the Kondo and RKKY couplings. Our results reveal an exponential suppression of the Kondo temperature T(K)~1/ξ(K) with the size of the effective impurity spin in the limit of large ferromagnetic RKKY coupling, a striking display of "Kondo resonance narrowing" in the two-impurity Kondo model. We also show how the antiferromagnetic RKKY interaction produces an effective decoupling of the impurities from the bulk already for intermediate strengths of this interaction, and, furthermore, exhibit how the non-Fermi liquid quantum critical point is signaled in the quantum entanglement between various parts of the system. PMID:23006288
Fano resonance in a normal metal/ferromagnet-quantum dot-superconductor device
NASA Astrophysics Data System (ADS)
Li, Lin; Cao, Zhan; Luo, Hong-Gang; Zhang, Fu-Chun; Chen, Wei-Qiang
2015-11-01
We investigate theoretically the Andreev transport through a quantum dot strongly coupled with a normal metal/ferromagnet and a superconductor (N/F-QD-S), in which the interplay between the Kondo resonance and the Andreev bound states (ABSs) has not been clearly clarified yet. Here we show that the interference between the Kondo resonance and the ABSs modifies seriously the line shape of the Kondo resonance, which manifests as a Fano resonance. The ferromagnetic lead with spin polarization induces an effective field, which leads to splitting of both the Kondo resonance and the ABSs. The spin polarization together with the magnetic field applied provides an alternative way to tune the line shape of the Kondo resonances, which is dependent of the relative positions of the Kondo resonance and the ABSs. These results indicate that the interplay between the Kondo resonance and the ABSs can significantly affect the Andreev transport, which could be tested by experiments.
A Maximally Supersymmetric Kondo Model
Harrison, Sarah; Kachru, Shamit; Torroba, Gonzalo; /Stanford U., Phys. Dept. /SLAC
2012-02-17
We study the maximally supersymmetric Kondo model obtained by adding a fermionic impurity to N = 4 supersymmetric Yang-Mills theory. While the original Kondo problem describes a defect interacting with a free Fermi liquid of itinerant electrons, here the ambient theory is an interacting CFT, and this introduces qualitatively new features into the system. The model arises in string theory by considering the intersection of a stack of M D5-branes with a stack of N D3-branes, at a point in the D3 worldvolume. We analyze the theory holographically, and propose a dictionary between the Kondo problem and antisymmetric Wilson loops in N = 4 SYM. We perform an explicit calculation of the D5 fluctuations in the D3 geometry and determine the spectrum of defect operators. This establishes the stability of the Kondo fixed point together with its basic thermodynamic properties. Known supergravity solutions for Wilson loops allow us to go beyond the probe approximation: the D5s disappear and are replaced by three-form flux piercing a new topologically non-trivial S3 in the corrected geometry. This describes the Kondo model in terms of a geometric transition. A dual matrix model reflects the basic properties of the corrected gravity solution in its eigenvalue distribution.
NASA Astrophysics Data System (ADS)
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.
Kondo effect in a quantum dot side-coupled to a topological superconductor
NASA Astrophysics Data System (ADS)
Lee, Minchul; Lim, Jong Soo; López, Rosa
2013-06-01
We investigate the dynamical and transport features of a Kondo dot side coupled to a topological superconductor (TS). The Majorana fermion states (MFSs) formed at the ends of the TS are found to be able to alter the Kondo physics profoundly: For an infinitely long wire where the MFSs do not overlap (ɛm=0) a finite dot-MFS coupling (Γm) reduces the unitary-limit value of the linear conductance by exactly a factor 3/4 in the weak-coupling regime (Γm
Kondo effect of trivalent Tm in Y 0.9Tm 0.1S
NASA Astrophysics Data System (ADS)
Haen, P.; Lapierre, F.; Mignot, J. M.; Flouquet, J.; Holtzberg, F.; Penney, T.
1983-02-01
The existence of a Kondo effect in a trivalent alloy Y 0.9Tm 0.1 S is shown by the Curie-Weiss behavior of the susceptibility and by a ln T decrease of Δϱ = ϱ alloy - ϱ YS above ˜ 12 K comparable with that observed in TmS. Comparisons are made with the Kondo dilute alloys of the intermediate valent system (Y,Tm)Se.
Yang, Yifeng; Urbano, Ricardo; Nicholas, Curro; Pines, David
2009-01-01
We report Knight shift experiments on the superconducting heavy electron material CeCoIn{sub 5} that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the {sup 115}In nuclear quadrupole resonance (NQR) spin-lattice relaxation rate T{sub 1}{sup -1} measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point (QCP) located at slightly negative pressure in CeCoIn{sub 5} and provide additional evidence for significant similarities between the heavy electron materials and the high T{sub c} cuprates.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-01
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature TD. At TD, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near TD.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-29
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}. PMID:27176534
Discovery of a 3d-transition-metal-based ferromagnetic Kondo lattice system
NASA Astrophysics Data System (ADS)
Us Saleheen, Ahmad; Samanta, Tapas; Lepkowski, Daniel; Shankar, Alok; Prestigiacomo, Joseph; Dubenko, Igor; Quetz, Abdiel; McDougald, Roy, Jr.; McCandless, Gregory; Chan, Julia; Adams, Philip; Young, David; Ali, Naushad; Stadler, Shane
2015-03-01
The formation of a Kondo lattice results in a wide variety of exotic phenomena associated with the competition between the Kondo effect and the RKKY interaction, such as heavy fermions, non-Fermi liquid behavior, unconventional superconductivity, and so on. A quantum critical point (QCP) has been frequently observed at the boundaries of competing phases for antiferromagnetic materials. However, the existence of a ferromagnetic (FM) QCP is unclear. Moreover, FM Kondo lattices are rare. Here we report the discovery of a FM Kondo lattice system Mn1-xFexCoGe, which is the first example of a 3d-metal-based system (i.e., not rare-earth-based). Resistivity, magnetic susceptibility, heat capacity and thermopower studies on a single crystal sample indicate that the anisotropic FM kondo lattice has formed along c-axis. The signature of a spin density wave transition was also observed above the Kondo minimum, below which the resistivity follows a log(T) behavior. This work was supported by the U.S. Department of Energy (Grant Nos. DE-FG02-13ER46946 and DE-FG02-06ER46291).
Observation of the underscreened Kondo effect in a molecular transistor.
Roch, Nicolas; Florens, Serge; Costi, Theo A; Wernsdorfer, Wolfgang; Balestro, Franck
2009-11-01
We present the first quantitative experimental evidence for the underscreened Kondo effect, an incomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozières and Blandin. The device consists of an even charge spin S=1 molecular quantum dot, obtained by electromigration of C60 molecules into gold nanogaps and operated in a dilution fridge. The persistence of logarithmic singularities in the low temperature conductance is demonstrated by a comparison to the fully screened configuration obtained in odd charge spin S=1/2 Coulomb diamonds. We also discover an extreme sensitivity of the underscreened Kondo resonance to the magnetic field that we confirm on the basis of numerical renormalization group calculations. PMID:20365950
Observation of the Underscreened Kondo Effect in a Molecular Transistor
NASA Astrophysics Data System (ADS)
Roch, Nicolas; Florens, Serge; Costi, Theo A.; Wernsdorfer, Wolfgang; Balestro, Franck
2009-11-01
We present the first quantitative experimental evidence for the underscreened Kondo effect, an incomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozières and Blandin. The device consists of an even charge spin S=1 molecular quantum dot, obtained by electromigration of C60 molecules into gold nanogaps and operated in a dilution fridge. The persistence of logarithmic singularities in the low temperature conductance is demonstrated by a comparison to the fully screened configuration obtained in odd charge spin S=1/2 Coulomb diamonds. We also discover an extreme sensitivity of the underscreened Kondo resonance to the magnetic field that we confirm on the basis of numerical renormalization group calculations.
Antiferromagnetism and Kondo screening on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Lin, Heng-Fu; Hong-Shuai, Tao; Guo, Wen-Xiang; Liu, Wu-Ming
2015-05-01
Magnetic adatoms in the honeycomb lattice have received tremendous attention due to the interplay between Ruderman-Kittel-Kasuya-Yosida interaction and Kondo coupling leading to very rich physics. Here we study the competition between the antiferromagnetism and Kondo screening of local moments by the conduction electrons on the honeycomb lattice using the determinant quantum Monte Carlo method. While changing the interband hybridization V, we systematically investigate the antiferromagnetic-order state and the Kondo singlet state transition, which is characterized by the behavior of the local moment, antiferromagnetic structure factor, and the short range spin-spin correlation. The evolution of the single particle spectrum are also calculated as a function of hybridization V, we find that the system presents a small gap in the antiferromagnetic-order region and a large gap in the Kondo singlet region in the Fermi level. We also find that the localized and itinerant electrons coupling leads to the midgap states in the conduction band in the Fermi level at very small V. Moreover, the formation of antiferromagnetic order and Kondo singlet are studied as on-site interaction U or temperature T increasing, we have derived the phase diagrams at on-site interaction U (or temperature T) and hybridization V plane. Project supported by the National Key Basic Research Special Foundation of China (Grants Nos. 2011CB921502 and 2012CB821305), the National Natural Science Foundation of China (Grants Nos. 61227902, 61378017, and 11434015), the State Key Laboratory for Quantum Optics and Quantum Optical Devices, China (Grant No. KF201403).
Effect of Spin-Orbit Coupling on Kondo Phenomena in f7-Electron Systems
NASA Astrophysics Data System (ADS)
Hotta, Takashi
2015-11-01
In order to promote our basic understanding of the Kondo behavior recently observed in europium compounds, we analyze an impurity Anderson model with seven f electrons at an impurity site by employing a numerical renormalization group method. The local part of the model consists of Coulomb interactions among f electrons, spin-orbit coupling λ, and crystalline electric field (CEF) potentials, while we consider the hybridization V between local f electrons and single-band conduction electrons with au symmetry. For λ = 0, we observe underscreening Kondo behavior for appropriate values of V, characterized by an entropy change from ln 8 to ln 7, in which one of the seven f electrons is screened by conduction electrons. When λ is increased, we obtain two types of behavior depending on the value of V. For large V, we find an entropy release of ln 7 at low temperatures, determined by the level splitting energy due to the hybridization. For small V, we also observe an entropy change from ln 8 to ln 2 by the level splitting due to the hybridization, but at low temperatures, ln 2 entropy is found to be released, leading to the Kondo effect. We emphasize that the Kondo behavior for small V is observed for realistic values of λ on the order of 0.1 eV. We also discuss the effect of CEF potentials and the multipole properties in the Kondo behavior reported in this paper.
NASA Astrophysics Data System (ADS)
Yanagisawa, Takashi
2015-07-01
We investigate the Kondo effect in Dirac systems, where Dirac electrons interact with the localized spin via the s-d exchange coupling. The Dirac electron in solid state has the linear dispersion and is described typically by the Hamiltonian such as Hk = vk · σ for the wave number k where σj are Pauli matrices. We derived the formula of the Kondo temperature TK by means of the Green's function theory for small J. The TK is determined from a singularity of Green's functions in the form T{K} ≃ bar{D}exp ( - {const}{.}/ρ |J|) when the exchange coupling |J| is small where bar{D} = D/√{1 + D2/(2μ )2} for a cutoff D and ρ is the density of states at the Fermi surface. When |μ| ≪ D, TK is proportional to |μ|: TK ≃ |μ| exp(-const./ρ|J|). The Kondo screening will, however, disappear when the Fermi surface shrinks to a point called the Dirac point, that is, TK vanishes when the chemical potential μ is just at the Dirac point. The resistivity and the specific heat exhibit a log-T singularity in the range TK < T ≪ |μ|/kB. Instead, for T ˜ O(|μ|) or T > |μ|, they never show log-T.
Quantum spins on star graphs and the Kondo model
NASA Astrophysics Data System (ADS)
Crampé, N.; Trombettoni, A.
2013-06-01
We study the XX model for quantum spins on the star graph with three legs (i.e., on a Y-junction). By performing a Jordan-Wigner transformation supplemented by the introduction of an auxiliary space we find a Kondo Hamiltonian of fermions, in the spin 1 representation of su(2), locally coupled with a magnetic impurity. In the continuum limit our model is shown to be equivalent to the 4-channel Kondo model coupling spin-1/2 fermions with a spin-1/2 impurity and exhibiting a non-Fermi liquid behavior. We also show that it is possible to find an XY model such that - after the Jordan-Wigner transformation - one obtains a quadratic fermionic Hamiltonian directly diagonalizable.
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.
Utilization of localized panel resonant behavior in wind turbine blades.
Griffith, Daniel Todd
2010-11-01
The shear webs and laminates of core panels of wind turbine blades must be designed to avoid panel buckling while minimizing blade weight. Typically, buckling resistance is evaluated by consideration of the load-deflection behavior of a blade using finite element analysis (FEA) or full-scale static loading of a blade to failure under a simulated extreme loading condition. This paper examines an alternative means for evaluating blade buckling resistance using non-destructive modal tests or FEA. In addition, panel resonances can be utilized for structural health monitoring by observing changes in the modal parameters of these panel resonances, which are only active in a portion of the blade that is susceptible to failure. Additionally, panel resonances are considered for updating of panel laminate model parameters by correlation with test data. During blade modal tests conducted at Sandia Labs, a series of panel modes with increasing complexity was observed. This paper reports on the findings of these tests, describes potential ways to utilize panel resonances for blade evaluation, health monitoring, and design, and reports recent numerical results to evaluate panel resonances for use in blade structural health assessment.
Motor resonance evoked by observation of subtle nonverbal behavior.
van Ulzen, Niek R; Fiorio, Mirta; Cesari, Paola
2013-01-01
This study was designed to combine two, otherwise separated, fields of research regarding motor resonance and mimicry by adopting a naturalistic mimicry paradigm while probing motor resonance with transcranial magnetic stimulation (TMS). At stake was whether the motor system resonates instantaneously with unobtrusive nonverbal behavior of another person. We measured excitability in the left and right hand while participants viewed sequences of video clips and static images. In the video clips an actor performed several clerical tasks, while either inconspicuously touching his face (face-touching (FT) condition) or not (no face-touching (NFT) condition). We found that excitability was higher in the FT condition than in the NFT and baseline conditions. Furthermore, our data showed a general heightened excitability in the left motor cortex relative to the right. Taken together, the results suggest that observed hand-face gestures--even though outside the primary focus of attention and occurring inconspicuously throughout an ongoing action setting--can cause instantaneous resonant activity in the observer's motor system. It thus supports the idea of motor resonance involvement in mimicry and demonstrates that this can be studied using a naturalistic mimicry paradigm. PMID:23758553
A Quantum Electrodynamics Kondo Circuit with Orbital and Spin Entanglement
NASA Astrophysics Data System (ADS)
Schiro, Marco; Deng, Guang-Wei; Henriet, Loic; Wei, Da; Li, Shu-Xiao; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guang-Can; Le Hur, Karyn; Guo, Guo-Ping
Recent progress in nanotechnology allows to engineer hybrid mesoscopic devices comprising on chip an artificial atom or quantum dot, capacitively coupled to a microwave (superconducting) resonator and to biased metallic leads. Here, we build such a prototype system where the artificial atom is a graphene double quantum dot (DQD) to probe non-equilibrium aspects of strongly-entangled many body states between light and matter at the nanoscale. Controlling the coupling of the photon field and the charge states of the DQD, we measure the microwave reflection spectrum of the resonator. When the DQD is at the charge degeneracy points, experimental results are consistent with a Kondo impurity model entangling charge, spin and orbital degrees of freedom with the quantum fluctuations of the cavity photon. The light coming out from the resonator reveals the formation of the Kondo or Abrikosov-Suhl resonance at low temperatures. We also explore other routes to investigate nonlinear transport by increasing the microwave power, the bias and gate voltages.
Multipeak Kondo effect in one- and two-electron quantum dots.
Vidan, A; Stopa, M; Westervelt, R M; Hanson, M; Gossard, A C
2006-04-21
We have fabricated a few-electron quantum dot that can be tuned down to zero electrons while maintaining strong coupling to the leads. Using a nearby quantum point contact as a charge sensor, we can determine the absolute number of electrons in the quantum dot. We find several sharp peaks in the differential conductance, occurring at both zero and finite source-drain bias, for the one- and two-electron quantum dot. We attribute the peaks at finite bias to a Kondo effect through excited states of the quantum dot and investigate the magnetic field dependence of these Kondo resonances. PMID:16712183
Influence of kinetic effects on the resonance behavior of the Multipole Resonance Probe
NASA Astrophysics Data System (ADS)
Oberrath, Jens; Mussenbrock, Thomas; Brinkmann, Ralf Peter
2012-10-01
Active plasma resonance spectroscopy is a well known diagnostic method. Many concepts of this method are theoretically investigated and realized as a diagnostic tool. One of these tools is the multipole resonance probe (MRP) [1]. The application of such a probe in plasmas with pressures of only a few Pa raises the question whether kinetic effects have to be taken into account or not. To address this question a kinetic model is necessary. A general kinetic model for an electrostatic concept of active plasma resonance spectroscopy has already been presented by the authors [2]. This model can be used to describe the dynamical behavior of the MRP, which is interpretable as a special case of the general model. Neglecting electron-neutral collisions, this model can be solved analytically. Based on this solution we derive an approximated expression for the admittance of the system to investigate the influence of kinetic effects on the resonance behavior of the MRP. [4pt] [1] M. Lapke et al., Plasma Sources Sci. Technol. 20, 2011, 042001[0pt] [2] J. Oberrath et al., Proceedings of the 30th International Conference on Phenomena in Ionized Gases, 28th August - 2nd September, 2011
Field-dependent ordered phases and Kondo phenomena in the filled skutterudite compound PrOs4As12
Maple, M. B.; Butch, N. P.; Frederick, N. A.; Ho, P.-C.; Jeffries, J. R.; Sayles, T. A.; Yanagisawa, T.; Yuhasz, W. M.; Chi, Songxue; Kang, H. J.; Lynn, J. W.; Dai, Pengcheng; McCall, S. K.; McElfresh, M. W.; Fluss, M. J.; Henkie, Z.; Pietraszko, A.
2006-01-01
Electrical resistivity, specific heat, and magnetization measurements to temperatures as low as 80 mK and magnetic fields up to 16 T were made on the filled skutterudite compound PrOs4As12. The measurements reveal the presence of two ordered phases at temperatures below approximately 2.3 K and in fields below approximately 3 T. Neutron-scattering experiments in zero field establish an antiferromagnetic ground state <2.28 K. In the antiferromagnetically ordered state, the electronic-specific heat coefficient γ ≈ 1 J/mol·K2 below 1.6 K and 0 ≤ H ≤ 1.25 T. The temperature and magnetic-field dependence of the electrical resistivity and specific heat in the paramagnetic state are consistent with single-ion Kondo behavior with a low Kondo temperature on the order of 1 K. The electronic-specific heat in the paramagnetic state can be described by the resonance-level model with a large zero-temperature electronic-specific heat coefficient that decreases with increasing magnetic field from approximately 1 J/mol·K2 at 3 T to approximately 0.2 J/mol·K2 at 16 T. PMID:16632603
Kondo interactions from band reconstruction in YbInCu(4).
Jarrige, I; Kotani, A; Yamaoka, H; Tsujii, N; Ishii, K; Upton, M; Casa, D; Kim, J; Gog, T; Hancock, J N
2015-03-27
We combine resonant inelastic x-ray scattering and model calculations in the Kondo lattice compound YbInCu_{4}, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. The bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasigap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system. PMID:25860761
Broken SU(4) symmetry in a Kondo-correlated carbon nanotube
NASA Astrophysics Data System (ADS)
Schmid, Daniel R.; Smirnov, Sergey; Margańska, Magdalena; Dirnaichner, Alois; Stiller, Peter L.; Grifoni, Milena; Hüttel, Andreas K.; Strunk, Christoph
2015-04-01
Understanding the interplay between many-body phenomena and nonequilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nanoelectronics. We demonstrate that the combination of Coulomb interaction, spin-orbit coupling, and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a field-theoretical Keldysh approach to the nonequilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.
Kondo interactions from band reconstruction in YbInCu4
Jarrige, I.; Kotani, A.; Yamaoka, H.; Tsujii, N.; Ishii, K.; Upton, M.; Casa, D.; Kim, J.; Gog, T.; Hancock, J. N.
2015-03-27
We combine resonant inelastic X-ray scattering (RIXS) and model calculations in the Kondo lattice compound YbInCu₄, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. In this study, the bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasi-gap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.
Kondo state for a compact Cr trimer on a metallic surface.
Kudasov, Yu B; Uzdin, V M
2002-12-30
The ground state of a Cr trimer supported on the Au(111) surface is investigated by means of a variational approach to the Coqblin-Schrieffer Hamiltonian. The temperature of Kondo-resonance formation (T(K)) for equilateral trimers increases drastically as compared to T(K) for a single Cr adatom. The Kondo state of a Cr trimer proves to be very sensitive to geometry and a small shift of any atom from the symmetrical position leads to a rapid decrease in T(K). These results are in good agreement with recent observations of the Kondo response of a single antiferromagnetic chromium trimer [T. Jamneala, Phys. Rev. Lett. 87, 256804 (2001)
Resonance behavior in the presence of space charge
Month, M.; Weng, W.T.
1983-01-01
An analysis is presented of the resonance behavior of particle beams in the presence of space charge fields. Since self-consistent requirements are ignored, the results describe onset or early behavior. It is shown that in a beam of uniform current resonances excited by magnetic field errors are stabilized by the detuning effect of the self-field space charge force. This situation is changed when a radiofrequency accelerating field is applied. As beam bunching results after rf turn-on, the space charge force becomes modulated along the bunches, vanishing at the ends. At these regions of small or vanishing space charge, stabilization from non-linear detuning tends to disappear, thus leaving particles susceptible to resonance blow-up. This picture of the effect of beam bunching can be studied by considering the phase space structure for particles at different positions along the bunches. A somewhat unusual conclusion is made on the use of this analysis to model beam capture in a synchrotron at low energy.
Spatiotemporal behavior and nonlinear dynamics in a phase conjugate resonator
NASA Technical Reports Server (NTRS)
Liu, Siuying Raymond
1993-01-01
The work described can be divided into two parts. The first part is an investigation of the transient behavior and stability property of a phase conjugate resonator (PCR) below threshold. The second part is an experimental and theoretical study of the PCR's spatiotemporal dynamics above threshold. The time-dependent coupled wave equations for four-wave mixing (FWM) in a photorefractive crystal, with two distinct interaction regions caused by feedback from an ordinary mirror, was used to model the transient dynamics of a PCR below threshold. The conditions for self-oscillation were determined and the solutions were used to define the PCR's transfer function and analyze its stability. Experimental results for the buildup and decay times confirmed qualitatively the predicted behavior. Experiments were carried out above threshold to study the spatiotemporal dynamics of the PCR as a function of Pragg detuning and the resonator's Fresnel number. The existence of optical vortices in the wavefront were identified by optical interferometry. It was possible to describe the transverse dynamics and the spatiotemporal instabilities by modeling the three-dimensional-coupled wave equations in photorefractive FWM using a truncated modal expansion approach.
Terahertz transmission and reflection studies of the topological Kondo insulator candidate SmB6
NASA Astrophysics Data System (ADS)
Morris, Christopher M.; Laurita, N. J.; Koopayeh, S.; Cottingham, P.; Phelan, W. A.; Schoop, L.; McQueen, T. M.; Armitage, N. P.
2015-03-01
The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures (T < 10 K) and high pressures. At low temperatures, a plateau is observed in the resistivity, contrary to the logarithmic divergence expected for a normal Kondo insulator. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator, a material with a Kondo insulating bulk, but topologically protected metallic surface states. Here, time domain terahertz spectroscopy (TDTS) is used to investigate the temperature dependent optical conductivity of single crystals of SmB6. A saturation of the transmission is observed associated with the resistance plateau as the bulk becomes insulating. A secondary bulk conduction mechanism remains down to the lowest measured temperature, 1.6 K. Additionally, FTIR measurements have been performed that show the Kondo gap of SmB6 opening at low temperatures. Work supported by The Institute of Quantum Matter under DOE Grant DE-FG02-08ER46544 and by the Gordon and Betty Moore Foundation.
Block entropy and quantum phase transition in the anisotropic Kondo necklace model
Mendoza-Arenas, J. J.; Franco, R.; Silva-Valencia, J.
2010-06-15
We study the von Neumann block entropy in the Kondo necklace model for different anisotropies {eta} in the XY interaction between conduction spins using the density matrix renormalization group method. It was found that the block entropy presents a maximum for each {eta} considered, and, comparing it with the results of the quantum criticality of the model based on the behavior of the energy gap, we observe that the maximum block entropy occurs at the quantum critical point between an antiferromagnetic and a Kondo singlet state, so this measure of entanglement is useful for giving information about where a quantum phase transition occurs in this model. We observe that the block entropy also presents a maximum at the quantum critical points that are obtained when an anisotropy {Delta} is included in the Kondo exchange between localized and conduction spins; when {Delta} diminishes for a fixed value of {eta}, the critical point increases, favoring the antiferromagnetic phase.
Kondo phase shift at the zero-bias anomaly of quantum point contacts
NASA Astrophysics Data System (ADS)
Brun, Boris; Martins, Frederico; Faniel, Sébastien; Hackens, Benoit; Cavanna, Antonella; Ulysse, Christian; Ouerghi, Albdelkarim; Gennser, Ulf; Mailly, Dominique; Simon, Pascal; Huant, Serge; Bayot, Vincent; Sanquer, Marc; Sellier, Hermann
The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts.
Phonon-assisted tunneling and two-channel Kondo physics in molecular junctions
Dias Da Silva, Luis G; Dagotto, Elbio R
2009-01-01
The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. We present theoretical results for a single molecule in the Kondo regime connected to left and right metallic leads, creating the usual coupling to a conduction channel with left-right parity even. A center-of-mass vibrational mode introduces an additional phonon-assisted tunneling through the antisymmetric odd channel. A non-Fermi-liquid fixed point, reminiscent of the two-channel Kondo effect, appears at a critical value of the phonon-mediated coupling strength. Our numerical renormalization-group calculations for this system reveal non-Fermi-liquid behavior at low temperatures over lines of critical points. Signatures of this strongly correlated state are prominent in the thermodynamic properties and in the linear conductance.
Can magnetic noise from Kondo traps explain high frequency flux noise in superconducting qubits?
NASA Astrophysics Data System (ADS)
Dias da Silva, Luis; de Sousa, Rogerio
2015-03-01
In solid state devices, charge and magnetic noise have common microscopic origin. Both occur due to the presence of Kondo traps nearby metallic wires. We use numerical renormalization group calculations to show that, despite their common origin, charge and magnetic noise have opposing behavior controlled by completely different energy scales. While magnetic noise follows an universal scaling with the Kondo temperature, charge noise remains well described by non-interacting theory even when the trap is deep into the Kondo regime. We show how these results may explain the high frequency (f= 1-10 GHz) Ohmic flux noise observed in SQUIDs and superconducting qubits. LGDS acknowledges support from Brazilian agencies FAPESP (2013/50220-7), CNPq (307107/2013-2) and PRP-USP NAP-QNano. RdS acknowledges support from the Canadian program NSERC-Discovery and a FAPESP-UVic exchange award.
NASA Astrophysics Data System (ADS)
Flottat, T.; Hébert, F.; Rousseau, V. G.; Scalettar, R. T.; Batrouni, G. G.
2015-07-01
We study, using quantum Monte Carlo simulations, the bosonic Kondo-Hubbard model in a two-dimensional square lattice. We explore the phase diagram and analyze the mobility of particles and magnetic properties. At unit filling, the transition from a paramagnetic Mott insulator to a ferromagnetic superfluid appears continuous, contrary to what was predicted with mean field. For double occupation per site, both the Mott insulating and superfluid phases are ferromagnetic and the transition is still continuous. Multiband tight-binding Hamiltonians can be realized in optical lattice experiments, which offer not only the possibility of tuning the different energy scales over wide ranges, but also the option of loading the system with either fermionic or bosonic atoms.
Mpemba-Like Behavior in Carbon Nanotube Resonators
NASA Astrophysics Data System (ADS)
Greaney, P. Alex; Lani, Giovanna; Cicero, Giancarlo; Grossman, Jeffrey C.
2011-12-01
Surprising Mpemba-like dissipation is observed during computer simulated ring-down of the flexural modes of a single-walled carbon nanotube resonator. Vibrations are made to decay to zero faster by adding a larger initial excitation. We liken this counterintuitive observation to the well-known Mpemba effect in which hot water freezes faster that cold water. In both cases, the system seems to pose a memory of its thermal history; a paradoxical result that is reconciled if the dissipative state of the system is not described uniquely by the system's average temperature. A vibrational mode projection algorithm is used to track the dissipation pathway, showing that dissipation is dependent strongly on the development of an athermal phonon population. The implications of Mpemba-like behavior in more general, and continuously driven, nanomechanical systems are discussed.
Ion Behavior in an Electrically Compensated Ion Cyclotron Resonance Trap
Brustkern, Adam M.; Rempel, Don L.; Gross, Michael L.
2010-01-01
We recently described a new electrically compensated trap in FT ion cyclotron resonance mass spectrometry and developed a means of tuning traps of this general design. Here, we describe a continuation of that research by comparing the ion transient lifetimes and the resulting mass resolving powers and signal-to-noise (S/N) ratios that are achievable in the compensated vs. uncompensated modes of this trap. Transient lifetimes are ten times longer under the same conditions of pressure, providing improved mass resolving power and S/N ratios. The mass resolving power as a function of m/z is linear (log-log plot) and nearly equal to the theoretical maximum. Importantly, the ion cyclotron frequency as a function of ion number decreases linearly in accord with theory, unlike its behavior in the uncompensated mode. This linearity should lead to better control in mass calibration and increased mass accuracy than achievable in the uncompensated mode. PMID:21499521
The Kondo effect in three-dimensional topological insulators
NASA Astrophysics Data System (ADS)
Xin, Xianhao; Yeh, Mao-Chuang
2013-07-01
We investigate the role of magnetic impurities in the transport properties of surface states on a three-dimensional topological insulator. First, we use second-order perturbation theory and the Boltzmann transport equation to calculate the magnetically induced resistivity in a topological insulator. Our result shows a non-perturbative behavior when conducting electrons and magnetic impurities’ spins are antiferromagnetically coupled. The surface resistivity is found to display an oscillatory rather than isotropic behavior compared to the conventional Kondo effect. Both the variational method and renormalization group (RG) analysis are employed to compute the Kondo temperature, through which the non-perturbative behavior is confirmed. We further study the RG flows and demonstrate that the RG trajectories flow into a strong coupling regime if coupling is antiferromagnetic. Our work is motivated by the recent transport experiments with surface currents on topological insulators. Our calculation is qualitatively consistent with the low temperature dip observed in the experimental R-T curve and might be one of the possible origins of the dip.
Chern Kondo Insulator in an Optical Lattice
NASA Astrophysics Data System (ADS)
Chen, Hua; Liu, Xiong-Jun; Xie, X. C.
2016-01-01
We propose to realize and observe Chern Kondo insulators in an optical superlattice with laser-assisted s and p orbital hybridization and a synthetic gauge field, which can be engineered based on the recent cold atom experiments. Considering a double-well square optical lattice, the localized s orbitals are decoupled from itinerant p bands and are driven into a Mott insulator due to the strong Hubbard interaction. Raman laser beams are then applied to induce tunnelings between s and p orbitals, and generate a staggered flux simultaneously. Because of the strong Hubbard interaction of s orbital states, we predict the existence of a critical Raman laser-assisted coupling, beyond which the Kondo screening is achieved, and then a fully gapped Chern Kondo phase emerges, with the topology characterized by integer Chern numbers. Being a strongly correlated topological state, the Chern Kondo phase is different from the single-particle quantum anomalous Hall state, and can be identified by measuring the band topology and double occupancy of s orbitals. The experimental realization and detection of the predicted Chern Kondo insulator are also proposed.
Chern Kondo Insulator in an Optical Lattice.
Chen, Hua; Liu, Xiong-Jun; Xie, X C
2016-01-29
We propose to realize and observe Chern Kondo insulators in an optical superlattice with laser-assisted s and p orbital hybridization and a synthetic gauge field, which can be engineered based on the recent cold atom experiments. Considering a double-well square optical lattice, the localized s orbitals are decoupled from itinerant p bands and are driven into a Mott insulator due to the strong Hubbard interaction. Raman laser beams are then applied to induce tunnelings between s and p orbitals, and generate a staggered flux simultaneously. Because of the strong Hubbard interaction of s orbital states, we predict the existence of a critical Raman laser-assisted coupling, beyond which the Kondo screening is achieved, and then a fully gapped Chern Kondo phase emerges, with the topology characterized by integer Chern numbers. Being a strongly correlated topological state, the Chern Kondo phase is different from the single-particle quantum anomalous Hall state, and can be identified by measuring the band topology and double occupancy of s orbitals. The experimental realization and detection of the predicted Chern Kondo insulator are also proposed. PMID:26871345
State identification and tunable Kondo effect of MnPc on Ag(001)
NASA Astrophysics Data System (ADS)
Kügel, Jens; Karolak, Michael; Krönlein, Andreas; Senkpiel, Jacob; Hsu, Pin-Jui; Sangiovanni, Giorgio; Bode, Matthias
2015-06-01
We present a detailed investigation of spectroscopic features located at the central metal ion of MnPc (where Pc represents phthalocyanine) on Ag(001) by means of scanning tunneling spectroscopy (STS) and first-principles theory. STS data taken close to the Fermi level reveal an asymmetric feature that cannot be fitted with a single Fano function representing a one-channel Kondo effect. Instead, our data indicate the existence of a second superimposed feature. Two potential physical origins, a second Kondo channel related to the dx z /y z orbitals, and a spectral feature of the dz2 orbital itself, are discussed. A systematic experimental and theoretical comparison of MnPc with CoPc and FePc indicates that the second feature observed on MnPc is caused by the dz2 orbital. This conclusion is corroborated by STM-induced dehydrogenation experiments on FePc and MnPc which in both cases result in a gradual shift towards more positive binding energies and a narrowing of the Kondo resonance. Theoretical analysis reveals that the latter is caused by the reduced hybridization between the d orbital and the substrate. Spatially resolved differential conductivity maps taken close to the respective peak positions show that the intensity of both features is highest over the central Mn ion, thereby providing further evidence against a second Kondo channel originating from the dx z /y z orbital of the central Mn ion.
The Kondo Effect and Controlled Spin Entanglement in Coupled Double-Quantum-Dots
NASA Astrophysics Data System (ADS)
Chang, Albert M.
2005-07-01
Semiconductor double-quantum dots represent an ideal system for studying the novel spin physics of localized spins. On each quantum dot when the number of electrons is odd and the net spin is 1/2, a strong coupling of this localized spin to conducting electrons in the leads gives rise to Kondo correlation. On the other hand, in the coupled double-quantum-dot if the inter-dot antiferromagnetic interaction is strong, the two spins can form a correlated spin-singlet state, quenching the Kondo effect. This competition between Kondo and antiferromagnetic correlation is studied in a controlled manner by tuning the inter-dot tunnel coupling. Increasing the inter-dot tunneling, we observe a continuous transition from a single-peaked to a double-peaked Kondo resonance in the differential conductance. On the double-peaked side, the differential conductance becomes suppressed at zero source-drain bias. The observed strong suppression of the differential conductance at zero bias provides direct evidence signaling the formation of an entangled spin-singlet state. This evidence for entanglement and the tunability of our devices bode well for quantum computation applications.
Bohm-Aharonov and Kondo effects on tunneling currents in a mesoscopic ring
Davidovich, M.A.; Anda, E.V.; Chiappe, G.
1997-03-01
We present an analysis of the Kondo effect on the Bohm-Aharonov oscillations of the tunneling currents in a mesoscopic ring with a quantum dot inserted in one of its arms. The system is described by an Anderson-impurity tight-binding Hamiltonian where the electron-electron interaction is restricted to the dot. The currents are obtained using nonequilibrium Green functions calculated through a cumulant diagrammatic expansion in the chain approximation. It is shown that at low temperature, even with the system out of resonance, the Kondo peak provides a channel for the electron to tunnel through the dot, giving rise to the Bohm-Aharonov oscillations of the current. At high temperature these oscillations are important only if the dot level is aligned to the Fermi level, when the resonance condition is satisfied. {copyright} {ital 1997} {ital The American Physical Society}
Intersite coupling effects in a Kondo lattice near an antiferromagnetic instability
NASA Astrophysics Data System (ADS)
Nakatsuji, Satoru
2003-03-01
Critcal fluctuations due to the proximity to a magnetic instability are believed to be the origin of a variety of non-Fermi-liquid behavior and unconventional superconductivity observed in heavy fermion systems. Near the quantum critical points, prominent effect of intersite coupling in Kondo lattice systems may appear. With this in mind, we studied the La dilution effects in CeCoIn_5, a heavy fermion superconductor located near an antiferromangetic instability [1,2]. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single impurity Kondo temperature TK and an intersite spin-liquid temperature T. The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with T^*. These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case. This work was supported by NSF DMR-9527035. [1] C. Petrovic ´it et al., J.Phys.: Condens. Matter ´bf 13, L337 (2001). [2] S. Nakatsuji ´it et al., Phys. Rev. Lett. 89, 106402 (2002) ^´ast Work done in collaboration with Zachary Fisk, Sunmog Yeo, Luis Balicas, Pedro Schlottmann, Pagliuso G. Pagliuso, Nelson O. Moreno, John L. Sarrao, and Joe D. Thompson
Alternative Kondo breakdown mechanism: Orbital-selective orthogonal metal transition
NASA Astrophysics Data System (ADS)
Zhong, Yin; Liu, Ke; Wang, Yong-Qiang; Luo, Hong-Gang
2012-09-01
In a recent paper of Nandkishore, Metlitski, and Senthil [Phys. Rev. B1098-012110.1103/PhysRevB.86.045128 86, 045128 (2012)], a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We extend this concept to study the corresponding quantum phase transition in the extended Anderson lattice model. It is found that the disordered state of slave spins in this model is an orbital-selective orthogonal metal, a generalization of the concept of the orthogonal metal in the Hubbard model. The quantum critical behaviors are multiscale and dominated by a z=3 and z=2 critical modes in the high- and low-temperature regime, respectively. Such behaviors are obviously in contrast to the naive expectation in the Hubbard model. The result provides alternative Kondo breakdown mechanism for heavy fermion compounds underlying the physics of the orbital-selective orthogonal metal in the disordered state, which is different from the conventional Kondo breakdown mechanism with the fractionalized Fermi-liquid picture. This work is expected to be useful in understanding the quantum criticality happening in some heavy fermion materials and other related strongly correlated systems.
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.
Kondo effect in charm and bottom nuclei
NASA Astrophysics Data System (ADS)
Yasui, Shigehiro
2016-06-01
The Kondo effect for isospin-exchange interaction between a D ¯, B meson and a valence nucleon in charm and bottom atomic nuclei including the discrete energy levels for valence nucleons is discussed. To investigate the binding energy by the Kondo effect, I introduce the mean-field approach for the bound state of the D ¯, B meson in charm and bottom nuclei. Assuming a simple model, I examine the validity of the mean-field approximation by comparing the results with the exact solutions. The effect of the quantum fluctuation is estimated beyond the mean-field approximation. The competition between the Kondo effect and the other correlations in valence nucleons, the isospin symmetry breaking and the nucleon pairings, are discussed.
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.
Global phase diagram and single particle excitations in Kondo insulators
NASA Astrophysics Data System (ADS)
Si, Qimiao; Pixley, Jedediah; Yu, Rong; Paschen, Silke
Motivated by quantum criticality in Kondo insulators tuned by pressure or doping we study the effects of magnetic frustration and the properties of the single particle excitations in a Kondo lattice model. Focusing on the Kondo insulating limit we study the Shastry-Sutherland Kondo lattice and determine the zero temperature phase diagram, which incorporates a valence bond solid, antiferromagnet, and Kondo insulating ground states, with metal-to-insulator quantum phase transitions. We argue that this phase diagram is generic and represents a ``global'' phase diagram of Kondo insulators in terms of quantum fluctuations and the Kondo interaction. We then focus on the momentum distribution of single particle excitations within the Kondo insulating ground state. We show how features of the Fermi-surface of the underlying conduction electrons appear in the Kondo insulating phase. Lastly, we discuss the implications of our results for quantum criticality in Kondo insulators as well as for the recent de Haas-von Alphen measurements in the Kondo insulator SmB6.
Effect of anisotropy in the S=1 underscreened Kondo lattice
NASA Astrophysics Data System (ADS)
Thomas, Christopher; da Rosa Simões, Acirete S.; Lacroix, Claudine; Iglesias, José Roberto; Coqblin, Bernard
2014-12-01
We study the effect of crystal field anisotropy in the underscreened S=1 Kondo lattice model. Starting from the two orbital Anderson lattice model and including a local anisotropy term, we show, through Schrieffer-Wolff transformation, that local anisotropy is equivalent to an anisotropic Kondo interaction (J∥≠J⊥). The competition and coexistence between ferromagnetism and Kondo effect in this effective model is studied within a generalized mean-field approximation. Several regimes are obtained, depending on the parameters, exhibiting or not coexistence of magnetic order and Kondo effect. Particularly, we show that a re-entrant Kondo phase at low temperature can be obtained. We are also able to describe phases where the Kondo temperature is smaller than the Curie temperature (TK
The physics of Kondo impurities in graphene
NASA Astrophysics Data System (ADS)
Fritz, Lars; Vojta, Matthias
2013-03-01
This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids.
The physics of Kondo impurities in graphene.
Fritz, Lars; Vojta, Matthias
2013-03-01
This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. PMID:23411583
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.
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Lee, Ting-Kuo; Mou, Chung-Yu
The energy gap in Dirac materials controls the topology and critical behaviors of the quantum phase transition associated with the critical point when the gap vanishes. However, it is often difficult to access the critical point as it requires tunablity of electronic structures. Here by exploiting the many-body screening interaction of localized spins and conduction electrons in a Kondo lattice, we demonstrate that the electronic band structures in a Kondo lattice are tunable in temperature. When spin-orbit interactions are included, we find that below the Kondo temperature, the Kondo lattice is a strong topological insulator at low temperature and undergoes a topological transition to a weak topological insulator at a higher temperature TD. At TD, Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our results indicate that the topological phase transition though a Dirac semi-metallic phase at finite temperatures also manifests profound physics and results in critical-like behavior both in magnetic and transport properties near TD. We acknowledge support from NCTS and Ministry of Science and Technology (MoST), Taiwan.
Transport across two interacting quantum dots: bulk Kondo, Kondo box and molecular regimes
NASA Astrophysics Data System (ADS)
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2014-03-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N non-interacting sites connecting both of them. The inter-dot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of small number of sites, so that Kondo box effects are present. For odd N and small coupling between the inter-dot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dots spins by the spin in the finite chain. As the coupling to the inter-dot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule spin by the leads. For even N the two-Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism. We finally study how the transport properties are affected as N is increased. We used exact multi-configurational Lanczos calculations and finite U slave-boson mean-field theory. The results obtained with both methods describe qualitatively and also quantitatively the same physics.
Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes
NASA Astrophysics Data System (ADS)
Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique
2015-03-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We acknowledge financial support from the Brazilian agencies FAPERJ and CNPq.
Transport across two interacting quantum dots: Bulk Kondo, Kondo box, and molecular regimes
NASA Astrophysics Data System (ADS)
Ribeiro, L. C.; Hamad, I. J.; Chiappe, G.; Anda, E. V.
2014-01-01
We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We finally study how the transport properties are affected as N is increased. For the study we used exact multiconfigurational Lanczos calculations and finite-U slave-boson mean-field theory at T =0. The results obtained with both methods describe qualitatively and also quantitatively the same physics.
Terahertz transmission studies of the topological Kondo insulator candidate SmB6
NASA Astrophysics Data System (ADS)
Laurita, Nicholas J.; Morris, Christopher M.; Koopayeh, Seyed; Cottingham, Patrick; Phelan, W. Adam; Schoop, Leslie; McQueen, Tyrel M.; Armitage, N. Peter
2014-03-01
The Kondo insulator SmB6 has long been known to display anomalous transport behavior at low temperatures (T < 10 K) and high pressures. At low temperatures, a plateau is observed in the resistivity, contrary to the divergence expected for a normal Kondo insulator. Recent theoretical calculations suggest that SmB6 may be the first topological Kondo insulator, a material with a Kondo insulating bulk, but topologically protected metallic surface states. Here, time domain terahertz spectroscopy (TDTS) is used to investigate the temperature dependent low frequency optical conductivity of single crystals of SmB6. We find evidence for a substantial bulk conductivity at a frequency of a few hundred GHz, which challenges the notion of this material as having a clean gap. The evidence for topological surface states and their properties will be discussed. Work supported by The Institute of Quantum Matter under DOE grant DE-FG02-08ER46544 and by the Gordon and Betty Moore Foundation through Grant GBMF2628.
Holographic optical traps for atom-based topological Kondo devices
NASA Astrophysics Data System (ADS)
Buccheri, F.; Bruce, G. D.; Trombettoni, A.; Cassettari, D.; Babujian, H.; Korepin, V. E.; Sodano, P.
2016-07-01
The topological Kondo (TK) model has been proposed in solid-state quantum devices as a way to realize non-Fermi liquid behaviors in a controllable setting. Another motivation behind the TK model proposal is the demand to demonstrate the quantum dynamical properties of Majorana fermions, which are at the heart of their potential use in topological quantum computation. Here we consider a junction of crossed Tonks–Girardeau gases arranged in a star-geometry (forming a Y-junction), and we perform a theoretical analysis of this system showing that it provides a physical realization of the TK model in the realm of cold atom systems. Using computer-generated holography, we experimentally implement a Y-junction suitable for atom trapping, with controllable and independent parameters. The junction and the transverse size of the atom waveguides are of the order of 5 μm, leading to favorable estimates for the Kondo temperature and for the coupling across the junction. Since our results show that all the required theoretical and experimental ingredients are available, this provides the demonstration of an ultracold atom device that may in principle exhibit the TK effect.
Spin fluctations and heavy fermions in the Kondo lattice
Khaliullin, G.G.
1994-09-01
This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodic lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.
Local moment formation and Kondo screening in impurity trimers.
Mitchell, Andrew K; Jarrold, Thomas F; Galpin, Martin R; Logan, David E
2013-10-24
We study theoretically a triangular cluster of three magnetic impurities, hybridizing locally with conduction electrons of a metallic host. Such a cluster is the simplest to exhibit frustration, an important generic feature of many complex molecular systems in which different interactions compete. Here, low-energy doublet states of the trimer are favored by effective exchange interactions produced by strong electronic repulsion in localized impurity orbitals. Parity symmetry protects a level crossing of such states on tuning microscopic parameters, while an avoided crossing arises in the general distorted case. Upon coupling to a metallic host, the behavior is shown to be immensely rich because collective quantum many-body effects now also compete. In particular, impurity degrees of freedom are totally screened at low temperatures in a Kondo-screened Fermi liquid phase, while degenerate ground states persist in a local moment phase. Local frustration drives the quantum phase transition between the two, which may be first order or of Kosterlitz-Thouless type, depending on symmetries. Unusual mechanisms for local moment formation and Kondo screening are found due to the orbital structure of the impurity trimer. Our results are of relevance for triple quantum dot devices. The problem is studied by a combination of analytical arguments and the numerical renormalization group. PMID:23527540
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).
Sarkar, T. P.; Gopinadhan, K.; Motapothula, M.; Saha, S.; Huang, Z.; Dhar, S.; Patra, A.; Lu, W. M.; Telesio, F.; Pallecchi, I.; Ariando; Marré, D.; Venkatesan, T.
2015-01-01
We report the observation of spatially separated Kondo scattering and ferromagnetism in anatase Ta0.06Ti0.94O2 thin films as a function of thickness (10–200 nm). The Kondo behavior observed in thicker films is suppressed on decreasing thickness and vanishes below ~25 nm. In 200 nm film, transport data could be fitted to a renormalization group theory for Kondo scattering though the carrier density in this system is lower by two orders of magnitude, the magnetic entity concentration is larger by a similar magnitude and there is strong electronic correlation compared to a conventional system such as Cu with magnetic impurities. However, ferromagnetism is observed at all thicknesses with magnetic moment per unit thickness decreasing beyond 10 nm film thickness. The simultaneous presence of Kondo and ferromagnetism is explained by the spatial variation of defects from the interface to surface which results in a dominantly ferromagnetic region closer to substrate-film interface while the Kondo scattering is dominant near the surface and decreasing towards the interface. This material system enables us to study the effect of neighboring presence of two competing magnetic phenomena and the possibility for tuning them. PMID:26265554
NASA Astrophysics Data System (ADS)
Sundar, Bhuvanesh; Mueller, Erich
2015-05-01
We propose an experimental protocol to directly observe the Kondo effect by scattering ultracold atoms with spin-dependent interactions. The Kondo effect is a transport anomaly which occurs when conduction electrons interact with magnetic impurities. We consider an ultracold system consisting of a gas of fermionic 6Li atoms and a gas of bosonic 87Rb atoms, where 6Li atoms play the role of conduction electrons and 87Rb atoms play the role of magnetic impurities. We propose a method to engineer Kondo-like interactions between them. To measure the Kondo effect, we imagine launching the 87Rb gas into the 6Li gas, and calculate the momentum transferred to the 6Li gas. We show that the temperature dependence of this momentum is logarithmic at low temperatures and has a minimum, characteristic of the Kondo effect and analogous to the behavior of electrical resistance of magnetic alloys. Experimental implementation of our proposal will give a new perspective on an iconic problem.
Buildup of the Kondo effect from real-time effective action for the Anderson impurity model
NASA Astrophysics Data System (ADS)
Bock, Sebastian; Liluashvili, Alexander; Gasenzer, Thomas
2016-07-01
The nonequilibrium time evolution of a quantum dot is studied by means of dynamic equations for time-dependent Green's functions derived from a two-particle-irreducible (2PI) effective action for the Anderson impurity model. Coupling the dot between two leads at different voltages, the dynamics of the current through the dot is investigated. We show that the 2PI approach is capable of describing the dynamical buildup of the Kondo effect, which shows up as a sharp resonance in the spectral function, with a width exponentially suppressed in the electron self-coupling on the dot. An external voltage applied to the dot is found to deteriorate the Kondo effect at the hybridization scale. The dynamic equations are evaluated within different nonperturbative resummation schemes, within the direct, particle-particle, and particle-hole channels, as well as their combination, and the results compared with those from other methods.
Interplay between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction
NASA Astrophysics Data System (ADS)
Prüser, Henning; Dargel, Piet E.; Bouhassoune, Mohammed; Ulbrich, Rainer G.; Pruschke, Thomas; Lounis, Samir; Wenderoth, Martin
2014-11-01
The interplay between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect is expected to provide the driving force for the emergence of many phenomena in strongly correlated electron materials. Two magnetic impurities in a metal are the smallest possible system containing all these ingredients and define a bottom-up approach towards a long-term understanding of concentrated/dense systems. Here we report on the experimental and theoretical investigation of iron dimers buried below a Cu(100) surface by means of low-temperature scanning tunnelling spectroscopy combined with density functional theory and numerical renormalization group calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl resonance, is strongly altered or even suppressed due to magnetic coupling between the impurities. It oscillates as a function of dimer separation revealing that it is related to indirect exchange interactions mediated by the conduction electrons.
Linear and nonlinear behavior of crystalline optical whispering gallery mode resonators
NASA Technical Reports Server (NTRS)
Savchenkov, Anatoliy A.; Matsko, Andrey B.; Ilchenko, Vladimir S.; Maleki, Lute
2004-01-01
We demonstrate strong nonlinear behavior of high-Q whispering gallery mode (WGM) resonators made out of various crystals adn devices based on the resonators. The maximum WGM optical Q-fact or achieved at room temperature exceeds 2X10 to the tenth power.
Pressure effects on the optical conductivity of Kondo insulators
Zhang, Sun
2001-06-01
The effects of pressure on the optical conductivity of Kondo insulators are studied in the framework of the slave-boson mean-field theory under the coherent potential approximation. A unified picture is presented for both the hole-type Kondo insulators [H. Okamura , Phys. Rev. B >58, R7496 (1998)] and the electron-type Kondo insulators [B. Bucher , Phys. Rev. Lett. >72, 522 (1994)]. The density of states of f electrons under the applied pressure and its variation with the concentration of the impurity doping are calculated self-consistently. The Kondo temperature and the optical conductivity are obtained, in agreement with the experiments qualitatively. The two contrasting pressure-dependent effects for the hole-type Kondo insulators and the electron-type Kondo insulators are also given as predictions for further observations.
The Helmholtz resonance behavior of single and multiple rooms
NASA Technical Reports Server (NTRS)
Hubbard, H. H.; Shepherd, K. P.
1986-01-01
The results of exploratory measurements of the noise fields inside rooms which are excited to resonance either acoustically or mechanically are presented. The data illustrate the nature and extent of the sound pressure level enhancements in single rooms and also how multiple rooms may resonate by means of either acoustic or mechanical coupling. Sound pressure level enhancements of about 5 dB were measured during resonance of rooms having flexible walls. For such conditions the sound pressure levels in the room were essentially uniform and in phase. Variability of up to 20 dB was measured in a room hallway complex having significant acoustic interactions. Resonant frequency prediction methods which work well at model scale, give only fair results for rooms.
Kondo effect in the presence of van Hove singularities: A numerical renormalization group study
NASA Astrophysics Data System (ADS)
Zhuravlev, A. K.; Irkhin, V. Yu.
2011-12-01
A numerical renormalization-group investigation of the one-center t-t' Kondo problem is performed for the square lattice accounting for logarithmic Van Hove singularities (VHS) in the electron density of states near the Fermi level. The magnetic susceptibility, entropy, and specific heat are calculated. The temperature dependencies of the thermodynamic properties in the presence of VHS turn out to be nontrivial. When the distance Δ between VHS and the Fermi level decreases, the inverse logarithm of the corresponding Kondo temperature TK demonstrates a crossover from the standard linear to square-root dependence on the s-d exchange coupling. The low-temperature behavior of the magnetic susceptibility and specific heat are investigated, and the Wilson ratio is obtained. For Δ→0 the Fermi-liquid behavior is broken.
Dynamical symmetries in Kondo tunneling through complex quantum dots.
Kuzmenko, T; Kikoin, K; Avishai, Y
2002-10-01
Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4). PMID:12366008
Charge Kondo effect in a triple quantum dot
NASA Astrophysics Data System (ADS)
Yoo, Gwangsu; Park, Jinhong; Lee, S. S.-B.; Sim, H.-S.
2014-03-01
We predict that the charge Kondo effect appears in a triangular triple quantum dot. The system has two-fold degenerate ground-state charge configurations, interdot Coulomb interactions, lead-dot electron tunnelings, but no interdot electron tunneling. We show, using bosonization and refermionization, that the system is described by the anisotropic Kondo model. The anisotropy can be tuned by changing lead-dot electron tunneling strength, which allows one to experimentally explore the transition between the ferromagnetic non-Fermi liquid and antiferromagnetic Kondo phases in the Kondo phase diagram. Using numerical renormalization group method, we demonstrate that the transition is manifested in electron conductances through the dot.
Kondo Effect in a Triple Quantum-Dot Array
NASA Astrophysics Data System (ADS)
Oguri, Akira; Nisikawa, Yunori; Hewson, A. C.
2006-09-01
We study the ground-state properties of a triple quantum dot based on a three-site Hubbard model connected to two non-interacting leads. Using the numerical renormalization group (NRG), the many-body phase shifts and dc conductance are calculated away from half-filling as a function of the onsite energy ɛd, which corresponds to the gate voltage. The results for conductance g show the typical Kondo plateaus of the Unitary limit g ≈ 2e2/h at some finite ranges of the gate-voltage corresponding to odd Nel (≈ 1, 3 and 5), where Nel is the total number of electrons in the triple dot. The conductance shows broad minima for even Nel(≈ 2 and 4). The local charge Nel shows a staircase behavior as a function of ɛd.
Interpreting the behavior of a quarter-wave transmission line resonator in a magnetized plasma
NASA Astrophysics Data System (ADS)
Gogna, G. S.; Karkari, S. K.; Turner, M. M.
2014-12-01
The quarter wave resonator immersed in a strongly magnetized plasma displays two possible resonances occurring either below or above its resonance frequency in vacuum, fo. This fact was demonstrated in our recent articles [G. S. Gogna and S. K. Karkari, Appl. Phys. Lett. 96, 151503 (2010); S. K. Karkari, G. S. Gogna, D. Boilson, M. M. Turner, and A. Simonin, Contrib. Plasma Phys. 50(9), 903 (2010)], where the experiments were carried out over a limited range of magnetic fields at a constant electron density, ne. In this paper, we present the observation of dual resonances occurring over the frequency scan and find that ne calculated by considering the lower resonance frequency is 25%-30% smaller than that calculated using the upper resonance frequency with respect to fo. At a given magnetic field strength, the resonances tend to shift away from fo as the background density is increased. The lower resonance tends to saturate when its value approaches electron cyclotron frequency, fce. Interpretation of these resonance conditions are revisited by examining the behavior of the resonance frequency response as a function of ne. A qualitative discussion is presented which highlights the practical application of the hairpin resonator for interpreting ne in a strongly magnetized plasma.
Interpreting the behavior of a quarter-wave transmission line resonator in a magnetized plasma
Gogna, G. S. Turner, M. M.; Karkari, S. K.
2014-12-15
The quarter wave resonator immersed in a strongly magnetized plasma displays two possible resonances occurring either below or above its resonance frequency in vacuum, f{sub o}. This fact was demonstrated in our recent articles [G. S. Gogna and S. K. Karkari, Appl. Phys. Lett. 96, 151503 (2010); S. K. Karkari, G. S. Gogna, D. Boilson, M. M. Turner, and A. Simonin, Contrib. Plasma Phys. 50(9), 903 (2010)], where the experiments were carried out over a limited range of magnetic fields at a constant electron density, n{sub e}. In this paper, we present the observation of dual resonances occurring over the frequency scan and find that n{sub e} calculated by considering the lower resonance frequency is 25%–30% smaller than that calculated using the upper resonance frequency with respect to f{sub o}. At a given magnetic field strength, the resonances tend to shift away from f{sub o} as the background density is increased. The lower resonance tends to saturate when its value approaches electron cyclotron frequency, f{sub ce}. Interpretation of these resonance conditions are revisited by examining the behavior of the resonance frequency response as a function of n{sub e}. A qualitative discussion is presented which highlights the practical application of the hairpin resonator for interpreting n{sub e} in a strongly magnetized plasma.
Resonance behavior of internal conversion coefficients at low γ-ray energy
NASA Astrophysics Data System (ADS)
Trzhaskovskaya, M. B.; Kibédi, T.; Nikulin, V. K.
2010-02-01
A resonance-like structure of internal conversion coefficients (ICCs) at low γ-ray energy (≲100 keV) is studied. Our calculations revealed new, previously unknown resonance minima in the energy dependence of ICCs for the ns shells at E2-E5 transitions. The resonances are the most defined for ICCs in light and medium elements with Z≲ 50. It is shown that ICCs may have up to four resonances for outer shells while it has been assumed so far that only one resonance exists. Well-pronounced resonances in ICCs at E1 transition were discovered for the ns shells with n⩾2 as well as for the np shells with n⩾3 and the nd shells with n⩾4 of all elements up to superheavy ones. Simple expressions for approximate values of the E1 resonance energy were obtained which are of importance for determination of the resonance energy range where the interpolation of ICCs taken from tables or databases may give significant errors. The occurrence of resonances in ICCs is explained by vanishing conversion matrix elements under changes of sign. The peculiarities of the behavior of the matrix elements and electron wave functions at the resonance energy are considered. Available experimental ICCs for electric transitions with energies near the expected position of resonances satisfactory agree with our calculations.
Kondo effect and STM spectroscopy of Dirac electrons in graphene
NASA Astrophysics Data System (ADS)
Sengupta, Krishnendu
2011-03-01
We show that graphene, whose low-energy quasiparticles display Dirac like behavior, may exhibit a two-channel Kondo effect in the presence of magnetic impurities. We present a large N analysis for a generic spin S local moment coupled to Dirac electrons in graphene and demonstrate that the corresponding Kondo temperature can be tuned by an experimentally controllable applied gate voltage. We also study the STM spectra of these Dirac electrons in the presence of such impurities and demonstrate that such spectra depend qualitatively on the position of the impurity atom in the graphene matrix. More specifically, for impurity atoms atop the hexagon center, the zero-bias tunneling conductance, as measured by a STM, shows a peak; for those atop a graphene site, it shows a dip. We provide a qualitative theoretical explanation of this phenomenon and show that this unconventional behavior is a consequence of conservation/breaking of pseudospin symmetry of the Dirac quasiparticles by the impurity. We also predict that tuning the Fermi energy to zero by a gate voltage would not lead to qualitative change in the shape of the conductance spectra when the impurity is atop the hexagon center. A similar tuning of the Fermi energy for the impurity atop a site, however, would lead to a change in the tunneling conductance from a dip to a peak via an antiresonance. We discuss some recent experiments on a doped graphene sample that seem to have qualitative agreement with our theory and suggest further experiments to test our predictions. DST, India.
Antiferromagnetic phases of the Kondo lattice
NASA Astrophysics Data System (ADS)
Eder, R.; Grube, K.; Wróbel, P.
2016-04-01
We discuss the paramagnetic and Néel-ordered phases of the Kondo lattice Hamiltonian on the two-dimensional square lattice by means of bond fermions. In the doped case we find two antiferromagnetic solutions, the first one with small ordered moment, heavy bands, and an antiferromagnetically folded large Fermi surface—i.e., including the localized spins—the second one with large ordered moment, light bands, and an antiferromagnetically folded conduction electron-only Fermi surface. The zero temperature phase diagram as a function of Kondo coupling and conduction electron density shows first- and second-order transition lines between the three different phases and agrees qualitatively with previous numerical studies. We compare to experiments on CeRh1 -xCoxIn5 and find qualitative agreement.
Scattering Theory of Kondo Mirages and Observation of Single Kondo Atom Phase Shift*
NASA Astrophysics Data System (ADS)
Fiete, Gregory A.; Hersch, Jesse S.; Heller, Eric J.; Manoharan, H. C.; Lutz, C. P.; Eigler, D. M.
2001-03-01
We explain the origin of the Kondo mirage seen in recent quantum corral Scanning Tunneling Microscope (STM) experiments with a scattering theory of electrons on the surfaces of metals. Our theory combined with experimental data provides the first direct observation of a single Kondo atom phase shift. The Kondo mirage observed at the empty focus of an elliptical quantum corral is shown to arise from multiple electron bounces off the corral wall adatoms in a manner analagous to the formation of a real image in optics. We demonstrate our theory with direct quantitive comparision to experimental data. *This research was supported by the National Science Foundation under Grant No. CHE9610501 and by ITAMP.
Orbital signatures of Fano-Kondo line shapes in STM adatom spectroscopy
NASA Astrophysics Data System (ADS)
Frank, Sebastian; Jacob, David
2015-12-01
We investigate the orbital origin of the Fano-Kondo line shapes measured in STM spectroscopy of magnetic adatoms on metal substrates. To this end we calculate the low-bias tunnel spectra of a Co adatom on the (001) and (111) Cu surfaces with our density functional theory-based ab initio transport scheme augmented by local correlations. In order to associate different d orbitals with different Fano line shapes we only correlate individual 3 d orbitals instead of the full Co 3 d shell. We find that Kondo peaks arising in different d levels indeed give rise to different Fano features in the conductance spectra. Hence, the shape of measured Fano features allows us to draw some conclusions about the orbital responsible for the Kondo resonance, although the actual shape is also influenced by temperature, effective interaction, and charge fluctuations. Comparison with a simplified model shows that line shapes are mostly the result of interference between tunneling paths through the correlated d orbital and the s p -type orbitals on the Co atom. Very importantly, the amplitudes of the Fano features vary strongly among orbitals, with the 3 z2 orbital featuring by far the largest amplitude due to its strong direct coupling to the s -type conduction electrons.
Robust topological surface state in Kondo insulator SmB{sub 6} thin films
Yong, Jie Jiang, Yeping; Zhang, Xiaohang; Greene, Richard L.; Usanmaz, Demet; Curtarolo, Stefano; Li, Linze; Pan, Xiaoqing; Shin, Jongmoon; Takeuchi, Ichiro
2014-12-01
Fabrication of smooth thin films of topological insulators with true insulating bulk are extremely important for utilizing their novel properties in quantum and spintronic devices. Here, we report the growth of crystalline thin films of SmB{sub 6}, a topological Kondo insulator with true insulating bulk, by co-sputtering both SmB{sub 6} and B targets. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicate films that are polycrystalline with a (001) preferred orientation. When cooling down, resistivity ρ shows an increase around 50 K and saturation below 10 K, consistent with the opening of the hybridization gap and surface dominated transport, respectively. The ratio ρ{sub 2K}/ρ{sub 300K} is only about two, much smaller than that of bulk, which indicates a much larger surface-to-bulk ratio. Point contact spectroscopy using a superconductor tip on SmB{sub 6} films shows both a Kondo Fano resonance and Andeev reflection, indicating an insulating Kondo lattice with metallic surface states.
Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model
Joyce, J.J.; Arko, A.J.; Andrews, A.B.
1993-09-01
The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.
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.
Field-Controlled Spin and Charge Distributions in Kondo System with a Triangular Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Koga, Mikito; Matsumoto, Masashige; Kusunose, Hiroaki
2013-09-01
The Kondo effect plays an important role in the emergence of electric polarization in a triangular triple-quantum-dot system, where one of the three dots is connected to a metallic lead through a point contact. The interplay between spin and charge distributions is investigated on the basis of an impurity Anderson model where the impurity-site cluster is described by a three-site Hubbard model. The numerical renormalization group analysis demonstrates that an applied magnetic field suppresses the Kondo effect and that the three-site spin correlations lead to an abrupt change in the local electric and magnetic polarizations. The controllability of this multiferroic behavior on the nanoscale is also discussed.
Anisotropic charge Kondo effect in a triple quantum dot.
Yoo, Gwangsu; Park, Jinhong; Lee, S-S B; Sim, H-S
2014-12-01
We predict that an anisotropic charge Kondo effect appears in a triple quantum dot, when the system has twofold degenerate ground states of (1,1,0) and (0,0,1) charge configurations. Using bosonization and refermionization methods, we find that at low temperature the system has the two different phases of massive charge fluctuations between the two charge configurations and vanishing fluctuations, which are equivalent with the Kondo-screened and ferromagnetic phases of the anisotropic Kondo model, respectively. The phase transition is identifiable by electron conductance measurement, offering the possibility of experimentally exploring the anisotropic Kondo model. Our charge Kondo effect has a similar origin to that in a negative-U Anderson impurity. PMID:25526143
Anisotropic Charge Kondo Effect in a Triple Quantum Dot
NASA Astrophysics Data System (ADS)
Yoo, Gwangsu; Park, Jinhong; Lee, S.-S. B.; Sim, H.-S.
2014-12-01
We predict that an anisotropic charge Kondo effect appears in a triple quantum dot, when the system has twofold degenerate ground states of (1,1,0) and (0,0,1) charge configurations. Using bosonization and refermionization methods, we find that at low temperature the system has the two different phases of massive charge fluctuations between the two charge configurations and vanishing fluctuations, which are equivalent with the Kondo-screened and ferromagnetic phases of the anisotropic Kondo model, respectively. The phase transition is identifiable by electron conductance measurement, offering the possibility of experimentally exploring the anisotropic Kondo model. Our charge Kondo effect has a similar origin to that in a negative-U Anderson impurity.
Magnetic frustration in itinerant systems: the Kondo polaron problem
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Batista, Cristian; Vekhter, Ilya
2013-03-01
We study the interplay between magnetic frustration and Kondo screening in Kondo lattices by analyzing the J1-J2 antiferromagnetic chain coupled to a conduction band. The system is tuned to the Majumdar-Ghosh point J2 =J1 / 2 which stabilizes a dimer valence-bond solid at weak Kondo coupling JK. We use an effective low-energy theory to demonstrate that sufficiently large JK results in a proliferation of ``Kondo polarons'', i.e. Kondo-screened domain-wall excitations of the dimer state, and collapse of the dimer order via a 2nd order quantum phase transition. At the quantum critical point, JK =JKc , these polarons become gapless, and we argue that the transition itself belongs to a 2D Ising universality class. For JK >JKc increasing concentration of the polarons leads to a continuous growth of the electron Fermi momentum until all spins are absorbed by the Fermi sea.
Calculation of the quasi-energies and resonances behavior of the hydrogen Lyman-alpha problem
NASA Technical Reports Server (NTRS)
Ruyten, Wilhelmus M.
1992-01-01
Recently, Bakshi and Kalman presented numerical results for the quasi-energies of the n = 2 multiplet in the hydrogen Lyman-alpha transition for a plasma in which both strong static and oscillating electric fields are present. Recent work on related magnetic and optical resonance problems provides a simplified mathematical treatment, as well as greater insight into the complex resonance behavior of this interaction.
NASA Astrophysics Data System (ADS)
Nan Yang, Shin; Kiswandhi, Alvin; Xie, Ju-Jun
2011-10-01
We study whether the nonmonotonic behavior found in the differential cross section of the φ-meson photoproduction near threshold can be described by a resonance. The resonant contribution is evaluated by using an effective Lagrangian approach. We find that, with the assumption of a JP = 3/2- resonance with mass of 2.10±0.03 GeV and width of 0.465±0.141 GeV, LEPS data can indeed be well described. The ratio of the helicity amplitudes A1/2/A3/2 calculated from the re-22 sulting coupling constants differs in sign from that of the known D13(2080). We further find that the addition of this postulated resonance can substantially improve the agreement between the existing theoretical predictions and the recent ω photoproduction data if a large value of the OZI evading parameter xOZI = 12 is assumed for the resonance.
Collapse Dynamics and Resonance Behavior of Axisymmetric Slender Liquid Bridges
NASA Astrophysics Data System (ADS)
Tsige, Mesfin; Alexander, J. I. D.; Rosenblatt, C.; Taylor, P. L.
2001-03-01
The evolution of axisymetric liquid bridges subjected to static and oscillatory forces have been studied numerically. When the liquid bridge is subject to constant axial gravity, the collapse time is found to be largely independent of the length of the bridge when other parameters are held constant. For the case of dynamic oscillations and a given forcing amplitude, the frequency of the first resonance peak is found to be maximum when the static body force is zero and decreases with increasing total body force or length of the bridge.
NASA Astrophysics Data System (ADS)
Yang, Bo; Zhang, Xiao; Zhang, Lu; Luo, Mao-Kang
2016-08-01
The long-time collective behavior of globally coupled Langevin equations in a dichotomous fluctuating potential driven by a periodic source is investigated. By describing the collective behavior using the moments of the mean field and single-particle displacements, we study stochastic resonance and synchronization using the exact steady-state solutions and related stability criteria. Based on the simulation results and the criterion of the stationary regime, the notable differences between the stationary and nonstationary regimes are demonstrated. For the stationary regime, stochastic resonance with synchronization is discussed, and for the nonstationary regime, the volatility clustering phenomenon is observed.
Kondo interactions from band reconstruction in ${\mathrm{YbInCu}}_{4}$
Jarrige, I.; Kotani, A.; Yamaoka, H.; Tsujii, N.; Ishii, K.; Upton, M.; Casa, D.; Kim, J.; Gog, T.; Hancock, J. N.
2015-03-27
We combine resonant inelastic X-ray scattering (RIXS) and model calculations in the Kondo lattice compound YbInCu₄, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T≃42 K. In this study, the bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasi-gap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.
Microwave memristive behavior in split-ring resonator metamaterials
NASA Astrophysics Data System (ADS)
Wu, H. Y.; Shi, S. K.; Wang, C. H.; Jiang, X. J.; Yu, G.; Qin, G. Q.; Fu, H.; Zhou, J.
2016-07-01
Photonic memristors, which behave as memristors operating with electromagnetic fields, present an effective means to achieve all-optical networking, and can promote the development of optical communications and computer technology. In this paper, we report a microwave memristive phenomenon at room temperature in metamaterials consisting of negative temperature coefficient thermistor ceramic disk and split-ring resonator (SRR). Hysteretic transmission-incident field power loops, the area of which varies with the scan rate of power, (similar to the fingerprint of memristors) were observed in the metamaterials. These effects are attributed to the increasing conductivity of the ceramic disk with increasing temperature generated by the interaction between electromagnetic waves and metamaterials. This work offers new opportunities for the development of photonic memristors.
Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB6
NASA Astrophysics Data System (ADS)
Butch, Nicholas P.; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A.; Booth, Corwin H.; Jeffries, Jason R.
2016-04-01
Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f -electron occupancy in the Kondo insulator SmB6 . Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.
Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB_{6}.
Butch, Nicholas P; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A; Booth, Corwin H; Jeffries, Jason R
2016-04-15
Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB_{6}. Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure. PMID:27127976
Two-channel Kondo effect and phonon-assisted transport in single-molecular junctions
NASA Astrophysics Data System (ADS)
Dias da Silva, Luis; Dagotto, Elbio
2009-03-01
The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. In this theoretical work, we study such interplay in a system consisting of a single molecule in a metallic break junction tuned (by gate voltages) to be in an ``odd-N'' coulomb blockade valley (Kondo-prone). The connection to left and right metallic leads creates the usual coupling to a conduction channel with left-right symmetry (the ``even"-parity channel). A center-of-mass vibrational mode introduces an additional, phonon-assisted tunneling through the asymmetric (``odd''-parity channel). Our numerical renormalization-group calculations reveal that the phonon-mediated coupling to the odd channel leads to the appearance of a two-channel Kondo (2chK) effect, characterized by a non-Fermi-liquid (NFL) fixed point. The ground-state has NFL properties for a critical value of the phonon-mediated coupling strength and critical lines are present for wide range of parameters, including the regime away from particle-hole symmetry. Signatures of this 2chK non-Fermi-liquid behavior are prominent in the thermodynamic properties as well as in the linear conductance.
Interplay between Kondo screening and local singlets in SU (N) -symmetric cold atoms
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Rey, Ana Maria
2015-03-01
We study collective phenomena in strongly interacting fermionic alkaline-earth atoms (AEAs) loaded in an optical lattice. Owing to the strong decoupling between electronic orbital and nuclear-spin degrees of freedom, AEAs prepared in the two lowest electronic states are predicted to obey an accurate SU (N > 2 I + 1) symmetry in their two-body collisions (I is the nuclear spin). The SU (N) symmetric models offer a great opportunity to generate exotic many-body behavior emerging from the increased degeneracy and strict conservation laws. We focus on a parameter regime that realizes an SU (N > 2) (Coqblin-Schrieffer) generalization of the usual Kondo lattice model, and show that for band fillings above one atom per site, the system exhibits a peculiar interplay between Kondo screening and formation of singlets between localized atoms. In the limit of large Kondo coupling, we derive an effective Hamiltonian and determine its phase diagram. Our results can be tested in experiments with ultracold 173 Yb or 87 Sr atoms and are relevant for the physics of heavy-fermion materials with magnetic frustration. Supported by AFOSR, MURI-AFOSR and NSF.
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.
Integrable Two-Impurity Kondo Model
Schlottmann, P.
1998-06-01
The exact solution by means of Bethe{close_quote}s {ital Ansatz} of a variant of the two-impurity Kondo problem is presented. The occupation of the singlet and triplet states, the expectation value {l_angle}{rvec S}{sub 1}{center_dot} {cflx S}{sub 2}{r_angle} , the homogeneous and staggered magnetic field susceptibilities, and the specific heat {gamma} coefficient are studied for the ground state as a function of the Ruderman-Kittel-Kasuya-Yosida{endash}coupling strength. {copyright} {ital 1998} {ital The American Physical Society}
Numerical analysis of the spatial range of the Kondo effect
Busser, C. A.; Martins, G. B.; Ribeiro, L. Costa; Vernek, E.; Anda, E. V.; Dagotto, Elbio R
2010-01-01
The spatial length of the Kondo screening is still a controversial issue related to Kondo physics. While renormalization-group and Bethe-Ansatz solutions have provided detailed information about the thermodynamics of magnetic impurities, they are insufficient to study the effect on the surrounding electrons, i.e., the spatial range of the correlations created by the Kondo effect between the localized magnetic moment and the conduction electrons. The objective of this work is to present a quantitative way of measuring the extension of these correlations by studying their effect directly on the local density of states (LDOS) at arbitrary distances from the impurity. The numerical techniques used, the embedded cluster approximation, the finite-U slave bosons, and numerical renormalization group, calculate the Green s functions in real space. With this information, one can calculate how the local density of states away from the impurity is modified by its presence, below and above the Kondo temperature, and then estimate the range of the disturbances in the noninteracting Fermi sea due to the Kondo effect, and how it changes with the Kondo temperature TK. The results obtained agree with results obtained through spin-spin correlations, showing that the LDOS captures the phenomenology of the Kondo cloud as well.
Self-other resonance, its control and prosocial inclinations: Brain-behavior relationships.
Christov-Moore, Leonardo; Iacoboni, Marco
2016-04-01
Humans seem to place a positive reward value on prosocial behavior. Evidence suggests that this prosocial inclination is driven by our reflexive tendency to share in the observed sensations, emotions and behavior of others, or "self-other resonance". In this study, we examine how neural correlates of self-other resonance relate to prosocial decision-making. Subjects performed two tasks while undergoing fMRI: observation of a human hand pierced by a needle, and observation and imitation of emotional facial expressions. Outside the scanner, subjects played the Dictator Game with players of low or high income (represented by neutral-expression headshots). Subjects' offers in the Dictator Game were correlated with activity in neural systems associated with self-other resonance and anticorrelated with activity in systems implicated in the control of pain, affect, and imitation. Functional connectivity between areas involved in self-other resonance and top-down control was negatively correlated with subjects' offers. This study suggests that the interaction between self-other resonance and top-down control processes are an important component of prosocial inclinations towards others, even when biological stimuli associated with self-other resonance are limited. These findings support a view of prosocial decision-making grounded in embodied cognition. PMID:26954937
NASA Astrophysics Data System (ADS)
Hayashi, Yuya; Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Ochiai, Akira
2016-03-01
We have measured the electrical resistivity of cerium monochalcogenides, CeS, CeSe, and CeTe, under high pressures of up to 8 GPa. The pressure dependences of the antiferromagnetic ordering temperature TN, crystal field splitting, and the ln T anomaly of the Kondo effect have been studied to cover the entire region from the magnetic ordering regime at low pressure to the Fermi liquid regime at high pressure. TN initially increases with increasing pressure, and starts to decrease at high pressure as expected from Doniach’s diagram. Simultaneously, the ln T behavior in the resistivity is enhanced, indicating the enhancement of the Kondo effect by pressure. It is also characteristic of CeXc that the crystal field splitting rapidly decreases at a common rate of -12.2 K/GPa. This leads to the increase in the degeneracy of the f state and the further enhancement of the Kondo effect. It is shown that the pressure-dependent degeneracy of the f state is a key factor for understanding the pressure dependence of TN, the Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.
Modulating resonance behaviors by noise recycling in bistable systems with time delay
Sun, Zhongkui Xu, Wei; Yang, Xiaoli; Xiao, Yuzhu
2014-06-01
In this paper, the impact of noise recycling on resonance behaviors is studied theoretically and numerically in a prototypical bistable system with delayed feedback. According to the interior cooperating and interacting activity of noise recycling, a theory has been proposed by reducing the non-Markovian problem into a two-state model, wherein both the master equation and the transition rates depend on not only the current state but also the earlier two states due to the recycling lag and the feedback delay. By virtue of this theory, the formulae of the power spectrum density and the linear response function have been found analytically. And the theoretical results are well verified by numerical simulations. It has been demonstrated that both the recycling lag and the feedback delay play a crucial role in the resonance behaviors. In addition, the results also suggest an alternative scheme to modulate or control the coherence or stochastic resonance in bistable systems with time delay.
Resonant-state expansions and the long-time behavior of quantum decay
Garcia-Calderon, Gaston; Maldonado, Irene; Villavicencio, Jorge
2007-07-15
It is shown that a representation of the decaying wave function as a resonant sum plus a nonexponential integral term may be written as a purely discrete resonant sum by evaluating at long times the integral term by the steepest descents method, and then expanding the resulting expression in terms of resonant states. This leads to a representation that is valid along the exponential and the inverse power in time regimes. A model calculation using the {delta} potential allows us to make a comparison of the expansion with numerical integrations in terms of continuum wave functions and, in the long time regime, with an exact analytic expression of the integral term obtained using the steepest descents method. The results demonstrate that resonant states give a correct description of the long-time behavior of decay.
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.
Spin dynamics and Kondo physics in optical tweezers
NASA Astrophysics Data System (ADS)
Lin, Yiheng; Lester, Brian J.; Brown, Mark O.; Kaufman, Adam M.; Long, Junling; Ball, Randall J.; Isaev, Leonid; Wall, Michael L.; Rey, Ana Maria; Regal, Cindy A.
2016-05-01
We propose to use optical tweezers as a toolset for direct observation of the interplay between quantum statistics, kinetic energy and interactions, and thus implement minimum instances of the Kondo lattice model in systems with few bosonic rubidium atoms. By taking advantage of strong local exchange interactions, our ability to tune the spin-dependent potential shifts between the two wells and complete control over spin and motional degrees of freedom, we design an adiabatic tunneling scheme that efficiently creates a spin-singlet state in one well starting from two initially separated atoms (one atom per tweezer) in opposite spin state. For three atoms in a double-well, two localized in the lowest vibrational mode of each tweezer and one atom in an excited delocalized state, we plan to use similar techniques and observe resonant transfer of two-atom singlet-triplet states between the wells in the regime when the exchange coupling exceeds the mobile atom hopping. Moreover, we argue that such three-atom double-tweezers could potentially be used for quantum computation by encoding logical qubits in collective spin and motional degrees of freedom. Current address: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Fano-Andreev effect in Quantum Dots in Kondo regime
NASA Astrophysics Data System (ADS)
Orellana, Pedro; Calle, Ana Maria; Pacheco, Monica; Apel, Victor
In the present work, we investigate the transport through a T-shaped double quantum dot system coupled to two normal leads and to a superconducting lead. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot and by means of a slave boson mean field approximation at low temperature regime. We inquire into the influence of intradot interactions in the electronic properties of the system as well. Our results show that Fano resonances due to Andreev bound states are exhibited in the transmission from normal to normal lead as a consequence of quantum interference and proximity effect. This Fano effect produced by Andreev bound states in a side quantum dot was called Fano-Andreev effect, which remains valid even if the electron-electron interaction are taken into account, that is, the Fano-Andreev effect is robust against e-e interactions even in Kondo regime. We acknowledge the financial support from FONDECYT program Grants No. 3140053 and 11400571.
NASA Astrophysics Data System (ADS)
Santos, J. T.; Holz, T.; Fernandes, A. J. S.; Costa, F. M.; Chu, V.; Conde, J. P.
2015-02-01
Diamond-based microelectromechanical resonators have the potential of enhanced performance due to the chemical inertness of the diamond structural layer and its high Young’s modulus, high wear resistance, low thermal expansion coefficient, and very high thermal conductivity. In this work, the resonance frequency and quality factor of MEMS resonators based on nanocrystalline diamond films are characterized under different air pressures. The dynamic behavior of 50-300 μm long linear bridges and double ended tuning forks, with resonance frequencies between 0.5 and 15 MHz and quality factors as high as 50 000 are described as a function of measurement pressure from high vacuum(~10 mTorr) up to atmospheric conditions. The resonance frequencies and quality factors in vacuum show good agreement with the theoretical models including anchor and thermoelastic dissipation (TED). The Young’s moduli for nanocrystalline diamond films extrapolated from experimental data are between 840-920 GPa. The critical pressure values, at which the quality factor starts decreasing due to dissipation in air, are dependent on the resonator length. Longer structures, with quality factors limited by TED and lower resonance frequencies, have low critical pressures, of the order of 1-10 Torr and go from an intrinsic dissipation, to a molecular dissipation regime and finally to a region of viscous dissipation. Shorter resonators, with higher resonance frequencies and quality factors limited by anchor losses, have higher critical pressures, some higher than atmospheric pressure, and enter directly into the viscous dissipation regime from the intrinsic region.
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.
MEAN MOTION RESONANCES IN EXOPLANET SYSTEMS: AN INVESTIGATION INTO NODDING BEHAVIOR
Ketchum, Jacob A.; Adams, Fred C.; Bloch, Anthony M.
2013-01-10
Motivated by the large number of extrasolar planetary systems that are near mean motion resonances, this paper explores a related type of dynamical behavior known as 'nodding'. Here, the resonance angle of a planetary system executes libration (oscillatory motion) for several cycles, circulates for one or more cycles, and then enters once again into libration. This type of complicated dynamics can affect our interpretation of observed planetary systems that are in or near mean motion resonance. This work shows that planetary systems in (near) mean motion resonance can exhibit nodding behavior, and outlines the portion of parameter space where it occurs. This problem is addressed using both full numerical integrations of the planetary systems and via model equations obtained through expansions of the disturbing function. In the latter approach, we identify the relevant terms that allow for nodding. The two approaches are in agreement, and show that nodding often occurs when a small body is in an external mean motion resonance with a larger planet. As a result, the nodding phenomenon can be important for interpreting observations of transit timing variations, where the existence of smaller bodies is inferred through their effects on larger, observed transiting planets. For example, in actively nodding planetary systems, both the amplitude and frequency of the transit timing variations depend on the observational time window.
NASA Astrophysics Data System (ADS)
Zhang, Xiang-Hua; Wang, Ling-Ling; Li, Xiao-Fei; Chen, Tong; Li, Quan
2015-09-01
Carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) are attractive in spintronics. Here, we propose GNR/CNT/GNR heterojunctions constructed by attaching zigzag-GNRs at the side-wall of CNT for spintronic devices. The thermal stability and electronic transport properties were explored using ab initio molecular dynamics simulations and nonequilibrium Green's function methods, respectively. Results demonstrate that the sp3-hybridized contacts formed at the interface assure a good thermal stability of the system and make the CNT to be regarded as resonator. Only the electron of one spin-orientation and resonant energy is allowed to transport, resulting in the remarkable spin-selective transport behavior at the ferromagnetic state.
Magnetic-field-tunable Kondo effect in alkaline-earth cold atoms
NASA Astrophysics Data System (ADS)
Isaev, Leonid; Rey, Ana Maria
We study quantum magnetism and emergent Kondo physics in strongly interacting fermionic alkaline-earth atoms in an optical lattice with two Bloch bands: one localized and one itinerant. For a fully filled narrow band (two atoms per lattice site) we demonstrate that an applied magnetic field provides an efficient control of the ground state degeneracy due to the field-induced crossing of singlet and triplet state of the localized atomic pairs. We exploit this singlet-triplet resonance, as well as magnetically tunable interactions of atoms in different electronic states via the recently-discovered inter-orbital Feshbach resonance, and demonstrate that the system exhibits a magnetic field-induced Kondo phase characterized by delocalization of local singlets and a large Fermi surface. We also determine the phase diagram of the system within an effective low-energy model that incorporates the above magnetic-field effect as well as atomic interactions in the two optical lattice bands. Our results can be tested with ultracold 173 Yb , and provide a model for the magnetic field-induced heavy-fermion state in filled skutterudites such as PrOs4Sb12 . This work was supported by the NSF (PIF-1211914 and PFC-1125844), AFOSR, AFOSR-MURI, NIST and ARO individual investigator awards.
Visualizing the formation of the Kondo lattice and the hidden order in URu2Si2
Aynajian, Pegor; da Silva Neto, Eduardo H.; Parker, Colin V.; Huang, Yingkai; Pasupathy, Abhay; Mydosh, John; Yazdani, Ali
2010-01-01
Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope to examine the novel electronic states that emerge from the uranium f states in URu2Si2. We find that, as the temperature is lowered, partial screening of the f electrons’ spins gives rise to a spatially modulated Kondo–Fano resonance that is maximal between the surface U atoms. At T = 17.5 K, URu2Si2 is known to undergo a second-order phase transition from the Kondo lattice state into a phase with a hidden order parameter. From tunneling spectroscopy, we identify a spatially modulated, bias-asymmetric energy gap with a mean-field temperature dependence that develops in the hidden order state. Spectroscopic imaging further reveals a spatial correlation between the hidden order gap and the Kondo resonance, suggesting that the two phenomena involve the same electronic states. PMID:20498090
Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite
Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao
2015-01-01
The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108 Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108 Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913
Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite.
Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao
2015-01-01
The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 10(8) Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 10(8) Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913
A universal scaling behavior in magnetic resonance peak in high temperature superconductivity
NASA Astrophysics Data System (ADS)
Shin, Seung Joon; Salk, Sung-Ho Suck
2015-08-01
Eminent inelastic neutron scattering (INS) measurements of high temperature cuprates currently lacking theoretical interpretations are the observed temperature dependence of magnetic resonance peak and linear scaling relation between the resonance peak energy, Eres and the superconducting transition temperature, Tc. Using our slave-boson approach of the t-J Hamiltonian (Phys. Rev. 64, 052501 (2001)) for this study, we show that starting from the pseudogap temperature T∗, the magnetic resonance peak increases with decreasing temperature, revealing its inflection point at Tc and that spin pairing correlations are responsible for d-wave superconductivity. We find that there exists a universal linear scaling behavior of Eres/Tc = const., irrespective of the Heisenberg exchange coupling.
Qubit-induced phonon blockade as a signature of quantum behavior in nanomechanical resonators
Liu Yuxi; Miranowicz, Adam; Gao, Y. B.; Bajer, Jiri; Sun, C. P.; Nori, Franco
2010-09-15
The observation of quantized nanomechanical oscillations by detecting femtometer-scale displacements is a significant challenge for experimentalists. We propose that a phonon blockade can serve as a signature of quantum behavior in nanomechanical resonators. In analogy to the photon blockade and Coulomb blockade for electrons, the main idea for phonon blockade is that the second phonon cannot be excited when there is one phonon in the nonlinear oscillator. To realize phonon blockade, a superconducting quantum two-level system is coupled to the nanomechanical resonator and is used to induce the phonon self-interaction. Using Monte Carlo simulations, the dynamics of the induced nonlinear oscillator is studied via the Cahill-Glauber s-parametrized quasiprobability distributions. We show how the oscillation of the resonator can occur in the quantum regime and demonstrate how the phonon blockade can be observed with the currently accessible experimental parameters.
{ital Ab Initio} Calculation of Crystalline Electric Fields and Kondo Temperatures in Ce Compounds
Han, J.; Alouani, M.; Cox, D.; Han, J.; Cox, D.; Alouani, M.
1997-02-01
We have calculated the band-f hybridizations for Ce{sub x}La{sub 1-x}M{sub 3} compounds (x=1 and x{r_arrow}0; M=Pb,In,Sn,Pd) within the local density approximation and fed this into a noncrossing approximation for the Anderson impurity model applied to both dilute and concentrated limits. Our calculations produce crystalline electric field splittings and Kondo temperatures with trends in good agreement with experiment and demonstrate the need for detailed electronic structure information on hybridization to describe the diverse behaviors of these Ce compounds. {copyright} {ital 1997} {ital The American Physical Society}
On the dynamics of bistable micro/nano resonators: Analytical solution and nonlinear behavior
NASA Astrophysics Data System (ADS)
Tajaddodianfar, Farid; Nejat Pishkenari, Hossein; Hairi Yazdi, Mohammad Reza; Maani Miandoab, Ehsan
2015-03-01
With the rapid development of micro/nano-electro-mechanical systems (MEMS/NEMS), arch shaped resonators are becoming increasingly attractive for different applications. Nevertheless, the dynamics of bistable resonators is poorly understood, and the conditions for their appropriate performance are not well known. In this paper, an initially curved arch shaped MEMS resonator under combined DC and AC distributed electrostatic actuation is investigated. A reduced order model obtained from first mode Galerkin's decomposition method is used for numerical and analytical investigations. We have used the Homotopy Analysis Method (HAM) in order to derive analytical solutions both for the amplitude and the temporal average of nonlinear vibrations. The obtained analytical expressions, validated by numerical simulations, are able to capture nonlinear behaviors including softening type vibrations and dynamic snap-through. We have used the derived analytical results in order to study the nonlinear vibrations of the bistable MEMS resonator. According to our results, in the bistability region the overall dynamic response of the system is described by means of a pair of softening type frequency responses merging together in a specific frequency band. The dynamic snap-through is then described by transitions between these two frequency responses, each of which corresponding to one of the stable configurations of the arch. This fresh insight to the problem can be used in the design and optimization of bistable resonators and determination of their sharp roll-off frequencies. A feature that can be implemented in the design of bandpass filters.
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
Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB_{6}
Fuhrman, W. T.; Leiner, Jonathan C.; Nikolić, P.; Granroth, Garrett E.; Stone, Matthew B.; Lumsden, Mark D.; DeBeer-Schmitt, Lisa M.; Alekseev, Pavel A.; Mignot, Jean-Michel; Koohpayeh, S. M.; Cottingham, P.; Phelan, William Adam; Schoop, L.; McQueen, T. M.; Broholm, C.
2015-01-21
In this paper, using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB_{6} and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering. Finally, we find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.
Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6
Fuhrman, W. T.; Leiner, Jonathan C.; Nikolić, P.; Granroth, Garrett E.; Stone, Matthew B.; Lumsden, Mark D.; DeBeer-Schmitt, Lisa M.; Alekseev, Pavel A.; Mignot, Jean-Michel; Koohpayeh, S. M.; et al
2015-01-21
In this paper, using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB6 and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering.more » Finally, we find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.« less
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.
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
Vernek, E.; Büsser, C. A.; Anda, E. V.; Feiguin, A. E.; Martins, G. B.
2014-03-31
A double quantum dot device, connected to two channels that only interact through interdot Coulomb repulsion, is analyzed using the numerical renormalization group technique. Using a two-impurity Anderson model, and realistic parameter values [S. Amasha, A. J. Keller, I. G. Rau, A. Carmi, J. A. Katine, H. Shtrikman, Y. Oreg, and D. Goldhaber-Gordon, Phys. Rev. Lett. 110, 046604 (2013)], it is shown that, by applying a moderate magnetic field and independently adjusting the gate potential of each quantum dot at half-filling, a spin-orbital SU(2) Kondo state can be achieved where the Kondo resonance originates from spatially separated parts of the device. Our results clearly link this spatial separation effect to currents with opposing spin polarizations in each channel, i.e., the device acts as a spin filter. In addition, an experimental probe of this polarization effect is suggested, pointing to the exciting possibility of experimentally probing the internal structure of an SU(2) Kondo state.
Quantum entanglement in the two-impurity Kondo model
Cho, Sam Young; McKenzie, Ross H.
2006-01-15
In order to quantify quantum entanglement in two-impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, namely the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, I. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two-impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created [and quantum information processing (QIP) will only be possible] if the RKKY interaction exchange energy, I, is at least several times larger than the Kondo temperature, T{sub K}. Quantitative criteria for QIP are given in terms of the impurity spin-spin correlation.
Haldane phase in one-dimensional topological Kondo insulators
NASA Astrophysics Data System (ADS)
Mezio, Alejandro; Lobos, Alejandro M.; Dobry, Ariel O.; Gazza, Claudio J.
2015-11-01
We investigate the ground-state properties of a recently proposed model for a topological Kondo insulator in one dimension (i.e., the p -wave Kondo-Heisenberg lattice model) by means of the density-matrix renormalization-group method. The nonstandard Kondo interaction in this model is different from the usual (i.e., local) Kondo interaction in that the localized spins couple to the "p -wave" spin density of conduction electrons, inducing a topologically nontrivial insulating ground state. Based on the analysis of the charge- and spin-excitation gaps, the string order parameter, and the spin profile in the ground state, we show that, at half filling and low energies, the system is in the Haldane phase and hosts topologically protected spin-1/2 end states. Beyond its intrinsic interest as a useful "toy model" to understand the effects of strong correlations on topological insulators, we show that the p -wave Kondo-Heisenberg model could be experimentally implemented in p -band optical lattices loaded with ultracold Fermi gases.
On the Resonance-Like Behavior in the pp Scattering Amplitudes
NASA Astrophysics Data System (ADS)
Otofuji, T.; Sakai, K.; Kanada, H.; Saito, S.; Yasuno, M.
1985-03-01
The series of ``dibaryons'' is investigated in detail by means of a coupled-channel model of the NN, N Delta and Delta Delta channels. The π and rho meson exchange potential is employed with cutoff form factors and inner hard core. It is shown that the model reproduces the series of the ``dibaryons'' of the natural-parity states; that is the resonance-like behavior (RLB) in the 1D2, 3F3, 1G4, (3H5) and 1I6 states. The masses and widths of these ``resonances'' agree well with those given by Auer et al. A detailed study shows that the RLB is mainly due to the coupling with the N Delta aligned states (NDAS) (L=J-2 and S=2), and that the NDAS give rise to a spectrum of rotational-like structure. It is suggested that aligned states (SAS) of L=J and S=2 bring about resonance-like behavior for the even-parity states in the higher energy region.
Gomez Sal, J.C.; Garcia Soldevilla, J.; Blanco, J.A.; Espeso, J.I.; Rodriguez Fernandez, J.; Luis, F.; Bartolome, F.; Bartolome, J.
1997-11-01
The low-temperature magnetic and transport properties of the orthorhombic CeNi{sub 0.4}Cu{sub 0.6} compound have been determined from the analysis of specific heat, ac magnetic susceptibility, electrical resistivity, elastic and inelastic neutron scattering. These measurements present intriguing experimental results that could not be explained within the usual phenomenology of Ce-based compounds. C{sub p} and {chi}{sub ac} present anomalies around 1 K corresponding to ferromagnetic order as confirmed by neutron diffraction. The magnetic structure is collinear with very reduced moments, 0.6{mu}{sub B}/Ce lying in the b direction. Additionally, a clear Kondo behavior is observed with a Kondo temperature T{sub K}=1.9K estimated from quasielastic neutron scattering. Above the ordering temperature, further anomalies are observed in C{sub p} and {chi}{sub ac} that could not be explained as originating from crystal electric field or Kondo effects. From the frequency and field dependence of the {chi}{sub ac}, above T{sub c}, a spin-glass state with a freezing temperature T{sub f}=2K is proposed for this compound. This unusual magnetic behavior is discussed in terms of mixed (positive and negative) Ruderman-Kittel-Kasuya-Yosida interactions, randomness (structural disorder), large hybridization (Kondo effect), and strong magnetocrystalline anisotropy (crystal electric field effects). {copyright} {ital 1997} {ital The American Physical Society}
Trichotomous Noise Induced Resonance Behavior for a Fractional Oscillator with Random Mass
NASA Astrophysics Data System (ADS)
Zhong, Suchuan; Wei, Kun; Gao, Shilong; Ma, Hong
2015-04-01
We investigate the stochastic resonance (SR) phenomenon in a fractional oscillator with random mass under the external periodic force. The fluctuations of the mass are modeled as a trichotomous noise. Applying the Shapiro-Loginov formula and the Laplace transform technique, we obtain the exact expression of the first moment of the system. The non-monotonic behaviors of the spectral amplification (SPA) versus the driving frequency indicate that the bona fide SR appears. The necessary and sufficient conditions for the emergence of the generalized stochastic resonance phenomena on the noise flatness and on the noise intensity in the particular case of are established. Particularly, the hypersensitive response of the SPA to the noise intensity is found, which is previously reported and believed to be absent in the case of dichotomous noise.
Evolution of the Kondo effect in a quantum dot probed by shot noise.
Yamauchi, Yoshiaki; Sekiguchi, Koji; Chida, Kensaku; Arakawa, Tomonori; Nakamura, Shuji; Kobayashi, Kensuke; Ono, Teruo; Fujii, Tatsuya; Sakano, Rui
2011-04-29
We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2. PMID:21635054
Cotunneling into a Kondo lattice with odd hybridization
NASA Astrophysics Data System (ADS)
Baruselli, Pier Paolo; Vojta, Matthias
2016-06-01
Cotunneling into Kondo systems, where an electron enters an f -electron material via a cotunneling process through the local-moment orbital, has been proposed to explain the characteristic line shapes observed in scanning-tunneling-spectroscopy (STS) experiments. Here we extend the theory of electron cotunneling to Kondo-lattice systems in which the bulk hybridization between conduction and f electrons is odd under inversion, being particularly relevant to Kondo insulators. Compared to the case of even hybridization, we show that the interference between normal tunneling and cotunneling processes is fundamentally altered: it is entirely absent for layered, i.e., quasi-two-dimensional materials, while its energy dependence is strongly modified for three-dimensional materials. We discuss implications for STS experiments.
Scanning Tunneling Electron Transport into a Kondo Lattice
NASA Astrophysics Data System (ADS)
Yang, Fu-Bin; Wu, Hua
2016-05-01
We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice. We calculate the density of states (DOS) and the tunneling current and differential conductance (DC) under different conduction-fermion band hybridization and temperature in the Kondo lattice. It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy. The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice. Supported by the National Natural Science Foundation of China under Grant No. 11547203, and the Research Project of Education Department in Sichuan Province of China under Grant No. 15ZB0457
NASA Astrophysics Data System (ADS)
Perozzi, E.; Murdin, P.
2000-11-01
A resonance in CELESTIAL MECHANICS occurs when some of the quantities characterizing the motion of two or more celestial bodies can be considered as commensurable, i.e. their ratio is close to an integer fraction. In a simplified form, this can be expressed as ...
The entanglement structure of the Kondo singlet in energy space
NASA Astrophysics Data System (ADS)
Yang, Chun; Feiguin, Adrian
We unveil the entanglement structure of the Kondo singlet in energy space by studying the contribution of each individual free electron eigenstate. This is a problem of two spins coupled to a bath, where the bath is formed by the remaining conduction electrons. Being a mixed state, we resort to the ''concurrence'' as a good measure of entanglement. Using the density matrix renormalization group and analytical variational calculations with the Yoshida wave-function, and slave bosons, we find a distinct transition between weak and strong coupling regimes characterized by very different entanglement distributions. We discuss implications to the theory of the Kondo cloud.
Robust Josephson-Kondo screening cloud in circuit quantum electrodynamics
NASA Astrophysics Data System (ADS)
Snyman, Izak; Florens, Serge
2015-08-01
We investigate the entanglement properties of a standard circuit-QED setup that consists of a Cooper pair box coupled to a long chain of Josephson junctions. We calculate the static charge polarization at finite distances along the device. Our calculations reveal a deep connection to the Kondo screening cloud, together with robust correlations that are difficult to measure in a condensed matter context. We also find weak sensitivity of these Kondo signatures to the actual parameters and design of the device, demonstrating the universality of the Josephson entanglement cloud.
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.
Observation of Strong Resonant Behavior in the Inverse Photoelectron Spectroscopy of Ce Oxide
Tobin, J G; Yu, S W; Chung, B W; Waddill, G D; Damian, E; Duda, L; Nordgren, J
2009-12-15
X-ray Emission Spectroscopy (XES) and Resonant Inverse Photoelectron Spectroscopy (RIPES) have been used to investigate the photon emission associated with the Ce3d5/2 and Ce3d3/2 thresholds. Strong resonant behavior has been observed in the RIPES of Ce Oxide near the 5/2 and 3/2 edges. Inverse Photoelectron Spectroscopy (IPES) and its high energy variant, Bremstrahlung Isochromat Spectroscopy (BIS), are powerful techniques that permit a direct interrogation of the low-lying unoccupied electronic structure of a variety of materials. Despite being handicapped by counting rates that are approximately four orders of magnitude less that the corresponding electron spectroscopies (Photoelectron Spectroscopy, PES, and X-ray Photoelectron Spectroscopy, XPS) both IPES and BIS have a long history of important contributions. Over time, an additional variant of this technique has appeared, where the kinetic energy (KE) of the incoming electron and photon energy (hv) of the emitted electron are roughly the same magnitude as the binding energy of a core level of the material in question. Under these circumstances and in analogy to Resonant Photoelectron Spectroscopy, a cross section resonance can occur, giving rise to Resonant Inverse Photoelectron Spectroscopy or RIPES. Here, we report the observation of RIPES in an f electron system, specifically the at the 3d{sub 5/2} and 3d{sub 3/2} thresholds of Ce Oxide. The resonant behavior of the Ce4f structure at the 3d thresholds has been addressed before, including studies of the utilization of the technique as a probe of electron correlation in a variety of Ce compounds. Interestingly, the first RIPES work on rare earths dates back to 1974, although under conditions which left the state of the surface and near surface regions undefined. Although they did not use the more modern terminology of 'RIPES,' it is clear that RIPES was actually first performed in 1974 by Liefeld, Burr and Chamberlain on both La and Ce based materials. In
NASA Astrophysics Data System (ADS)
Pillet, J.-D.; Joyez, P.; Žitko, Rok; Goffman, M. F.
2013-07-01
We performed tunneling spectroscopy of a carbon nanotube quantum dot (QD) coupled to a metallic reservoir either in the normal or in the superconducting state. We explore how the Kondo resonance, observed when the QD's occupancy is odd and the reservoir is normal, evolves towards Andreev bound states (ABS) in the superconducting state. Within this regime, the ABS spectrum observed is consistent with a quantum phase transition from a singlet to a degenerate magnetic doublet ground state, in quantitative agreement with a single-level Anderson model with superconducting leads.
NASA Astrophysics Data System (ADS)
Maurand, Romain; Meng, Tobias; Bonet, Edgar; Florens, Serge; Marty, Laëtitia; Wernsdorfer, Wolfgang
2012-01-01
We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic) dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.
Constructive influence of the induced electron pairing on the Kondo state
Domański, T.; Weymann, I.; Barańska, M.; Górski, G.
2016-01-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681
Constructive influence of the induced electron pairing on the Kondo state
NASA Astrophysics Data System (ADS)
Domański, T.; Weymann, I.; Barańska, M.; Górski, G.
2016-03-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon.
Constructive influence of the induced electron pairing on the Kondo state.
Domański, T; Weymann, I; Barańska, M; Górski, G
2016-01-01
Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681
NASA Astrophysics Data System (ADS)
Xu, N.; Shi, X.; Biswas, P. K.; Matt, C. E.; Dhaka, R. S.; Huang, Y.; Plumb, N. C.; Radović, M.; Dil, J. H.; Pomjakushina, E.; Conder, K.; Amato, A.; Salman, Z.; Paul, D. McK.; Mesot, J.; Ding, H.; Shi, M.
2013-09-01
Recent theoretical calculations and experimental results suggest that the strongly correlated material SmB6 may be a realization of a topological Kondo insulator. We have performed an angle-resolved photoemission spectroscopy study on SmB6 in order to elucidate elements of the electronic structure relevant to the possible occurrence of a topological Kondo insulator state. The obtained electronic structure in the whole three-dimensional momentum space reveals one electron-like 5d bulk band centered at the X point of the bulk Brillouin zone that is hybridized with strongly correlated f electrons, as well as the opening of a Kondo band gap (ΔB ˜ 20 meV) at low temperature. In addition, we observe electron-like bands forming three Fermi surfaces at the center Γ¯ point and boundary X¯ point of the surface Brillouin zone. These bands are not expected from calculations of the bulk electronic structure, and their observed dispersion characteristics are consistent with surface states. Our results suggest that the unusual low-temperature transport behavior of SmB6 is likely to be related to the pronounced surface states sitting inside the band hybridization gap and/or the presence of a topological Kondo insulating state.
Photoemission spectroscopy and X-ray diffraction analysis of 3D topological and Kondo insulators
NASA Astrophysics Data System (ADS)
Shibayev, Pavel
2015-03-01
The advantage of studying 3D topological insulators (TIs), compounds that have attracted the attention of many in the condensed matter field, is the ability for their existence at room temperature and no magnetic fields, allowing both for resolving their band structure via angle-resolved photoemission spectroscopy (ARPES) and understanding electrical transport and other properties via X-ray diffraction (XRD) and point-contact spectroscopy (PCS). A comprehensive quantitative analysis of Bi2Se3, a 3D TI, was carried out using these methods. The Bi2Se3\\ crystals were synthesized in-house at Princeton University. A first-principles calculation based on density functional theory, DFT, was performed using the Abinit software. The band structure of the crystal was then resolved via ARPES at the Advanced Light Source in LBNL, resulting in a surprisingly stark and clear single Dirac cone. A large band gap was confirmed, suggesting an increased potential for applications. In contrast, Kondo insulators are found in rare-earth based materials with f-electron degrees of freedom. Photon energy dependent dispersion relationships and temperature dependence studies were performed on a Kondo candidate CeB6 via ARPES, showing an even number of Dirac cones and a non-TI behavior. Analysis of I-V characteristics through PCS will follow, in addition to characterization via Bruker XRD for both compounds. Research group led by Professor M. Zahid Hasan (Princeton University).
Critical-field theory of the Kondo lattice model in two dimensions
Kim, Ki-Seok
2005-05-15
In the context of the U(1) slave-boson theory we derive a critical-field theory near the quantum-critical point of the Kondo lattice model in two spatial dimensions. First, we argue that strong gauge fluctuations in the U(1) slave-boson theory give rise to confinement between spinons and holons, thus causing 'neutralized' spinons in association with the slave-boson U(1) gauge field. Second, we show that critical fluctuations of Kondo singlets near the quantum-critical point result in a new U(1) gauge field. This emergent gauge field has nothing to do with the slave-boson U(1) gauge field. Third, we find that the slave-boson U(1) gauge field can be exactly integrated out in the low-energy limit. As a result we find a critical-field theory in terms of renormalized conduction electrons and neutralized spinons interacting via the new emergent U(1) gauge field. Based on this critical-field theory we obtain the temperature dependence of the specific heat and the imaginary part of the self-energy of the renormalized electrons. These quantities display non-Fermi-liquid behavior near the quantum-critical point.
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.
Magnetic structure of the Kondo lattice compound CeZn0.6Sb2
NASA Astrophysics Data System (ADS)
Chen, Y.; Lynn, J. W.; Lee, H.; Klavins, P.; Fisk, Z.; Nakatsuji, S.; Bao, W.; Thompson, J.; Park, T.; Macaluso, R.; Chan, J.; Carter, B.
2006-03-01
The new Kondo lattice compound CeZn0.6Sb2 has a tetragonal structure with space group P4/nmm and shows ferromagnetic behavior below 2.5 K. The Curie-Weiss temperature is 22 K along the tetragonal ab plane, indicating ferromagnetic interactions in the plane. Along the c axis, however, the Curie-Weiss temperature is -145 K, suggesting antiferromagnetic exchange interaction in this direction [1]. We determined the magnetic structure of CeZn0.6Sb2 using single crystal neutron diffraction. (h,0,l) and (h,h,l) scattering planes were investigated. We found CeZn0.6Sb2 orders ferromagnetically at TC=2.5 K. The magnetic structure is collinear with a low temperature ordered Ce moment of 1.3 (1) μB that lies in the ab plane. In addition, we measured the order parameter of the ferromagnetic transition. [1] Studies of the ferromagnetic Kondo lattice system of single crystal CeZnSb2, H. Lee, S. Nakatsuji, Y. Chen, W. Bao, R. Macaluso, J. Chan, T. Park, B. Carter, P. Klavins, J. Thompson, Z. Fisk, BAPS, Session L41, 2005.
Kondo effect in a topological insulator quantum dot
NASA Astrophysics Data System (ADS)
Xin, Xianhao; Zhou, Di
2015-04-01
We investigate theoretically the nonequilibrium transport properties of a topological insulator quantum dot (TIQD) in the Coulomb blockade and Kondo regime. An Anderson impurity model is applied to a TIQD system coupled to two external leads, and we show that the model realizes the spin-orbital Kondo effect at the Dirac point where the edge states are not split by a finite-size effect, leading to an additional S U (4 ) symmetry because of the presence of strong mixture among four internal degrees of freedom. In a more realistic situation where the degeneracy is lifted due to the finite-size effect, we demonstrate that there is a richer structure in transport measurements. We illustrate a continuous crossover from four (spin and orbital) Coulomb peaks with large interpair spacing and small intrapair spacing to a double-peak structure in the local density of states (LDOS) as increasing the hybridization strength Γ within the Coulomb blockade regime. When temperature falls below the Kondo temperature TK, four Kondo peaks show up in the nonequilibrium LDOS. Two of them are located at the chemical potential of each lead, and the other two are shifted away from the chemical potential by an amount proportional to the TIQD's bare energy level, leading to a triple-peak structure in the differential conductance when a bias voltage is applied.
Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12.
Hagiwara, Kenta; Ohtsubo, Yoshiyuki; Matsunami, Masaharu; Ideta, Shin-Ichiro; Tanaka, Kiyohisa; Miyazaki, Hidetoshi; Rault, Julien E; Fèvre, Patrick Le; Bertran, François; Taleb-Ibrahimi, Amina; Yukawa, Ryu; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Sumida, Kazuki; Okuda, Taichi; Iga, Fumitoshi; Kimura, Shin-Ichi
2016-01-01
A synergistic effect between strong electron correlation and spin-orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). One TKI candidate has been experimentally observed on the KI SmB6(001), and the origin of the surface states (SS) and the topological order of SmB6 has been actively discussed. Here, we show a metallic SS on the clean surface of another TKI candidate YbB12(001) using angle-resolved photoelectron spectroscopy. The SS shows temperature-dependent reconstruction corresponding to the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c-f hybridization is metallic, forming a closed Fermi contour surrounding on the surface Brillouin zone and agreeing with the theoretically expected behaviour for SS on TKIs. These results demonstrate the temperature-dependent holistic reconstruction of two-dimensional states localized on KIs surface driven by the Kondo effect. PMID:27576449
NASA Astrophysics Data System (ADS)
Si, Qimiao; Goswami, Pallab
2014-03-01
Heavy fermion systems represent a prototypical setting to study magnetic quantum phase transitions. In this context, we study the spin one-half Kondo-Heisenberg model on a honeycomb lattice at half filling. The problem is approached from the Kondo destroyed, antiferromagnetically ordered insulating phase. We describe the local moments in terms of a coarse grained quantum non-linear sigma model, and show that the skyrmion defects of the antiferromagnetic order parameter host a number of competing order parameters. In addition to the spin Peierls, charge and current density wave order parameters, we identify for the first time Kondo singlets as the competing dual orders of the antiferromagnetism, which can be related to each other via generalized chiral transformations of the underlying fermions. We also show that the conduction electrons acquire a Berry phase through their coupling to the hedgehog configurations of the Néel order, which cancels the Berry phase of the local moments. Our results demonstrate the competition between the Kondo-singlet formation and spin-Peierls order when the antiferromagnetic order is suppressed, thereby shedding new light on the global phase diagram of heavy fermion systems at zero temperature. NSF.
NASA Astrophysics Data System (ADS)
Zhong, Yin; Wang, Yu-Feng; Lu, Han-Tao; Luo, Hong-Gang
2014-08-01
We have studied Kondo spin liquid phase of Kondo necklace models from the perspective of quantum O(N) non-linear sigma model (NLSM) field theory, particularly we focus on its possible topologically nontrivial phases. In the one-dimensional case, the Kondo spin liquid phase is a usual quantum disordered phase in contrast to the well-known topologically nontrivial Haldane phase due to destructive interference effect of topological θ term. In the two-dimensional case, the system can be mapped onto an O(4)-like NLSM with some O(3) anisotropy. Interestingly, if hedgehog-like point defects are included together with the restoration of the full O(4) symmetry, our model is identical to a kind of SU(2) symmetry-protected topological (SPT) state, which highlights a possible link between the extended Kondo necklace models and the desirable SPT states. Additionally, if the system has the expanded O(5) symmetry instead, the effective NLSM with the Wess-Zumino-Witten term is just a description of the surface modes of a three-dimensional SPT state. The deviations from fully symmetrical cases are discussed. We expect that the results might provide useful threads to identify certain microscopic bilayer antiferromagnet models (and related materials), which can support the SPT states.
NASA Astrophysics Data System (ADS)
Kerouedan, Julien; Quéffélec, Patrick; Talbot, Philippe; Quendo, Cédric; DeBlasi, Serge; LeBrun, Alain
2008-10-01
This paper demonstrates how micro-cracks at the surface of metals can be detected and imaged by near-field microwave techniques from the crack-induced variations of the resonance frequency and of the resonant circuit quality factor. It deals with two resonant sensors: a quarter wavelength microstrip line resonator terminated by an electric dipole and an original dual-behavior resonator (DBR) band-pass filter probe. The detection principle is developed, at first, from the use of the electric dipole probe. The low sensitivity of the electric dipole resonator led us to investigate whether first-order band-pass filters based on dual behavior resonators were able to detect a 200 µm wide and 3 mm deep rectangular EDM notch at the surface of a steel plate used to validate our method. Simulation data and measurements results carried out on a stainless steel mock-up with several 200 µm wide EDM rectangular notches showed that the DBR sensor is more sensitive than the electric dipole probe, and highlighted the link between the spatial resolution and the width of the high-frequency stub of the DBR filter. Moreover, we demonstrate the notch detection for any orientation of the defect in relation to the DBR sensor and the ability to differentiate between notches of different depths. Simulation data and measurement results are presented and discussed.
Kondo effect in magnetic tunnel junctions with an AlOx tunnel barrier
NASA Astrophysics Data System (ADS)
Zheng, Chao; Shull, Robert D.; Chen, P. J.; Pong, Philip W. T.
2016-06-01
The influence of the magnetization configuration on the Kondo effect in a magnetic tunnel junction is investigated. In the parallel configuration, an additional resistance contribution (R*) below 40 K exhibits a logarithmic temperature dependence, indicating the presence of the Kondo effect. However, in the anti-parallel configuration, the Kondo-effect-associated spin-flip scattering has a nontrivial contribution to the tunneling current, which compensates the reduction of the current directly caused by Kondo scattering, making R* disappear. These results indicate that suppression and restoration of the Kondo effect can be experimentally achieved by altering the magnetization configuration, enhancing our understanding of the role of the Kondo effect in spin-dependent transport.
Zaĭchenko, M I; Merzhanova, G Kh; Demina, A V
2010-01-01
Rats divided into groups of "impulsive" and "self-controlled" animals by their preference of either high valuable but delayed or a low valuable but immediate food reward were studied by the method of "emotional resonance". It was shown that all rats of the "self-controlled" group choosing a high valuable although delayed reinforcement did not escape the defensive signals of another animal of the same species and for the most part of the trial time preferred to stay in the dark "house". The majority of animals belonging to the "impulsive" group (80%) spent more than a half of the time of the experiment in the bright compartment and thus saved a partner from electrical stimulation. The existence of some general mechanisms that underlie these two types of behavior is discussed. PMID:20469594
NASA Astrophysics Data System (ADS)
Wang, Zhi-Yun; Chen, Pei-Jie; Zhang, Liang-Ying
2015-05-01
By using a generalized Langevin equation to describe the vertical oscillations of a general relativistic disk subjected to a memory-damped friction and a stochastic force, we derive the power spectrum density (PSD) of accretion disk oscillating luminosity by the method of Laplace transform, and discuss the influence of the system parameters on the resonant behavior in PSD curves. The results show that as the damping strength α and memory time τ of the friction increase, the variation of PSD with spectrum frequency f from monotonous decreasing to occurring maximums, and the phenomenon of a general stochastic resonance (SR) with a single peak and multi-peaks can be found in PSD curves. The radial distance parameter n, the mass M, and spin parameter a* of the black hole determine the inherent frequency of vertical oscillations in the disk, and they have significant influences on the SR phenomena in a system of black hole binaries. Project supported by the National Natural Science Foundation of China (Grant No. 11045004) and the Key Program of the Scientific Research Foundation of the Education Bureau of Hubei Province, China (Grant No. D20132603).
Non-Kondo Mechanism for Resistivity Minimum in Spin Ice Conduction Systems
NASA Astrophysics Data System (ADS)
Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi
2012-02-01
We present a mechanism of resistivity minimum in conduction electron systems coupled with localized moments, which is distinguished from the Kondo effect. Instead of the spin-flip process in the Kondo effect, electrons are elastically scattered by local spin correlations which evolve in a particular way under geometrical frustration as decreasing temperature. This is demonstrated by the cellular dynamical mean-field theory for a spin-ice-type Kondo lattice model on a pyrochlore lattice. Peculiar temperature dependences of the resistivity, specific heat, and magnetic susceptibility in the non-Kondo mechanism are compared with the experimental data in metallic Ir pyrochlore oxides.
Domijan, Dražen; Šetić, Mia
2016-01-01
Research on grounded cognition suggests that the processing of a word or concept reactivates the perceptual representations that are associated with the referent object. The objective of this work is to demonstrate how behavioral and functional neuroimaging data on grounded cognition can be understood as different manifestations of the same cortical circuit designed to achieve stable category learning, as proposed by the adaptive resonance theory (ART). We showed that the ART neural network provides a mechanistic explanation of why reaction times in behavioral studies depend on the expectation or attentional priming created by the word meaning (Richter and Zwaan, 2009). A mismatch between top-down expectation and bottom-up sensory data activates an orienting subsystem that slows execution of the current task. Furthermore, we simulated the data from functional neuroimaging studies of color knowledge retrieval that showed anterior shift (Chao and Martin, 1999; Thompson-Schill, 2003) and an overlap effect (Simmons et al., 2007; Hsu et al., 2011) in the left fusiform gyrus. We explain the anterior effect as a result of the partial activation of different components of the same ART circuit in the condition of passive viewing. Conversely, a demanding perceptual task requires activation of the whole ART circuit. This condition is reflected in the fMRI image as an overlap between cortical activation during perceptual and conceptual processing. We conclude that the ART neural network is able to explain how the brain grounds symbols in perception via perceptual simulation. PMID:26903933
Domijan, Dražen; Šetić, Mia
2016-01-01
Research on grounded cognition suggests that the processing of a word or concept reactivates the perceptual representations that are associated with the referent object. The objective of this work is to demonstrate how behavioral and functional neuroimaging data on grounded cognition can be understood as different manifestations of the same cortical circuit designed to achieve stable category learning, as proposed by the adaptive resonance theory (ART). We showed that the ART neural network provides a mechanistic explanation of why reaction times in behavioral studies depend on the expectation or attentional priming created by the word meaning (Richter and Zwaan, 2009). A mismatch between top-down expectation and bottom-up sensory data activates an orienting subsystem that slows execution of the current task. Furthermore, we simulated the data from functional neuroimaging studies of color knowledge retrieval that showed anterior shift (Chao and Martin, 1999; Thompson-Schill, 2003) and an overlap effect (Simmons et al., 2007; Hsu et al., 2011) in the left fusiform gyrus. We explain the anterior effect as a result of the partial activation of different components of the same ART circuit in the condition of passive viewing. Conversely, a demanding perceptual task requires activation of the whole ART circuit. This condition is reflected in the fMRI image as an overlap between cortical activation during perceptual and conceptual processing. We conclude that the ART neural network is able to explain how the brain grounds symbols in perception via perceptual simulation. PMID:26903933
Low-temperature magnetic fluctuations in the Kondo insulator SmB6
NASA Astrophysics Data System (ADS)
Biswas, P. K.; Salman, Z.; Neupert, T.; Morenzoni, E.; Pomjakushina, E.; von Rohr, F.; Conder, K.; Balakrishnan, G.; Hatnean, M. Ciomaga; Lees, M. R.; Paul, D. McK.; Schilling, A.; Baines, C.; Luetkens, H.; Khasanov, R.; Amato, A.
2014-04-01
We present the results of a systematic investigation of the magnetic properties of the three-dimensional Kondo topological insulator SmB6 using magnetization and muon-spin relaxation/rotation (μSR) measurements. The μSR measurements exhibit magnetic field fluctuations in SmB6 below ˜15 K due to electronic moments present in the system. However, no evidence for magnetic ordering is found down to 19 mK. The observed magnetism in SmB6 is homogeneous in nature throughout the full volume of the sample. Bulk magnetization measurements on the same sample show consistent behavior. The agreement between μSR, magnetization, and NMR results strongly indicate the appearance of intrinsic bulk magnetic in-gap states associated with fluctuating magnetic fields in SmB6 at low temperature.
Low temperature transport properties of the quadrupolar Kondo lattice system PrTi2Al20
NASA Astrophysics Data System (ADS)
Sakai, Akito; Nakatsuji, Satoru
2013-08-01
We have investigated the low temperature transport properties of the cubic Γ3 compound PrTi2Al20. This is a quadrupolar Kondo lattice system where the nongmagnetic quadrupoles, which form a long-range order at low temperatures, have strong hybridization with the conduction electrons. A sharp drop of the resistivity due to a ferroquadrupole ordering is observed at T Q = 2.0 K. The T 2 dependence of the resistivity and the large Sommerfeld coefficient γ above T Q suggest the formation of a heavy-fermion state. The temperature dependence of the resistivity below T Q does not show a power law but exponential law behavior, indicating the emergence of an anisotropy gap Δ in the collective mode associated with the ferroquadrupole order below T Q. The Fisher-Langer relation holds around T Q, suggesting the higher order scattering processes than those in Born approximation are not dominant for this ferroquadrupole ordering.
Two-dimensional Fermi surfaces in Kondo insulator SmB₆.
Li, G; Xiang, Z; Yu, F; Asaba, T; Lawson, B; Cai, P; Tinsman, C; Berkley, A; Wolgast, S; Eo, Y S; Kim, Dae-Jeong; Kurdak, C; Allen, J W; Sun, K; Chen, X H; Wang, Y Y; Fisk, Z; Li, Lu
2014-12-01
In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6. PMID:25477456
NASA Technical Reports Server (NTRS)
Dlugach, Janna M.; Mishchenko, Michael I.
2014-01-01
By using the results of highly accurate T-matrix computations for randomly oriented oblate and prolate spheroids and Chebyshev particles with varying degrees of asphericity, we analyze the effects of a deviation of water-droplet shapes from that of a perfect sphere on the behavior of Lorenz-Mie morphology-dependent resonances of various widths. We demonstrate that the positions and profiles of the resonances can change significantly with increasing asphericity. The absolute degree of asphericity required to suppress a Lorenz-Mie resonance is approximately proportional to the resonance width. Our results imply that numerical averaging of scattering characteristics of real cloud droplets over sizes may rely on a significantly coarser size-parameter resolution than that required for ideal, perfectly spherical particles.
NASA Astrophysics Data System (ADS)
Dlugach, Janna M.; Mishchenko, Michael I.
2014-10-01
By using the results of highly accurate T-matrix computations for randomly oriented oblate and prolate spheroids and Chebyshev particles with varying degrees of asphericity, we analyze the effects of a deviation of water-droplet shapes from that of a perfect sphere on the behavior of Lorenz-Mie morphology-dependent resonances of various widths. We demonstrate that the positions and profiles of the resonances can change significantly with increasing asphericity. The absolute degree of asphericity required to suppress a Lorenz-Mie resonance is approximately proportional to the resonance width. Our results imply that numerical averaging of scattering characteristics of real cloud droplets over sizes may rely on a significantly coarser size-parameter resolution than that required for ideal, perfectly spherical particles.
Resonances and resonance widths
Collins, T.
1986-05-01
Two-dimensional betatron resonances are much more important than their simple one-dimensional counterparts and exhibit a strong dependence on the betatron phase advance per cell. A practical definition of ''width'' is expanded upon in order to display these relations in tables. A primarily pedagogical introduction is given to explain the tables, and also to encourage a wider capability for deriving resonance behavior and wider use of ''designer'' resonances.
Kondo effect goes anisotropic in vanadate oxide superlattices
NASA Astrophysics Data System (ADS)
Rotella, H.; Pautrat, A.; Copie, O.; Boullay, P.; David, A.; Mercey, B.; Morales, M.; Prellier, W.
2015-11-01
We study the transport properties in SrVO3/LaVO3 (SVO/LVO) superlattices deposited on SrTiO3 (STO) substrates. We show that the electronic conduction occurs in the metallic LVO layers with a galvanomagnetism typical of a 2D Fermi surface. In addition, a Kondo-like component appears in both the thermal variation of resistivity and the magnetoresistance. Surprisingly, in this system where the STO interface does not contribute to the measured conduction, the Kondo correction is strongly anisotropic. We show that the growth temperature allows a direct control of this contribution. Finally, the key role of vanadium mixed valency stabilized by oxygen vacancies is enlightened.
Kondo and Majorana doublet interactions in quantum dots
NASA Astrophysics Data System (ADS)
Kim, Younghyun; Liu, Dong E.; Gaidamauskas, Erikas; Paaske, Jens; Flensberg, Karsten; Lutchyn, Roman
We study the properties of a quantum dot coupled to a normal lead and a time-reversal topological superconductor with Majorana Kramers pair at the end. We explore the phase diagram of the system as a function of Kondo and Majorana-induced coupling strengths using perturbative renormalization group study and slave-boson mean-field theory. We find that, in the presence of coupling between a quantum dot and a Majorana doublet, the system flows to a new fixed point controlled by the Majorana doublet, rather than the Kondo coupling, which is characterized by correlations between a localized spin and the fermion parity of each spin sector of the topological superconductor. We find that this fixed point is stable with respect to Gaussian fluctuations. We also investigate the effect of spin-spin interaction between a quantum dot and Majorana doublet and compare the result with a case where a normal lead is directly coupled to Majorana doublet.
Characterization of a correlated topological Kondo insulator in one dimension
NASA Astrophysics Data System (ADS)
Hagymási, I.; Legeza, Ö.
2016-04-01
We investigate the ground state of a p -wave Kondo-Heisenberg model introduced by Alexandrov and Coleman with an Ising-type anisotropy in the Kondo interaction and correlated conduction electrons. Our aim is to understand how they affect the stability of the Haldane state obtained in the SU(2)-symmetric case without the Hubbard interaction. By applying the density-matrix renormalization group algorithm and calculating the entanglement entropy we show that in the anisotropic case a phase transition occurs and a Néel state emerges above a critical value of the Coulomb interaction. These findings are also corroborated by the examination of the entanglement spectrum and the spin profile of the system which clarify the structure of each phase.
First principles electron transport simulations in the Kondo regime
NASA Astrophysics Data System (ADS)
Rungger, Ivan; Radonjic, Milos; Appelt, Wilhelm; Chioncel, Liviu; Droghetti, Andrea
When magnetic atoms, molecules or thin films are brought into contact with metals the electron-electron interaction leads to the appearance of the correlated Kondo state at low temperatures. In this talk we will present results for the electronic structure and conductance in the Kondo regime of recent STM and break junction experiments for stable radical molecules, which correspond to spin half molecular magnets. We will outline the methodological approach to evaluate the conductance of such systems from first principles, as implemented in the Smeagol electron transport code. The method combines the density functional theory (DFT) with Anderson impurity solvers within the continuum time quantum Monte Carlo (CTQMC) and numerical renormalization group (NRG) approaches.
Ferromagnetic Kondo Effect in a Triple Quantum Dot System
NASA Astrophysics Data System (ADS)
Baruselli, P. P.; Requist, R.; Fabrizio, M.; Tosatti, E.
2013-07-01
A simple device of three laterally coupled quantum dots, the central one contacted by metal leads, provides a realization of the ferromagnetic Kondo model, which is characterized by interesting properties like a nonanalytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Tuning the gate voltages of the lateral dots allows us to study the transition from a ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field.
Ferromagnetic Kondo effect in a triple quantum dot system.
Baruselli, P P; Requist, R; Fabrizio, M; Tosatti, E
2013-07-26
A simple device of three laterally coupled quantum dots, the central one contacted by metal leads, provides a realization of the ferromagnetic Kondo model, which is characterized by interesting properties like a nonanalytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Tuning the gate voltages of the lateral dots allows us to study the transition from a ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field. PMID:23931401
Neutron scattering from the Kondo Insulator SmB6
NASA Astrophysics Data System (ADS)
Broholm, Collin
A review of neutron scattering work probing the Kondo insulator SmB6 is presented with special emphasis on assessing the topology of the underlying strongly renormalized band structure. A 14 meV excition dominates the spectrum and is evidence of strong electron correlations [1]. Though the data generally supports the proposal that SmB6 is a topological Kondo insulator, specific heat and high-resolution neutron scattering data show a continuum of states well below the bulk transport gap, which enrich the problem and may connect to the recent surprising de Haas van Alpen results. ``Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6,'' W. T. Fuhrman, J. Leiner, P. Nikolic, G. E. Granroth, M. B. Stone, M. D. Lumsden, L. DeBeer-Schmitt, P. A. Alekseev, J.-M. Mignot, S. M. Koohpayeh, P. Cottingham, W. Adam Phelan, L. Schoop, T. M. McQueen, and C. Broholm, Phys. Rev. Lett. 114, 036401 (2015). Supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Grant No. DEFG02-08ER46544 and the Gordon and Betty Moore Foundation.
Kondo physics from quasiparticle poisoning in Majorana devices
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.
Kondo physics from quasiparticle poisoning in Majorana devices
Plugge, S.; Tsvelik, A. M.; Zazunov, A.; Eriksson, E.; Egger, R.
2016-03-24
Here, we present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M = 2 attached leads, such “dangerous” quasiparticle poisoning processes cause a spin S = 1/2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effectmore » of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M > 3, the topological Kondo fixed point re-emerges, though now it involves only M–1 leads. As a consequence, for M = 3, the low-energy fixed point becomes trivial corresponding to decoupled leads.« less
Observation of the two-channel Kondo effect
NASA Astrophysics Data System (ADS)
Potok, R. M.; Rau, I. G.; Shtrikman, Hadas; Oreg, Yuval; Goldhaber-Gordon, D.
2007-03-01
Some of the most intriguing problems in solid-state physics arise when the motion of one electron dramatically affects the motion of surrounding electrons. Traditionally, such highly correlated electron systems have been studied mainly in materials with complex transition metal chemistry. Over the past decade, researchers have learned to confine one or a few electrons within a nanometre-scale semiconductor `artificial atom', and to understand and control this simple system in detail3. Here we combine artificial atoms to create a highly correlated electron system within a nano-engineered semiconductor structure. We tune the system in situ through a quantum phase transition between two distinct states, each a version of the Kondo state, in which a bound electron interacts with surrounding mobile electrons. The boundary between these competing Kondo states is a quantum critical point-namely, the exotic and previously elusive two-channel Kondo state, in which electrons in two reservoirs are entangled through their interaction with a single localized spin.
Quantum phase transitions and anomalous Hall effect in a pyrochlore Kondo lattice
NASA Astrophysics Data System (ADS)
Grefe, Sarah; Ding, Wenxin; Si, Qimiao
The metallic variant of the pyrochlore iridates Pr2Ir2O7 has shown characteristics of a possible chiral spin liquid state [PRL 96 087204 (2006), PRL 98, 057203 (2007), Nature 463, 210 (2010)] and quantum criticality [Nat. Mater. 13, 356 (2014)]. An important question surrounding the significant anomalous Hall response observed in Pr2Ir2O7 is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on the pyrochlore lattice. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations and determine the zero-temperature phase diagram. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr2Ir2O7 and related frustrated Kondo-lattice systems.
Optical Study of Interactions in a d-Electron Kondo Lattice with Ferromagnetism
Burch, K. S.; Schafgans, A.; Butch, N. P.; Sayles, T. A.; Maple, M. B.; Sales, Brian C; Mandrus, David; Basov, D. N.
2005-01-01
We report on a comprehensive optical, transport, and thermodynamic study of the Zintl compound Yb{sub 14}MnSb{sub 11}, demonstrating that it is the first ferromagnetic Kondo lattice compound in the underscreened limit. We propose a scenario whereby the combination of Kondo and Jahn-Teller effects provides a consistent explanation of both transport and optical data.
Reappearance of the Kondo effect in serially coupled symmetric triple quantum dots
NASA Astrophysics Data System (ADS)
Cheng, Yongxi; Wei, Jianhua; Yan, Yijing
2015-12-01
We investigate the spectral properties of a serially coupled triple quantum dot (STQD) system by means of the hierarchical equations of motion (HEOM) approach. We find that with the increase of the interdot coupling t, the first Kondo screening is followed by another Kondo effect reappearing due to the transition from the respective Kondo singlet state of individual QD to the coherence bonding state generated among the three QDs. The reappearance of the Kondo effect results in the three-peak structure of the spectral functions of peripheral QD-1(3). By investigating the susceptibility χ, we find that the local susceptibility of intermediate QD-2 is a positive value at weak interdot coupling, while it changes into a negative value at strong interdot coupling, at which the STQD system gives rise to the reappearance of the Kondo effect. We also find that the slopes of 1/χ will deviate from a straight line behaviour at low temperature in the reappearing Kondo regime. In addition, the influence of temperature and dot-lead coupling strength on the reappearing Kondo effect as well as the Kondo-correlated transport properties are afterwards exploited in detail.
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.
Scanning tunneling spectroscopy of a magnetic atom on graphene in the Kondo regime
Zhuang, Huai -Bin; Sun, Qing -feng; Xie, X. C.
2009-06-23
In this study, the Kondo effect in the system consisting of a magnetic adatom on the graphene is studied. By using the non-equilibrium Green function method with the slave-boson mean field approximation, the local density of state (LDOS) and the conductance are calculated. For a doped graphene, the Kondo phase is present at all time. Surprisingly, two kinds of Kondo regimes are revealed. But for the undoped graphene, the Kondo phase only exists if the adatom’s energy level is beyond a critical value. The conductance is similar to the LDOS, thus, the Kondo peak in the LDOS can be observed with the scanning tunneling spectroscopy. In addition, in the presence of a direct coupling between the STM tip and the graphene, the conductance may be dramatically enhanced, depending on the coupling site.
Scanning tunneling spectroscopy of a magnetic atom on graphene in the Kondo regime
Zhuang, Huai -Bin; Sun, Qing -feng; Xie, X. C.
2009-06-23
In this study, the Kondo effect in the system consisting of a magnetic adatom on the graphene is studied. By using the non-equilibrium Green function method with the slave-boson mean field approximation, the local density of state (LDOS) and the conductance are calculated. For a doped graphene, the Kondo phase is present at all time. Surprisingly, two kinds of Kondo regimes are revealed. But for the undoped graphene, the Kondo phase only exists if the adatom’s energy level is beyond a critical value. The conductance is similar to the LDOS, thus, the Kondo peak in the LDOS can be observedmore » with the scanning tunneling spectroscopy. In addition, in the presence of a direct coupling between the STM tip and the graphene, the conductance may be dramatically enhanced, depending on the coupling site.« less
Exploring the phase diagram of the two-impurity Kondo problem
NASA Astrophysics Data System (ADS)
Spinelli, A.; Gerrits, M.; Toskovic, R.; Bryant, B.; Ternes, M.; Otte, A. F.
2015-11-01
A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present a study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. The pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third-order transport model, allows us to independently determine the degree of Kondo screening in each phase.