The Experts below are selected from a list of 23346 Experts worldwide ranked by ideXlab platform
Shoucheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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kondo effect in the helical edge liquid of the quantum spin hall state
Physical Review Letters, 2009Co-Authors: Joseph Maciejko, Chaoxing Liu, Yuval Oreg, Shoucheng ZhangAbstract:Following the recent observation of the quantum spin Hall (QSH) effect in HgTe quantum wells, an important issue is to understand the effect of impurities on transport in the QSH regime. Using linear response and renormalization group methods, we calculate the edge conductance of a QSH insulator as a function of temperature in the presence of a Magnetic Impurity. At high temperatures, Kondo and/or two-particle scattering give rise to a logarithmic temperature dependence. At low temperatures, for weak Coulomb interactions in the edge liquid, the conductance is restored to unitarity with unusual power laws characteristic of a "local helical liquid," while for strong interactions, transport proceeds by weak tunneling through the Impurity where only half an electron charge is transferred in each tunneling event.
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Magnetic impurities on the surface of a topological insulator
Physical Review Letters, 2009Co-Authors: Qin Liu, Chaoxing Liu, Shoucheng ZhangAbstract:The surface states of a topological insulator are described by an emergent relativistic massless Dirac equation in 2 + 1 dimensions. In contrast with graphene, there is an odd number of Dirac points, and the electron spin is directly coupled to the momentum. We show that a Magnetic Impurity opens up a local gap and suppresses the local density of states. Furthermore, the Dirac electronic states mediate an RKKY interaction among the Magnetic impurities which is always ferroMagnetic, whenever the chemical potential lies near the Dirac point. Through this exchange mechanism, Magnetic atoms uniformly deposited on the surface of a topological insulator could naturally form a ferroMagnetically ordered film. These effects can be directly measured in STM experiments. We also study the case of quenched disorder through a renormalization group analysis.
Chaoxing Liu - One of the best experts on this subject based on the ideXlab platform.
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kondo effect in the helical edge liquid of the quantum spin hall state
Physical Review Letters, 2009Co-Authors: Joseph Maciejko, Chaoxing Liu, Yuval Oreg, Shoucheng ZhangAbstract:Following the recent observation of the quantum spin Hall (QSH) effect in HgTe quantum wells, an important issue is to understand the effect of impurities on transport in the QSH regime. Using linear response and renormalization group methods, we calculate the edge conductance of a QSH insulator as a function of temperature in the presence of a Magnetic Impurity. At high temperatures, Kondo and/or two-particle scattering give rise to a logarithmic temperature dependence. At low temperatures, for weak Coulomb interactions in the edge liquid, the conductance is restored to unitarity with unusual power laws characteristic of a "local helical liquid," while for strong interactions, transport proceeds by weak tunneling through the Impurity where only half an electron charge is transferred in each tunneling event.
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Magnetic impurities on the surface of a topological insulator
Physical Review Letters, 2009Co-Authors: Qin Liu, Chaoxing Liu, Shoucheng ZhangAbstract:The surface states of a topological insulator are described by an emergent relativistic massless Dirac equation in 2 + 1 dimensions. In contrast with graphene, there is an odd number of Dirac points, and the electron spin is directly coupled to the momentum. We show that a Magnetic Impurity opens up a local gap and suppresses the local density of states. Furthermore, the Dirac electronic states mediate an RKKY interaction among the Magnetic impurities which is always ferroMagnetic, whenever the chemical potential lies near the Dirac point. Through this exchange mechanism, Magnetic atoms uniformly deposited on the surface of a topological insulator could naturally form a ferroMagnetically ordered film. These effects can be directly measured in STM experiments. We also study the case of quenched disorder through a renormalization group analysis.
C S Ting - One of the best experts on this subject based on the ideXlab platform.
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validity of the equation of motion approach to the kondo problem in the large n limit
Physical Review B, 2009Co-Authors: Jianxin Zhu, C S TingAbstract:The Anderson Impurity model for Kondo problem is investigated for arbitrary spin-orbital degeneracy $N$ of the Magnetic Impurity by the equation-of-motion method (EOM). By employing a different decoupling scheme, a set of self-consistent equations for the one-particle Green's function is derived and numerically solved in the large-$N$ approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction $U$, we show that the Kondo resonance at the Impurity site exists for all $N\ensuremath{\ge}2$. The approach removes the pathology in the standard EOM for $N=2$ and has the same level of applicability as noncrossing approximation. For $N=2$, an exchange field splits the Kondo resonance into only two peaks as predicted by a more rigorous numerical renormalization-group method. The temperature dependence of the Kondo resonance peak is also discussed.
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validity of equation of motion approach to kondo problem in the large n limit
Physical Review Letters, 2008Co-Authors: Jianxin Zhu, C S TingAbstract:The Anderson Impurity model for Kondo problem is investigated for arbitrary orbit-spin degeneracy N of the Magnetic Impurity by the equation of motion method (EOM). By employing a new decoupling scheme, a self-consistent equation for the one-particle Green function is derived and numerically solved in the large-N approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction U, we show that the Kondo resonance at the Impurity site exists for all N {>=} 2. The approach removes the pathology in the standard EOM for N = 2, and has the same level of applicability as non-crossing approximation. For N = 2, an exchange field splits the Kondo resonance into only two peaks, consist with the result from more rigorous numerical renormalization group (NRG) method. The temperature dependence of the Kondo resonance peak is also discussed.
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local quasiparticle states near a zn Impurity with induced Magnetic moment in a high t c superconductor
Physical Review B, 2001Co-Authors: Jianxin Zhu, C S TingAbstract:The local quasiparticle density of states around a unitary Impurity with a Kondo-like Magnetic moment induced at its nearest neighbors in a d-wave superconductor is studied within the slaveboson mean-field approach. The Hamiltonian is exactly diagonalized and the results are obtained self-consistently. We show that the interference between the strong Impurity potential scattering and the Kondo effect leads to novel quasiparticle spectra around the Impurity, which are strikingly different from the case of a single unitary or Magnetic Impurity. The recent STM image of the local differential tunneling conductance around a Zn Impurity in a high-Tc cuprate can be essentially explained if the blocking effect of BiO surface layer between the tip and probed CuO2 plane [Zhu et al., Phys. Rev. B 62, 6207 (2000)] is taken into account.
L Szunyogh - One of the best experts on this subject based on the ideXlab platform.
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universal distribution of Magnetic anisotropy of impurities in ordered and disordered nanograins
Physical Review B, 2015Co-Authors: Attila Szilva, P Balla, Olle Eriksson, Gergely Zarand, L SzunyoghAbstract:We examine the distribution of the Magnetic anisotropy experienced by a Magnetic Impurity embedded in a metallic nanograin. As an example of a generic Magnetic Impurity with a partially filled d shell, we study the case of d(1) impurities embedded into ordered and disordered Au nanograins, described in terms of a realistic band structure. Confinement of the electrons induces a Magnetic anisotropy that is large, and can be characterized by five real parameters, coupling to the quadrupolar moments of the spin. In ordered (spherical) nanograins, these parameters exhibit symmetrical structures and reflect the symmetry of the underlying lattice, while for disordered grains they are randomly distributed and, for stronger disorder, their distribution is found to be characterized by random matrix theory. As a result, the probability of having small Magnetic anisotropies K-L is suppressed below a characteristic scale Delta(E), which we predict to scale with the number of atoms N as Delta(E) similar to 1/N-3/2. This gives rise to anomalies in the specific heat and the susceptibility at temperatures T similar to Delta(E) and produces distinct structures in the Magnetic excitation spectrum of the clusters that should be possible to detect experimentally.
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effect of spin orbit interaction on a Magnetic Impurity in the vicinity of a surface
Physical Review Letters, 2006Co-Authors: L Szunyogh, Gergely Zarand, S Gallego, M C Munoz, B L GyorffyAbstract:We propose a new mechanism for surface-induced Magnetic anisotropy to explain the thickness dependence of the Kondo resistivity of thin films of dilute Magnetic alloys. The surface anisotropy energy, generated by spin-orbit coupling on the Magnetic Impurity itself, is an oscillating function of the distance d from the surface and decays as 1/d2. Numerical estimates based on simple models suggest that this mechanism, unlike its alternatives, gives rise to an effect of the desired order of magnitude.
Jianxin Zhu - One of the best experts on this subject based on the ideXlab platform.
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validity of the equation of motion approach to the kondo problem in the large n limit
Physical Review B, 2009Co-Authors: Jianxin Zhu, C S TingAbstract:The Anderson Impurity model for Kondo problem is investigated for arbitrary spin-orbital degeneracy $N$ of the Magnetic Impurity by the equation-of-motion method (EOM). By employing a different decoupling scheme, a set of self-consistent equations for the one-particle Green's function is derived and numerically solved in the large-$N$ approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction $U$, we show that the Kondo resonance at the Impurity site exists for all $N\ensuremath{\ge}2$. The approach removes the pathology in the standard EOM for $N=2$ and has the same level of applicability as noncrossing approximation. For $N=2$, an exchange field splits the Kondo resonance into only two peaks as predicted by a more rigorous numerical renormalization-group method. The temperature dependence of the Kondo resonance peak is also discussed.
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validity of equation of motion approach to kondo problem in the large n limit
Physical Review Letters, 2008Co-Authors: Jianxin Zhu, C S TingAbstract:The Anderson Impurity model for Kondo problem is investigated for arbitrary orbit-spin degeneracy N of the Magnetic Impurity by the equation of motion method (EOM). By employing a new decoupling scheme, a self-consistent equation for the one-particle Green function is derived and numerically solved in the large-N approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction U, we show that the Kondo resonance at the Impurity site exists for all N {>=} 2. The approach removes the pathology in the standard EOM for N = 2, and has the same level of applicability as non-crossing approximation. For N = 2, an exchange field splits the Kondo resonance into only two peaks, consist with the result from more rigorous numerical renormalization group (NRG) method. The temperature dependence of the Kondo resonance peak is also discussed.
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local quasiparticle states near a zn Impurity with induced Magnetic moment in a high t c superconductor
Physical Review B, 2001Co-Authors: Jianxin Zhu, C S TingAbstract:The local quasiparticle density of states around a unitary Impurity with a Kondo-like Magnetic moment induced at its nearest neighbors in a d-wave superconductor is studied within the slaveboson mean-field approach. The Hamiltonian is exactly diagonalized and the results are obtained self-consistently. We show that the interference between the strong Impurity potential scattering and the Kondo effect leads to novel quasiparticle spectra around the Impurity, which are strikingly different from the case of a single unitary or Magnetic Impurity. The recent STM image of the local differential tunneling conductance around a Zn Impurity in a high-Tc cuprate can be essentially explained if the blocking effect of BiO surface layer between the tip and probed CuO2 plane [Zhu et al., Phys. Rev. B 62, 6207 (2000)] is taken into account.
