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Hiroshi Kontani - One of the best experts on this subject based on the ideXlab platform.

  • Multipole fluctuation theory for Heavy Fermion Systems: Application to multipole orders in CeB 6
    Physical Review B, 2019
    Co-Authors: Rina Tazai, Hiroshi Kontani
    Abstract:

    In Heavy Fermion Systems, the emergence of rich phenomena, such as hidden orders and superconductivities, is made possible by multipole degrees of freedom. However, many of them remain unsolved since the origin of the higher-rank multipole interaction is not well understood. Among these issues, we focus on the quadrupole order in ${\mathrm{CeB}}_{6}$, which is a famous multipolar Heavy Fermion system that has been actively studied for decades. We analyze the multiorbital periodic Anderson model for ${\mathrm{CeB}}_{6}$, and find that magnetic, quadrupole, and octupole fluctuations all develop cooperatively due to the strong intermultipole coupling given by higher-order many-body effects, called vertex corrections. It is found that the antiferroquadrupole order in ${\mathrm{CeB}}_{6}$ is driven by the interference between magnetic-multipole fluctuations. The discovered intermultipole coupling mechanism is a potential origin of numerous hidden orders in various Heavy Fermion Systems.

  • fully gapped s wave superconductivity enhanced by magnetic criticality in Heavy Fermion Systems
    Physical Review B, 2018
    Co-Authors: Rina Tazai, Hiroshi Kontani
    Abstract:

    Diverse multipole fluctuations inherent in Heavy-Fermion Systems cause an amazing variety of superconducting states. Here, the authors discover theoretically that the electron-phonon coupling is strongly dressed and magnified owing to interference between multipole fluctuations. They achieve this by going beyond the conventional Migdal approximation. For this reason, even if the original electron-phonon interaction is small, phonon-mediated superconductivity can emerge near the magnetic criticality, contrary to expectations. This mechanism is responsible for the fully gapped $s$-wave superconductivity in CeCu${}_{2}$Si${}_{2}$.

  • intrinsic spin and orbital hall effects in Heavy Fermion Systems
    Physical Review B, 2010
    Co-Authors: T Tanaka, Hiroshi Kontani
    Abstract:

    We study the intrinsic spin Hall effect (SHE) based on the orbitally degenerate periodic Anderson model, which is an effective model for Heavy Fermion Systems. In the very low resistivity regime, the magnitude of the intrinsic spin Hall conductivity (SHC) is estimated as $2000\ensuremath{\sim}3000\ensuremath{\hbar}\text{ }{e}^{\ensuremath{-}1}\text{ }{\ensuremath{\Omega}}^{\ensuremath{-}1}\text{ }{\text{cm}}^{\ensuremath{-}1}$; it is about ten times larger than that in Pt. Its sign is negative (positive) in Ce (Yb) compound Systems with ${f}^{1}$ $({f}^{13})$ configuration. Interestingly, the obtained expression for the SHC depends only on the density of conduction electrons but is independent of the strength of the $c\text{\ensuremath{-}}f$ mixing potential and the mass-enhancement factor. The origin of the huge SHE is the spin-dependent Berry phase induced by the complex $f$-orbital wave function, which we call the ``orbital Aharonov-Bohm effect.''

  • Degeneracy Dpendence of the Kadowaki–Woods Relation in Heavy-Fermion Systems
    Journal of the Physical Society of Japan, 2007
    Co-Authors: Naohito Tsujii, Hiroshi Kontani, Kazuyoshi Yoshimura
    Abstract:

    In this paper, we show the results of experimental and theoretical studies on Kadowaki–Woods (KW) relation of Heavy-Fermion Systems with degeneracy N . Experimental data revealed that the A /γ 2 becomes significantly smaller than that of the KW relation, A /γ 2 ∼ a 0 = 1 ×10 -5 µΩ cm (mol K/mJ) 2 . Especially for Yb Systems with the full degeneracy N =8, A /γ 2 = 0.04 a 0 . Theoretical study based on the Fermi-liquid theory has shown that the KW relation is generally expressed as; A /γ 2 = \frac{a_{0}}{\frac{1}{2}N(N-1)}, for Heavy-Fermion Systems with degeneracy. This relation is in good agreement with the above experimental data. Furthermore, this relation can be simplified as the grand KW-relation: \tilde A /\tildeγ 2 = a 0 , where \tilde A = A /½ N ( N -1) and \tildeγ = γ/½ N ( N -1). We review these progress, and make discussions on some specific problems.

  • Grand Kadowaki Woods relation of Heavy-Fermion Systems with degeneracy
    Physica B-condensed Matter, 2006
    Co-Authors: Naohito Tsujii, Hiroshi Kontani, Kazuyoshi Yoshimura
    Abstract:

    Abstract Recent experimental and theoretical studies have revealed that the Kadowaki–Woods relation is not valid for Heavy-Fermion Systems with large degeneracy, like intermediate-valence Yb- and Ce-compounds. Instead, we have successfully derived a new universal relation, namely, the grand Kadowaki–Woods relation for general degeneracy. This relation is found to be valid in the whole range of f-electron based Systems with various degeneracies.

Gerd Czycholl - One of the best experts on this subject based on the ideXlab platform.

  • Influence of disorder on the transport properties of Heavy-Fermion Systems
    Physical Review B, 2008
    Co-Authors: Claas Grenzebach, Frithjof B. Anders, Gerd Czycholl, Thomas Pruschke
    Abstract:

    The influence of substitutional disorder on the transport properties of Heavy-Fermion Systems is investigated. We extend the dynamical mean-field theory treatment of the periodic Anderson model (PAM) to a coherent-potential approximation for disordered strongly correlated electron Systems. Considering two distinct local environments of a binary alloy ${A}_{c}{B}_{1\ensuremath{-}c}$ with arbitrary concentration $c$, we explore two types of disorder: on the $f$ site and on the ligand sites. We calculate the spectral functions and self-energies for the disordered PAM as well as the temperature dependence of the resistivity and the thermoelectric power. The characteristic concentration dependence as well as the order of magnitude of transport properties are reproduced for metallic Heavy-Fermion Systems and Kondo insulators. In particular, sign changes of the Seebeck coefficient as function of temperature and concentration are observed.

  • On the influence of disorder onto transport properties of Heavy-Fermion Systems
    arXiv: Strongly Correlated Electrons, 2007
    Co-Authors: Claas Grenzebach, Frithjof B. Anders, Gerd Czycholl, Thomas Pruschke
    Abstract:

    The influence of substitutional disorder on the transport properties of Heavy-Fermion Systems is investigated. We extend the dynamical mean-field theory treatment of the periodic Anderson model (PAM) to a coherent-potential approximation for disordered strongly correlated electron Systems. Considering two distinct local environments of a binary alloy $A_c B_{1-c}$ with arbitrary concentration $c$, we explore two types of disorder: on the f site and on the ligand sites. We calculate the spectral functions and self-energies for the disordered PAM as well as the temperature dependence of the resistivity and the thermoelectric power. The characteristic concentration dependence as well as the order of magnitude of transport properties is reproduced for metallic Heavy-Fermion Systems and Kondo insulators. In particular, sign changes of the Seebeck coefficient as function of temperature and concentration are observed.

  • Transport properties of Heavy-Fermion Systems within DMFT/NRG
    Physica B: Condensed Matter, 2006
    Co-Authors: Claas Grenzebach, Frithjof B. Anders, Gerd Czycholl
    Abstract:

    We calculate the temperature dependence of the transport properties of Heavy-Fermion Systems such as resistivity, optical conductivity, thermoelectric power, the electronic part of the thermal conductivity, and the "figure of merit." The one-particle properties of the periodic Anderson model are obtained within dynamical mean-field theory for the paramagnetic phase using Wilson's numerical renormalization group and the modified perturbation theory as impurity solvers. We discuss the dependence of the transport properties on the band filling, valence, and Coulomb correlation $U$. The typical experimental findings can be reproduced and understood, in particular the temperature dependence of the resistance and the thermoelectric power and their absolute magnitude for both metallic Heavy-Fermion Systems and Kondo insulators. For large values of $U$, we find a negative Seebeck coefficient $S(T)$ for an intermediate-temperature regime as observed in $S(T)$ of CeCu$_2$Si$_2$. We analyze different estimates for possible characteristic low-temperature scales of the lattice. Our results indicate a one-parameter scaling of thermodynamic and some transport properties with a strongly occupancy-dependent scaling function. This is consistent with a strong-coupling local Fermi-liquid fixed point of the effective site governing all low-lying excitations for $T\to 0$ in the paramagnetic phase.Comment: 17 pages, 24 figures, published versio

  • Conductivity and thermopower of Heavy Fermion Systems with disorder
    Physica B-condensed Matter, 2005
    Co-Authors: Claas Grenzebach, Gerd Czycholl
    Abstract:

    Abstract We investigate the influence of disorder (impurities) on the electronic (transport) properties of Heavy Fermion Systems, which are described by the periodic Anderson model (PAM). In this paper we consider disorder within the conduction band. The PAM is mapped onto an effective single impurity Anderson model (SIAM) by dynamical mean-field theory (DMFT), and the modified perturbation theory (MPT)—an approximation that is exact up to second order in the Coulomb correlation U and reproduces the atomic limit—is used for the effective SIAM. To include the scattering by the impurities we use the coherent potential approximation (CPA) which is consistent with the DMFT. For various concentrations c of the impurities we calculate the resistivity as well as the thermoelectrical power in a situation describing a Kondo insulator in the pure case ( c = 0 ).

  • Transport Properties of Heavy Fermion Systems
    Concepts in Electron Correlation, 2003
    Co-Authors: Claas Grenzebach, Frithjof B. Anders, Gerd Czycholl, Thomas Pruschke
    Abstract:

    We calculate the temperature dependence of the transport properties of Heavy-Fermion Systems such as resistivity, optical conductivity, thermoelectric power, the electronic part of the thermal conductivity, and the ``figure of merit.'' The one-particle properties of the periodic Anderson model are obtained within dynamical mean-field theory for the paramagnetic phase using Wilson's numerical renormalization group and the modified perturbation theory as impurity solvers. We discuss the dependence of the transport properties on the band filling, valence, and Coulomb correlation $U$. The typical experimental findings can be reproduced and understood, in particular the temperature dependence of the resistance and the thermoelectric power and their absolute magnitude for both metallic Heavy-Fermion Systems and Kondo insulators. For large values of $U$, we find a negative Seebeck coefficient $S(T)$ for an intermediate-temperature regime as observed in $S(T)$ of $\mathrm{Ce}{\mathrm{Cu}}_{2}{\mathrm{Si}}_{2}$. We analyze different estimates for possible characteristic low-temperature scales of the lattice. Our results indicate a one-parameter scaling of thermodynamic and some transport properties with a strongly occupancy-dependent scaling function. This is consistent with a strong-coupling local Fermi-liquid fixed point of the effective site governing all low-lying excitations for $T\ensuremath{\rightarrow}0$ in the paramagnetic phase.

J. D. Thompson - One of the best experts on this subject based on the ideXlab platform.

  • plutonium based Heavy Fermion Systems
    Annual Review of Condensed Matter Physics, 2015
    Co-Authors: Eric D. Bauer, J. D. Thompson
    Abstract:

    An effective mass of charge carriers that is significantly larger than the mass of a free electron develops at low temperatures in certain lanthanide- and actinide-based metals, including those formed with plutonium, owing to strong electron-electron interactions. This Heavy-Fermion mass is reflected in a substantially enhanced electronic coefficient of specific heat γ, which for elemental Pu is much larger than that of normal metals. By our definition, there are twelve Pu-based Heavy-Fermion compounds, most discovered recently, whose basic properties are known and discussed. Relative to other examples, these Pu-based Heavy-Fermion Systems are particularly complex owing in part to the possible simultaneous presence of multiple, nearly degenerate 5fn configurations. This complexity poses significant opportunities as well as challenges, including understanding the origin of unconventional superconductivity in some of these materials.

  • Plutonium-Based Heavy-Fermion Systems
    Annual Review of Condensed Matter Physics, 2015
    Co-Authors: Eric D. Bauer, J. D. Thompson
    Abstract:

    An effective mass of charge carriers that is significantly larger that the mass of a free electron develops at low temperatures in certain lanthanide- and actinide-based metals, including those formed with plutonium, due to strong electron-electron interactions. This Heavy-Fermion mass is reflected in a substantially enhanced electronic coefficient of specific heat $\gamma$, which for elemental Pu itself is much larger than that of normal metals. By our definition, there are twelve Pu-based Heavy-Fermion compounds, most discovered recently, whose basic properties are known and discussed. Relative to other examples, these Pu-based Heavy-Fermion Systems are particularly complex due in part to the possible simultaneous presence of multiple, nearly degenerate 5f$^n$ configurations. This complexity poses significant opportunities as well as challenges, including understanding the origin of unconventional superconductivity in some of these materials.

G. C. Rout - One of the best experts on this subject based on the ideXlab platform.

Hilbert Von Löhneysen - One of the best experts on this subject based on the ideXlab platform.

  • RECENT PROGRESS IN THE STUDY OF Heavy-Fermion Systems
    Hyperfine Interactions, 1997
    Co-Authors: Hilbert Von Löhneysen
    Abstract:

    Recent experiments on Heavy‐Fermion Systems have focused on the following issues: (i) non‐Fermi‐liquid behavior occurring either because of cooperative effects at a magnetic instability, i.e. at a T=0 phase transition between magnetically ordered and nonmagnetic groundstates driven by parameters such as chemical composition or pressure, or because of single‐ion effects such as the two‐channel Kondo effect or a distribution of Kondo temperatures; (ii) the symmetry of the order parameter in Heavy‐Fermion superconductors and the interplay of (often weak) magnetism and superconductivity. A review of recent developments in these areas is given.