Hideaki Maebashi

Huge Enhancement of Impurity Scattering due to Critical Valence Fluctuations in a Ce-Based Heavy Electron System

On the basis of the Ward–Pitaevskii identity, the residual resistivity ρ 0 is shown to exhibit huge enhancement around the quantum critical point of valence transition in Ce-based heavy electron systems. This explains the sharp peak of ρ 0 observed in CeCu 2 Ge 2 under a pressure of P ∼16 GPa where the superconducting transition temperature also exhibits a sharp peak.

Electrical Conductivity of Interacting Fermions. I. General Formulation

Electrical conductivity σ(ω, T ) of a lattice electron system due only to mutual Coulomb interaction is studied on the basis of the Fermi liquid theory, ω and T being the external frequency and the temperature, respectively. Based on the Kubo formula to respect the consistency between the selfenergy and the vertex corrections, a formulation of σ(ω, T ) is given in terms of memory function which is extended to the matrix form. In this formulation, it is explicitly demonstrated that, in the absence of Umklapp processes, T 2 -term in the resistivity vanishes as it should in spite of the fact that the total current is not conserved.

Electrical Conductivity of Interacting Fermions. II. Effects of Normal Scattering Processes in the Presence of Umklapp Scattering Processes

The electrical resistivity due only to mutual Coulomb interaction of the d -dimensional lattice electron systems ( d ≥2) in the presence of Umklapp scattering processes is studied on the basis of the Fermi liquid theory. It is shown that normal scattering processes generally contribute to the resistivity if Umklapp scattering processes are present. This fact gives a natural explanation of the resistivity of the d =∞ Hubbard model which is determined only by the damping rate of quasi-particles, γ. In the case of d =2, however, it is shown that the resistivity is proportional to T 2 , T being the temperature, even when normal scattering processes, which give T 2 log T -contribution to γ, contribute to the resistivity. In the special case of the square lattice, where the transfer integrals are only between the nearest neighbors, the coefficient of the T 2 -term in the second order of the interaction is shown to diverge as (1/δ) log (1 / δ) when δ→0, δ being the doping rate away from half-filling.

A route to small Drude weight in metals with nested spin fluctuations and enhanced impurity scattering associated with quantum critical phenomena

Abstract It is discussed that the small Drude weight D observed in high- T c cuprates is compatible with the small renormalization amplitude z and not enhanced effective mass m ∗ of quasiparticles even in the framework of Fermi liquid theory. In particular, such a situation is expected if the Fermi surface of quasiparticle is nested as expected near the magnetic metal–insulator transition point. It is also discussed that the quantum critical fluctuations give rise to enhancement of impurity potential through the vertex correction of scattering leading to enhancement of “residual resistivity”. Two cases, physically interesting, are discussed: (1) non-magnetic impurity scattering near the ferromagnetic critical point and (2) non-magnetic impurity near the charge density critical point. The latter case has some relevance to the reduction of superconducting transition temperature of high- T c cuprates in the underdoped region.

Anomalous Fermi Liquid Effects in Two-Dimensional Hubbard Model near Half-Filling

The Landau parameters F 0 s , F 0 a , F 1 s and F 1 a in the two-dimensional Hubbard model are calculated by the second order perturbation method of Abrikosov-Khalatnikov. The following points are revealed as the half-filling is approached: (1) F 0 a changes its sign from negative to positive, if the Coulomb interaction U is strong enough, i.e., \(U/t\gtrsim 2.0 \). This means that the spin density oscillations, zero spin-sound, can propagate there; (2) F 1 s changes its sign from positive to negative, so that we can understand, on the basis of the anisotropic Fermi liquid theory, the behavior of the Drude weight whose magnitude decreases as the half-filling is approached even if there were no mass enhancement; (3) From the results of F 0 s and F 0 a , it is shown that both the charge and spin susceptibility decrease rapidly close to the half-filling. The latter is regarded as the so-called spin-gap behavior.

Enhanced Spin Susceptibility toward the Charge-Ordering Transition in a Two-Dimensional Extended Hubbard Model

We investigate the charge and spin susceptibilities in the vicinity of a charge-ordering transition point on the basis of a two-dimensional extended Hubbard model with nearest-neighbor Coulomb interaction on a square lattice. In order to evaluate the leading contribution of vertex corrections, we construct a new iterative method generating a series of non-skeleton diagrammatic conserving approximations, and utilize the first approximation for the calculation of response functions. This approximation can determine a charge-ordering transition point and static susceptibilities on an equal footing in a sense that the compressibility and spin-susceptibility sum rules are satisfied. As a prominent effect of vertex corrections, we find that the uniform spin susceptibility is enhanced owing to charge fluctuations that develop toward the charge-ordering transition. We also discuss the experimental relevance of our theory for organic conductors, together with its connection to Landaus Fermi-liquid theory.

Coulomb Frustrated Phase Separation in Quasi-Two-Dimensional Organic Conductors on the Verge of Charge Ordering

We study a 3/4-filled two-dimensional extended Hubbard model under the fluctuation–exchange approximation. We find that this model undergoes phase separation in a region of nonzero temperature, where the quantum critical phenomenon of charge ordering dominates. By considering the long-range Coulomb interaction that frustrates this phase separation, we present a mechanism for generating a glassy state in a quasi-two-dimensional organic conductor on the verge of charge ordering.

Charge and Spin States of Transition-Metal Atoms in a Hemoprotein Based on the Extended Haldane-Anderson Model

The charge and spin states of transition-metal atoms in a hemoprotein are studied based on the extended Haldane–Anderson model in which exchange interaction between localized d electrons and orbita...

Crossover Temperature from Non-Fermi Liquid to Fermi Liquid Behavior in Two Types of Impurity Kondo Model

Numerical renormalization-group results on entropy of the anisotropic two-channel Kondo model with the band-width cutoff ( D ) in the presence of a magnetic field ( h ) are obtained to determine crossover temperature from the non-Fermi liquid to Fermi liquid fixed point. It is found that the crossover temperature ( T x ) is given by T x ≡ r T K ∼ D (Δ J / J av ) 2 e -1/ J av when ( h / T K ) 2 ≪ r ≪1 , where T K , J av and Δ J are the Kondo temperature, the average and difference of the exchange coupling constants, respectively. This result indicates that non-Fermi liquid behavior can be seen even if Δ J ≫ T K . Robust similarities of the crossover behavior in the region around the non-Fermi liquid critical point to that of the two-impurity Kondo model are also discussed.

Effects of orbital correlation on Drude weight in ferromagnetic metallic phase of La1−xSrxMnO3

Abstract It is argued that a large discrepancy between the Drude weight and the specific heat coefficient observed in ferromagnetic metallic phase of La1−xSrxMnO3 can be understood as a result of a Fermi-liquid correction F1s due to backward scattering of quasi-particles mediated by antiferro-orbital fluctuations. The Ward identity requires that the single-particle spectral weight at the Fermi level vanishes when F1s→−3.