Dynamical mean-field theory for the anisotropic Kondo semiconductor: Temperature and magnetic field dependence

Abstract

We investigate the periodic Anderson model with k-dependent c-f mixing reproducing the point nodes of the hybridization gap by using the dynamical mean-field theory combined with the exact diagonalization method. At low temperature below a coherence temperature T0, the imaginary part of the self-energy is found to be proportional to T 2 and the pseudogap with two characteristic energies∆1 and∆2 is clearly observed for T ≪ T0, while the pseudogap is smeared with increasing T and then disappears at high temperature T > ∼ T0 due to the evolution of the imaginary self-energy. When the Coulomb interaction between f electrons U increases,∆1,∆2, and T0 together with Tmax at which the magnetic susceptibility is maximum decrease in proportion to the renormalization factor Z resulting in a heavy-fermion semiconductor with a large mass enhancement m * /m = Z −1 for large U . We also examine the effect of the external magnetic field H and find that the magnetization M shows two metamagnetic anomalies H1 and H2 corresponding to∆1 and∆2 which are reduced due to the effect of H together with Z. Remarkably, Z −1 is found to be largely enhanced due to H especially for H1 < ∼ H < ∼ H2, where the field induced heavy-fermion state is realized. The obtained results seem to be consistent with the experimental results observed in the anisotropic Kondo semiconductors such as CeNiSn. * takemi@phys.sc.niigata-u.ac.jp 1 A. C. Hewson, The Kondo Problem to Heavy Fermions (Cambridge University Press, 1993). 2 J. W. Allen, B. Batlogg, and P. Wachter, Phys. Rev. B,

Thermoelectricity in correlated narrow-gap semiconductors

“…Having in mind anisotropic Kondo insulators, Yamada and Ono [329] studied the PAM with non-local hybridizations. They evidenced, among others, that the uniform and the local magnetic susceptibility virtually coincide down to T max χ .…”

Thermoelectricity in correlated narrow-gap semiconductors

“…As a proxy for the experimental crossover in the spin response, we consider the maximum, T max χ , in the local (DMFT) susceptibility χ ω=0 loc (T ) = g 2 β 0 dτ LL S L z (τ )S L z (0) 49 . We limit the sum over 49 In the PAM the uniform and the local magnetic susceptibility practically coincide down to T max χ [330]. For a discussion of local vs. uniform susceptibility for the Hubbard model, see Section (II C) and Section (II D 1).…”

“…local susceptibility is actually larger than the uniform susceptibility, potentially aggravating congruency with experiment. In the periodic Anderson model, the local and uniform susceptibility coincide above T max χ [330]. This impasse is solved as follows: (i) experimentally: As mentioned before, magnetic neutron spectroscopy experiments [160,161] evidenced a ferromagnetic-like susceptibility, i.e., a χ(q, ω → 0) that is peaked at q = 0 and equivalent points.…”

“…Having in mind anisotropic Kondo insulators, Yamada and Ono [330] studied the PAM with non-local hybridizations. They evidenced, among others, that the uniform and the local magnetic susceptibility virtually coincide down to T max χ .…”

Kramers doublet ground state in topological Kondo insulators

“…To illustrate the point consider the hybridization block c † k V m J (k)f k for one of the Kramers' doublets Γ 5/2 m J . Following previous work [23] the 2 × 2 hybridization matrix reads…”