A Theory of Anisotropic Semiconductor of Heavy Fermions

TL;DR

This paper presents a theoretical model explaining anisotropic hybridization gaps in heavy fermion semiconductors, accounting for experimental anomalies in compounds like CeNiSn through momentum-dependent hybridization effects.

Contribution

It introduces a novel theory linking {oldsymbol{k}}-dependent hybridization to anisotropic gaps and explains experimental phenomena in heavy fermion semiconductors.

Findings

Hybridization gap depends on momentum {oldsymbol{k}}.

Impurity scattering significantly affects residual density of states.

Weak {oldsymbol{k}}-dependence of self-energy leads to semimetallic behavior.

Abstract

It is demonstrated that a {\veck}-dependence of the hybridization matrix element between $f$- and conduction electrons can give rise to an anisotropic hybridization gap of heavy fermions if the filling of electrons corresponds to that of the band insulator. The most interesting case occurs when the hybridization vanishes along some symmetry axis of the crystal reflecting a particular symmetry of the crystal field. The results of a model calculation are consistent with wide range of anomalous properties observed in CeNiSn and its isostructural compounds, the anisotropic semiconductor of heavy fermions. In particular, highly sensitive effect of impurity scattering on the residual density of states for zero energy excitation and the anisotropic temperature dependence of the resistivity are well explained. It is also discussed that a weak semimetallic behavior arises through the weak $\veck$-dependence of the $f$-electron self-energy $\Sigma_{f}(\veck,0)$.