A Theory of Anisotropic Semiconductor of Heavy Fermions

Abstract

It is demonstrated that a k-dependence of the hybridizationmatrix element between f- and conduction electrons can give rise toan anisotropic hybridization gap of heavy fermions if the filling ofelectrons corresponds to that of the band insulator. The most interestingcase occurs when the hybridization vanishes along some symmetry axisof the crystal reflecting a particular symmetry of the crystal field.The results of a model calculation are consistent with wide range ofanomalous properties observed in CeNiSn and its isostructural compounds, the anisotropic semiconductor of heavy fermions. In particular, highlysensitive effect of impurity scattering on the residual density ofstates for zero energy excitation and the anisotropic temperaturedependence of the resistivity are well explained. It is also discussedthat a weak semimetallic behavior arises through the weak k-dependence\of the f-electron self-energy Σ_f(k, 0).