Gap-anisotropic model for the narrow-gap Kondo insulators

TL;DR

This paper introduces a theoretical model explaining the formation of a nodal hybridization gap in certain Kondo insulators, emphasizing the role of Hund's interactions and crystal symmetry in shaping the electronic state.

Contribution

The model demonstrates how Hund's interactions and crystal symmetry considerations lead to a dynamically generated nodal Kondo semimetal state in specific insulators.

Findings

Hund's interactions influence the shape of cerium ions

Nodal Kondo semimetal state is energetically favored in low symmetry crystals

The theory accounts for the hybridization gap with nodes in $CeNiSn$ and $CeRhSb$

Abstract

A theory is presented which accounts for the dynamical generation of a hybridization gap with nodes in the Kondo insulating materials $CeNiSn$ and $CeRhSb$. We show that Hunds interactions acting on virtual $4f^2$ configurations of the cerium ion can act to dynamically select the shape of the cerium ion by generating a Weiss field which couples to the shape of the ion. In low symmetry crystals where the external crystal fields are negligible, this process selects a nodal Kondo semimetal state as the lowest energy configuration.