Theory for Magnetic Anisotropy of Field-Induced Insulator-to-Metal Transition in Cubic Kondo Insulator YbB_{12}

TL;DR

This paper presents a theoretical study of magnetic anisotropy in the insulator-to-metal transition of YbB_{12}, revealing how magnetic field direction influences gap closing, with results aligning well with experimental observations.

Contribution

It introduces a detailed band model calculation that explains the anisotropic gap closing in YbB_{12} under magnetic fields, improving upon previous qualitative analyses.

Findings

Magnetization curves are nearly isotropic due to cubic symmetry.

Gap closes faster in the (100) direction than in (110) and (111).

Numerical calculations agree better with experimental data.

Abstract

Magnetization and energy gap of Kondo insulator YbB_{12} are calculated theoretically based on the previously proposed tight-binding model composed of Yb 5d$\epsilon$ and 4f $\Gamma_8$ orbitals. It is found that magnetization curves are almost isotropic, naturally expected from the cubic symmetry, but that the gap-closing field has an anisotropy: the gap closes faster for the field in (100) direction than in (110) and (111) directions, in accord with the experiments. This is qualitatively understood by considering the maximal eigenvalues of the total angular momentum operators projected on each direction of the magnetic field. But the numerical calculation based on the band model yields better agreement with the experiment.