The field-angle anisotropy of proximate Kitaev systems under an in-plane magnetic field

TL;DR

This study explores how magnetic excitations in proximate Kitaev systems respond to in-plane magnetic fields, revealing anisotropic behaviors and their relation to non-Abelian spin liquid phases, using exact diagonalization and spin wave theory.

Contribution

It provides a detailed analysis of field-angle dependence of magnetic excitations and their anisotropic gaps near the critical field in Kitaev systems, linking theory with experimental observations.

Findings

Magnetic excitation gap is determined by magnon at M points.

Gap exhibits strong anisotropy with field direction.

Specific heat shows anisotropic behavior similar to non-Abelian spin liquid predictions.

Abstract

We have investigated the field-angle behaviors of magnetic excitations under an in-plane magnetic field for proximate Kitaev systems. By employing the exact diagonalization method in conjunction with the linear spin wave theory, we have demonstrated that the magnetic excitation gap in the polarized phase is determined by the magnon excitation at $M$ points and has a strong anisotropy with respect to the field direction in the vicinity of the critical field limit. The specific heat from this magnon excitation bears qualitatively the same anisotropic behaviors as expected one for the non-Abelian spin liquid phase in the Kitaev model and experimentally observed one of the intermediate phases in $\alpha$-RuCl$_3$.