Classical Kitaev model in a magnetic field

TL;DR

This paper analyzes the classical Kitaev honeycomb model under magnetic fields, revealing a spin liquid regime, its properties, and robustness to site dilution, with implications for spin-orbit coupled magnets.

Contribution

It provides a detailed analysis of the classical Kitaev model in a magnetic field, identifying a spin liquid phase and its characteristics, including correlations and response to dilution.

Findings

Existence of a finite-field spin liquid regime

Short-range correlations in finite field

Robustness of magnetization to site dilution

Abstract

Motivated by experiments on spin-orbit coupled magnets with Kitaev exchange in magnetic fields, we present an analysis of the classical Kitaev honeycomb model in the presence of a magnetic field. We show that there is a spin liquid regime that exists within a finite window of fields from zero up to a finite threshold before transitioning into the polarized paramagnet. We uncover constraints that spins need to satisfy in the ground state and show that they determine the exact limiting zero temperature behavior of the heat capacity and magnetic susceptibility within the spin liquid as a function of field. When the field is finite, both the two-point spin and the quadrupolar correlations are short-ranged, in contrast to the zero-field case. We rationalize an effective mass for the quadrupolar correlations in terms of a coarse-grained theory with fluctuating effective charge degrees of freedom. Finally, we show that weak site-dilution does not change the magnetization within the spin liquid -- a kind of "perfect" compensation of the site dilution.