Deformed triangular lattice antiferromagnets in a magnetic field: role of spatial anisotropy and Dzyaloshinskii-Moriya interactions

TL;DR

This study investigates how spatial anisotropy, Dzyaloshinskii-Moriya interactions, and quantum fluctuations influence the complex magnetic phases of a triangular antiferromagnet, explaining experimental observations in Cs_2CuBr_4.

Contribution

It provides a comprehensive analysis of the interplay between anisotropy, Dzyaloshinskii-Moriya interactions, and quantum effects in shaping the phase diagram of triangular antiferromagnets, combining multiple theoretical approaches.

Findings

Identification of numerous incommensurate and commensurate phases

Explanation of the rich phase diagram observed in Cs_2CuBr_4

Insights into the competition between different interactions and quantum fluctuations

Abstract

Recent experiments on the anisotropic spin-1/2 triangular antiferromagnet Cs_2CuBr_4 have revealed a remarkably rich phase diagram in applied magnetic fields, consisting of an unexpectedly large number of ordered phases. Motivated by this finding, we study the role of spatial anisotropy, Dzyaloshinskii-Moriya interactions, and quantum fluctuations on the magnetization process of a triangular antiferromagnet, coming from the semiclassical limit. The richness of the problem stems from two key facts: 1) the classical isotropic model exhibits a large accidental ground state degeneracy, and 2) these three ingredients compete with one another and split this degeneracy in opposing ways. Using a variety of complementary approaches, including extensive Monte Carlo numerics, spin-wave theory, and an analysis of Bose-Einstein condensation of magnons at high fields, we find that their interplay gives rise to a complex phase diagram consisting of numerous incommensurate and commensurate phases. Our results shed light on the observed phase diagram for Cs_2CuBr_4 and suggest a number of future theoretical and experimental directions that will be useful for obtaining a complete understanding of this material's interesting phenomenology.