Ground states of a frustrated spin-1/2 antifferomagnet: Cs_2CuCl_4 in a magnetic field

TL;DR

This paper investigates the magnetic ground states of Cs$_2$CuCl$_4$ under magnetic fields, combining classical and quantum approaches to match experimental observations and understand phase behavior.

Contribution

It provides a comprehensive analysis of the phase diagram and quantum fluctuations in Cs$_2$CuCl$_4$ using classical, spinwave, and Bose gas methods, highlighting the effects of anisotropy and interactions.

Findings

Phase diagram as a function of magnetic field strength for both directions.

Quantum fluctuations modify the ordering wavevector and moments.

Theoretical results align well with experimental data.

Abstract

We present detailed calculations of the magnetic ground state properties of Cs$_2$CuCl$_4$ in an applied magnetic field, and compare our results with recent experiments. The material is described by a spin Hamiltonian, determined with precision in high field measurements, in which the main interaction is antiferromagnetic Heisenberg exchange between neighboring spins on an anisotropic triangular lattice. An additional, weak Dzyaloshinkii-Moriya interaction introduces easy-plane anisotropy, so that behavior is different for transverse and longitudinal field directions. We determine the phase diagram as a function of field strength for both field directions at zero temperature, using a classical approximation as a first step. Building on this, we calculate the effect of quantum fluctuations on the ordering wavevector and components of the ordered moments, using both linear spinwave theory and a mapping to a Bose gas which gives exact results when the magnetization is almost saturated. Many aspects of the experimental data are well accounted for by this approach.