Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4

TL;DR

This paper investigates the spin dynamics of Cs_2CuCl_4, revealing limitations of linear spin wave theory and highlighting the importance of magnon interactions and quantum effects in understanding its magnetic excitations.

Contribution

The study extends beyond linear spin wave theory by incorporating magnon interactions via a 1/S expansion, providing a more accurate description of the dynamical structure factor.

Findings

Significant spectral weight shift to higher energies compared to linear theory

Presence of strong scattering continua in experimental data

Failure of 1/S expansion to explain large quantum renormalization of exchange energies

Abstract

We study dynamical properties of the anisotropic triangular quantum antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have established that the dynamical spin correlations cannot be understood within a linear spin wave analysis. We go beyond linear spin wave theory by taking interactions between magnons into account in a 1/S expansion. We determine the dynamical structure factor and carry out extensive comparisons with experimental data. We find that compared to linear spin wave theory a significant fraction of the scattering intensity is shifted to higher energies and strong scattering continua are present. However, the 1/S expansion fails to account for the experimentally observed large quantum renormalization of the exchange energies.