Raman scattering in a Heisenberg {\boldmath $S=1/2$} antiferromagnet on the triangular lattice

TL;DR

This paper studies two-magnon Raman scattering in a $S=1/2$ Heisenberg antiferromagnet on a triangular lattice, revealing how quantum corrections and magnon interactions shape the spectral features and continuum.

Contribution

It provides a detailed analysis of how 1/S corrections and magnon-magnon interactions affect Raman spectra in a non-collinear antiferromagnet, highlighting differences from collinear cases.

Findings

1/S corrections significantly alter the Raman intensity profile.

Final-state interactions produce a broad Raman continuum around twice the roton energy.

The spectral support narrows and peaks are modified due to quantum effects.

Abstract

We investigate two-magnon Raman scattering from the $S=1/2$ Heisenberg antiferromagnet on the triangular lattice, considering both the effect of renormalization of the one-magnon spectrum by 1/S corrections and final-state magnon-magnon interactions. The bare Raman intensity displays two peaks related to one-magnon van-Hove singularities. We find that 1/S self-energy corrections to the one-magnon spectrum strongly modify this intensity profile. The central Raman-peak is significantly enhanced due to plateaus in the magnon dispersion, the high frequency peak is suppressed due to magnon damping, and the overall spectral support narrows considerably. Additionally we investigate final-state interactions by solving the Bethe-Salpeter equation to $O(1/S)$. In contrast to collinear antiferromagnets, the non-collinear nature of the magnetic ground state leads to an irreducible magnon scattering which is retarded and non-separable already to lowest order. We show that final-state interactions lead to a rather broad Raman-continuum centered around approximately twice the 'roton'-energy. We also discuss the dependence on the scattering geometry.