Flat spin wave dispersion in a triangular antiferromagnet

TL;DR

This paper investigates the spin wave spectrum of a 2D triangular quantum antiferromagnet using 1/S expansion, revealing a nearly flat magnon dispersion and significant corrections due to non-collinearity, aligning with recent series expansion results.

Contribution

It provides the first-order 1/S expansion analysis showing flat magnon dispersion in a triangular antiferromagnet, highlighting non-trivial quantum corrections.

Findings

Magnon dispersion is nearly flat in large parts of the Brillouin zone.

First-order 1/S corrections are significant due to non-collinearity.

Results agree quantitatively with recent series expansion studies.

Abstract

The excitation spectrum of a S=1/2 2D triangular quantum antiferromagnet is studied using 1/S expansion. Due to the non-collinearity of the classical ground state significant and non-trivial corrections to the spin wave spectrum appear already in the first order in 1/S in contrast to the square lattice antiferromagnet. The resulting magnon dispersion is almost flat in a substantial portion of the Brillouin zone. Our results are in quantitative agreement with recent series expansion studies by Zheng, Fjaerestad, Singh, McKenzie, and Coldea [PRL 96, 057201 (2006) and cond-mat/0608008].