Dynamic correlations of frustrated quantum spins from high-temperature expansion

TL;DR

This paper introduces a high-temperature expansion method to compute the dynamic structure factor of frustrated quantum spin systems, enabling unbiased analysis of complex models at intermediate temperatures.

Contribution

It develops a dynamic high-temperature expansion approach for the DSF, providing benchmarks and applying it to frustrated 2D and 3D antiferromagnets, including recent experimental data.

Findings

Reproduced DSF for S=1 pyrochlore NaCaNi2F7.

Gained insights into the intermediate temperature regime of the S=1/2 triangular lattice.

Provided an open-source tool for arbitrary lattice geometries.

Abstract

For quantum spin systems in equilibrium, the dynamic structure factor (DSF) is among the most feature-packed experimental observables. However, from a theory perspective it is often hard to simulate in an unbiased and accurate way, especially for frustrated and high-dimensional models at intermediate temperature. To address this challenge, we compute the DSF from a dynamic extension of the high-temperature expansion to frequency moments. We focus on nearest-neighbor Heisenberg models with spin-lengths S=1/2 and 1. We provide comprehensive benchmarks and consider a variety of frustrated two- and three-dimensional antiferromagnets as applications. In particular we shed new light on the anomalous intermediate temperature regime of the S=1/2 triangular lattice model and reproduce the DSF measured recently for the S=1 pyrochlore material NaCaNi2F7. An open-source numerical implementation for arbitrary lattice geometries is also provided.