On thermal fluctuations in quantum magnets

TL;DR

This study investigates how thermal fluctuations influence the dynamics of a gapped quantum magnet, revealing non-universal line broadening behaviors and introducing a new paradigm for quantum system analysis.

Contribution

It combines experimental neutron scattering with theoretical analysis to challenge the universality of line broadening in 1D quantum systems.

Findings

Observation of thermally induced central peak

Identification of asymmetric scattering continuum

Counterexample to universality assertions

Abstract

The effect of thermal fluctuations on the dynamics of a gapped quantum magnet is studied using inelastic neutron scattering on copper nitrate, a model material for the one-dimensional (1D) bond alternating Heisenberg chain, combined with theoretical and numerical analysis. We observe and interpret the thermally induced central peak due to intraband scattering as well as the thermal development of an asymmetric continuum of scattering. We relate this asymmetric line broadening to hard core constraints and quasi-particle interactions. Our findings are a counter example to recent assertions of universality of line broadening in 1D systems and are to be considered as a new paradigm of behaviour, applicable to a broad range of quantum systems.