Finite-temperature lineshapes in gapped quantum spin chains

TL;DR

This paper analyzes how the dynamical structure factor in gapped quantum spin chains evolves with temperature, revealing asymmetric lineshapes that become Lorentzian only at very low temperatures, aiding experimental data interpretation.

Contribution

It applies integrable quantum field theory to determine the low-temperature evolution of DSF lineshapes in gapped spin chains, highlighting asymmetry and temperature dependence.

Findings

Lineshapes are asymmetric at finite temperatures.

Lorentzian lineshapes occur only at very low temperatures.

Results are relevant for interpreting neutron scattering experiments.

Abstract

We consider the finite-temperature dynamical structure factor (DSF) of gapped quantum spin chains such as the spin one Heisenberg model and the transverse field Ising model in the disordered phase. At zero temperature the DSF in these models is dominated by a delta-function line arising from the coherent propagation of single particle modes. Using methods of integrable quantum field theory we determine the evolution of the lineshape at low temperatures. We show that the line shape is in general asymmetric in energy and becomes Lorentzian only at temperatures far below the gap. We discuss the relevance of our results for the analysis of inelastic neutron scattering experiments on gapped spin chain systems such as CsNiCl_3 and YBaNiO_5.