Finite-temperature lineshapes in gapped quantum spin chains

Understand

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.