Abstract
Inelastic neutron-scattering and finite-temperature density matrix renormalization group (DMRG) calculations are used to investigate the spin excitation spectrum of the Heisenberg spin chain compound at several temperatures in a magnetic field near saturation. Critical correlations characteristic of the predicted quantum phase transition occurring at saturation are shown to be consistent with the observed neutron spectra. The data is well described with a scaling function computed using a free fermion description of the spins, valid close to saturation, and the corresponding scaling limits. One of the most prominent nonuniversal spectral features of the data is a novel thermally activated longitudinal mode that remains underdamped across most of the Brillouin zone.
1 More- Received 18 July 2017
DOI:https://doi.org/10.1103/PhysRevB.96.134406
©2017 American Physical Society