Finite temperature dynamical correlations for the dimerized spin-1/2 chain

TL;DR

This paper uses DMRG to analyze how finite temperature affects the dynamical spin correlations in a dimerized spin-1/2 chain under magnetic fields, revealing temperature-induced spectral features and broadening effects.

Contribution

It provides a detailed numerical and analytical study of finite temperature dynamical correlations in a dimerized spin chain, including spectral broadening and thermal excitations.

Findings

Spectral features vary significantly with magnetic field strength.

Finite temperature causes additional spectral features from thermal excitations.

Temperature broadens the dispersion of spin-flip excitations asymmetrically.

Abstract

We use the density matrix renormalization group method (DMRG) to compute the frequency and momentum resolved spin-spin correlation functions of a dimerized spin-1/2 chain under a magnetic field at finite temperature. The spectral features strongly depend on the regime of the magnetic field. For increasing magnetic fields, the transitions from a gapped spin liquid phase to a Tomonaga-Luttinger liquid, and then to a totally polarized phase, can be identified in the spectra. Compared to the zero temperature case, the finite temperature excitations give rise to additional spectral features that we compute numerically and identify analytically as transitions from thermally excited states. We compute quantitatively the broadening of the dispersion of a single spin-flip excitation due to the temperature and find a strong asymmetric broadening. We discuss the consequences of these findings for neutron experiments on dimerized one dimensional quantum chains.