Quantum critical dynamical response of the twisted Kitaev spin chain

TL;DR

This paper provides exact calculations of the dynamical response of a twisted Kitaev spin chain at quantum criticality, revealing universal and non-universal features, and explores effects of symmetry breaking and disorder relevant for experiments.

Contribution

It offers the first exact analysis of the dynamical structure factor of the twisted Kitaev spin chain across its quantum critical point, including effects of symmetry breaking and disorder.

Findings

Universal power-law divergence at critical point

Localization-delocalization transition in disordered fields

Finite frequency signatures of quantum criticality

Abstract

The dynamical structure factor of the transverse field Ising model (TFIM) shows universal power-law divergence at its quantum critical point, signatures of which have been arguably observed in inelastic neutron scattering studies of quantum spin chain materials, for example CoNb2O6. However, it has been recently suggested that its microscopic description is better captured in terms of a twisted Kitaev spin chain (TKSC) with bond-anisotropic couplings. Here, we present exact results for the dynamical structure factor of the TKSC across its quantum critical point, analyzing both the universal low-frequency response and the non-universal high-energy features. In addition, we explore extensions of the model including broken glide symmetry as well as the case of random, and incommensurate magnetic fields. Notably, in the latter case the fermionic excitations exhibit a localization-delocalization transition, which is manifest in the dynamical response as a distinct signature at finite frequency. We discuss the relevance of these features for the observation of quantum critical response in experiments.