Signatures of Confinement in Raman Spectroscopy of Ising Spin Chains

Abstract

<p>Confinement of excitations is usually considered as a phenomenon of high-energy physics. How-<br> ever, over the recent years, related effects have been discussed in condensed matter settings as well.<br> A paradigmatic example is the formation of mesonic bound states in spin chains with linear con-<br> finement between domain walls. A prominent candidate material is the quasi-one dimensional Ising<br> magnet CoNb2O6 for which mesonic bound states have been detected by neutron scattering exper-<br> iments. In this work, we study the Raman response of a twisted Kitaev chain in the presence of a<br> magnetic field as a minimal model for confinement in CoNb2O6 and compute the response within<br> the theory by Fleury and Loudon. We show that the bound states directly manifest themselves as<br> sharp peaks in the Raman response, which we numerically compute using Matrix Product States.<br> We find that the main features of the spectrum can be well understood by a trial wave-function,<br> which contains a few solitonic excitations only. Moreover, when approaching the critical regime<br> Raman spectroscopy can be used to directly detect Ising quantum criticality via the emergence of<br> the famous E8 symmetry in the response spectrum.</p&gt