Research Update: lattice dynamics of excitonic insulator Ta2Ni(Se1-xSx)5

What role does crystalline lattice play in the emergence of electronic order? Following our previous work on the excitonic soft mode and emergent coherence of Ta2NiSe5 (WebLink: npj Quantum Materials 6, 52 (2021) ArXiv Link: arXiv:2007.07344 PDF: File), we explore the lattice dynamics of the excitonic insulator candidate family Ta2Ni(Se1-xSx)5 by means of Raman scattering. Strong interactions between optical phonons and a continuum of soft quadrupolar excitons lead to broad asymmetric lineshapes and anomalous temperature dependence of the phonon signatures. They further develop a model allowing to disentangle the intrinsic responses of excitons and phonons and assess their respective contributions in the phase diagram. 

WebLink: PhysRevB.104.045102 (2021) ArXiv Link: arXiv:2102.07912 PDF: File (Editors’ Suggestion)