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TT: Fachverband Tiefe Temperaturen

TT 23: Poster Session: Emerging Phenomena in Superconducting Low Dimensional Hybrid Systems

TT 23.3: Poster

Donnerstag, 30. September 2021, 13:30–16:00, P

Electronic phase diagram of the excitonic insulator candidates Ta₂Ni(Se_1−xS_x)₅ — •Pavel Volkov¹, Mai Ye¹, Himanshu Lohani², Irena Feldman², Amit Kanigel², and Girsh Blumberg^1,3 — ¹Rutgers University — ²Technion — ³NICPB, Tallin

Excitonic insulator is a phase driven by Coulomb attraction between electrons and holes leading to a proliferation of particle-hole pairs. However, excitonic insulators break lattice symmetries, raising the question of whether a particular transition is excitonic or structural. I will demonstrate that electronic Raman scattering can be used to elucidate the transition origin in the Ta₂Ni(Se_1−xS_x)₅ family of candidate materials. In particular, at low x the transition is excitonic-driven and shows deviations from mean-field predictions indicating strong correlations. At large sulfur content, the contribution of excitons diminishes and the transition becomes purely structural. The study reveals a quantum phase transition of an excitonic insulator masked by a preemptive structural order.