Skip to main content
Physics CAMP: Role of electron-phonon interaction in a 1D excitonic system
Add to Calendar 2023-09-25T19:45:00 2023-09-25T20:45:00 UTC Physics CAMP: Role of electron-phonon interaction in a 1D excitonic system 339 Davey Laboratory
Start DateMon, Sep 25, 2023
3:45 PM
End DateMon, Sep 25, 2023
4:45 PM
Presented By
Yu He, Yale University
Event Series: CAMP Seminar

The search for spontaneously formed excitons in solid state materials has lasted for more than half a century. Despite intense experimental effort, a concurrent structural transition caused by electron-phonon interaction often complicates the search. Lately, Ta2Ni(Se,S)5 system has received increasing attention as a potential quasi-1D excitonic insulator, with a normal state continuously tunable from a semimetal to a semiconductor. Combining angle-resolved photoemission spectroscopy and first principles calculation, we discover negative electronic compressibility in charge-doped ground state, and electron-phonon interaction may be solely accountable [1]. We also report an anomalous sudden disappearance of "pre-formed" excitons in the normal state across the semimetal-to-semiconductor transition, which contradicts Coulomb-interaction-only models [2]. By comparing the experimental phase diagram with existing model predictions, we highlight the importance of electron-phonon interaction in the general consideration of "excitonic insulators" especially at low dimensions.
Reference: [1] Chen et al., arXiv:2203.06817 [2] Chen et al., to appear