X-ray Diffraction Study of Single-Layer ZrTe₂

Excitonic insulators, wherein bound electron-hole pairs called excitons emerge and renormalize the electronic structures of semiconductors and semimetals, are fundamental platforms for manipulating the many-body physics of bosonic quasiparticles. While excitonic systems have been artificially created via electrical and optical means, few materials themselves are predicted to harbor an excitonic ground state. Specifically, our group’s recent angle-resolved photoemission spectroscopy (ARPES) results, together with first-principles calculations, have revealed an excitonic insulator phase transition in single-layer ZrTe₂, which is entirely absent in the bulk limit; this excitonic phase can be relevant to the mechanism of the charge density wave (CDW) phase in single-layer ZrTe₂, but little to no evidence from surface X-ray diffraction—the most direct probe of CDW and its associated atomic lattice displacements—has yet been offered. In this talk, we will present our recent X-ray diffraction data on single-layer ZrTe₂. The results are pertinent to understanding the nature of the novel CDW phase transition in single‑layer ZrTe₂.