Anomalous excitonic phase diagram in band-gap-tuned Ta2Ni(Se,S)5

Journal Article · Sat Nov 18 00:00:00 UTC 2023 · Nature Communications

DOI: https://doi.org/10.1038/s41467-023-43365-1 · OSTI ID:2217222

Chen, Cheng; Tang, Weichen ; Chen, Xiang ; Kang, Zhibo ; Ding, Shuhan ; Scott, Kirsty; Wang, Siqi; Li, Zhenglu ; Ruff, Jacob P. C.; Hashimoto, Makoto ; Lu, Dong-Hui ; Jozwiak, Chris ; Bostwick, Aaron ; Rotenberg, Eli ; da Silva Neto, Eduardo H. ; Birgeneau, Robert J. ; Chen, Yulin ; Louie, Steven G. ; Wang, Yao ; He, Yu

Abstract During a band-gap-tuned semimetal-to-semiconductor transition, Coulomb attraction between electrons and holes can cause spontaneously formed excitons near the zero-band-gap point, or the Lifshitz transition point. This has become an important route to realize bulk excitonic insulators – an insulating ground state distinct from single-particle band insulators. How this route manifests from weak to strong coupling is not clear. In this work, using angle-resolved photoemission spectroscopy (ARPES) and high-resolution synchrotron x-ray diffraction (XRD), we investigate the broken symmetry state across the semimetal-to-semiconductor transition in a leading bulk excitonic insulator candidate system Ta ₂ Ni(Se,S) ₅ . A broken symmetry phase is found to be continuously suppressed from the semimetal side to the semiconductor side, contradicting the anticipated maximal excitonic instability around the Lifshitz transition. Bolstered by first-principles and model calculations, we find strong interband electron-phonon coupling to play a crucial role in the enhanced symmetry breaking on the semimetal side of the phase diagram. Our results not only provide insight into the longstanding debate of the nature of intertwined orders in Ta ₂ NiSe ₅ , but also establish a basis for exploring band-gap-tuned structural and electronic instabilities in strongly coupled systems.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC02-05CH11231; AC02-76SF00515; SC0022874; SC0024524
• OSTI ID: 2217222
• Journal Information: Nature Communications, Journal Name: Nature Communications Journal Issue: 1 Vol. 14; ISSN 2041-1723
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United Kingdom
• Language: English