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

• Type of Material: Article
• Authors: Cheng Chen, University of Oxford; Weichen Tang, University of California Berkeley; Xiang Chen, University of California Berkeley; Zhibo Kang, Yale University; Shuhan Ding, Clemson University; Kirsty Scott, Yale University; Siqi Wang, Yale University; Zhenglu Li, University of California Berkeley; Jacob P. C. Ruff, Cornell University; Makoto Hashimoto, SLAC National Accelerator Laboratory; Dong-Hui Lu, SLAC National Accelerator Laboratory; Chris Jozwiak, Lawrence Berkeley National Laboratory; Aaron Bostwick, Lawrence Berkeley National Laboratory; Eli Rotenberg, Lawrence Berkeley National Laboratory; Eduardo H. da Silva Neto, Yale University; Robert J. Birgeneau, University of California Berkeley; Yulin Chen, University of Oxford; Steven G. Louie, University of California Berkeley; Yao Wang, Emory University; Yu He, Yale University
• Language: English
• Date: 2023
• Publisher: Nature
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2023
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): https://doi.org/10.1038%2Fs41467-023-43365-1
• Title of Journal or Parent Work: Nature Communications
• Volume: 14
• Start Page: 7512
• Grant/Funding Information: Use of the Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. M. H. and D. L. acknowledge the support of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Contract No. DE-AC02-76SF00515. This research used resources of the Advanced Light Source, a US DOE Office of Science User Facility under Contract No. DE-AC02-05CH11231. Research conducted at the Center for High-Energy X-ray Science (CHEXS) is supported by the National Science Foundation (BIO, ENG and MPS Directorates) under award DMR-1829070. Work at Lawrence Berkeley National Laboratory was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 within the Quantum Materials Program (KC2202) which provided the numerical simulations and within the Theory of Materials Program (KC2301) which provided the DFT calculations. The quantum many-body simulations (S.D. and Y.W.) are supported initially by U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Early Career Award No. DE-SC0022874 and are completed with the support under award No. DE-SC0024524. The many-body and DFT simulations were performed on the Frontera and Stampede2 computing system, respectively, at the Texas Advanced Computing Center. The work at Yale University is partially supported by the National Science Foundation (NSF) under DMR-2239171.
• Keywords: Electronic properties and materials; Phase transitions and critical phenomena
• Research Categories: Physics, Molecular

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 Ta2Ni(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 Ta2NiSe5, but also establish a basis for exploring band-gap-tuned structural and electronic instabilities in strongly coupled systems.