biostudies-literatureChen CU.S. Department of EnergyU.S. Department of Energy (DOE)DOE | SC | Basic Energy Sciences (BES)National Science Foundation (NSF)DOE | SC | Basic Energy SciencesNational Science Foundation7512https://www.ebi.ac.uk/biostudies/studies/S-EPMC10657405biostudies-literatureUnknown14(1)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<sub>2</sub>Ni(Se,S)<sub>5</sub>. A broken symmetry phase is found to be continuously suppressedNature communicationsAnomalous excitonic phase diagram in band-gap-tuned Ta<sub>2</sub>Ni(Se,S)<sub>5</sub>.PMC10657405DE-AC02-05-CH11231DMR-2239171DE-SC0022874Rotenberg Eda Silva Neto EHBirgeneau RJChen CKang ZLouie SGScott KLi ZRuff JPCHe YDing SBostwick AWang SHashimoto MChen YChen XTang WJozwiak CWang YLu DHfalseAnomalous excitonic phase diagram in band-gap-tuned Ta<sub>2</sub>Ni(Se,S)<sub>5</sub>.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<sub>2</sub>Ni(Se,S)<sub>5</sub>. A broken symmetry phase is found to be continuously suppressed2023-01-01T00:00:00Z2023 Nov2025-04-22T09:27:43.992Z2025-04-05T23:04:31.541ZS-EPMC106574053798041910.1038/s41467-023-43365-1