Pal, S and Grover, S and Harnagea, L and Telang, P and Singh, A and Muthu, DVS and Waghmare, UV and Sood, AK (2020) Destabilizing excitonic insulator phase by pressure tuning of exciton-phonon coupling. In: Physical Review Research, 2 (4).
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Abstract
Ta2NiSe5 is an excitonic insulator (EI) exhibiting bound electron-hole pairs condensed at room temperature, which transforms to a small-gap semiconducting state above T=325 K simultaneously undergoing a phonon-related structural transition. Despite the clear experimental evidence for strong exciton-phonon coupling, its role and the origin of EI state in terms of BCS versus Bose-Einstein condensation mechanisms are unclear. Motivated by the tunability of these mechanisms with pressure, we report Raman experiments under pressure of Ta2NiSe5 and first-principles theoretical analysis of two pressure-induced transitions at 1 and 3 GPa. We present a simple method to derive the exciton-phonon coupling within density functional theory and show using a model Hamiltonian that reducing strength of this coupling relative to electronic gap and phonon frequency destabilizes the EI state with pressure. In addition to connecting with the Raman anomalies observed under pressure, our simple picture explains the recently observed phonon-coupled state of exciton condensate. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
| Item Type: | Journal Article |
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| Publication: | Physical Review Research |
| Publisher: | American Physical Society |
| Additional Information: | The copyright for this article belongs to the Author(s). |
| Keywords: | Bose-Einstein condensation; Density functional theory; Excitons; Hamiltonians; Nickel compounds; Selenium compounds; Statistical mechanics; Tantalum compounds, Exciton-phonon couplings; Excitonic insulator; Experimental evidence; Model Hamiltonians; Phonon frequencies; Pressure-induced transitions; Raman experiments; Structural transitions, Phonons |
| Department/Centre: | Division of Physical & Mathematical Sciences > Physics |
| Date Deposited: | 10 Jan 2023 09:22 |
| Last Modified: | 10 Jan 2023 09:22 |
| URI: | https://eprints.iisc.ac.in/id/eprint/79015 |
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