Abstract
AbstractExcitonic insulator is a coherent electronic phase that results from the formation of a macroscopic population of bound particle-hole pairs—excitons. With only a few candidate materials known, the collective excitonic behavior is challenging to observe, being obscured by crystalline lattice effects. Here we use polarization-resolved Raman spectroscopy to reveal the quadrupolar excitonic mode in the candidate zero-gap semiconductor Ta2NiSe5 disentangling it from the lattice phonons. The excitonic mode pronouncedly softens close to the phase transition, showing its electronic character, while its coupling to noncritical lattice modes is shown to enhance the transition temperature. On cooling, we observe the gradual emergence of coherent superpositions of band states at the correlated insulator gap edge, with strong departures from mean-field theory predictions. Our results demonstrate the realization of a strongly correlated excitonic state in an equilibrium bulk material.
Funder
NSF | Directorate for Mathematical & Physical Sciences | Division of Materials Research
Publisher
Springer Science and Business Media LLC
Subject
Condensed Matter Physics,Electronic, Optical and Magnetic Materials
Reference55 articles.
1. Keldysh, L. V. & Kopaev, Y. Possible instability of the semimetallic state toward Coulomb interaction. Sov. Phys. Solid State 6, 2219 (1965).
2. Kohn, W. Excitonic phases. Phys. Rev. Lett. 19, 439–442 (1967).
3. Halperin, B. I. & Rice, T. M. Possible anomalies at a semimetal-semiconductor transistion. Rev. Mod. Phys. 40, 755–766 (1968).
4. Kohn, W. & Sherrington, D. Two kinds of bosons and Bose condensates. Rev. Mod. Phys. 42, 1–11 (1970).
5. Jérome, D., Rice, T. M. & Kohn, W. Excitonic insulator. Phys. Rev. 158, 462–475 (1967).
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