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Zero-gap semiconductor to excitonic insulator transition in Ta₂NiSe₅.

ABSTRACT: The excitonic insulator is a long conjectured correlated electron phase of narrow-gap semiconductors and semimetals, driven by weakly screened electron-hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta₂NiSe₅ is a narrow-gap semiconductor with a small one-electron bandgap E_G of <50 meV. Below T_C=326 K, a putative excitonic insulator is stabilized. Here we report an optical excitation gap E_op ∼0.16 eV below T_C comparable to the estimated exciton binding energy E_B. Specific heat measurements show the entropy associated with the transition being consistent with a primarily electronic origin. To further explore this physics, we map the T_C-E_G phase diagram tuning E_G via chemical and physical pressure. The dome-like behaviour around E_G∼0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta₂NiSe₅.

SUBMITTER: Lu YF

PROVIDER: S-EPMC5316885 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Zero-gap semiconductor to excitonic insulator transition in Ta2NiSe5.

Lu Y F YF Kono H H Larkin T I TI Rost A W AW Takayama T T Boris A V AV Keimer B B Takagi H H

Nature communications 20170216

The excitonic insulator is a long conjectured correlated electron phase of narrow-gap semiconductors and semimetals, driven by weakly screened electron-hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta2NiSe5 is a narrow-gap semiconductor with a small one-electron bandgap EG of <50 meV. Below TC=326 K, a putative excitonic insulator is stabilized. Here we report an opti ...[more]

PMID: 28205553

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