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Journal Article

Zero-gap semiconductor to excitonic insulator transition in Ta2NiSe5

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Boris,  A.
Department Solid State Spectroscopy (Bernhard Keimer), Max Planck Institute for Solid State Research, Max Planck Society;

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Keimer,  B.
Department Solid State Spectroscopy (Bernhard Keimer), Max Planck Institute for Solid State Research, Max Planck Society;

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Takagi,  H.
Department Quantum Materials (Hidenori Takagi), Max Planck Institute for Solid State Research, Max Planck Society;

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Citation

Lu, Y., Kono, H., Larkin, T., Rost, A., Takayama, T., Boris, A., et al. (2017). Zero-gap semiconductor to excitonic insulator transition in Ta2NiSe5. Nature Communications, 8: 14408.


Cite as: https://hdl.handle.net/21.11116/0000-000E-CF9A-C
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 similar to 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 domelike behaviour around E(G similar to)0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta2NiSe5.