Zero-gap semiconductor to excitonic insulator transition in Ta<sub>2</sub>NiSe<sub>5</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 28205553.
- Also identified by DOI 10.1038/ncomms14408 and PMC identifier 5316885.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
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. Ta<sub>2</sub>NiSe<sub>5</sub> is a narrow-gap semiconductor with a small one-electron bandgap E<sub>G</sub> of <50 meV. Below T<sub>C</sub>=326 K, a putative excitonic insulator is stabilized. Here we report an optical excitation gap E<sub>op</sub> ∼0.16 eV below T<sub>C</sub> comparable to the estimated exciton binding energy E<sub>B</sub>. 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<sub>C</sub>-E<sub>G</sub> phase diagram tuning E<sub>G</sub> via chemical and physical pressure. The dome-like behaviour around E<sub>G</sub>∼0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta<sub>2</sub>NiSe<sub>5</sub>.