Abstract
Atomically thin nanosheets, as recently realized using van der Waals layered materials, offer a versatile platform for studying the stability and tunability of the correlated electron phases in the reduced dimension. Here, we investigate a thickness-dependent excitonic insulating (EI) phase on a layered ternary chalcogenide Ta2NiSe5. Using Raman spectroscopy, scanning tunneling spectroscopy, and in-plane transport measurements, we found no significant changes in crystalline and electronic structures as well as disorder strength in ultrathin Ta2NiSe5 crystals with a thickness down to five layers. The transition temperature, Tc, of ultrathin Ta2NiSe5 is reduced from its bulk value by ΔTc/Tcbulk ≈ -9%, which strongly contrasts the case of 1T-TiSe2, another excitonic insulator candidate, showing an increase of Tc by ΔTc/Tcbulk ≈ +30%. This difference is attributed to the dominance of interband Coulomb interaction over electron-phonon interaction and its zero-ordering wave vector due to the direct band gap structure of Ta2NiSe5. The out-of-plane correlating length of the EI phase is estimated to have monolayer thickness, suggesting that the EI phase in Ta2NiSe5 is highly layer-confined and in the strong coupling limit.
Original language | English |
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Pages (from-to) | 8888-8894 |
Number of pages | 7 |
Journal | ACS Nano |
Volume | 10 |
Issue number | 9 |
DOIs | |
State | Published - 27 Sep 2016 |
Bibliographical note
Publisher Copyright:© 2016 American Chemical Society.
Keywords
- direct band gap semiconductor
- excitonic insulator
- interband Coulomb interaction
- ternary chalcogenides
- ultrathin crystals
- van der Waals materials