Thermodynamic behavior of correlated electron-hole fluids in van der Waals heterostructures

Ruishi Qi; Andrew Y Joe; Zuocheng Zhang; Yongxin Zeng; Tiancheng Zheng; Qixin Feng; Jingxu Xie; Emma Regan; Zheyu Lu; Takashi Taniguchi; Kenji Watanabe; Sefaattin Tongay; Michael F Crommie; Allan H MacDonald; Feng Wang

doi:10.1038/s41467-023-43799-7

Thermodynamic behavior of correlated electron-hole fluids in van der Waals heterostructures

Nat Commun. 2023 Dec 13;14(1):8264. doi: 10.1038/s41467-023-43799-7.

Authors

Ruishi Qi^#^{1

2}, Andrew Y Joe^#^{3

4}, Zuocheng Zhang¹, Yongxin Zeng⁵, Tiancheng Zheng^{1

6}, Qixin Feng^{1

2}, Jingxu Xie^{2

7}, Emma Regan^{1

2

7}, Zheyu Lu^{2

7}, Takashi Taniguchi⁸, Kenji Watanabe⁹, Sefaattin Tongay¹⁰, Michael F Crommie^{1

2}, Allan H MacDonald⁵, Feng Wang^{11

12

13}

Affiliations

¹ Department of Physics, University of California, Berkeley, CA, 94720, USA.
² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
³ Department of Physics, University of California, Berkeley, CA, 94720, USA. [email protected].
⁴ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. [email protected].
⁵ Department of Physics, University of Texas at Austin, Austin, TX, 78712, USA.
⁶ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, China.
⁷ Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, 94720, USA.
⁸ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.
⁹ Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.
¹⁰ School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA.
¹¹ Department of Physics, University of California, Berkeley, CA, 94720, USA. [email protected].
¹² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. [email protected].
¹³ Kavli Energy NanoSciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. [email protected].

^# Contributed equally.

Abstract

Coupled two-dimensional electron-hole bilayers provide a unique platform to study strongly correlated Bose-Fermi mixtures in condensed matter. Electrons and holes in spatially separated layers can bind to form interlayer excitons, composite Bosons expected to support high-temperature exciton condensates. The interlayer excitons can also interact strongly with excess charge carriers when electron and hole densities are unequal. Here, we use optical spectroscopy to quantitatively probe the local thermodynamic properties of strongly correlated electron-hole fluids in MoSe₂/hBN/WSe₂ heterostructures. We observe a discontinuity in the electron and hole chemical potentials at matched electron and hole densities, a definitive signature of an excitonic insulator ground state. The excitonic insulator is stable up to a Mott density of ~0.8 × 10¹² cm^-2 and has a thermal ionization temperature of ~70 K. The density dependence of the electron, hole, and exciton chemical potentials reveals strong correlation effects across the phase diagram. Compared with a non-interacting uniform charge distribution, the correlation effects lead to significant attractive exciton-exciton and exciton-charge interactions in the electron-hole fluid. Our work highlights the unique quantum behavior that can emerge in strongly correlated electron-hole systems.

Abstract

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