Signatures of the exciton gas phase and its condensation in monolayer 1T-ZrTe2

Yekai Song; Chunjing Jia; Hongyu Xiong; Binbin Wang; Zhicheng Jiang; Kui Huang; Jinwoong Hwang; Zhuojun Li; Choongyu Hwang; Zhongkai Liu; Dawei Shen; Jonathan A Sobota; Patrick Kirchmann; Jiamin Xue; Thomas P Devereaux; Sung-Kwan Mo; Zhi-Xun Shen; Shujie Tang

doi:10.1038/s41467-023-36857-7

Signatures of the exciton gas phase and its condensation in monolayer 1T-ZrTe₂

Nat Commun. 2023 Feb 27;14(1):1116. doi: 10.1038/s41467-023-36857-7.

Authors

Yekai Song^{1

2}, Chunjing Jia^{3

4}, Hongyu Xiong^{3

5

6}, Binbin Wang⁷, Zhicheng Jiang¹, Kui Huang⁷, Jinwoong Hwang^{5

8

9}, Zhuojun Li^{1

2}, Choongyu Hwang¹⁰, Zhongkai Liu⁷, Dawei Shen^{1

11}, Jonathan A Sobota^{3

5}, Patrick Kirchmann^{3

5}, Jiamin Xue⁷, Thomas P Devereaux^{3

5}, Sung-Kwan Mo¹², Zhi-Xun Shen^{13

14}, Shujie Tang^{15

16}

Affiliations

¹ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, PR China.
² 2020 X-Lab, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, PR China.
³ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁴ Department of Physics, University of Florida, Gainesville, FL, USA.
⁵ Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, CA, USA.
⁶ Key Laboratory for Power Machinery and Engineering of MOE, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, PR China.
⁷ School of Physical Science and Technology, ShanghaiTech University, Shanghai, PR China.
⁸ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁹ Department of Physics, Kangwon National Univerisity, Chuncheon, Korea.
¹⁰ Department of Physics, Pusan National University, Busan, Korea.
¹¹ National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China.
¹² Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. SKMo@lbl.gov.
¹³ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA. zxshen@stanford.edu.
¹⁴ Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, CA, USA. zxshen@stanford.edu.
¹⁵ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, PR China. tangsj@mail.sim.ac.cn.
¹⁶ 2020 X-Lab, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, PR China. tangsj@mail.sim.ac.cn.

Abstract

The excitonic insulator (EI) is a Bose-Einstein condensation (BEC) of excitons bound by electron-hole interaction in a solid, which could support high-temperature BEC transition. The material realization of EI has been challenged by the difficulty of distinguishing it from a conventional charge density wave (CDW) state. In the BEC limit, the preformed exciton gas phase is a hallmark to distinguish EI from conventional CDW, yet direct experimental evidence has been lacking. Here we report a distinct correlated phase beyond the 2×2 CDW ground state emerging in monolayer 1T-ZrTe₂ and its investigation by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The results show novel band- and energy-dependent folding behavior in a two-step process, which is the signatures of an exciton gas phase prior to its condensation into the final CDW state. Our findings provide a versatile two-dimensional platform that allows tuning of the excitonic effect.

Abstract

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