Discovery of a Single-Band Mott Insulator in a van der Waals Flat-Band Compound

Shunye Gao; Shuai Zhang; Cuixiang Wang; Shaohua Yan; Xin Han; Xuecong Ji; Wei Tao; Jingtong Liu; Tiantian Wang; Shuaikang Yuan; Gexing Qu; Ziyan Chen; Yongzhao Zhang; Jierui Huang; Mojun Pan; Shiyu Peng; Yong Hu; Hang Li; Yaobo Huang; Hui Zhou; Sheng Meng; Liu Yang; Zhiwei Wang; Yugui Yao; Zhiguo Chen; Ming Shi; Hong Ding; Huaixin Yang; Kun Jiang; Yunliang Li; Hechang Lei; Youguo Shi; Hongming Weng; Tian Qian

doi:10.1103/physrevx.13.041049

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arXiv · 2205.11462

Discovery of a Single-Band Mott Insulator in a van der Waals Flat-Band Compound

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Abstract

The Mott insulator provides an excellent foundation for exploring a wide range of strongly correlated physical phenomena, such as high-temperature superconductivity, quantum spin liquid, and colossal magnetoresistance. A Mott insulator with the simplest degree of freedom is an ideal and highly desirable system for studying the fundamental physics of Mottness. In this study, we have unambiguously identified such an anticipated Mott insulator in a van der Waals layered compound Nb3Cl8. In the high-temperature phase, where interlayer coupling is negligible, density functional theory calculations for the monolayer of Nb3Cl8 suggest a half-filled flat band at the Fermi level, whereas angle-resolved photoemission spectroscopy experiments observe a large gap. This observation is perfectly reproduced by dynamical mean-field theory calculations considering strong electron correlations, indicating a correlation-driven Mott insulator state. Since this half-filled band derived from a single 2a1 orbital is isolated from all other bands, the monolayer of Nb3Cl8 is an ideal realization of the celebrated single-band Hubbard model. Upon decreasing the temperature, the bulk system undergoes a phase transition, where structural changes significantly enhance the interlayer coupling. This results in a bonding-antibonding splitting in the Hubbard bands, while the Mott gap remains dominant. Our discovery provides a simple and seminal model system for investigating Mott physics and other emerging correlated states.

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Shunye Gao, Shuai Zhang, Cuixiang Wang, Shaohua Yan, Xin Han, Xuecong Ji, Wei Tao, Jingtong Liu, Tiantian Wang, Shuaikang Yuan, Gexing Qu, Ziyan Chen, Yongzhao Zhang, Jierui Huang, Mojun Pan, Shiyu Peng, Yong Hu, Hang Li, Yaobo Huang, Hui Zhou, Sheng Meng, Liu Yang, Zhiwei Wang, Yugui Yao, Zhiguo Chen, Ming Shi, Hong Ding, Huaixin Yang, Kun Jiang, Yunliang Li, Hechang Lei, Youguo Shi, Hongming Weng, Tian Qian. 2022-05-23. Discovery of a Single-Band Mott Insulator in a van der Waals Flat-Band Compound. https://doi.org/10.1103/physrevx.13.041049

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