Electronic structures and Mott state of epitaxial TaS2 monolayers

• Published in: Science China. Physics, mechanics & astronomy Vol. 67; no. 5; p. 256811
• Main Authors: Tian, Qichao, Ding, Chi, Qiu, Xiaodong, Meng, Qinghao, Wang, Kaili, Yu, Fan, Mu, Yuyang, Wang, Can, Sun, Jian, Zhang, Yi
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01-05-2024; Springer Nature B.V
• Subjects: Astronomy; Charge density waves; Classical and Continuum Physics; Density functional theory; Electrons; Emission analysis; Emission spectroscopy; Energy; Energy bands; Energy gap; Fermi level; Graphene; Mathematical analysis; Molecular beam epitaxy; Molecular beams; Monolayers; Observations and Techniques; Physics; Physics and Astronomy; Room temperature; Spectrum analysis; Spin liquid; Superconductivity; Temperature dependence; Mott insulating state; charge density wave; TaS; angle-resolved photoemission spectroscopy
• ISSN: 1674-7348; 1869-1927
• DOI: 10.1007/s11433-023-2328-1

Layered material TaS
2
hosts multiple structural phases and exotic correlated quantum states, including charge density wave (CDW), superconductivity, quantum spin liquid, and Mott insulating state. Here, we synthesized TaS
2
monolayers in H and T phases using the molecular beam epitaxial (MBE) method and studied their electronic structures via angle-resolved photo-emission spectroscopy (ARPES). We found that the H phase TaS
2
(H-TaS
2
) monolayer is metallic, with an energy band crossing the Fermi level. In contrast, the T phase TaS
2
(T-TaS
2
) monolayer shows an insulated energy gap at the Fermi level, while the normal calculated band structure implies it should be metallic without any band gap. However, by considering Hubbard interaction potential
U
, further density functional theory (DFT) calculation suggests that monolayer T-TaS
2
could be a CDW Mott insulator, and the DFT+
U
calculation matches well with the ARPES result. More significantly, the temperature-dependent ARPES result indicates that the CDW Mott state in the T-TaS
2
monolayer is more robust than its bulk counterpart and can persist at room temperature. Our results reveal that the dimensional effect can enhance the CDW Mott state and provide valuable insights for further exploring the exotic properties of monolayer TaS
2
.