Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe2 film |
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Affiliation: | 1. National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China;2. Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences, Suzhou 215123, China;3. Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China;4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China |
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Abstract: | As a special order of electronic correlation induced by spatial modulation, the charge density wave (CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning—tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the ($sqrt{7}$ × $sqrt{3}$) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe2} film. Combining the variable-temperature angle-resolved photoemission spectroscopic (ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts Δ1 and Δ2. The gap part Δ1 that closes around ~ 150 K is accompanied with the vanish of the ($sqrt{7}$ × $sqrt{3}$) CDW phase. While another momentum-dependent gap part Δ2 can survive up to ~ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure Δ1 + Δ2, which suggests different forming mechanisms between the ($sqrt{7}$ × $sqrt{3}$) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe2} film as a two-dimensional (2D) material. |
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Keywords: | charge density waves VSe2 band structures STM ARPES |
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