Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe₂ film

【摘要】 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（■） 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 ?₁ and ?₂. The gap part ?1 that closes around ～ 150 K is accompanied with the vanish of the（■） CDW phase. While another momentum-dependent gap part ?₂ 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 ?₁ + ?₂, which suggests different forming mechanisms between the（■） 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.更多还原

【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（■） 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 ?₁ and ?₂. The gap part ?1 that closes around ～ 150 K is accompanied with the vanish of the（■） CDW phase. While another momentum-dependent gap part ?₂ 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 ?₁ + ?₂, which suggests different forming mechanisms between the（■） 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.更多还原