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 tempera-tures,we discover a hidden incommensurate stripe-like CDW order besides the(√7×√3)CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe2 film.Combining the variable-temperature angle-resolved photoemission spec-troscopic(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(√7×√3)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(√7×√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.

National Laboratory of Solid State Microstructure,School of Physics,Nanjing University,Nanjing 210093,China;Vacuum Interconnected Nanotech Workstation(Nano-X),Suzhou Institute of Nano-Tech and Nano-Bionics(SINANO),Chinese Academy of Sciences,Suzhou 215123,China;Department of Applied Physics,Nanjing University of Science and Technology,Nanjing 210094,China;Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China

[1]Junyu Zong;Yang Xie;Qinghao Meng;Qichao Tian;Wang Chen;Xuedong Xie;Shaoen Jin;Yongheng Zhang;Li Wang;Wei Ren;Jian Shen;Aixi Chen;Pengdong Wang;Fang-Sen Li;Zhaoyang Dong;Can Wang;Jian-Xin Li;Yi Zhang-.Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe2 film)[J].中国物理B（英文版）,2022(10):153-161

VSe2,ARPES

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