Phase changings in the surface layers of T_d-WTe₂ driven by alkali-metal deposition

The discovery of phase changings in two-dimensional (2D) materials driven by external stimuli not only helps to understand the various intriguing phases in 2D materials but also provides directions for constructing new functional devices. Here, by combining angle-resolved photoemission spectroscopy (ARPES) and in-situ alkali-metal deposition, we studied how alkali-metal adatoms affect the electronic structure of T_d-WTe₂ on two different cleaved surfaces. We found that depending on the polarization direction of the cleaved surface, the alkali-metal deposition triggered two successive phase transitions on one surface of WTe₂, while on the other surface, no phase transition was found. We attributed the observed phase transitions to a T_d↑–1T′–T_d↓ structural transition driven by an alkali-metal induced sliding of WTe₂ layers. By comparing the band structure obtained in different structural phases of WTe₂, we found that the evolution of band structure across different phases is characterized by an energy scale that could be related to the degree of orbital hybridization between two adjacent WTe₂ layers. Our results demonstrate a method that manipulates the surface structure of bulk 2D materials. It also builds a direct correlation between the electronic structure and the degree of interlayer misalignment in this intriguing 2D material.