Laser Illumination Induced Superconductor-to-Semiconductor Phase Transitions in WS₂

The ability to precisely manipulate crystal phase transitions in 2D TMDs is advantageous for controlling their physical properties and creating devices. In these TMD materials there has been noteworthy progress in achieving structural phase transitions between 2H and 1T or 1T' crystal phases. In WS₂, the 2M phase has been recently identified as an intrinsic 2D topological superconductor, with a notably high superconducting transition temperature of 8.8 K, and a semiconducting 2H phase. However, transitions between the 2M and 2H phases in WS₂, as well as other phases in 2D TMDs, remain poorly understood. In this study, we demonstrate local phase transitions from superconducting 2M to semiconducting 2H phases in WS₂ atomic layers via laser irradiation. Using scanning tunneling microscopy (STM), we find that the region exhibiting the 2H phase shows a hexagonal shape with a width of ~800nm surrounded by an atomically sharp transition from 2H and 2M crystal structure phase. Our research, which identifies a novel local structural transition from superconducting to semiconducting phases in 2D TMD atomic layers, opens potential applications in phase-change electronic devices, particularly in the context of superconducting quantum devices, along with potential engineering of the local topology.