Phase Stability and Structural Transition of Emergent Topological Superconductor Candidate 2M-WS₂

2M-WS2 is a promising topological superconductor candidate with a high superconducting transition temperature that holds Majorana bound states and provides an important material platform for application potentials in topological quantum computing. However, the metastable 2M-WS2 undergoes a phase transition to be semiconducting 2H-WS2 under specific conditions, degrading the quality of the sample. Here, we demonstrate the temperature and thickness dependence of the 2M-to-2H structural phase transition of the 2M-WS2 nanoflake based on Raman spectroscopy measurements. The critical temperature of such a phase transition decreases as the thickness of the 2M-WS2 nanoflake increases, indicating a negative impact on the performance of 2M-WS2-based electronic devices. Interestingly, laser irradiation can also induce such a 2M-to-2H structural transition, and the critical laser power to induce such a transition depends on the substrate of 2M-WS2 nanoflakes, which is consistent with our simulation results. Our findings pave the way toward the fabrication of practical electronic devices based on 2M-WS2 nanoflakes.