Photo-induced phase transition from topological to trivial insulator in a doped (Pb, Sn)Se

The surface electronic structure of a topological crystalline insulator (TCI) is protected by crystal symmetries and can be tuned by various parameters including electric field, pressure, strain, and doping. Here, we use light to control the electronic structure of Bi-doped (Pb, Sn)Se(111) thin film grown by molecular beam epitaxy. In this system, the TCI phase turns into a Z2 topological insulator phase due to lattice distortion. Using time and angle-resolved photoemission spectroscopy, we observe a photo-induced spectral weight suppression at low energies, indicating a topological-insulator to trivial-insulator phase transition. By contrast, such a gap-opening behavior is indiscernible in an undoped (Pb, Sn)Se, which rules out a simple sample heating origin. To explain our results, we propose that local laser irradiation enhancesthe lattice distortion, originally induced by Bi doping, via an anisotropic lattice expansion, which evolves the phase transition from a TCI phase to a trivial insulator phase. Our work may provide a new route to control topological properties by light.