Experimental Observation of Dirac-like Surface States and Topological Phase Transition in Pb1-xSnxTe ( 111 ) Films

The surface of a topological crystalline insulator (TCI) carries an even number of Dirac cones protected by crystalline symmetry. We epitaxially grew here high-quality ${\mathrm{Pb}}_{1{-}x}{\mathrm{Sn}}_{x}\mathrm{Te}(111)$ films and investigated the TCI phase by in situ angle-resolved photoemission spectroscopy. ${\mathrm{Pb}}_{1{-}x}{\mathrm{Sn}}_{x}\mathrm{Te}(111)$ films undergo a topological phase transition from a trivial insulator to TCI via increasing the Sn/Pb ratio, accompanied by a crossover from $n$-type to $p$-type doping. In addition, a hybridization gap is opened in the surface states when the thickness of the film is reduced to the two-dimensional limit. The work demonstrates an approach to manipulating the topological properties of TCI, which is of importance for future fundamental research and applications based on TCI.