Topological Crystalline Insulators in the SnTe Material Class

Topological crystalline insulators are new states of matter in which the topological nature of electronic structures arises from crystal symmetries. Here we predict the first material realization of topological crystalline insulator in the semiconductor SnTe by identifying its non-zero topological index. We predict that as a manifestation of this non-trivial topology, SnTe has metallic surface states with an even number of Dirac cones on high-symmetry crystal surfaces such as {001}, {110} and {111}. These surface states form a new type of high-mobility chiral electron gas, which is robust against disorder and topologically protected by reflection symmetry of the crystal with respect to {110} mirror plane. Breaking this mirror symmetry via elastic strain engineering or applying an in-plane magnetic field can open up a continuously tunable band gap on the surface, which may lead to wide-ranging applications in thermoelectrics, infra-red detection and tunable electronics. Closely related semiconductors PbTe and PbSe also become topological crystalline insulators after band inversion by pressure, strain and alloying.National Science Foundation (U.S.) (NSF Graduate Research Fellowship number 0645960)Massachusetts Institute of Technology (start-up funds from MIT)United States. Dept. of Energy (Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, Grant number DE-FG02-07ER46352)Ministry of Science and Technology of the People's Republic of China (No. 2011CB921901)Ministry of Science and Technology of the People's Republic of China (No. 2011CB606405)National Natural Science Foundation (China)National Science Foundation (U.S.) (NSF Grant number DMR-1005541