A topological insulator protected by time-reversal symmetry is realized via spin-orbit interaction-driven band inversion. The topological phase in the Bi 1-x Sb x system is due to an odd number of band inversions. A related spin-orbit system, the Pb 1-x Sn x Te, has long been known to contain an even number of inversions based on band theory. Here we experimentally investigate the possibility of a mirror symmetry-protected topological crystalline insulator phase in the Pb 1-x Sn x Te class of materials that has been theoretically predicted to exist in its end compound SnTe. Our experimental results show that at a finite Pb composition above the topological inversion phase transition, the surface exhibits even number of spin-polarized Dirac cone states revealing mirror-protected topological order distinct from that observed in Bi 1-x Sb x . Our observation of the spin-polarized Dirac surface states in the inverted Pb 1-x Sn x Te and their absence in the non-inverted compounds related via a topological phase transition provide the experimental groundwork for opening the research on novel topological order in quantum devices.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Biochemistry, Genetics and Molecular Biology(all)