Xu, Su-YangLiu, ChangAlidoust, N.Neupane, M.Qian, D.Belopolski, I.Denlinger, J. D.Wang, Y. J.Lin, H.Wray, L. A.Landolt, G.Slomski, B.Dil, J. H.Marcinkova, A.Morosan, E.Gibson, Q.Sankar, R.Chou, F. C.Cava, R. J.Bansil, A.Hasan, M. Z.2015-06-232015-06-232015-06-23201210.1038/ncomms2191https://infoscience.epfl.ch/handle/20.500.14299/115354WOS:000315992100027A topological insulator protected by time-reversal symmetry is realized via spin-orbit interaction-driven band inversion. The topological phase in the Bi1-xSbx system is due to an odd number of band inversions. A related spin-orbit system, the Pb1-xSnxTe, 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 Pb1-xSnxTe 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 Bi1-xSbx. Our observation of the spin-polarized Dirac surface states in the inverted Pb1-xSnxTe 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.text::journal::journal article::research article