Topological crystalline insulators (TCI's) are a class of materials which can support non-trivial band topology protected by crystalline symmetry. Using analytic and numerical methods, we study the effect of bulk magnetic impurities on a model of (Sn,Pb)Te alloys which are believed to be TCI’s in their topological state. When the system bulk is insulating, gapless surface states are present whose energetics are affected by the magnetic ordering on the surface, particularly when it breaks the mirror symmetry. This leads to a rich variety of ferromagnetic orderings, with the number of degenerate magnetization directions dependent on which surfaces are exposed and on the doping of those surfaces. In particular we find metallic states with two-fold easy axes as well as ones with six orientations on the (111) surface. The (001) surface by contrast hosts an 8-fold insulating state. The nature of domain walls between different orderings has interesting consequences for transport on the surfaces as well as the universality classes of thermal disordering transitions.
Herbert Fertig is a Professor of Physics at Indiana University in Bloomington. He received his undergraduate degree from Princeton University and his Ph.D. from Harvard University under the direction of Bert Halperin in 1988. After a postdoctoral fellowship with Sankar Das Sarma at the University of Maryland, he joined the faculty of the University of Kentucky in 1991, moving to Indiana in 2004. Professor Fertig was elected a Fellow of the American Physical Society in 2001, was chosen as a Lady Davis Fellow for 2006–7, and in 2008, he was recognized as an Outstanding Referee for the Physical Review journals. His research focuses mostly on low-dimensional electron systems, with particular interests in quantum Hall effects, and recently on graphene.
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