Topological insulators on a Mobius Strip
  We study the two dimensional Chern insulator and spin Hall insulator on a non-orientable Riemann surface, the Mobius strip, where the usual bandstructure topological invariant is not defined. We show that while the flow pattern of edge currents can detect the twist of the Mobius strip in the case of Chern insulator, it can not do so in spin Hall insulator. 
Langtao Huang, Dung-Hai Lee
cond-mat.mes-hall