Speaker
Masatoshi Sato
Description
Using the twisted equivariant K-theory, we complete a
classification of topological crystalline insulators and
superconductors in the presence of additional order-two
nonsymmorphic space group symmetries. The order-two
nonsymmorphic space groups include half lattice translation
with Z2 flip, glide, two-fold screw, and their magnetic space
groups. It is pointed out that the nonsymmorphic space
groups allow ℤ2 topological phases even in the absence of
time-reversal and/or particle-hole symmetries. Furthermore,
the coexistence of the nonsymmorphic space group with the
time-reversal and/or particle-hole symmetries provides novel
ℤ4 topological phases. We argue that the corresponding
surface states have Mobius twisted structures in the
momentum space.
