## Filling constraints for spin-orbit coupled insulators in symmorphic and nonsymmorphic crystals

**Speaker:**Haruki Watanabe, University of Tokyo

**When:**March 9, 2016 (Wed), 11:00AM to 01:00PM (add to my calendar)

**Location:**SCI 328

*This event is part of the Condensed Matter Theory Seminar Series. *

Quantum spin liquids are exotic insulators in which the electron’s spin, charge, and fermionic statistics are carried by separate excitations. They have received attention for their potential as a quantum memory and as a parent state for high-temperature superconductivity. A key principle guiding the search for experimental candidate materials is the absence of conventional order in insulators at “fractional” electron filling. Previous results established what constitutes fractional filling, but assumed the spin rotation symmetry that is typically broken in real materials by spin-orbit couplings. In this talk, assuming the time-reversal symmetry instead of the spin conservation, we establish useful filling conditions for all 230 space groups. This should aid in the search for quantum spin liquids and topological semimetals. We will also discuss its implication on noninteracting band structures and introduce a new type of topological crystalline insulator, which we call `filling-enforced quantum band insulators’.

Ref: [1] HW, H.C. Po, A. Vishwanath, & M. Zaletel, PNAS 112, 14551 (2015) [2] H.C. Po, HW, M. Zaletel & A. Vishwanath, arXiv:1506.03816