Topological <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>Z</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> invariant in Kitaev spin liquids: Classification of gapped spin liquids beyond projective symmetry group
Physical review research