A (2+1)-dimensional gapped quantum many-body system can have a topologically protected energy current at its edge. The magnitude of this current is determined entirely by the temperature and the chiral central charge, a quantity associated with the effective field theory of the edge. We derive a formula for the chiral central charge that, akin to the topological entanglement entropy, is completely determined by the many-body ground state wave function in the bulk. According to our formula, nonzero chiral central charge gives rise to a topological obstruction that prevents the ground state wave function from being real-valued in any local product basis.

%B Phys. Rev. Lett. %V 128 %P 176402 %8 4/28/2022 %G eng %U https://arxiv.org/abs/2110.06932 %N 17 %R 10.1103/PhysRevLett.128.176402