Boundary topological orders of ()d fermionic symmetry protected topological states
Phys. Rev. B 113, 125105 – Published 2 March, 2026
DOI: https://doi.org/10.1103/bjvz-tmj2
Abstract
We investigate ()d topological orders (TOs) in fermionic systems with anomalous symmetry, where its subgroup is the fermion parity. Such an anomalous symmetry arises as a discrete subgroup of the chiral U(1) symmetry of copies of Weyl fermions of the same chirality. Inspired by the crystalline correspondence principle, we deform the anomalous symmetry of a (3 + 1)d Weyl fermion to the anomalous symmetry. Then we microscopically construct symmetry preserving gapped boundary states of the closely related ()d symmetry protected topological state (with being the -fold rotation), whenever it is possible. For , we show that the ()d symmetric gapped state admits a topological gauge theory description at low energy and propose that a similar theory saturates the corresponding anomaly. For , our construction admits no topological quantum field theory (TQFT) symmetric gapped state; while for , we find a non-TQFT symmetric gapped state via stacking lower-dimensional ()d non-discrete-gauge-theory TO inhomogeneously. For other values of , no symmetric gapped state is possible within our construction, which is consistent with the no-go theorem by Cordova-Ohmori.