Field theory of higher-order topological crystalline response, generalized global symmetries and elasticity tetrads

Abstract

We discuss the higher-order topological field theory and response of topological crystalline insulators with no other symmetries. We show how the topology and geometry of the system is organised in terms of the elasticity tetrads which are ground state degrees of freedom labelling lattice topological charges, higher-form conservation laws and responses on sub-dimensional manifolds of the bulk system. In a crystalline insulator, they classify higher-order global symmetries in a transparent fashion. This coincides with the dimensional hierarchy of topological terms, the multipole expansion, and anomaly inflow, related to a mixed number of elasticity tetrads and electromagnetic gauge fields. In the continuum limit of the elasticity tetrads, the semi-classical expansion can be used to derive the higher-order or embedded topological responses to global U(1) symmetries, such as electromagnetic gauge fields with explicit formulas for the higher-order quasi-topological invariants in terms of the elasticity tetrads and Green's functions. The topological responses and readily generalized in parameter space to allow for e.g. multipole pumping. Our simple results further bridge the recently appreciated connections between topological field theory, higher form symmetries and gauge fields, fractonic excitations and topological defects with restricted mobility elasticity in crystalline insulators.