Higher-order topolectrical semimetal realized via synthetic gauge fields

Abstract

Classical bosonic systems may be tailored to support topological order and unidirectional edge transport exploiting gauge fields. Here, we theoretically explore how synthetic gauge fields may be used to induce higher-order topological phases and zero-energy boundary states. We demonstrate these principles in two types of three-dimensional topolectrical circuits with synthetic gauge fields threading through their reduced two-dimensional lattices, leading to a half-quantized quadrupole charge within a region of the momentum space. We theoretically show the emergence of nodal line rings and Weyl points in the bulk dispersion, whose projected surfaces and hinges support surface Fermi arcs and flat hinge Fermi arcs emanating from the nodal line ring and Weyl points, representing the spectral signature of higher-order topological semimetals. These analogs of higher-order semimetals realized in electric circuits using synthetic gauge fields may be extended to various photonic platforms and find applications in photonic crystals, nano-optics, and cold atom research.