  The realization of high-performance, small-footprint, on-chip inductors
remains a challenge in radio-frequency and power microelectronics, where they
perform vital energy transduction in filters and power converters. Modern
planar inductors consist of metallic spirals that consume significant chip
area, resulting in low inductance densities. We present a novel method for
magnetic energy transduction that utilizes ferromagnetic islands (FIs) on the
surface of a 3D time-reversal-invariant topological insulator (TI) to produce
paradigmatically different inductors. Depending on the chemical potential, the
FIs induce either an anomalous or quantum anomalous Hall effect in the
topological surface states. These Hall effects direct current around the FIs,
concentrating magnetic flux and producing a highly inductive device. Using a
novel self-consistent simulation that couples AC non-equilibrium Green
functions to fully electrodynamic solutions of Maxwell's equations, we
demonstrate excellent inductance densities up to terahertz frequencies, thus
harnessing the unique properties of topological materials for practical device
applications.
