Fabry-Perot interference in three dimensional second-order topological insulator constrictions

The gapless chiral hinge states of three dimensional second-order topological insulators (SOTIs) support a quantized conductance plateau on thick nanowire. Here, we numerical study the conductance of SOTI constrictions. According to finite size effects, the hinge states in narrow region could be hybridized, which will induce reflection at the two ends of constrictions. The conductance exists the Fabry-Perot oscillation pattern because of multiple reflections. We also study the impact of the magnetic field on the Fabry-Perot interference. We show the dimensional effect that the magnetic field leads to the electrons being localized on two hinges. Our results are robust against moderate disorder so that we expect these Fabry-Perot patterns could be observed in experiments.