Fabry-Pérot interference and zero quantized conductance in topological helical hinge states

Abstract Helical three-dimensional second-order topological insulators (3D SOTIs) are characterized by
 Kramers pairs of counter-propagating hinge states and gapped surface states. Here, we theoretically
 investigate quantum coherent transport in a dumbbell-shaped nanowire constructed from helical
 SOTIs. Using scattering matrix analysis and numerical simulations, we find that the two-terminal
 conductance exhibits Fabry-Pérot (FP) oscillations and a zero quantized conductance plateau. FP
 oscillations arise from multiple quantum reflections at both ends of the constriction, which stem
 from momentum mismatch. And the zero quantized conductance plateau is caused by the finite size
 effect of constriction, which may be seen as the off state of an electrical switch. These results can
 be realized by tuning the gate voltage or bias voltage. The FP interferometer and electrical switch
 offer a viable strategy for the application of topological hinge states, which remain robust against
 disorder of appropriate strength and constriction at distinct positions.