Edge Mode Transport through Nanoscale Channels in the Topological Insulator Cadmium Arsenide

Two-dimensional topological insulators (2D TIs) can feature dissipationless, one-dimensional charge transport via edge modes, offering a rich ground for studying exotic quasi-particles and geometric phases useful for quantum information applications. However, there are few experimentally-realized 2D TIs with clear edge mode transport, and their coherence is typically limited by disorder to short length scales. In this work, we study the edge mode transport of the 2D TI Cd₃As₂ in nanoscale channels defined by finger gates. At finite magnetic field, we demonstrate selective transmission of quantum Hall edge modes through the channel by tuning the finger gate. We find that localized states arising from disorder facilitate percolation of reflected edge modes through the channel when the finger gate is tuned through a Landau level. We study the device in the unipolar and bipolar regimes and confirm non-spin-selective equilibration between edge modes, which is unique to systems with strong spin-orbit coupling. In accordance with past work on quantum point contacts in Cd₃As₂, we observe a remnant conductance when the channel is tuned into the topological gap, suggesting conduction via helical edge modes through the channel. Exact quantization is precluded by broken time reversal symmetry and disorder, which we address with experiments at zero field and by varying the channel width.