Quantized Conductance through Surface States in High Quality Three-Dimensional Dirac Semimetal Cd₃As₂ Nanowire/Nanoribbon p-n Junctions

We report the observation of quantized conductance in high-mobility three-dimensional Dirac semimetal Cd$_3$As$_2$ nanowire and nanoribbon p-n junctions. By employing suspended device geometries with dual local gates, we form tunable p-n junctions and realize ballistic transport across sub-micron channel lengths. In a wide nanoribbon device with a channel width of $\sim 330$ nm, conductance plateaus appear at integer multiples of $2e^2/h$ in the n-n regime under high magnetic fields. Numerical simulations suggest that these features represent unresolved spin-split subbands due to the smaller subband spacing in wider channels, and support the interpretation that the observed quantization may originate from surface-state-dominated conduction. In contrast, narrower nanoribbons and nanowires exhibit conductance steps of $1e^2/h$, demonstrating spin-resolved subbands likely due to enhanced confinement effects. From spin-resolved subband spectroscopy, we extract an effective Land\'e $g$-factor of $\sim 43$ for the first subband in the bulk gap, establishing these nanostructures as a prospective platform for fault-tolerant quantum electronics.