Radio-Frequency Detection of Fabry–Pérot Interference and Quantum Capacitance in Long-Channel Three-Dimensional Dirac Semimetal Cd₃As₂ Nanowires

We demonstrate phase-coherent transport in suspended long-channel Cd₃As₂ nanowire devices using both direct current (DC) transport and radiofrequency (RF) reflectometry measurements. By integrating Cd₃As₂ nanowires with on-chip superconducting LC resonators, we achieve sensitive detection of both resistance and quantum capacitance variations. In a long-channel device (<i>L</i> ≈ 1.8 μm), clear Fabry–Pérot (FP) interference patterns are observed in both DC and RF measurements, providing strong evidence for ballistic electron transport. RF reflectometry reveals gate-dependent modulations of the resonance frequency arising from quantum capacitance oscillations induced by changes in the density of states and FP interference. These oscillations exhibit a quasi-periodic structure that closely correlates with the FP patterns in DC transport measurements. In another device of a Cd₃As₂ nanowire Josephson junction (<i>L</i> ≈ 730 nm, superconducting Al contacts), FP interference patterns are too weak to be resolved in DC conductance but are detectable using RF reflectometry. These results demonstrate the high quality of our Cd₃As₂ nanowires and the versatility of RF reflectometry, establishing their potential for applications in topological quantum devices such as Andreev qubits or gatemon architectures.