4 pi-Periodic Supercurrent from Surface States in Cd3As2 Nanowire-Based Josephson Junctions

The combination of superconductivity and surface states in Dirac semimetal can produce a 4 pi-periodic supercurrent in a Josephson junction configuration, which can be revealed by the missing of odd Shapiro steps (especially the n = 1 step). However, the suppression of the n = 1 step is also anticipated in the high-power oscillatory regime of the ordinary 2 pi-periodic Josephson effect, which is irrelevant to the 4 pi-periodic supercurrent. Here, in order to identify the origin of the suppressed n = 1 step, we perform the measurements of radio frequency irradiation on Nb-Dirac semimetal Cd3As2 nanowire-Nb junctions with continuous power dependence at various frequencies. Besides the n = 1 step suppression, we uncover a residual supercurrent of first node at the n = 0 step, which provides a direct and predominant signature of the 4 pi-periodic supercurrent. Furthermore, by tuning the gate voltage, we can modulate the surface and bulk state contribution and the visibility of the n = 1 step. Our results provide deep insights to explore the topological superconductivity in Dirac semimetals.