Abstract
Cd3As2 is a three-dimensional Dirac semimetal with separated Dirac points in momentum space. In spite of extensive transport and spectroscopic studies on its exotic properties, the evidence of superconductivity in its surface states remains elusive. Here, we report the observation of proximity-induced surface superconductivity in Nb/Cd3As2 hybrid structures. Our four-terminal transport measurement identifies a pronounced proximity-induced pairing gap (gap size comparable to Nb) on the surfaces, which exhibits a flat conductance plateau in differential conductance spectra, consistent with our theoretical simulations. The surface supercurrent from Nb/Cd3As2/Nb junctions is also achieved with a Fraunhofer/SQUID-like pattern under out-of-plane/in-plane magnetic fields, respectively. The resultant mapping shows a predominant distribution on the top and bottom surfaces as the bulk carriers are depleted, which can be regarded as a higher dimensional analog of edge supercurrent in two-dimensional quantum spin Hall insulators. Our study provides the evidence of surface superconductivity in Dirac semimetals.
Highlights
Cd3As2 is a three-dimensional Dirac semimetal with separated Dirac points in momentum space
Across the junction are shown in Fig. 1b with three drops at Tc1 = 8.4 K, Tc2 ~ 8.2 K, and Tc3 ~ 4.0 K corresponding to Nb superconducting for Tc1 and proximity-induced superconductivity for Tc2 and Tc3, respectively, since Nb has been in zero-resistance state at 8.3 K (Fig. 1b inset, see details in Supplementary Note 3 and Supplementary Fig. 4)
Our experiments on the Nb/Cd3As2 and Nb/Cd3As2/Nb hybrid structures demonstrate the surface superconductivity with a large proximity gap from the parent superconductor, and a detailed supercurrent distribution is extracted from the superconducting quantum interference (SQI) measurements
Summary
Cd3As2 is a three-dimensional Dirac semimetal with separated Dirac points in momentum space. Referred to as Weyl or Dirac points, these gapless nodes in the bulk can be connected by open strings formed by topologically protected surface states on the boundaries, called Fermi-arc states[6]. Due to their anomalous electromagnetic responses[7,8,9,10,11,12,13,14], as well as the interesting interplay between bulk and surface Fermi arcs[15,16], topological semimetals have been studied intensively in recent years[5]. In topological insulator/superconductor (TI/SC) junctions, it is generally believed that the induced superconducting gap in the surface states is small due to high interfacial barriers and Fermi surface mismatch[27,28,29]
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