Phase tuning of multiple Andreev reflections of Dirac fermions and the Josephson supercurrent in Al-MoTe₂-Al junctions.

Abstract

When an electron is incident on a superconductor from a metal, it is reflected as a hole in a process called Andreev reflection. If the metal <i>N</i> is sandwiched between two superconductors <i>S</i> in an <i>SNS</i> junction, multiple Andreev reflections (MARs) occur. We have found that, in <i>SNS</i> junctions with high transparency ([Formula: see text]) based on the Dirac semimetal MoTe₂, the MAR features are observed with exceptional resolution. By tuning the phase difference [Formula: see text] between the bracketing Al superconductors, we establish that the MARs coexist with a Josephson supercurrent [Formula: see text]. As we vary the junction voltage <i>V</i>, the supercurrent amplitude [Formula: see text] varies in step with the MAR order <i>n</i>, revealing a direct relation between them. Two successive Andreev reflections serve to shuttle a Cooper pair across the junction. If the pair is shuttled coherently, it contributes to [Formula: see text]. The experiment measures the fraction of pairs shuttled coherently vs. <i>V</i>. Surprisingly, superconductivity in MoTe₂ does not affect the MAR features.