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

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 N is sandwiched between two superconductors S in an SNS junction, multiple Andreev reflections (MARs) occur. We have found that, in SNS junctions with high transparency (tau -> 1) based on the Dirac semimetal MoTe2, the MAR features are observed with exceptional resolution. By tuning the phase difference phi between the bracketing Al superconductors, we establish that the MARs coexist with a Josephson supercurrent I-s = I-A sin phi. As we vary the junction voltage V, the supercurrent amplitude I-A varies in step with the MAR order n, 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 I-s. The experiment measures the fraction of pairs shuttled coherently vs. V. Surprisingly, superconductivity in MoTe2 does not affect the MAR features.

Automated summary

This study investigates the MAR features in high-transparency SNS junctions based on the Dirac semimetal MoTe2. It is found that MARs coexist with a Josephson supercurrent, and the amplitude of the supercurrent varies with the MAR order as the junction voltage is varied. The experiment measures the coherence of Cooper pairs shuttling across the junction and reveals a direct relation between the coherence and MARs. Surprisingly, the superconductivity in MoTe2 does not affect the MAR features.