Tuning the interfacial transport behavior in a superconducting van der Waals heterostructure

The interaction between the metallic and superconducting components at the interface of superconductor–normal metal (S-N) systems enables a variety of quantum phenomena, including the Josephson effect, Andreev reflection, and proximity-induced superconductivity, which are of significant interest both theoretically and practically. Nevertheless, due to varying physical mechanisms, achieving and fine-tuning multiple such phenomena within a single S-N system continues to be a challenge. In this work, we employ NbSe2 and WTe2 to fabricate an S-N-S heterostructure. Below the superconducting transition temperature of NbSe2, two distinct resistance-temperature behaviors are observed: a continuous decrease in junction resistance with temperature decrease, indicative of the superconducting proximity effect and consistent with the BCS model, and an increase in resistance attributed to competition between Andreev reflection (AR) and normal reflection at a low-transparency interface, which can be suppressed by applying a small bias current or a magnetic field. Our results indicate the signature of the coexistence of proximity-induced superconductivity with AR in the measured S-N-S heterojunction, demonstrating the tunability of charge carrier transport behavior at the interface. This finding enhances our understanding of such systems and holds potential for the development of superconducting electronics, quantum computing, and energy harvesting technologies.