Andreev pair injection into a transition metal dichalcogenide monolayer

We demonstrate Andreev pair injection across Nb-WS₂ junction evident as Andreev reflection in differential conductivity spectra below Nb critical temperature Tc. The superconducting- 2D semiconducting junction defined by a focused ion beam, shaped Nb pads, and semi-dry transfer of single layer CVD-grown WS₂ crystals ensured the mechanical integrity of the 2D TMD film, reduced contamination and defects at Nb-WS₂ junction, enabling the pristine study of the interface and facilitating Andreev pair injection. We observed enhanced conductivity in dI/dV spectra for junction voltages smaller than the corresponding Nb superconducting gap, which vanishes as the device temperature is increased above the Tc. The position and the temperature dependence of the conductivity peaks suggest proximity effect-related phenomena explained by developed modified BTK theory. The presented results are crucial for the future implementation of proximity-based 2D hybrid devices including quantum light sources and superconducting field-effect transistors based on superconductor-semiconductor junctions.