Van-der-Waals integration of superconducting tunneling devices

Layered materials can be exfoliated to very thin films. In our group we utilize a technique called “mechanical transfer”, which allows stacking of such materials into new types of heterostructures which can involve layers of distinct functionalities. In my talk I will describe this fabrication technique, and demonstrate how we build a new type of device which consists of a layered superconductor (NbSe₂), on which we deposit an ultra-thin layer of the semiconductor WSe₂. Together, these two materials form a tunneling device, which can be cooled to extremely low temperatures (20 mK) in a dilution cryostat fitted with special filters which allow very sensitive energy spectroscopy. Our tunneling spectra allow tracking the evolution of the superconductor order parameter at the presence of strong magnetic fields, and quantifying its stability. Specifically, the depairing energy scale can be evaluated, and its origin – orbital or spin – identified. Thus, we are able to identify which of the two bands participating in NbSe₂ superconductivity is associated with this material’s remarkable stability against in-plane magnetic field.