Quantum constriction at the interface between a superconducting nanocrystal and an electron accumulation layer

In the recent work of Vlaic et al. (2017), it has been shown that Pb nanocrystals (NCs) grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first Scanning Tunneling Spectroscopy (STM) study of the superconducting parity effect across the Anderson limit. The observation of Coulomb blockade implies the existence of a tunnel barrier between the NCs and the substrate. This tunnel barrier has been ascribed to a quantum constriction of the electronic wave function at the interface between the NCs and the electron accumulation layer owing to its large Fermi wavelength. In this proceeding, we detail and review the arguments leading to this conclusion.