Spectrocopic visualization of aluminum islands in the Coulomb blocakade regime deposited on InAs nanowires

Hybrid InAs/Al nanowires are studied as a platform for topological superconductivity. Here we visualize spectroscopically the Coulomb blockade regime of aluminum islands deposited in situ on InAs nanowires. We find no changes in the chemical potential before and after aluminum deposition signifying absence of charge doping and of local band bending at the immediate vicinity of the islands. On the aluminum islands we find Coulomb blockade features typical to double barrier tunneling junction. From these we characterize the resistive and capacitive properties of the nanowire-aluminum interface. We identify a finite barrier for tunneling of electrons across that interface. Our observations strongly reflect on the ability to induce robust topological superconductivity by deposition of aluminum on InAs nanowires.