Figure 3: Theoretical simulation.

(a) Theoretical model (top): a cylindrical nanowire (black, grey, white) with length L_N+L (100 nm+800 nm), where the latter part is partially coated by a superconductor leaving the bottom surface uncovered. (Scheme shows L=100 nm for clarity.) The wire radius R is 40 nm and the superconducting film has a thickness R_s=10 nm. (Our wire radius varies from device to device between 30 and 50 nm, and we have confirmed that our simulations give similar results within this range.) The wire is terminated from both sides with infinite leads (pink). Front lead is normal, back lead is normal/superconductor. Each little circle represents a three-dimensional mesh site with a size of 7 nm. White circles depict a potential barrier with a width W=60 nm in the uncovered wire section forming a quantum point contact (QPC). Grey circles represent the smoothness of the barrier which is set to 5 nm. Experimental geometry (bottom): cross-sectional schematic shows the nanowire (NW), the normal contact (N) and the superconducting contact (S). Superconductivity is induced in the nanowire section underneath the superconducting contact. Transport is ballistic through a proximitized wire section, whose length far exceeds L_N, the length of the non-covered wire between the contacts. (b) Numerical simulation for devices with different mean free paths (see Supplementary Fig. 5). Black trace is for G_n corresponding to a mean free path 10 μm, the rest are for G_s corresponding to a mean free path ranging from 1 μm (pink) to 20 μm (blue). (c) Above-gap (black) and subgap (red) conductance for device D. (d,e) Comparison between the measurement (device C) and the simulation of a ballistic device with l_e=10 μm. The induced superconducting gap edges for higher subbands, visible in the simulation as four symmetric peaks outside the gap around V ∼±1 mV, are not observed in the experiment (see Methods for details).