Electrostatic control of the proximity effect in the bulk of semiconductor-superconductor hybrids

<p>The proximity effect in semiconductor-superconductor nanowires is expected to generate an in-<br> duced gap in the semiconductor. The magnitude of this induced gap, together with the semicon-<br> ductor properties like the spin-orbit coupling and g - factor, depends on the coupling between the<br> materials. It is predicted that this coupling can be adjusted through the use of electric fields. We<br> study this phenomena in InSb/Al/Pt hybrids using nonlocal spectroscopy. We show that these<br> hybrids can be tuned such that the semiconductor and superconductor are strongly coupled. In this<br> case, the induced gap is similar to the superconducting gap in the Al/Pt shell and closes only at<br> high magnetic fields. In contrast, the coupling can be suppressed which leads to a strong reduction<br> of the induced gap and critical magnetic field. At the crossover between the strong-coupling and<br> weak-coupling regimes, we observe the closing and reopening of the induced gap in the bulk of a<br> nanowire. Contrary to expectations, it is not accompanied by the formation of zero-bias peaks in<br> the local conductance spectra. As a result, this cannot be attributed conclusively to the anticipated<br> topological phase transition and we discuss possible alternative explanations.</p>