Superconducting proximity effect in inverted InAs/GaSb quantum well structures with Ta electrodes

We report on a systematic study of the proximity effect in top-gated InAs/GaSb quantum wells in contact with a superconducting Ta electrode. We find that the electronic transport across the InAs-Ta interface exhibits distinct zero-bias behavior, either a conductance (dI/dV) peak or dip, depending on the interfacial transparency. For a relatively resistive interface, we observe a dI/dV peak at zero bias, accompanied by two dI/dV dips at high bias voltages, consistent with previous works. When a transparent InAs-Ta interface is achieved, a zero-bias dV/dI dip appears with two coherent-peak-like features forming at bias voltages corresponding to the superconducting gap of Ta. The dI/dV spectra of the transparent InAs-Ta interface at different gate voltages can be fit well using the standard BTK model and the temperature dependence follows a BCS-like behavior. Our work demonstrates the possibility of achieving the highly transparent interfaces in InAs/GaSb hybrid structures, needed for studying the intriguing Andreev bound states in this two-dimensional topological system.