Proximity Effects in AlGaSb/InAs surface quantum wells*

We demonstrate a robust superconducting proximity effect in 24 nm wide AlGaSb/InAs surface quantum wells with sputtered Nb contacts at a temperature of 1.6 K, which has applications towards mesoscopic and topological superconductivity. Through transport characterization we observe high quality single-subband and second subband magnetotransport with quantized integer quantum Hall plateaus observed to filling factor ν = 2 in magnetic fields of up to B = 18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinchoff to 3 x 10¹² cm^-2. Landau fan diagrams at high densities exhibit features from the crossing of spin-split Landau levels from different subbands and curvature due to large spin-orbit interaction. A large Rashba spin-orbit coefficient on the order of 100 meV·Å is obtained through weak anti-localization measurements. An effective mass of 0.03m_e is determined from temperature-dependent magnetoresistance measurements. Josephson junctions fabricated with a contact separation of 200 nm exhibit products I_cR_N = 495 μV and I_exR_N = 2.0 mV of normal resistance R_N, critical current I_c, and excess current I_ex.