Andreev Reflection in the Quantum Hall Regime at an Al/InAs Junction on a Cleaved Edge

TL;DR

This study demonstrates a high-quality superconductor/semiconductor junction that allows coexistence of superconductivity and quantum Hall effects, revealing Andreev reflection and opening pathways for exploring exotic quasiparticles.

Contribution

We fabricated a novel Al/InAs junction with a cleaved edge geometry that maintains superconductivity under high magnetic fields and exhibits high Andreev reflection efficiency.

Findings

Superconductivity coexists with quantum Hall effects down to Landau-level filling factor 3.

High Andreev reflection probability exceeds 50% in the quantum Hall regime.

The junction demonstrates a nearly barrier-free interface with conductance enhancement limited only by Fermi velocity mismatch.

Abstract

We have fabricated a superconductor/semiconductor (S/Sm) junction composed of Al and InAs using cleaved edge overgrowth. By exploiting the unique geometry with a thin Al/Pt/Al trilayer formed on the side surface of an in-situ cleaved heterostructure wafer containing an InAs quantum well, we achieve a superconducting critical field of 5 T, allowing superconductivity and quantum Hall (QH) effects to coexist down to Landau-level filling factor nu = 3. Andreev reflection at zero magnetic field shows a conductance enhancement that is limited solely by the Fermi velocity mismatch, demonstrating a virtually barrier-free, high-quality S/Sm junction. Bias spectroscopy in the QH regime reveals the opening of a superconducting gap, with the reduced downstream resistance demonstrating that the electron-hole Andreev conversion probability consistently exceeds 50%. Our results, obtained in a new experimental regime characterized by a clean edge-contacted junction with a superconducting electrode narrower than the coherence length, open new avenues for both theoretical and experimental studies of the interplay between superconductivity and QH effects and the engineering of exotic quasiparticles.