Andreev reflection of quantum Hall states through a quantum point contact

TL;DR

This study explores how a quantum point contact can tune Andreev reflection between quantum Hall states and a superconductor, revealing quantized and continuous regimes that deepen understanding of their interplay in 2D electron systems.

Contribution

It introduces a novel experimental setup using a QPC to control Andreev reflection at the QH-superconductor interface, providing new insights into edge mode behavior.

Findings

Andreev reflection can be tuned from 50% to 10% using QPC voltage.

Presence of quantized plateaus in Andreev reflection indicates edge mode pinching.

The setup enables controlled study of superconductivity and quantum Hall effect interactions.

Abstract

We investigate the interplay between the quantum Hall (QH) effect and superconductivity in InAs surface quantum well (SQW)/NbTiN heterostructures using a quantum point contact (QPC). We use QPC to control the proximity of the edge states to the superconductor. By measuring the upstream and downstream resistances of the device, we investigate the efficiency of Andreev conversion at the InAs/NbTiN interface. Our experimental data is analyzed using the Landauer-Buttiker formalism, generalized to allow for Andreev reflection processes. We show that by varying the voltage of the QPC, $V_{QPC}$, the average Andreev reflection, $A$, at the QH-SC interface can be tuned from 50% to 10%. The evolution of $A$ with $V_{QPC}$ extracted from the measurements exhibits plateaus separated by regions for which $A$ varies continuously with $V_{QPC}$. The presence of plateaus suggests that for some ranges of $V_{QPC}$ the QPC might be pinching off almost completely from the QH-SC interface some of the edge modes. Our work shows a new experimental setup to control and advance the understanding of the complex interplay between superconductivity and QH effect in two-dimensional electron gas systems.