Thermoelectric Scanning Gate Interferometry on a Quantum Point Contact

TL;DR

This paper introduces a novel thermoelectric scanning gate microscopy technique to study quantum point contacts, revealing unique interference patterns and phase information in thermoelectric transport not accessible by traditional methods.

Contribution

The work develops and demonstrates a new TSGM method for probing thermoelectric effects in quantum devices, providing insights into energy derivatives of transmission.

Findings

Observation of interference patterns in TSGM images.

Detection of large phase jumps in thermoelectric fringes.

Enhanced sensitivity to energy derivatives of transmission.

Abstract

We introduce a new scanning probe technique derived from scanning gate microscopy (SGM) in order to investigate thermoelectric transport in two-dimensional semiconductor devices. The thermoelectric scanning gate Microscopy (TSGM) consists in measuring the thermoelectric voltage induced by a temperature difference across a device, while scanning a polarized tip that locally changes the potential landscape. We apply this technique to perform interferometry of the thermoelectric transport in a quantum point contact (QPC). We observe an interference pattern both in SGM and TSGM images, and evidence large differences between the two signals in the low density regime of the QPC. In particular, a large phase jump appears in the interference fringes recorded by TSGM, which is not visible in SGM. We discuss this difference of sensitivity using a microscopic model of the experiment, based on the contribution from a resonant level inside or close to the QPC. This work demonstrates that combining scanning gate microscopy with thermoelectric measurements offers new information as compared to SGM, and provides a direct access to the derivative of the device transmission with respect to energy, both in amplitude and in phase.