Gate-defined quantum point contacts in a germanium quantum well

TL;DR

This study demonstrates high-quality gate-defined quantum point contacts in strained germanium quantum wells, revealing quantized conductance, energy subband spacing, and Zeeman splitting, establishing a reliable platform for quantum device research.

Contribution

It introduces a reproducible fabrication of quantum point contacts in germanium wells and characterizes their quantum transport properties under various conditions.

Findings

Quantized conductance plateaus at zero magnetic field

Energy spacing between subbands ranges from 1.5 to 5 meV

Zeeman splitting with g-factors around 6.6 for holes

Abstract

We report an experimental study of quantum point contacts defined in a high-quality strained germanium quantum well with layered electric gates. At zero magnetic field, we observe quantized conductance plateaus in units of 2$e^2/h$. Bias-spectroscopy measurements reveal that the energy spacing between successive one-dimensional subbands ranges from 1.5 to 5\,meV as a consequence of the small effective mass of the holes and the narrow gate constrictions. At finite magnetic fields perpendicular to the device plane, the edges of the conductance plateaus get splitted due to the Zeeman effect and Land\'{e} $g$ factors are estimated to be $\sim6.6$ for the holes in the germanium quantum well. We demonstrate that all quantum point contacts in the same device have comparable performances, indicating a reliable and reproducible device fabrication process. Thus, our work lays a foundation for investigating multiple forefronts of physics in germanium-based quantum devices that require quantum point contacts as a building block.