Single-Hole Pump in Germanium

TL;DR

This paper demonstrates a single-hole quantum pump in germanium, achieving quantized current at high frequencies, expanding the material options for quantum standards of electric current.

Contribution

It introduces a novel germanium-based single-hole pump with tunable barriers, demonstrating quantized current in an unexplored semiconductor material.

Findings

Quantized current plateaux observed up to 100 MHz

Operation affected by disorder and charge fluctuations

Proposed fabrication improvements for better performance

Abstract

Single-charge pumps are the main candidates for quantum-based standards of the unit ampere because they can generate accurate and quantized electric currents. In order to approach the metrological requirements in terms of both accuracy and speed of operation, in the past decade there has been a focus on semiconductor-based devices. The use of a variety of semiconductor materials enables the universality of charge pump devices to be tested, a highly desirable demonstration for metrology, with GaAs and Si pumps at the forefront of these tests. Here, we show that pumping can be achieved in a yet unexplored semiconductor, i.e. germanium. We realise a single-hole pump with a tunable-barrier quantum dot electrostatically defined at a Ge/SiGe heterostructure interface. We observe quantized current plateaux by driving the system with a single sinusoidal drive up to a frequency of 100 MHz. The operation of the prototype was affected by accidental formation of multiple dots, probably due to disorder potential, and random charge fluctuations. We suggest straightforward refinements of the fabrication process to improve pump characteristics in future experiments.