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.
Highlights
A single-charge pump is an electronic device that can generate quantized electric current by clocking the transfer of individual charged quasi-particles with an external periodic drive [1]
In order to tune the device into a single-quantum dots (QDs) operation regime, the transconductance is measured as a function of dc voltages applied to both barriers with the rf source turned off
As highlighted by the dashed lines in panel (d), on occasions the coulomb peaks present abrupt discontinuities. This fact is an indication that random charge rearrangements are occurring in or in the vicinity of the QD, resulting in discrete jumps in the current level at a given operation point
Summary
A single-charge pump is an electronic device that can generate quantized electric current by clocking the transfer of individual charged quasi-particles (electrons, holes or cooper pairs) with an external periodic drive [1]. The pumped current can be expressed as I = nef, where e is the elementary charge, f is the frequency of the drive and n is an integer representing the number of particles transferred per period. The development of this technology has been mainly motivated by its possible application for quantum-based standards of electric. At the core of the any quantum standard lies the concept of universality This is the idea that the operation of the standard is based on fundamental principles of nature, rather than being dependent on its specific physical implementation. A study of this kind has shown that there is agreement at a level of
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