Single-electron transport driven by surface acoustic waves: moving quantum dots versus short barriers

TL;DR

This study explores how surface acoustic waves induce quantized electron transport through quantum point contacts, revealing interference effects and multiple quantization mechanisms, including effects of short potential barriers.

Contribution

It demonstrates the coexistence of different quantization mechanisms in acoustoelectric current and highlights the influence of short barriers on electron transport.

Findings

Current exhibits quantized plateaus at multiples of ef.

Interference effects cause a 1.1 MHz beat period in the current.

Multiple quantization mechanisms can operate simultaneously.

Abstract

We have investigated the response of the acoustoelectric current driven by a surface-acoustic wave through a quantum point contact in the closed-channel regime. Under proper conditions, the current develops plateaus at integer multiples of ef when the frequency f of the surface-acoustic wave or the gate voltage Vg of the point contact is varied. A pronounced 1.1 MHz beat period of the current indicates that the interference of the surface-acoustic wave with reflected waves matters. This is supported by the results obtained after a second independent beam of surface-acoustic wave was added, traveling in opposite direction. We have found that two sub-intervals can be distinguished within the 1.1 MHz modulation period, where two different sets of plateaus dominate the acoustoelectric-current versus gate-voltage characteristics. In some cases, both types of quantized steps appeared simultaneously, though at different current values, as if they were superposed on each other. Their presence could result from two independent quantization mechanisms for the acoustoelectric current. We point out that short potential barriers determining the properties of our nominally long constrictions could lead to an additional quantization mechanism, independent from those described in the standard model of 'moving quantum dots'.