Finger-gate array quantum pumps:pumping characteristics and mechanisms

TL;DR

This paper investigates the pumping mechanisms of finger-gate array quantum pumps in narrow channels, revealing how different configurations and symmetry breaking influence adiabatic and nonadiabatic electron transport.

Contribution

It identifies distinct pumping mechanisms for single and multiple finger-gate arrays, highlighting the role of time-dependent Bragg reflection and symmetry breaking in quantum pumping.

Findings

Pumping in single FG pairs is due to inelastic scattering at subband thresholds.

For N>2, the dominant mechanism is time-dependent Bragg reflection.

Symmetry breaking enables robust pumping with specific phase differences.

Abstract

We study the pumping effects, in both the adiabatic and nonadiabatic regimes, of a pair of \QTR{it}{finite} finger-gate array (FGA) on a narrow channel. Connection between the pumping characteristics and associated mechanisms is established. The pumping potential is generated by ac biasing the FGA pair. For a single pair (N=1) of finger gates (FG's), the pumping mechanism is due to the coherent inelastic scattering of the traversing electron to its subband threshold. For a pair of FGA with pair number $N>2$, the dominant pumping mechanism becomes that of the time-dependent Bragg reflection. The contribution of the time-dependent Bragg reflection to the pumping is enabled by breaking the symmetry in the electron transmission when the pumping potential is of a predominant propagating type. This propagating wave condition can be achieved both by an appropriate choice of the FGA pair configuration and by the monitoring of a phase difference $\phi $ between the ac biases in the FGA pair. The robustness of such a pumping mechanism is demonstrated by considering a FGA pair with only pair number N=4.