Attractive and driven interaction in quantum dots: mechanisms for geometric pumping

TL;DR

This paper investigates geometric charge pumping in quantum dots with tunable electron-electron interactions, revealing unique mechanisms and resonances, especially under attractive interactions, and emphasizing the importance of spin degeneracies.

Contribution

It provides an analytical framework for understanding geometric pumping in quantum dots with both static and dynamic interactions, highlighting mechanisms unique to interaction-driven driving.

Findings

Identification of a pumping resonance in attractive interaction regimes.

Discovery of a pumping mechanism specific to interaction modulation.

Sensitivity of pumping response to spin degeneracies and symmetry breaking.

Abstract

We analyze time-dependent transport through a quantum dot with electron-electron interaction that is statically tunable to both repulsive and attractive regimes, or even dynamically driven. Motivated by the recent experimental realization [Hamo et. al, Nature 535, 395 (2016)] of such a system in a static double quantum dot we compute the geometric pumping of charge in the limit of weak tunneling, high temperature and slow driving. We analyze the pumping responses for all pairs of driving parameters (gate voltage, bias voltage, tunnel coupling, electron-electron interaction). We show that the responses are analytically related when these different driving protocols are governed by the same pumping mechanism, which is characterized by effective driving parameters that differ from the experimental ones. For static attractive interaction we find a characteristic pumping resonance despite the 'attractive Coulomb blockade' that hinders stationary transport. Moreover, we identify a pumping mechanism that is unique to driving of the interaction. Finally, although a single-dot model with orbital pseudo-spin describes most of the physics of the mentioned experimental setup, it is crucial to account for the additional (real-) spin degeneracies of the double dot and the associated electron-hole symmetry breaking. This is necessary because the pumping response is more sensitive than DC transport measurements and detects this difference through pronounced qualitative effects.