Carbon nanotube-based quantum pump in the presence of superconducting lead

TL;DR

This paper investigates a quantum electron pump based on carbon nanotubes with superconducting leads, revealing how resonant Andreev reflection influences pumped current, its dependence on system parameters, and differences between nanotube types.

Contribution

It introduces a detailed analysis of a superconductor-carbon-nanotube quantum pump, highlighting the role of Andreev reflection and the impact of nanotube geometry on pumped current.

Findings

Pumped current can be positive or negative depending on system parameters.

Resonant Andreev reflection causes a double peak structure in the pumped current.

Pumped current scales quadratically with pumping amplitude in weak regime, linearly in strong regime.

Abstract

Parametric electron pump through superconductor-carbon-nanotube based molecular devices was investigated. It is found that a dc current, which is assisted by resonant Andreev reflection, can be pumped out from such molecular device by a cyclic variation of two gate voltages near the nanotube. The pumped current can be either positive or negative under different system parameters. Due to the Andreev reflection, the pumped current has the double peak structure around the resonant point. The ratio of pumped current of N-SWNT-S system to that of N-SWNT-N system (I^{NS}/I^N) is found to approach four in the weak pumping regime near the resonance when there is exactly one resonant level at Fermi energy inside the energy gap. Numerical results confirm that in the weak pumping regime the pumped current is proportional to the square of the pumping amplitude V_p, but in the strong pumping regime the pumped current has the linear relation with V_p. Our numerical results also predict that pumped current can be obtained more easily by using zigzag tube than by using armchair tube.