In this paper, we investigate the thermoelectric performance of a double-dot device driven by time-dependently modulated gate voltages. We show that if the modulation frequency $\Omega$ is sufficiently small, not only quantized charge pumping can be realized, but also the heat current flowing in the leads is quantized and exhibits plateaux in units of $\frac{\Omega }{2\pi }{k}_{\mathrm{B}}T\ln 2$. The factor $\ln 2$ stems from the degeneracy of the double-dot states involved in transport. This opens the possibility of using the pumping cycle to transfer heat against a temperature gradient or to extract work from a hot reservoir with Carnot efficiency. However, the performance of a realistic device is limited by dissipative effects due to leakage currents and finite-frequency operation, which we take into account rigorously by means of a generalized master equation approach in the regime where the double dot is weakly coupled to the leads. We show that despite these effects, the efficiency of a double-dot charge pump performing work against a dc source can reach of up to 70$\%$ of the ideal value.

• Received 21 March 2013

DOI:https://doi.org/10.1103/PhysRevB.87.245423