Three-terminal vibron-coupled hybrid quantum dot thermoelectric refrigeration

Abstract

A three-terminal nanoscale refrigeration concept based on a vibron-coupled quantum dot hybrid system coupled to two contacts and a phonon bath is proposed and analyzed in detail. While investigating the non-trivial role of electron-phonon interactions, we show that, although they are well known to be detrimental from a general refrigeration perspective, they can be engineered to favorably improve the trade-off between the cooling power (CP) and the coefficient-of-performance (COP). Furthermore, an additional improvement in the trade-off can be facilitated by applying a high thermal bias. However, the allowed maximum of the thermal bias being strongly limited by the electron-phonon coupling, in turn, determines the lowest achievable temperature of the cooled body. It is further demonstrated that such interactions drive a phonon flow between the dot and bath whose direction and magnitude depend on the temperature difference between the dot and bath. To justify its impact in optimizing the peak CP and COP, we show that a weak coupling with the bath is preferable when the phonons relax through it and a strong coupling is suitable in the opposite case when the phonons are extracted from the bath. Finally, in studying the effect of asymmetry in electronic couplings, we show that a stronger coupling is favorable with the contact whose temperature is closer to that of the bath. Combining these aspects, we believe that this study could offer important guidelines for a possible realization of molecular and quantum dot thermoelectric refrigerator.