Thermal transport in mesoscopic devices

New mechanisms for controlling heat flow and for converting heat to work in small-scale solid-state systems are highly desirable, particularly when considering the rapid miniaturization and ever-increasing power densities of electronic devices. Mesoscopic structures, being much larger than individual atoms but still small enough to exhibit some quantum-mechanical features, offer a versatile platform for studying thermal phenomena at reduced length scales. We perform a theoretical study of two types of mesoscopic heat transport devices, namely heat rectifiers and heat engines. A rectifier is a device which allows heat to flow in one direction but flow in the other direction is suppressed. Two different rectifiers are proposed: one is a nonlinear oscillator controlling photonic heat flow in a microwave circuit, the other is a pair Coulomb blockade islands rectifying electronic heat currents. Particularly the latter device offers rectification performance unparallelled in the literature. We also propose a new class of thermoelectric heat engines where electrons are transported between two reservoirs but heat is exchanged between the transport system and a third reservoir by microwave photons. Heat and charge flows are therefore separated, offering much greater flexibility than usual thermoelectrics. Also the two heat baths can be widely separated. With an appropriate setup this device can reach very high efficiencies.