Cooling mechanisms in molecular conduction junctions

TL;DR

This paper explores various mechanisms by which molecular conduction junctions can be cooled under applied bias, using simple models and different theoretical approaches to demonstrate the feasibility of current-induced cooling.

Contribution

It introduces new models and mechanisms for cooling in molecular junctions, including depletion of high-energy electrons, coherent sub-resonance transport, and driven activated transport.

Findings

Cooling via electron depletion of high-energy states

Analogies to atomic laser cooling mechanisms

Feasibility of current-induced cooling in molecular junctions

Abstract

While heating of a current carrying Ohmic conductors is an obvious consequence of the diffusive nature of the conduction in such systems, current induced cooling has been recently reported in some molecular conduction junctions. In this paper we demonstrate by simple models the possibility of cooling molecular junctions under applied bias, and discuss several mechanisms for such an effect. Our model is characterized by single electron tunneling between electrodes represented by free electron reservoirs through a system characterized by it electron levels, nuclear vibrations and their structures. We consider cooling mechasims resulting from (a) cooling of one electrode surface by tunneling induced depletion of high energy electrons; (b) cooling by coherent sub resonance electronic transport analogous to atomic laser nduced cooling and (c) the incoherent analog of process (b) - cooling by driven activated transport. The non-equilibrium Green function formulation of junction transport is used in the first two cases, while a master equation approach is applied in the analysis of the third.