Heating and heat conduction in molecular junctions are considered within a general nonequilibrium Green's function formalism. We obtain a unified description of heating in current-carrying molecular junctions as well as the electron and phonon contributions to the thermal flux, including their mutual influence. Ways to calculate these contributions, their relative importance, and ambiguities in their definitions are discussed. A general expression for the phonon thermal flux is derived and used in a different "measuring technique" to define and quantify "local temperature" in nonequilibrium systems. Superiority of this measuring technique over the usual approach that defines effective temperature using the equilibrium phonon distribution is demonstrated. Simple bridge models are used to illustrate the general approach, with numerical examples.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 10 Apr 2007