Thermoelectric signatures of coherent transport in single-molecule heterojunctions

An exact expression for the heat current in an interacting nanostructure is derived and used to calculate the thermoelectric response of three representative single-molecule junctions formed from isoprene, 1,3-benzenedithiol, and [18]-annulene. Dramatic enhancements of the thermopower S and Lorenz number L are predicted when the junction is tuned across a node in the transmission function, with universal maximum values S _max ) (π/3 ^1/2)(k _B/e) and L _max ) (7π ²/5)(k _B ²/e ²). The effect of a finite minimum transmission probability due, e.g., to incoherent processes or additional nonresonant channels, is also considered.