Enhancement of thermoelectric efficiency in a two-level molecule

Electron and energy transport through a two-level molecule (quantum dot) with intra- and inter-level Coulomb correlations is studied using the non-equilibrium Green function formalism. Thermoelectric coefficients are determined in the regime of linear transport for a wide range of gate voltages and temperature. At low temperatures Coulomb blockade effects lead to oscillations of thermal conductance which are well correlated with oscillations in electron conductance. Due to different probabilities of particular one- and two-particle configurations, the intensities of the peaks corresponding to resonant states are different, which results in the selection of channels active in the transport. Additional selection can be obtained for molecules with level-dependent tunnelling rates to external electrodes. In such systems, channels with strongly reduced heat transfer can appear, which results in an enhancement of the thermal efficiency.