Optimal thermoelectric figure of merit of a molecular junction

Abstract

We show that a molecular junction can give large values of the thermoelectric figure of merit $ZT$, and so could be used as a solid state energy conversion device that operates close to the Carnot efficiency. The mechanism is similar to the Mahan-Sofo model for bulk thermoelectrics -- the Lorenz number goes to zero violating the Wiedemann-Franz law while the thermopower remains non-zero. The molecular state through which charge is transported must be weakly coupled to the leads, and the energy level of the state must be of order $k_{B}T$ away from the Fermi energy of the leads. In practice, the figure of merit is limited by the phonon thermal conductance; we show that the largest possible $ZT\sim ({\tilde{G}}_{th}^{ph}{)}^{-1/2}$, where ${\tilde{G}}_{th}^{ph}$ is the phonon thermal conductance divided by the thermal conductance quantum.

4 pages, 2 figures

References in corpus (2)

• Violation of the Wiedemann-Franz Law in a Single-Electron Transistor
• Coherent phonon scattering effects on thermal transport in thin semiconductor nanowires

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