Quantum Enhancement of the Spin-Thermopower in Single-Molecule Junctions*

The thermoelectric effect allows heat to be directly converted into electricity in a device with no moving parts.  In systems with broken time-reversal symmetry, a spin-voltage may be generated in response to a temperature gradient via the analagous spin-thermopower effect.

We derive general expressions for the linear-response spin-dependent transport and apply them to investigate the thermoelectric and thermodynamic response of single-molecule junctions with destructive quantum interference features (nodes) in a channel of their transmission spectrum.  We calculate the transport of two node-possessing junctions using both manybody (Molecular Dyson Equation) and effective single-particle (extended Huckel) electronic structure theories and observe that the thermopower, ZT, and the thermodynamic efficiency are nearly identical in all cases, provided the node is sufficiently detuned from all molecular resonances and other nodes.  

We find that the entropy and spin currents through a junction are differntially affected by a node, giving rise to a peak in the spin-thermopower and spin-dependent thermodynamic efficiency when the spin-splitting is commensurate with the peaks of the thermopower spectrum.  The influence of off-resonant transport is also discussed.