A surface-plasmon-coupled thermoelectric apparatus includes a first surface-plasmon substrate and a thermoelectric substrate electrically coupled to a plurality of electrodes. The substrates are electrically isolated from each other, and a first face of the thermoelectric substrate opposes a first face of the first surface-plasmon substrate to define a phonon insulating gap. A method of transferring thermal energy across the phonon insulating gap includes creating a first surface-plasmon polariton at the first surface-plasmon substrate when the first surface-plasmon substrate is coupled to a first thermal reservoir. Also included is creating a nonequilibrium state between the electron temperature and the phonon temperature at a first face of the thermoelectric substrate, when a second face of the thermoelectric substrate is coupled to a second thermal reservoir. Also included is coupling the first surface plasmon polariton with electrons in the thermoelectric substrate across the phonon insulating gap, thereby transferring thermal energy between the thermal reservoirs through the phonon insulating gap.