Large phonon drag thermopower boosted by massive electrons and phonon leaking in LaAlO(3)/LaNiO(3)/LaAlO(3) heterostructure

[Image: see text] An unusually large thermopower (S) enhancement is induced by heterostructuring thin films of the strongly correlated electron oxide LaNiO(3). The phonon-drag effect, which is not observed in bulk LaNiO(3), enhances S for thin films compressively strained by LaAlO(3) substrates. By a reduction in the layer thickness down to three unit cells and subsequent LaAlO(3) surface termination, a 10 times S enhancement over the bulk value is observed due to large phonon drag S (S(g)), and the S(g) contribution to the total S occurs over a much wider temperature range up to 220 K. The S(g) enhancement originates from the coupling of lattice vibration to the d electrons with large effective mass in the compressively strained ultrathin LaNiO(3), and the electron–phonon interaction is largely enhanced by the phonon leakage from the LaAlO(3) substrate and the capping layer. The transition-metal oxide heterostructures emerge as a new playground to manipulate electronic and phononic properties in the quest for high-performance thermoelectrics.