Large phonon-drag enhancement induced by narrow quantum confinement at the LaAlO₃/SrTiO₃ interface

The thermoelectric power of the two-dimensional electron system (2DES) at the LaAlO₃/SrTiO₃ interface is explored below room temperature, in comparison with that of Nb-doped SrTiO₃ single crystals. For the interface, we find a region below T =50 K where thermopower is dominated by phonon drag, whose amplitude is hugely amplified with respect to the corresponding bulk value, reaching values ∼mV/K and above. The phonon-drag enhancement at the interface is traced back to the tight carrier confinement of the 2DES, and represents a sharp signature of strong electron-acoustic phonon coupling at the interface.