Effect of Pb(Zr0.52Ti0.48)O3 thin films on electron transport at the LaAlO3/SrTiO3 interface by surface acoustic waves

Surface acoustic waves (SAWs) are capable tools for providing mechanical control over the electronic properties of functional materials. Coupling SAWs with the LaAlO3/SrTiO3 (LAO/STO) conducting interface is particularly interesting as this interface exhibits extraordinary features, such as high mobility at low temperature, ferromagnetism, and superconductivity below 200 mK. For SAW generation, piezoelectricity is indispensable, and due to lack of that in the LAO/STO system, a 200 nm thick Pb(Zr0.52Ti0.48)O3 (PZT) film was grown on top of LAO. SAW excitation and propagation was demonstrated on a PZT/LAO/STO multilayer structure. We further employed SAWs in order to transport free electrons confined to the LAO/STO interface, detected as an acoustoelectric voltage at room temperature. Electrical characterization of the interface was carried out by Van der Pauw measurements. We found that having a PZT layer on top of LAO/STO considerably degraded the interfacial conductivity. The degradation became more pronounced at low temperatures. We attribute these effects to the filling of oxygen vacancies due to interlayer oxygen migration, combined with carrier freeze-out at low temperatures.