Reversible metal-insulator transition of Ar-irradiated LaAlO₃/SrTiO₃ interfaces

The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAlO₃ (LAO) and SrTiO₃, can be made completely insulating by low-energy, 150-eV, Ar⁺ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation

Room-Temperature Giant Persistent Photoconductivity in SrTiO3/LaAlO3 Heterostructures

SrTiO3/LaAlO3 interfaces show an unprecedented photoconductivity effect that is persistent even at room temperature and giant as it gives rise to a conductivity increase of about 5 orders of magnitude at room temperature. The persistent photoconductivity effects play a paramount role in the still controversial intrinsic behavior of the SrTiO3/LaAlO3 interfaces, as even a limited exposure to visible light is able to strongly modify the electrical transport properties of the interface even above room temperature, while only an appropriate thermal treatment in a dark environment can completely suppress the persistent photoconductivity effect unveiling the intrinsic conduction mechanism of the interface. Moreover, our study demonstrates that the origin of the high conductivity, revealed at the STO/LAO interface at room temperature, is purely electronic