Study Of The Interactions Between Light And LaAlO₃/SrTiO₃ Heterostructure System

Transition metal oxides,which exhibit a host of intriguing and exotic properties due to the strong coupling of charge,spin,orbital,lattice degrees of freedom,have attracted extensive scientific attention.In the heterointerface systems,the broken symmetry,the discontinuities of the order parameters?such as chemical potential,polarity?,as well as the mixed valence of thetransition metal may lead to the emergence of fascinating novel phenomena.Light,as an external stimuli,can effectively tune the properties of materials;while in turn,the absorption of light is helpful for energy harvest.However,the study of the interaction between light and transition metal oxide heterostructures is relatively lacking.Hence,in this thesis,I focus on the study of the interactions between light and LaAlO₃/SrTiO₃?LAO/STO?heterostructure system.The detailed results are as follows:1.Studies of photovoltaic effect based on LAO/STO heterostructures.By constructing the metal/LAO/STO structure,remarkable ultraviolet photovoltaic effect based on LAO/STO heterostructures was observed for the first time;meanwhile,using such a photovoltaic device design as aneffective probe,we establish the existence of theresidual polar potential in ultrathin LAO films on STO substrate.The direct observationof the intrinsic polar potential within the unit-cell-scale LAO films was achieved by this work,which provides further insight into the underlyingphysical origin of the interfacial 2DEG and also demonstrate the photovoltaic application of such polar/nonpolar oxide heterostructures.2.Photoelectric effect studies of the hybrid systems which consist of graphene and LAO/STO.When transferred onto LAO/STO heterostructures,graphene exhibits greatly enhanced ultraviolet photoconductivity for the proximal couplingto LAO/STO,hence we proposed a new-concept VUV detector based on graphene/LAO/STO system.Meanwhile,in light of this phenomenon,we demonstrate the existence of a built-in polar field within LAO layer,especially in the insulating LAO/STO with LAO thickness less than the critical 4 unit cells for the first time,providing strong evidences in favor of the "polar catastrophe" scenario.Besides,we also design a novel broad-spectrum photodetector based on the hybrid structure of graphene and LAO/STO.3.Studies of optically tuned transport properties of LAO/STO interfacial 2DEG at low temperature.The weak localization?WL?and weak anti-localization?WAL?effects of the interfacial 2DEG were observed at low temperature,from which the spin splitting energy can be deduced.When illuminated by infrared or visible light,persistent photoconductivity effect of the interfacial 2DEG emerges,giving rise to the nonvolatile change of the spin-orbital coupling strength.However,such photo-induced nonvolatile change can be erased by the sweep of gate voltage or a warming-cooling cycle.This finding may pave a new waytoward the exploration of oxide-based spintronic devices.