First Principle Study Of The LaAlO₃/SrTiO₃ Interface Electronic Structure

With abundant chemical components and structural phases,the perovskite transition metal oxides have exhibited plentiful novel and complex physical properties.The lattice or electronic reconstruction of the perovskite oxide interface due to spatial symmetry breaking can produce various novelty properties that may not be possessed by its constituent bulk materials.In contrast with the single-interface oxide heterojunction,the high density of interfaces in transition metal oxide superlattices will introduce an additional degree of complexity,thus exhibiting complex physical properties that may not be present at a single-interface.Thus,it's important to understand,predict and tailoring the physical properties of the oxide superlattice.At present,in basic physical understanding,the origin of the quasi-two-dimensional electron gas at LaAlO₃/SrTiO₃?001?interface still remains controversial.Especially the effect of ion relaxation is unclear.Exploration effective control strategies is an important step toward the new physics and practical applications.This paper focuses on the two aspects mentioned above and includes three parts,as shown below:Based on the density functional theory,we employ first-principle calculations to investigate the atomic structure and electronic structure of multi-type LaAlO₃/SrTiO₃superlattices.?1?There are varieties of control methods that can be used to regulate the2DEG properties at the interface of the LaAlO₃/SrTiO₃ heterostructure.Most achieved through the application of external fields.By artificially introducing interfacial cation intermixing,we proposed that interfacial alloy structures Al_1-xTi_xO₂(or Ti_1-xAl_xO₂)can be constructed.When x is less than 25%,the spin-polarized electrons is completely confined at the interface.?2?Based on the‘polar catastrophe'scenario the crystal orientation has played an important role to define a‘polar interface'.In this scenario,no conductivity would be expected at the interface between LaAlO₃ and?110?-oriented SrTiO₃,which should have no polar discontinuity at the interface.We propose that polar?LaAlO₃?_N/?SrTiO₃?_N?110?superlattices can be realized when np-type?LaAlO₃?_N/?SrTiO₃?_N?001?superlattices are constructed in a 45?stepped pattern.By applying uniaxial in-plane strains,an unexpected indirect-to-direct bandgap transition occurs in the polar LaAlO₃/SrTiO₃?110?superlattices.?3?The size,shape and connectivity of oxide octahedra are essential for understanding and controlling the emergent functional properties of ABO₃ perovskites.We demonstrate that interfacial oxygen octahedral coupling and hole-doping,in addition to epitaxial strain,are the key factors underlying the formation of multiple types of oxygen octahedral rotations in LaAlO₃/SrTiO₃?001?superlattices.We also confirm that oxygen octahedral rotations and deformations play an essential role in insulator–metal transitions.The obtained results in this paper provide compelling evidence of the polar-catastrophe scenario and new strategies for the control of the physical properties of confined electron-hole systems.