Theoretical Study On The Magnetic And Electronic Structures Of LaXO₃?X=Fe,Al?/SrTio₃?BaTio₃/SrTio₃ Heterostructures Tunned By Electric Field

Perovskite oxide has rich physical properties and potential application value.It is an ideal platform for studying the electronic correlation,because the s electrons of the transition metal are transferred to the oxygen ions,and the remaining strongly associated d electrons determine their physical properties,such as electron transport,magnetic,thermal conductivity,and superconductivity.These electronic correlations cause mutual coupling between lattice,spin,charge,and orbital degrees of freedom,allowing perovskite oxides to exhibit many peculiar physical and chemical properties,such as high dielectric constant,piezoelectricity,pyroelectricity,thermoelectricity,ferroelectricity,high temperature superconductivity,clossal magnetoresistance effect,multiferroicity,and magnetoelectric effect.In recent years,with the continuous maturity of epitaxial synthesis technology,heterostructure materials composed of bulky perovskite oxides with different crystal structures and different electronic properties have become one of the hotspots in condensed matter physics and materials science communities.The physical properties of heterostructures are different from ones of the corresponding bulk materials,such as magnetic,metallic properties,ferroelectricity,and superconductivity.Here,the first-principles method based on density functional theory is used to study the regulation of the magnetic and electronic structure of LaFeO3/SrTiO3 heterostructures by external electric field.It is found that the external electric field can effectively regulate the energy band dispersion near the Fermi level of the LaFeO3/SrTiO3 heterostructure witn n-type and p-type heterointerfaces.For the LaFeO3/SrTiO3 heterostructure with n-type interface,a negative electric field can weaken the band shift and even lead to a two-dimensional electron gas,which is accompanied by a reversible insulator-metal/half-metal transition at the n-type interface.In addition,the transition from G-type antiferromagnetism to ferrimagnetism appears when applying the electric field.For the LaFeO3/SrTiO3 heterostructure with p-type interface,the external electric field has a good regulation effect on its electronic structure.Our theoretical research work has further paved the way for the experimental design of new magnetoelectric interface materials.Thiel et al.found that external electric field can induce an insulator-metal transition in a heterointerface composed of polar LaAlO3 and non-polar SrTiO3.Here,we explore the possible reasons for such phenomenon.We calculated the p-type interface of LaAlO3/SrTiO3 heterostructure with different layers by first-principles method.We explain how the polarization potential of the LaAlO3 part overcomes the band gap of SrTiO3,so that the O-2p band of the SrTiO3 surface overlaps with the La-f band of the LaAlO3 surface,and how the external electric field cooperates with the spontaneous polarization and effectively modulates the band dispersion near the Fermi level,thereby inducing an insulator-metal transition in the insulating heterostructure.In addition,the external electric field has a certain regulation effect on the electronic structure of the BaTiO3/SrTiO3 heterostructure with n-type interface.The external electric field can effectively regulate the band shift of the BaTiO3/SrTiO3 heterostructure,and induces the insulator-metal transition of the system.Our research is conducive to expanding the material range of nano-oxide electronic devices,and has important guiding significance for the study of oxide heterostructures with intrinsic polarization.