UNRAVELS · UNderstanding, descRibing And Visualizing Electronic charge in noveL oxide heteroStructures

UNderstanding, descRibing And Visualizing Electronic charge in noveL oxide heteroStructures

In recent years with the improving of experimental techniques in thin film deposition and with the possibility to measure, visualize and control at atomic scale the electron charge, Transition Metal Oxides and their heterostructures revealed to be promising building blocks for revolutionary oxide electronics (oxitronics). The properties of the interface region between two oxides, determined by the coupling of the properties of each oxide, are at the origin of different microscopic mechanisms: charge fluctuations, disproportionation, symmetry breaking, spin frustration. These atomic scale interactions drive the macroscopic behavior of the heterostructures in a way to generate new and yet unpredicted properties:magnetic/ferroelectric polarization,H-Tc superconductivity, fast metal-insulator phase transitions, domain walls,multiferroicity. The aim of this project is to use ab initio parameter-free calculations based on DFT methodologies to investigate the electronic structure and the spectroscopic properties of oxides side-by-side with the experiment. Ab initio techniques are essential to investigate and predict correlation features at the atomistic level, evaluating the role of geometry reconstruction at the interface, predicting the charge redistribution, calculating the electronic structure across the phase transition and the band offsets at the interfaces.I have studied how strain and structural and chemical defects and the presence of interfaces tends to alter the charge localization and the magnetic configuration with respect the pristine oxides systems. I showed how different geometric reconstructions due to epitaxial strain and defects affect the charge occupation of orbitals and the electronic structure in the atomic layers surroundings the interface and deeper into the substrate. The electronic structure and the magnetic configuration can be affected by the number of atomic layers constituting the heterostructure and eventually by the presence of different capping thin films at the surface. The systems subdue an iso-structural electronic phase transition from insulating to metallic configuration. Also the magnetic structure is affected by the presence of different magnetic atoms with a mixed valence configuration. Thanks to DFT simulations we have demonstrated for some paradigmatic oxides and their heterostuctures (I.e: SrTiO3-LaAlO3, LaMnO3-LaNiO3) which are the mechanisms occurring at the atomic scale that permit to control their electronic and magnetic properties. DFT simulations helped to guide the experiments in the proper realization of such complex heterostructures in order to achieve a wide range of functionalities to implement into innovating and faster technological devices.

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