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2D gases in oxide nanostructures revealed by high space, energy and momentum resolved spectroscopy

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Title: 2D gases in oxide nanostructures revealed by high space, energy and momentum resolved spectroscopy

Scientific Responsibles: Jean-Pascal Rueff and Alexandre Gloter

Laboratory : SOLEIL synchrotron and Laboratoire de Physiques des Solides @ Université Paris Saclay

Type of Contract: PhD Student contract (36 months)

Start date of the PhD thesis: September/December 2021


Complex oxides such as ABO3 perovskites form a vast class of materials with a plethora of fascinating, intrinsic physical functionalities. The intriguing interplay of charge, spin, and orbital ordering in these systems superimposed by lattice effects opens a scientifically rewarding playground for both fundamental and application-oriented research. In particular, the possibility of externally modifying the properties of thin-film complex oxides by epitaxial strain or artificial boundaries, and thus potentially generating novel properties (2D gas, superconductivity, magnetism, ...) at the interfaces between films opens up many perspectives and new applications [1]. Among these properties, the occurrence of 2D electron gases and their possible applications for spin-to-charge conversion, and/or in contact with ferro-electric, could result in new devices with reduced energy consumption [2]. In this thesis, the student will use and develop a combination of state-of-the-art synchrotron spectroscopy and electron spectro-microscopy techniques to unravel the structural and electronic structure of such oxide materials at the atomic scale in connection with their optical and transport properties [3]. The thesis will focus on novel oxide materials prepared as bulk, thin films or heterostructures such as SrTiO3/manganite, SrTiO3/metal, BaTiO3/metal, or BiFeO3/metal. Their electronic structure will be investigated by advanced synchrotron techniques including hard x-ray photoelectron spectroscopy (HAXPES) and inelastic X-ray scattering (IXS) [4] at high resolution which can probe the electronic properties and fundamental excitations of materials. In parallel, the PhD student will perform space and momentum resolved scanning transmission electron microscope - electron energy loss spectroscopy (STEM-EELS) [5] with unprecedented resolution with the aim at unravelling the electronic and orbital / symmetry reconstruction of thin film, interface or superlattices. These structural and electronic properties will be discussed with respect to the physical measurements and ab-initio modelling.
Keywords 2D gases, interface physic, thin film, ferro-electricity, electron microscopy, electron spectroscopy, X-Ray inelastic scattering, material modelling.

In?Depth Atomic Mapping of Polarization Switching in a Ferroelectric Field?Effect Transistor, X Li, Q Zhu, L Vistoli, A Barthélémy, M Bibes, S Fusil, V Garcia, A Gloter, Advanced Materials Interfaces 7 (2020) ; Role of point and line defects on the electronic structure of LaAlO3/SrTiO3 interfaces, A Gloter et al. APL Materials 8, 041103 (2020).

[2] Spin and orbital Edelstein effects in a two-dimensional electron gas: Theory and application to SrTiO3 interfaces, A. Johansson, B. Gobel, J. Henk, M. Bibes, I. Mertig. Phys Rev. Research 3, 013275 (2021).

[3] Depth profiling charge accumulation from a ferroelectric into a doped mott insulator, M. Marinova, J. E. Rault, A. Gloter, S. Nemsak, G. K. Palsson, J.-P. Rueff, C. S. Fadley, C. Carrétéro, H. Yamada, K. March, V. Garcia, S. Fusil, A. Barthélémy, O. Stéphan, C. Colliex, and M. Bibes, Nano Letters 15, 2533–2541 (2015).

[4] Resonant inelastic x-ray scattering study of doping and temperature dependence of low-energy excitations in La1-xSrxVO3, K. Ruotsalainen, M. Gatti, J.M. Ablett, F. Yakhou-Harris, J.-P. Rueff, A. David, W. Prellier, A. Nicolaou, arXiv:2004.11200 (2020) ; Two-dimensional electron systems in perovskite oxide heterostructures: Role of the polarity-induced substitutional defects, Lin et al. Physical Review Materials 4 (11), 115002 (2020).

[5] Low-energy Electronic Excitations in Transition-metal Oxide as Probed by STEM-EELS Spectromicroscopy, A Gloter, C Su, X Li, K Ruotsalainen, A Nicolaou, O Stephan, Microscopy and Microanalysis 26 (S2), 1750-1751 (2020).

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