Transition metal oxides (TMOs) are an ideal arena for the study of electronic correlations because the s-electrons of the transition metal ions are removed and transferred to oxygen ions, and hence the strongly correlated d-electrons determine their physical properties such as electrical transport, magnetism, optical response, thermal conductivity, and superconductivity. These electron correlations prohibit the double occupancy of metal sites and induce a local entanglement of charge, spin, and orbital degrees of freedom. This gives rise to a variety of phenomena, e.g., Mott insulators, various charge/spin/orbital orderings, metal-insulator transitions, multiferroics, and superconductivity. In recent years, there has been a burst of activity to manipulate these phenomena, as well as create new ones, using oxide heterostructures. Most fundamental to understanding the physical properties of TMOs is the concept of symmetry of the order parameter. As Landau recognized, the essence of phase transitions is the change of the symmetry. For example, ferromagnetic ordering breaks the rotational symmetry in spin space, i.e., the ordered phase has lower symmetry than the Hamiltonian of the system. There are three most important symmetries to be considered here. (i) Spatial inversion (I), defined as r → -r. In the case of an insulator, breaking this symmetry can lead to spontaneous electric polarization, i.e. ferroelectricity, or pyroelectricity once the point group belongs to polar group symmetry. (ii) Time-reversal symmetry (T) defined as t → -t. In quantum mechanics, the time-evolution of the wave-function? is given by the phase factor e{sup -iEt/{h_bar}} with E being the energy, and hence time-reversal basically corresponds to taking the complex conjugate of the wave-function. Also the spin, which is induced by the 'spinning' of the particle, is reversed by time-reversal. Broken T-symmetry is most naturally associated with magnetism, since the spin operator changes sign with T-operation. (iii) Gauge symmetry (G), which is associated with a change in the phase of the wave-function as? → e{sup i{theta}}?. Gauge symmetry is connected to the law of charge conservation, and broken G-symmetry corresponds to superconductivity/superfluidity. To summarize, the interplay among these electronic degrees of freedom produces various forms of symmetry breaking patterns of I, T, and G, leading to novel emergent phenomena, which can appear only by the collective behavior of electrons and cannot be expected from individual electrons. Figure 1 shows this schematically by means of several representative phenomena. From this viewpoint, the interfaces of TMOs offer a unique and important laboratory because I is already broken by the structure itself, and the detailed form of broken I-symmetry can often be designed. Also, two-dimensionality usually enhances the effects of electron correlations by reducing their kinetic energy. These two features of oxide interfaces produce many novel effects and functions that cannot be attained in bulk form. Given that the electromagnetic responses are a major source of the physical properties of solids, and new gauge structures often appear in correlated electronic systems, we put 'emergent electromagnetism' at the center of Fig. 1.

Novel phenomena and functionalities at epitaxial complex oxide heterostructures have been attracting huge scientific attention because of the intriguing fundamental physics as well as potential for technological applications that they embody. Essentially, charge and spin reconstruction at the interface can lead to exotic properties, which are completely different from those inherent to the individual materials, for example, a conductive interface between two insulating materials and interface ferromagnetism in the proximity of an antiferromagnet. The interplay between charge and spin degrees of freedom can be particularly intriguing, leading to a fascinating realm, called multiferroic. In this dissertation, a systematic study is performed on the electronic (charge) and magnetic (spin) interaction/reconstruction across the interface of an all-oxide model heterostructure system consisting of the ferromagnet (FM) La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and the multiferroic (ferroelectric and antiferromagnetic) BiFeO$_3$ (BFO). The study demonstrates two pathways of using these exotic interfacial properties to control bulk properties, both the ferroelectricity in BFO and ferromagnetism in LSMO. The journey starts with the growth of high-quality BFO/LSMO heterostructures with unit-cell precision control using reflection high-energy electron diffraction combined with pulsed-laser deposition, providing an important platform for the investigation of electronic and magnetic coupling phenomena across the interface. First, we have observed a novel consequence of the interface electronic interaction due to the so-called ``polar discontinuity'', namely, a built-in electrostatic potential accumulates across the heterointerface, and provides deterministic control of ferroelectric polarization states in thin films. This observation suggests a strong, delocalized effect with important implications for future electronics based on such materials. Secondly, we have revealed a strong magnetic coupling at this interface, manifested in the form of an enhanced coercive field as well as a significant exchange-bias coupling. Based on our x-ray magnetic circular dichroism studies, the origin of the exchange-bias coupling is attributed to a novel ferromagnetic state formed in the antiferromagnetic BFO sublattice at the interface with LSMO. Thirdly, using a field effect geometry, we have proposed a pathway to use an electric field to control the magnetism in LSMO in which the ground state of the interfacial ferromagnetic state is strongly correlated with the ferroelectric polarization. Magnetotransport measurements clearly demonstrate a reversible switch/control between two distinct exchange-bias states by isothermally switching the ferroelectric polarization of BFO. This is an important step towards controlling magnetization with the electric field, which may enable a new class of electrically controllable spintronic devices and provide a new basis for producing electrically controllable spin-polarized currents. Finally, combining experimental results with first-principle and phenomenological model calculations, a microscopic model has been proposed to understand the underlying physics of the magnetoelectric coupling, providing further insights on achieving the electric-field control of magnetism. In summary, our studies on the interfacial electronic and magnetic properties at BFO/LSMO heterointerfaces have revealed a strong interplay between the charge, spin, orbital and lattice degrees of freedom at the interface, which will have important implications for a new pathway to use the interface properties to control bulk functionalities (ferroelectric polarization and ferromagnetic magnetization in this study). Such couplings at the interface may be extended to other oxides and will bring into play remarkable physical concepts to this developing field of complex oxide heterointerfaces.

Epitaxial Growth of Complex Metal Oxides, Second Edition reviews techniques and recent developments in the fabrication quality of complex metal oxides, which are facilitating advances in electronic, magnetic and optical applications. Sections review the key techniques involved in the epitaxial growth of complex metal oxides and explore the effects of strain and stoichiometry on crystal structure and related properties in thin film oxides. Finally, the book concludes by discussing selected examples of important applications of complex metal oxide thin films, including optoelectronics, batteries, spintronics and neuromorphic applications. This new edition has been fully updated, with brand new chapters on topics such as atomic layer deposition, interfaces, STEM-EELs, and the epitaxial growth of multiferroics, ferroelectrics and nanocomposites. Examines the techniques used in epitaxial thin film growth for complex oxides, including atomic layer deposition, sputtering techniques, molecular beam epitaxy, and chemical solution deposition techniques Reviews materials design strategies and materials property analysis methods, including the impacts of defects, strain, interfaces and stoichiometry Describes key applications of epitaxially grown metal oxides, including optoelectronics, batteries, spintronics and neuromorphic applications

This Final Report describes the scientific accomplishments that have been achieved with support from grant DE-FG02-06ER46273 during the period 6/1/2012- 5/31/2016. The overall goals of this program were focused on the behavior of epitaxial oxide heterostructures at atomic length scales (Ångstroms), and correspondingly short time-scales (fs -ns). The results contributed fundamentally to one of the currently most active frontiers in condensed matter physics research, namely to better understand the intricate relationship between charge, lattice, orbital and spin degrees of freedom that are exhibited by complex oxide heterostructures. The findings also contributed towards an important technological goal which was to achieve a better basic understanding of structural and electronic correlations so that the unusual properties of complex oxides can be exploited for energy-critical applications. Specific research directions included: probing the microscopic behavior of epitaxial interfaces and buried layers; novel materials structures that emerge from ionic and electronic reconfiguration at epitaxial interfaces; ultrahigh-resolution mapping of the atomic structure of heterointerfaces using synchrotron-based x-ray surface scattering, including direct methods of phase retrieval; using ultrafast lasers to study the effects of transient strain on coherent manipulation of multi-ferroic order parameters; and investigating structural ordering and relaxation processes in real-time.

Functional oxides are used both as insulators and metallic conductors in key applications across all industrial sectors. This makes them attractive candidates in modern technology ? they make solar cells cheaper, computers more efficient and medical instrumentation more sensitive. Based on recent research, experts in the field describe novel materials, their properties and applications for energy systems, semiconductors, electronics, catalysts and thin films. This monograph is divided into 6 parts which allows the reader to find their topic of interest quickly and efficiently. * Magnetic Oxides * Dopants, Defects and Ferromagnetism in Metal Oxides * Ferroelectrics * Multiferroics * Interfaces and Magnetism * Devices and Applications This book is a valuable asset to materials scientists, solid state chemists, solid state physicists, as well as engineers in the electric and automotive industries.

Oxide interfaces have attracted considerable attention in recent years due to emerging novel properties that do not exist in the corresponding parent compounds. Furthermore, modern atomic-scale growth and probe techniques enable the formation and study of new artificial interface states distinct from the bulk state. A central issue in controlling the novel behavior in oxide heterostructures is to understand how various physical variables (spin, charge, lattice and/or orbital hybridization) interact with each other. In particular, density function theory (DFT) has provided significant insight into underlying physics of materials at the atomic level, giving quantitative results consistent with experiment. In this dissertation using density functional theory methods, we explore the electronic, magnetic and structural properties developed near the interface in SrTiO3/LaAlO3, EuO/LaAlO3, Fe/PbTiO3/Pt, Fe//BaTiO3/Pt and Cs/SrTiO3 heterostructures. We study the interplay between physical interactions, and quantify parameters that determine physical properties of hetetrostructures. These theoretical studies help understanding how physical variables couple with each other and how they determine new properties at oxide interfaces.