Subband Structure of a Two-Dimensional Electron Gas Formed at the Polar Surface of the Strong Spin-Orbit Perovskite KTaO3 PDF Download
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Languages : en
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We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, we find no experimental signatures of a Rashba spin splitting, which has important implications for the interpretation of transport measurements in both KTaO3- and SrTiO3-based 2DEGs. The polar nature of the KTaO3(100) surface appears to help mediate formation of the 2DEG as compared to non-polar SrTiO3(100).
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Languages : en
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Book Description
We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, we find no experimental signatures of a Rashba spin splitting, which has important implications for the interpretation of transport measurements in both KTaO3- and SrTiO3-based 2DEGs. The polar nature of the KTaO3(100) surface appears to help mediate formation of the 2DEG as compared to non-polar SrTiO3(100).
Author: Claudia Cancellieri
Publisher: Springer
ISBN: 3319749897
Category : Technology & Engineering
Languages : en
Pages : 326
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This book summarizes the most recent and compelling experimental results for complex oxide interfaces. The results of this book were obtained with the cutting-edge photoemission technique at highest energy resolution. Due to their fascinating properties for new-generation electronic devices and the challenge of investigating buried regions, the book chiefly focuses on complex oxide interfaces. The crucial feature of exploring buried interfaces is the use of soft X-ray angle-resolved photoemission spectroscopy (ARPES) operating on the energy range of a few hundred eV to increase the photoelectron mean free path, enabling the photons to penetrate through the top layers – in contrast to conventional ultraviolet (UV)-ARPES techniques. The results presented here, achieved by different research groups around the world, are summarized in a clearly structured way and discussed in comparison with other photoemission spectroscopy techniques and other oxide materials. They are complemented and supported by the most recent theoretical calculations as well as results of complementary experimental techniques including electron transport and inelastic resonant X-ray scattering.
Author: Jianli Cheng
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Languages : en
Pages : 185
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Two-dimensional electron gas (2DEG) formed at the interface between two insulating perovskite oxides has provided a versatile playground to explore emergent interfacial electronic and magnetic properties. In this thesis our efforts centered on studying the electronic and structural properties of different 2DEG heterostructures (HS), with the goal of designing novel 2DEG HS using first-principles methods. In the first project we studied the [delta]-doping effects on the electronic and energetic properties of LaAlO3/SrTiO3 HS with 23 transition-metal (TM) dopants. It has been found that there is a trade-off between achieving small electron effective mass and obtaining an energetically favorable TM-doped LaAlO3/SrTiO3 system. More importantly, in addition to the experimentally confirmed Mn dopant, we proposed that Fe, Co, Ni, Ru, Rh, Pd, Os and Ir elements can also be promising dopants to yield light effective mass bands and good energetic stability. In the second project we compared the electronic and energetic properties of TiO2/LaAlO3 and LaAlO3/TiO2 HS. We found that TiO2/LaAlO3 is intrinsically metallic and has a larger interfacial charge carrier density, smaller electron effective mass and a stronger interface cohesion than LaAlO3/TiO2, which shows an insulator-to-metal transition at 4 unit cells of LaAlO3. In the third project we introduced a hitherto unknown 2DEG formed at the interface between spinel MgAl2O4 and SrTiO3. Our integrated approach combining experimental measurements and first-principles calculations reveals that an atomic-thin interfacial Ti-Al-O layer with a thickness of about 4Å is key to the observed metallic transport. The 2DEG observed at spinel/perovskite interface implies the existence of emergent phenomena at the interfaces between spinel group minerals and perovskite oxides. In the fourth and fifth project we explored the possibility of creating 2DEG in nonpo- lar/nonpolar perovskite oxide HS. We found that the lattice-mismatch-induced compression strain from the substrate leads to a large polarization in the film, which then drives the charge transfer from the film to the substrate and results in a 2DEG at the interface. In addition, by using high-throughput first-principles calculations and a group of combinatory descriptors, we rapidly designed more than 300 novel nonpolar/nonpolar 2DEG HS. In the final project we introduced Grain Boundary Maker (GBMaker), an efficient and open-source Python library for generating atomic coordinates in periodic grain boundary models. It is designed to construct various grain boundary structures from cubic and non-cubic initial configurations. GBMaker is expected to greatly accelerate the theoretical investigation of grain boundary properties and facilitate the experimental analysis of grain boundary structures as well.
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Languages : en
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Theoretical studies with the help of first-principles electronic structure calculations and tight-binding based Hamiltonian models aimed to understand the Rashba effect in the 2D electron gas at the surfaces and interfaces of polar perovskite oxides are discussed. First-principles calculations on a slab of KTaO3 show that the spin-splitting is orbital dependent and is greatly suppressed by the lattice relaxation close to the surface. However, the electron gas is amenable to tuning by external potentials perpendicular to the surface and can be used to control Rashba splitting. Construction of a minimal model Hamiltonian to study d orbitals under uniform electric field is explained. The potential introduces new matrix elements between orbitals by breaking the symmetry and distorting the lattice. When coupled with spin orbit interaction, this results in lifting the spin degeneracy. (C) 2014 Elsevier B.V. All rights reserved.
Author: YIGE. CHEN
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Languages : en
Pages :
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The study of topological phases of matter has attracted much attention recently, providing a promising route to understanding the classification of various phases in condensed matter physics. The Iridates, which are Iridium-based compounds, have already shown rich physical phenomena and can be a perfect platform to reveal topological phases in materials with strong spin-orbit coupling. This thesis focuses on possible exotic topological phases that stem from the interplay between strong spin-orbit coupling and non-trivial band structure in three-dimensional perovskite Iridates and other layered Iridate materials. Firstly, motivated from previous band structure results of SrIrO$_3$, we predict that three-dimensional perovskite Iridates can realize a new class of metals dubbed ``topological crystalline metals" with surface states protected by lattice symmetry and a pair of topological invariants. We show that these novel metallic phases can give rise to various non-trivial topological phases when different symmetries are broken, including a Weyl and nodal-line semimetal . Secondly, we provide a generic condition to identify a novel three-dimensional topological semi-metallic phase in materials with strong spin-orbit coupling. Such a semi-metallic phase is featured by bulk gapless four-fold degenerate nodal-line excitations. By using perovskite Iridates SrIrO$_3$ as an example, we give an explicit mathematical proof on the validity of this condition as well as verify the existence of such bulk nodal-line band degeneracy in the tight-binding model. Thirdly, we propose that a topological insulator can exist in a two-dimensional single layer Iridium oxide superlattice under certain lattice distortions; a tight-binding model is constructed using the basis of an effective J$_{\rm eff}$=1/2 pseudo-spins. A topological magnetic insulator with quantum anomalous Hall effect is found in the bilayer superlattice when a magnetic order or magnetic field is present in the system. Lastly, a pair of helical Majorana fermions emerges at the interface of a two-dimensional Weyl semimetal and a d-wave superconductor. We focused on the most promising and feasible realization: Iridium oxide layer without inversion symmetry, which is classified as Weyl semimetal, in proximity to d-wave high temperature Cuprates. In conclusion, we provide some future directions related to the topological phases in Iridates.
![Theory of D[subscript 0] Perovskites and Their Heterostructures PDF](https://books.google.com/books/content/images/frontcover/B1PnoAEACAAJ?fife=w80-h100)
Author: Guru Bahadur Singh Khalsa
Publisher:
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Category :
Languages : en
Pages : 300
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The recent discovery of a two-dimensional electron (2DEG) gas at interfaces between nonpolar SrTiO3 (STO) with other polar perovskites has lead to an enormous amount of research. Among this 2DEGs most interesting properties are two-dimensional superconductivity and ferromagnetism, sometimes concurrent. This study provides a starting point in understanding the reconstruction of bulk perovskite t2[subscript g] bands near a surface or polar interface. First a symmetry constrained [k arrow] · [p arrow] model is developed for an arbitrary pseudocubic bulk perovskite. This [k arrow] · [p arrow] model is applied to studies of bulk STO under external strain and to the Shubnikov - de Haas effect in lightly doped STO to high magnetic fields. Then a simplified electronic structure model is developed for surfaces and interfaces. This model includes non-linear and non-local screening effects by a single polar lattice mode. Generalization of the lattice screening model is discussed. Bonding within a single perovskite layer is then investigated further to understand Rashba interactions and their connection with microscopic material parameters. Next the optical conductivity of quantum confined t2[subscript g] bands is investigated. Finally some possible future work based on the ideas developed in this thesis are explained.
Author: Trevor Jeffrey Anderson
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Languages : en
Pages : 143
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The incorporation of 5d electrons in perovskite ABO3 materials creates a complex interplay between spin-orbit coupling and electron-electron correlation that can unlock rich physical phenomena such as spin liquids, topological states, and spin-to-charge current conversion. Among these 5d perovskites is SrIrO3, which has attracted significant attention as a candidate material to experimentally realize exotic band topologies that arise from the 5d electrons in the heavy iridium atom. However, SrIrO3 is a polymorph that assumes a non-perovskite crystal structure in ambient conditions, which hinders study of the perovskite-phase physical properties. Thus, thin film epitaxy is a critical prerequisite for experimentally unlocking the fascinating behavior of this material. This thesis will discuss the structural and physical behavior of epitaxial SrIrO3 thin films interfaced with other perovskites and ferromagnetic Ni0.81Fe0.19 (Permalloy). First, synthesis and epitaxial arrangement of SrIrO3 along the (001) direction will be discussed to motivate the results presented in the subsequent chapters. Next, synthesis of perovskite SrIrO3 on the polar (111) surface will be presented: the first and only report to date. Having established this geometric synthesis of SrIrO3, our comparison of the polar (111) and non-polar (001) SrIrO3/SrTiO3 interfacial structure is presented. Here, we demonstrate preferential B-site interfacial intermixing along the polar direction due to the reconstructed (111) surface that results from the surface polarity and substrate surface treatment prior to film growth. This result suggests the possibility of geometrically engineering the perovskite B-site d-shell electronic state at interfaces. In the final section of this thesis, I will discuss the Permalloy/SrIrO3 interface, in which epitaxial SrIrO3 can produce a highly efficient spin-orbit torque on the ferromagnetic moment of Permalloy at room temperature via the spin Hall effect that arises from the SrIrO3 band structure. Furthermore, the torque efficiency shows strong dependence on changes to the SrIrO3 crystal structure that manifest due to constraints imposed by the underlying substrate. This large, tunable spin-orbit torque result suggests that epitaxial SrIrO3 thin films could be a platform for robust room-temperature spintronics. Overall, the work in this thesis demonstrates the promising flexibility of SrIrO3 as a candidate material to design strongly-correlated 5d-electrons at interfaces.
Author: Mildred Dresselhaus
Publisher: Springer
ISBN: 3662559226
Category : Science
Languages : en
Pages : 521
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Book Description
This book fills a gap between many of the basic solid state physics and materials sciencebooks that are currently available. It is written for a mixed audience of electricalengineering and applied physics students who have some knowledge of elementaryundergraduate quantum mechanics and statistical mechanics. This book, based on asuccessful course taught at MIT, is divided pedagogically into three parts: (I) ElectronicStructure, (II) Transport Properties, and (III) Optical Properties. Each topic is explainedin the context of bulk materials and then extended to low-dimensional materials whereapplicable. Problem sets review the content of each chapter to help students to understandthe material described in each of the chapters more deeply and to prepare them to masterthe next chapters.
Author: Joseph Woicik
Publisher: Springer
ISBN: 3319240439
Category : Science
Languages : en
Pages : 576
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Book Description
This book provides the first complete and up-to-date summary of the state of the art in HAXPES and motivates readers to harness its powerful capabilities in their own research. The chapters are written by experts. They include historical work, modern instrumentation, theory and applications. This book spans from physics to chemistry and materials science and engineering. In consideration of the rapid development of the technique, several chapters include highlights illustrating future opportunities as well.
Author: Aparna Thankappan
Publisher: Academic Press
ISBN: 0128129166
Category : Technology & Engineering
Languages : en
Pages : 521
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Book Description
Perovskite Photovoltaics: Basic to Advanced Concepts and Implementation examines the emergence of perovskite photovoltaics, associated challenges and opportunities, and how to achieve broader development. Consolidating developments in perovskite photovoltaics, including recent progress solar cells, this text also highlights advances and the research necessary for sustaining energy. Addressing different photovoltaics fields with tailored content for what makes perovskite solar cells suitable, and including commercialization examples of large-scale perovskite solar technology. The book also contains a detailed analysis of the implementation and economic viability of perovskite solar cells, highlighting what photovoltaic devices need to be generated by low cost, non-toxic, earth abundant materials using environmentally scalable processes. This book is a valuable resource engineers, scientists and researchers, and all those who wish to broaden their knowledge on flexible perovskite solar cells. Includes contributions by leading solar cell academics, industrialists, researchers and institutions across the globe Addresses different photovoltaics fields with tailored content for what makes perovskite solar cells different Provides commercialization examples of large-scale perovskite solar technology, giving users detailed analysis on the implementation, technical challenges and economic viability of perovskite solar cells
