Electronic and Magnetic Properties of Candidate Materials for Kitaev Physics Using a Combination of Density Functional Theory and Many-body Methods PDF Download

Author: Ying Li
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Great interest has emerged recently in the search for Kitaev spin liquid states in real materials. Such states rely on strongly anisotropic magnetic interactions, which have been suggested to exist in a number of candidate materials based on Ir and Ru. This thesis concentrates on two priority purposes. The first is the investigation of electronic and magnetic properties of candidate materials Na2IrO3, [alpha]-Li2IrO3, [alpha]-RuCl3, [gamma]-Li2IrO3, and Ba3YIr2O9 for Kitaev physics where both spin-orbit coupling and correlation effects are important. The second is the method development for the microscopic description of correlated materials combining many-body methods and density functional theory (DFT). ...

Author: Rolf E. Hummel
Publisher: Springer
ISBN: 3642865380
Category : Technology & Engineering
Languages : en
Pages : 448

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Book Description
Books are seldom finished. At best, they are abandoned. The second edition of "Electronic Properties of Materials" has been in use now for about seven years. During this time my publisher gave me ample opportunities to update and improve the text whenever the Ibook was reprinted. There were about six of these reprinting cycles. Eventually, however, it became clear that substantially more new material had to be added to account for the stormy developments which occurred in the field of electrical, optical, and magnetic materials. In particular, expanded sections on flat-panel displays (liquid crystals, electroluminescence devices, field emission displays, and plasma dis. : plays) were added. Further, the recent developments in blue- and green emitting LED's and in photonics are included. Magnetic storage devices also underwent rapid development. Thus, magneto-optical memories, magneto resistance devices, and new' magnetic materials needed to be covered. The sections on dielectric properties, ferroelectricity, piezoelectricity, electrostric tion, and thermoelectric properties have been expanded. Of course, the entire text was critically reviewed, updated, and improved. However, the most extensive change I undertook was the conversion of all equations to SI units throughout. In most of the world and in virtually all of the interna tional scientific journals use of this system of units is required. If today's students do not learn to utilize it, another generation is "lost" on this matter. In other words, it is important that students become comfortable with SI units.

Author: Feliciano Giustino
Publisher: Oxford University Press, USA
ISBN: 0199662444
Category : Mathematics
Languages : en
Pages : 303

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The book explains the fundamental ideas of density functional theory, and how this theory can be used as a powerful method for explaining and even predicting the properties of materials with stunning accuracy.

Author: Shiyuan Gao
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 117

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Book Description
Two-dimensional (2D) materials with single or a few atomic layers, such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs), and the heterostructures or one-dimensional (1D) nanostructures they form, have attracted much attention recently as unique platforms for studying many condensed-matter phenomena and holds great potentials for nanoelectronics and optoelectronic applications. Apart from their unique intrinsic properties which has been intensively studied for over a decade by now, they also allow external control of many degrees of freedom, such as electrical gating, doping and layer stacking. In this thesis, I present a theoretical study of the electronic and optical properties of many different 2D materials and nanostructures using first-principles density functional theory and many-body perturbation theory. I will show what we learn from these theoretical calculations about the relation between the partially extended, partially confined structure and the tunability of their electronic and optical properties with free-carrier doping and electrical gating. First, we investigate the effect of free-carrier doping on the quasiparticle and exciton properties of 2D material. On one hand, we discuss the origin of the doping-induced band gap renormalization in 2D materials and demonstrate the simplifications that can be made to the theory to allow more efficient calculation. On the other hand, using MoS2 as an example, we study the effect of dynamical screening on the electron-hole interaction and excitonic properties in doped 2D material using the Bethe-Salpeter Equation. Combining them, we show that the quasiparticle band gap of 2D material drops as a non-linear function of doping density by several hundred meV due to the free-carrier screening, but this is offset by the drop in the exciton binding energy and makes the exciton energy remain nearly constant. Then, we switch gear to study the effect of electrical gating on excitons in bilayer TMDC heterostructures. We reveal the important role of interlayer coupling in deciding the band alignment and excitonic properties. We show that due to the interlayer coupling of valence states, the excitons are superpositions of intralayer and interlayer electron-hole pairs which can be described by a simple tight-binding model. As a result, their dipole oscillator strength and radiative lifetime can be tuned by over an order of magnitude with a practical external gate field of a few V/nm. Finally, we study the effect of quantum confinement on the formation of magnetism in confined nanostructures. In two one-dimensional structures, graphene nanoribbon and tellurium chain, we find doped free-carriers can have half-metallic ferromagnetic ground state due to the Stoner mechanism. This comes from the quantum-confinement of the electronic state which enhances the density of state and Stoner parameter at the same time. For graphene nanoribbons, we find magnetism in general edge types with large spin polarization energy up to 17 meV/carrier. It can bypass the requirement of specific zigzag edge in previous proposals of graphene nanoribbon magnetism. For tellurium chain, we find magnetic ground state with a significant 6 meV/carrier spin-polarization energy. Due to the strong spin-orbit interaction of tellurium and its unique helical chain structure with chirality, the spins of the magnetic carriers are pinned along a specific direction with an enhanced magnetic anisotropy energy that is larger than the spin-polarization energy, making it of broad interest for spintronics applications.

Author: Alamgir Kabir
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659900907
Category :
Languages : en
Pages : 216

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In this book, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using available codes, to study the magnetic properties of small (2 to 5-atom) Fe and FePt clusters provide meaningful results: dynamical effects lead to a reduction of the cluster magnetic moment as compared to that obtained from DFT or DFT+U (U being the Coulomb repulsion parameter). We have subsequently developed our own nanoDFT+DMFT code and applied it to examine the magnetization of iron particles containing10-147 atoms. Our results for the cluster magnetic moments are in a good agreement with experimental data. In particular, we are able to reproduce the oscillations in magnetic moment with size as observed in the experiments.

Author: Pradeep Fulay
Publisher: CRC Press
ISBN: 1498701736
Category : Science
Languages : en
Pages : 719

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Book Description
This book integrates materials science with other engineering subjects such as physics, chemistry and electrical engineering. The authors discuss devices and technologies used by the electronics, magnetics and photonics industries and offer a perspective on the manufacturing technologies used in device fabrication. The new addition includes chapters on optical properties and devices and addresses nanoscale phenomena and nanoscience, a subject that has made significant progress in the past decade regarding the fabrication of various materials and devices with nanometer-scale features.

Author: Junling Wang
Publisher: CRC Press
ISBN: 1315355264
Category : Science
Languages : en
Pages : 374

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Book Description
"a very detailed book on multiferroics that will be useful for PhD students and researchers interested in this emerging field of materials science" —Dr. Wilfrid Prellier, Research Director, CNRS, Caen, France Multiferroics has emerged as one of the hottest topics in solid state physics in this millennium. The coexistence of multiple ferroic/antiferroic properties makes them useful both for fundamental studies and practical applications such as revolutionary new memory technologies and next-generation spintronics devices. This book provides an historical introduction to the field, followed by a summary of recent progress in single-phase multiferroics (type-I and type-II), multiferroic composites (bulk and nano composites), and emerging areas such as domain walls and vortices. Each chapter addresses potential technological implications. There is also a section dedicated to theoretical approaches, both phenomenological and first-principles calculations.

Author: Uko Ofe
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659586439
Category :
Languages : en
Pages : 228

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Book Description
Density Functional Theory has proved to be a fast and efficient method for calculating various properties of solid insulating materials. From our studies, we have observed that calculations of the structural and electronic properties of alkali metal hydrides LiH, NaH, KH, RbH and CsH) and alkaline earth metal hydrides (BeH2, MgH2, CaH2, SrH2 and BaH2) reveal the exact problem with the description for these compounds within PBE formulation of generalized gradient approximation (GGA), which is our principal focus.Generally, for the hydrides accurate calculation of the band gap requires computationally extensive approach as GW method or time-dependent DFT. In this work, a new and more efficient method, GGA + U, which significantly improves the description of the electronic structure in DFT has been used; thus, in this proposed method, our results were in agreement with other theoretical and experimental results obtained by other investigators. GGA+U approach is based on the Hubbard model applied for exchange-correlation function to hydrogen atoms, even though the metal hydrides are not strongly correlated materials.

Author: Emilio Scalise
Publisher: Springer
ISBN: 3319071823
Category : Technology & Engineering
Languages : en
Pages : 157

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Book Description
Ge and III–V compounds, semiconductors with high carrier mobilities, are candidates to replace Si as the channel in MOS devices. 2D materials – like graphene and MoS_2 – are also envisioned to replace Si in the future. This thesis is devoted to the first-principles modeling of the vibrational properties of these novel channel materials. The first part of the thesis focuses on the vibrational properties of various oxides on Ge, making it possible to identify the vibrational signature of specific defects which could hamper the proper functioning of MOSFETs. The second part of the thesis reports on the electronic and vibrational properties of novel 2D materials like silicene and germanene, the Si and Ge 2D counterparts of graphene. The interaction of these 2D materials with metallic and non-metallic substrates is investigated. It was predicted, for the first time, and later experimentally confirmed, that silicene could be grown on a non-metallic template like MoS_2, a breakthrough that could open the door to the possible use of silicene in future nanoelectronic devices.

Author: Maurizio Ferconi
Publisher:
ISBN:
Category : Electronic structure
Languages : en
Pages : 280

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Book Description
Most of the work done in the physics of two-dimensional structures is either limited by the size of the systems that are studied due to the use of exact diagonalization techniques which do not allow to go beyond structures with only few electrons, or by other methods which do not include exchange-correlation effects, or correlation effects only. There are instances in which these effects cannot be neglected. In order to fill this gap we decided to use a density functional approach, which proved to be reliable in other problems. In Chapter 3 I shall present original results on the study of the ground-state properties of quantum dots in the presence of a magnetic field of arbitrary strength obtained within a current-density functional approach. The results obtained agree very well with those obtained by means of exact diagonalization approaches. In the regime not accessible by the latter methods we show how important are exchange-correlation effects, and we also make an analysis of correlation effects, by comparison with Hartree-Fock results. In Chapter 4 we address and study the density profile at the edge of a confined two-dimensional electron gas in the fractional quantum Hall regime. The strong correlation effects are accounted for in a density functional approach. I show that there exists a transition between two regimes as a function of the smoothness of the confining potential. In Chapter 5, we study the magnetophonon dispersion relations of a two-dimensional Wigner crystal in the presence of a strong magnetic field, and of its shear modulus, that we derived within a density functional scheme, that therefore includes correlation effects, and has the advantage of being analytical. In Chapter 6 I present a theory for the calculation of the pinning gap and magnetophonon spectrum of a disordered Wigner crystal. Its main feature resides in the inclusion in the pinning energy of the contribution arising from distortions of the crystal on all length scales.