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Author: Jan Bundesmann Publisher: Universitatsverlag Regensburg ISBN: 9783868451153 Category : Languages : en Pages : 0
Book Description
Graphene, a two-dimensional material consisting of carbon atoms arranged in a honeycomb lattice, has become famous for the evidence that its electronic structure approximately corresponds to the one of massless Dirac fermions. However, in order to correctly describe graphene , the spin, which plays an essential role in the physics of Dirac fermions, has to be replaced by the so-called pseudospin, an intrinsic property of the honeycomb lattice which is not related to the electrons' real spin. If, now, the real spin is considered, too, the effective Hamiltonian has to be extended by terms which have no equivalents in the original Dirac Hamiltonian. While charge transport properties can be predicted from Dirac physics very realiably, the extended Hamiltonian leads to new phenomena in the context of spin transport. In this thesis two distinct topics are investigated theoretically. The presented results are mainly based on numerical simulations using a recursive Green's function algorithm. The first part of this thesis covers spin relaxation in graphene. Different sources of spin relaxation are investigated with a particular focus on the role of locally varying spin-orbit coupling and adatoms. The second part covers edge magnetism in graphene zigzag nanoribbons. It is shown how magnetic clusters form even in the presence of a potential which is not homogeneous in space. Different signatures of zigzag edge magnetization on charge and spin transport are presented.
Author: Jan Bundesmann Publisher: Universitatsverlag Regensburg ISBN: 9783868451153 Category : Languages : en Pages : 0
Book Description
Graphene, a two-dimensional material consisting of carbon atoms arranged in a honeycomb lattice, has become famous for the evidence that its electronic structure approximately corresponds to the one of massless Dirac fermions. However, in order to correctly describe graphene , the spin, which plays an essential role in the physics of Dirac fermions, has to be replaced by the so-called pseudospin, an intrinsic property of the honeycomb lattice which is not related to the electrons' real spin. If, now, the real spin is considered, too, the effective Hamiltonian has to be extended by terms which have no equivalents in the original Dirac Hamiltonian. While charge transport properties can be predicted from Dirac physics very realiably, the extended Hamiltonian leads to new phenomena in the context of spin transport. In this thesis two distinct topics are investigated theoretically. The presented results are mainly based on numerical simulations using a recursive Green's function algorithm. The first part of this thesis covers spin relaxation in graphene. Different sources of spin relaxation are investigated with a particular focus on the role of locally varying spin-orbit coupling and adatoms. The second part covers edge magnetism in graphene zigzag nanoribbons. It is shown how magnetic clusters form even in the presence of a potential which is not homogeneous in space. Different signatures of zigzag edge magnetization on charge and spin transport are presented.
Author: Ralitsa L. Dragomirova Publisher: ISBN: Category : Graphene Languages : en Pages :
Book Description
Shot noise is the name given to the time-dependent non-equilibrium current (or voltage) fluctuations which persist down to zero temperature and are fundamentally related to the discrete nature of the electron charge. Over the past two decades it has become a major tool for gathering information about microscopic mechanisms of transport and correlations between charges which cannot be extracted from traditional conductance measurements. Recently a handful of theoretical and experimental studies have suggested that shot noise in systems with spin-dependent interactions provides a sensitive probe to differentiate between scattering from magnetic impurities, spin-flip scattering, and continuous spin precession effects on semiclassical or quantum transport of injected spin-polarized currents. This is due to the fact that any spin flip converts spin-[arrow up] subsystem particle into a spin-[arrow down] subsystem particle, where the two subsystems differ when spin degeneracy is lifted. Thus, the nonconservation of the number of particles in each subsystem generates additional source of current fluctuations. Here we generalize the scattering theory of quantum shot noise to include the full spin-density matrix of electrons. This formalism yields the spin-resolved shot noise power applicable for a generic spintronic device where partially polarized charge current or even pure spin current is injected from a spin-filtering or ferromagnetic electrode into a quantum-coherent nanostructure governed by arbitrary spin-dependent interactions. The developed formalism [2, 5] is applied in Chapter 5 to diffusive multichannel quantum wires with the Rashba spin-orbit (SO) coupling sandwiched between ferromagnetic source and ferromagnetic or normal drain electrodes. The crucial role played by the SO interactions in all-electrical control of spin in semiconductor nanostructures has ignited recent studies of their signatures on the shot noise. We investigate what is the effect of the Rahsba SO coupling on the shot noise and look for a relationship between the degree of quantum coherence of transported spins and the shot noise of charge currents. This allows us to propose electrical shot noise-based scheme to probe spin as a measurable degree of freedom. Injection of unpolarized charge current through the longitudinal leads of a four-terminal two-dimensional electron gas with the Rashba SO coupling and SO scattering off extrinsic impurities is responsible not only for the pure spin Hall cur- rent in the transverse leads, but also for nonequilibrium random time-dependent current fluctuations. We employ the spin-dependent scattering approach in Chapter 6 [3, 5] to analyze the shot noise of transverse pure spin Hall current and zero charge current, or transverse spin current and non-zero charge Hall current, driven by unpolarized or spin-polarized injected longitudinal charge current, respectively. Since any spin-flip acts as an additional source of noise, we argue that these shot noises provide a unique experimental tool to differentiate between intrinsic and extrinsic SO mechanisms underlying the spin Hall effect in paramagnetic devices. Recently graphene--a one-atom-thick crystal of carbon atoms arranged into a honeycomb lattice--has emerged as one of the most promising materials for future nanoelectronic devices. It combines exceptional sample quality and accessibility with the unique possibility to explore quantum electrodynamics phenomena in a condensed matter system since current is carried by massless Dirac fermions behaving as charged neutrinos. Furthermore, special nanostructures derived from graphene, the so called zigzag nanoribbons, favor ferromagnetic ordering along their edges. Recently shot noise measurements have been used to characterize ballistic transport through evanescent states introduced into clean undoped graphene strips by the attached metallic electrodes. We demonstrate in Chapter 7 [4] that this shot noise can be substantially modified in zigzag nanoribbons due to the topology of their edges inducing localized states that facilitate ferromagnetic ordering along the edge when electron-electron interactions are taken into account.
Author: Dinh Van Tuan Publisher: Springer ISBN: 3319255711 Category : Science Languages : en Pages : 162
Book Description
This thesis presents an in-depth theoretical analysis of charge and spin transport properties in complex forms of disordered graphene. It relies on innovative real space computational methods of the time-dependent spreading of electronic wave packets. First a universal scaling law of the elastic mean free path versus the average grain size is predicted for polycrystalline morphologies, and charge mobilities of up to 300.000 cm2/V.s are determined for 1 micron grain size, while amorphous graphene membranes are shown to behave as Anderson insulators. An unprecedented spin relaxation mechanism, unique to graphene and driven by spin/pseudospin entanglement is then reported in the presence of weak spin-orbit interaction (gold ad-atom impurities) together with the prediction of a crossover from a quantum spin Hall Effect to spin Hall effect (for thallium ad-atoms), depending on the degree of surface ad-atom segregation and the resulting island diameter.
Author: Hassan Raza Publisher: Springer Science & Business Media ISBN: 3642229840 Category : Science Languages : en Pages : 611
Book Description
Graphene is a perfectly two-dimensional single-atom thin membrane with zero bandgap. It has attracted huge attention due to its linear dispersion around the Dirac point, excellent transport properties, novel magnetic characteristics, and low spin-orbit coupling. Graphene and its nanostructures may have potential applications in spintronics, photonics, plasmonics and electronics. This book brings together a team of experts to provide an overview of the most advanced topics in theory, experiments, spectroscopy and applications of graphene and its nanostructures. It covers the state-of-the-art in tutorial-like and review-like manner to make the book useful not only to experts, but also newcomers and graduate students.
Author: Evgeny Y. Tsymbal Publisher: CRC Press ISBN: 0429805268 Category : Science Languages : en Pages : 646
Book Description
Spintronics Handbook, Second Edition offers an update on the single most comprehensive survey of the two intertwined fields of spintronics and magnetism, covering the diverse array of materials and structures, including silicon, organic semiconductors, carbon nanotubes, graphene, and engineered nanostructures. It focuses on seminal pioneering work, together with the latest in cutting-edge advances, notably extended discussion of two-dimensional materials beyond graphene, topological insulators, skyrmions, and molecular spintronics. The main sections cover physical phenomena, spin-dependent tunneling, control of spin and magnetism in semiconductors, and spin-based applications. Features: Presents the most comprehensive reference text for the overlapping fields of spintronics (spin transport) and magnetism. Covers the full spectrum of materials and structures, from silicon and organic semiconductors to carbon nanotubes, graphene, and engineered nanostructures. Extends coverage of two-dimensional materials beyond graphene, including molybdenum disulfide and study of their spin relaxation mechanisms Includes new dedicated chapters on cutting-edge topics such as spin-orbit torques, topological insulators, half metals, complex oxide materials and skyrmions. Discusses important emerging areas of spintronics with superconductors, spin-wave spintronics, benchmarking of spintronics devices, and theory and experimental approaches to molecular spintronics. Evgeny Tsymbal's research is focused on computational materials science aiming at the understanding of fundamental properties of advanced ferromagnetic and ferroelectric nanostructures and materials relevant to nanoelectronics and spintronics. He is a George Holmes University Distinguished Professor at the Department of Physics and Astronomy of the University of Nebraska-Lincoln (UNL), Director of the UNL’s Materials Research Science and Engineering Center (MRSEC), and Director of the multi-institutional Center for NanoFerroic Devices (CNFD). Igor Žutić received his Ph.D. in theoretical physics at the University of Minnesota. His work spans a range of topics from high-temperature superconductors and ferromagnetism that can get stronger as the temperature is increased, to prediction of various spin-based devices. He is a recipient of 2006 National Science Foundation CAREER Award, 2005 National Research Council/American Society for Engineering Education Postdoctoral Research Award, and the National Research Council Fellowship (2003-2005). His research is supported by the National Science Foundation, the Office of Naval Research, the Department of Energy, and the Airforce Office of Scientific Research.
Author: Evgeny Y. Tsymbal Publisher: ISBN: 9781498769723 Category : Magnetism Languages : en Pages : 0
Book Description
The second edition offers an update on the single most comprehensive survey of the two intertwined fields of spintronics and magnetism, covering the diverse array of materials and structures, including silicon, organic semiconductors, carbon nanotubes, graphene, and engineered nanostructures. It focuses on seminal pioneering work, together with the latest in cutting-edge advances, notably extended discussion of two-dimensional materials beyond graphene, topological insulators, skyrmions, and molecular spintronics. The main sections cover physical phenomena, spin-dependent tunneling, control of spin and magnetism in semiconductors, and spin-based applications.
Author: Evgeny Y. Tsymbal Publisher: CRC Press ISBN: 0429750897 Category : Science Languages : en Pages : 735
Book Description
Spintronics Handbook, Second Edition offers an update on the single most comprehensive survey of the two intertwined fields of spintronics and magnetism, covering the diverse array of materials and structures, including silicon, organic semiconductors, carbon nanotubes, graphene, and engineered nanostructures. It focuses on seminal pioneering work, together with the latest in cutting-edge advances, notably extended discussion of two-dimensional materials beyond graphene, topological insulators, skyrmions, and molecular spintronics. The main sections cover physical phenomena, spin-dependent tunneling, control of spin and magnetism in semiconductors, and spin-based applications.
Author: Javier Munárriz Arrieta Publisher: Springer ISBN: 3319070886 Category : Science Languages : en Pages : 126
Book Description
The thesis covers a broad range of electronic, optical and opto-electronic devices and various predicted physical effects. In particular, it examines the quantum interference transistor effect in graphene nanorings; tunable spin-filtering and spin-dependent negative differential resistance in composite heterostructures based on graphene and ferromagnetic materials; optical and novel electro-optical bistability and hysteresis in compound systems and the real-time control of radiation patterns of optical nanoantennas. The direction of the main radiation lobe of a regular plasmonic array can be changed abruptly by small variations in external control parameters. This optical effect, apart from its relevance for applications, is a revealing example of the Umklapp process and, thus, is a visual manifestation of one of the most fundamental laws of solid state physics: the conservation of the quasi-momentum to within a reciprocal lattice vector. The thesis analyzes not only results for particular device designs but also a variety of advanced numerical methods which are extended by the author and described in detail. These methods can be used as a sound starting point for further research.
Author: Jan Bundesmann
Author: Jan Bundesmann
Author: Ralitsa L. Dragomirova
Author: Dinh Van Tuan
Author: Qingtian Zhang
Author: Hassan Raza
Author: 詹舜州
Author: Evgeny Y. Tsymbal
Author: Evgeny Y. Tsymbal
Author: Evgeny Y. Tsymbal
Author: Javier Munárriz Arrieta