Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport in Graphene

This chapter brings together the physical underpinnings of field-effect transistors operating in their nanoscale limits. It tackles the change in dominant behavior from scattering-limited long-channel transport to mesoscopic and few scattering events limits in quantized channels. It looks at electrostatics and a transistor’s controllability as dimensions are shrunk—the interplay of geometry and control—and then brings out the operational characteristics in “off”-state, e.g., the detailed nature of insulator’s implications or threshold voltage’s statistical variations grounded in short-range and long-range effects, and “on”-state, where quantization, quantized channels, ballistic transport and limited scattering are important. It also explores the physical behavior for zero bandgap and monoatomic layer materials by focusing on real-space and reciprocal-space funneling as one of the important dimensional change consequences through a discussion of parasitic resistances.

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The Damping Term, from First Principles

10.1093/oso/9780198788669.003.0006 ◽

2017 ◽

Author(s):

Olle Eriksson ◽

Anders Bergman ◽

Lars Bergqvist ◽

Johan Hellsvik

Keyword(s):

Density Functional Theory ◽

First Principles ◽

Density Functional ◽

Spin Dynamics ◽

Damping Term ◽

Functional Theory ◽

Basic Principles ◽

Sham Equation ◽

Damping Parameter ◽

Simulation Cell

In the previous chapters we described the basic principles of density functional theory, gave examples of how accurate it is to describe static magnetic properties in general, and derived from this basis the master equation for atomistic spin-dynamics; the SLL (or SLLG) equation. However, one term was not described in these chapters, namely the damping parameter. This parameter is a crucial one in the SLL (or SLLG) equation, since it allows for energy and angular momentum to dissipate from the simulation cell. The damping parameter can be evaluated from density functional theory, and the Kohn-Sham equation, and it is possible to determine its value experimentally. This chapter covers in detail the theoretical aspects of how to calculate theoretically the damping parameter. Chapter 8 is focused, among other things, on the experimental detection of the damping, using ferromagnetic resonance.

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Strong Coupling of Electron and Nuclear Spins: Outlook and Prospects

10.1093/oso/9780198807308.003.0011 ◽

2018 ◽

Author(s):

M. M. Glazov

Keyword(s):

Energy Spectrum ◽

Charge Carrier ◽

Strong Coupling ◽

Nuclear Spin ◽

Spin Dynamics ◽

Spin Polaron ◽

Nuclear Spins ◽

Deep Impurity ◽

Impurity Centers ◽

Ordered State

In this chapter, some prospects in the field of electron and nuclear spin dynamics are outlined. Particular emphasis is put ona situation where the hyperfine interaction is so strong that it leads to a qualitative rearrangement of the energy spectrum resulting in the coherent excitation transfer between the electron and nucleus. The strong coupling between the spin of the charge carrier and of the nucleus is realized, for example in the case of deep impurity centers in semiconductors or in isotopically purified systems. We also discuss the effect of the nuclear spin polaron, that is ordered state, formation at low enough temperatures of nuclear spins, where the orientation of the carrier spin results in alignment of the spins of nucleus interacting with the electron or hole.

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Electron Spin Decoherence by Nuclei

10.1093/oso/9780198807308.003.0007 ◽

2018 ◽

Author(s):

M. M. Glazov

Keyword(s):

Electron Spin ◽

Spin Dynamics ◽

Magnetic Moments ◽

Host Lattice ◽

Spin Model ◽

Relaxation Processes ◽

Nuclear Spins ◽

Model Calculations ◽

Spin Decoherence ◽

Quantum Mechanical Approach

The discussion of the electron spin decoherence and relaxation phenomena via the hyperfine interaction with host lattice spins is presented here. The spin relaxation processes processes limit the conservation time of spin states as well as the response time of the spin system to external perturbations. The central spin model, where the spin of charge carrier interacts with the bath of nuclear spins, is formulated. We also present different methods to calculate the spin dynamics within this model. Simple but physically transparent semiclassical treatment where the nuclear spins are considered as largely static classical magnetic moments is followed by more advanced quantum mechanical approach where the feedback of electron spin dynamics on the nuclei is taken into account. The chapter concludes with an overview of experimental data and its comparison with model calculations.

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