Two-Dimensional Materials and Topological Insulators for Spintronics: A Theoretical Study of Spin-Charge Effects
[Thesis]
Farzaneh, Seyed Mohammad
Rakheja, Shaloo
New York University Tandon School of Engineering
2021
167 p.
Ph.D.
New York University Tandon School of Engineering
2021
The goal of spintronics is to provide a faster and more efficient computing platform than the CMOS in conventional electronics; that is memory and logic devices that operate based on the spin of electrons. In contrast to conventional electronics, which is based on the control of the charge of electrons, spintronics concerns with the control of the spin of electrons as the unit of information. Spintronics has already seen a degree of success in the span of three decades since the discovery of the giant magnetoresistance which has lead to successful commercial applications such as the magnetic field sensors and read heads in hard disk drives and the magnetic random access memory. In the past decade or so new material systems have been introduced which show promising capabilities in terms of spintronics and could be used to generate and control spins without the need for magnets. These capabilities include macroscopic spin transport in two-dimensional materials such as graphene and phosphorene, spin splitting and the quantum spin Hall insulating phase in silicene, germanene, stanene, and plumbene, and efficient spin generation via the spin Hall effect in topological insulators. However, these materials are still far from replacing the magnets in spin-based memory and logic devices due to their relatively recent emergence and unexplored physical properties. In this dissertation we study the spin properties of these novel crystalline systems such as two-dimensional materials and topological insulators and provide a better understanding of how they can be utilized in spintronics applications. Several numerical and analytic methods, such as the density functional theory, group theory, k dot p method, linear response theory, etc, are used in combinations with each other to quantify various spin properties such as extrinsic spin-orbit coupling and spin relaxation time in phosphorene, electric-field-induced spin splitting and spin Hall conductivity in silicene, germanene, stanene, and plumbene, as well as spin Hall conductivity and spin Hall angle in typical topological insulators namely Sb2Se3 , Sb2Te3 , Bi2Se3 , and Bi2Te3. This work provides a better understanding of the spin-charge phenomena in these materials and discusses how they could be leveraged to generate, transfer, and detect spins fully electronically and to get one step closer to more efficient, faster, and nonvolatile spin-based memory and logic devices.