spintransport

Spin transport refers to the transport of spin angular momentum in solid-state systems, describing how spin polarization, or spin currents, propagate and relax in materials independently of charge flow. It encompasses diffusion, drift, and transfer of spin across interfaces, and is central to spintronics, where spin rather than charge is used to process information.

Spin currents can be carried by itinerant electrons, holes, or collective spin excitations such as magnons. Key concepts include the spin diffusion length, which characterizes how far spin polarization persists before relaxing, and spin relaxation and dephasing times. Spin-orbit coupling enables interconversion between charge and spin currents, as in the spin Hall effect and its inverse, and spin transfer torque describes the transfer of spin angular momentum from a current to localized magnetic moments, potentially altering magnetization.

Theoretical approaches include drift-diffusion models like the Valet-Fert formalism, semiclassical Boltzmann transport, and quantum kinetic theories. At the level of magnetization dynamics, the Landau-Lifshitz-Gilbert equation is often coupled to spin accumulation to describe torque and damping.

Experimentally, spin transport is probed with nonlocal spin valve measurements, spin pumping, and optical techniques. Materials of interest include ferromagnet/normal metal heterostructures, semiconductors, topological insulators, and two-dimensional materials such as graphene, with reported spin diffusion lengths ranging from a few nanometers to several micrometers depending on material and temperature.

Applications of spin transport knowledge include spintronic devices such as magnetic random-access memory, spin-based transistors and logic, magnetic sensors, and energy-efficient information processing. Ongoing research seeks to understand interfacial effects, spin coherence, and ways to engineer long-range spin transport.