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Concept
Rashba effect
Summary
The Rashba effect, also called Bychkov–Rashba effect, is a momentum-dependent splitting of spin bands in bulk crystals and low-dimensional condensed matter systems (such as heterostructures and surface states) similar to the splitting of particles and anti-particles in the Dirac Hamiltonian. The splitting is a combined effect of spin–orbit interaction and asymmetry of the crystal potential, in particular in the direction perpendicular to the two-dimensional plane (as applied to surfaces and heterostructures). This effect is named in honour of Emmanuel Rashba, who discovered it with Valentin I. Sheka in 1959 for three-dimensional systems and afterward with
Yurii A. Bychkov in 1984 for two-dimensional systems.
Remarkably, this effect can drive a wide variety of novel physical phenomena, especially operating electron spins by electric fields, even when it is a small correction to the band structure of the two-dimensional metallic state. An example of a physical phenomenon that can be explained by Rashba model is the anisotropic magnetoresistance (AMR).
Additionally, superconductors with large Rashba splitting are suggested as possible realizations of the elusive Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, Majorana fermions and topological p-wave superconductors.
Lately, a momentum dependent pseudospin-orbit coupling has been realized in cold atom systems.
The Rashba effect is most easily seen in the simple model Hamiltonian known as the Rashba Hamiltonian
where is the Rashba coupling, is the momentum and is the Pauli matrix vector.
This is nothing but a two-dimensional version of the Dirac Hamiltonian (with a 90 degree rotation of the spins).
The Rashba model in solids can be derived in the framework of the k·p perturbation theory or from the point of view of a tight binding approximation. However, the specifics of these methods are considered tedious and many prefer an intuitive toy model that gives qualitatively the same physics (quantitatively it gives a poor estimation of the coupling ).
Official source
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