Rashba effect
Rashba effect — splitting by spin in solids (particularly in heterostructures) by strong spin-orbit interaction. Named in honour of Emmanuel Rashba, co-worker of National Academy of Sciences of USSR who discovered it.
If a potential gradient is applied perpendicular to the semiconductor hetero junction plane, a spin-orbit interaction in proportion to the potential gradient as well as two-dimensional wavevector k is exerted to the electrons. As a result the electron spin is quantized in the direction perpendicular to both the plane normal and k, thus splitting the energy band[1][2].
In free space Hamiltonian of spin-orbit coupling is on inverce proportion to double Einstein energy 
. But for semiconductors, in nearly-free electron model it is on inverse proportion to band gap energy 
. Typically 
and 
, so spin-orbit coupling in solids is considerably stronger in comparison with free space. Heterostructures have asymmetric spatial zone and internal electric field distribution. It results in splitting of electron states for electrons with opposite spins along axis of wave vectors. It is called Rashba effect. In contrast to Rashba effect splitting in external magnetic fields change energies of electrons with opposite spins.
Spin-orbit coupling of Rashba type plays important role in the internal spin Hall effect.
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Application
Unlike regular electronic circuitry, spintronic devices foster current based on the electron's spin, leading to much higher efficiencies as a consequence of reduced heat loss. However, spintronics is not yet ready to manufacture, mainly because manipulating spin is difficult and often requires very low temperatures. A crucial ingredient is the electric control of spin, achievable through spin-orbit interaction (SOI), which couples the electron's motion to its spin. This was demonstrated in a semiconductor (Bismuth selenide) that is far larger than has ever been seen before and could lead the way towards room-temperature spintronic devices[3].
References
Further reading
- Chu, Junhao; Sher, Arden (2009) Device Physics of Narrow Gap Semiconductors Springer pp. 328—334 ISBN 9781441910394
- Heitmann, Detlef (2010) Quantum Materials, Lateral Semiconductor Nanostructures, Hybrid Systems and Nanocrystals Springer pp. 307—309 ISBN 9783642105524
External links
- Ulrich Zuelicke (30 Nov – 1 Dec 2009). "Rashba effect: Spin splitting of surface and interface states" (in en). Institute of Fundamental Sciences and MacDiarmid Institute for Advanced Materials and Nanotechnology Massey University, Palmerston North, New Zealand. http://www.massey.ac.nz/~uzuelick/Cluster09.pdf. Retrieved 2011-09-02.