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The Spin Hall Effect and related transport phenomena originating from the coupling of the charge
and spin currents due to spin-orbit interaction were predicted in 1971 by Dyakonov and Perel [1, 2].
Following the suggestion in [3], the first experiments in this domain were done by Fleisher's group at
Ioffe Institute in Saint Petersburg [4, 5], providing the first observation of what is now called the
Inverse Spin Hall Effect. As to the Spin Hall Effect itself, it had to wait for 33 years before it was
experimentally discovered by two groups in Santa Barbara (US) [6] and in Cambridge (UK) [7].
These observations aroused considerable interest and triggered intense research, both experimental
and theoretical, with hundreds of publications.
The Spin Hall Effect consists in spin accumulation at the boundaries of a current-carrying
conductor, the directions of the spins being opposite at the opposing boundaries. For a cylindrical
wire the spins wind around the surface. The boundary spin polarization is proportional to the current
and changes sign when the direction of the current is reversed.
The term "Spin Hall Effect" was introduced by Hirsch [8] in 1999. It is indeed somewhat similar
to the normal Hall effect, where charges of opposite signs accumulate at the sample boundaries due
to the action of the Lorentz force in magnetic field. However, there are significant differences. First,
no magnetic field is needed for spin accumulation. On the contrary, if a magnetic field perpendicular
to the spin direction is applied, it will destroy the spin polarization. Second, the value of the spin
polarization at the boundaries is limited by spin relaxation, and the polarization exists in relatively
wide spin layers determined by the spin diffusion length, typically on the order of 1 μm (as opposed
to the much smaller Debye screening length where charges accumulate in the normal Hall effect).
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