Spin Hall Effect

Schematic representation of the spin Hall effect: a stream (red) of electrons moves through the lattice of a solid. Depending on the orientation of their spin (green), the electrons are deflected laterally. This corresponds to a transverse spin current (blue).

The spin Hall effect is a quantum mechanical effect that can be seen in analogy to the classic Hall effect , but does not lead to differences in the distribution of electrical charge across the direction of the electrical current, but to differences in the distribution of the spin alignment Electrons.

When an electric current flows through a solid, the electrons are deflected perpendicular to the direction of the current, depending on the orientation of their spin (quantum mechanical intrinsic angular momentum). A spin current flows  across the direction of the electrical current, so that the spins are polarized in opposite directions on opposite sides. There is no electrical voltage associated with the spin current itself as is the case with the usual Hall effect. The spin current is proportional to the electric field that drives the electron motion: . Here called the spin Hall conductivity . ${\displaystyle j_{s}}$ ${\displaystyle E}$ ${\displaystyle j_{s}=\sigma _{sH}\cdot E}$ ${\displaystyle \sigma _{sH}\ }$

In contrast to the classic Hall effect, no external magnetic field is required. The effect is based on the spin-dependent scattering of the electrons (so-called Mott scattering ) at defects in the sample (extrinsic spin-Hall effect). But there is a second mechanism. In spin-orbit-coupled systems, the spin-Hall effect also occurs in ideal systems that have no defects (intrinsic spin-Hall effect), as was independently predicted by two groups in 2003 ( Shoucheng Zhang and colleagues for p-type Semiconductors and independent from Allan H. MacDonald , Jairo Sinova and colleagues for n-type semiconductors).

Experiments

Theoretically, the Spin-Hall effect was predicted in 1971 by Michail Djakonow and Wladimir Perel , but experimentally for the first time in 2004 by Yuichiro Katō, David Awschalom and others. a. proven. The effect is proven z. As in GaAs - semiconductor structures at temperatures of 30  K . Compared to the usual Hall effect, which has been known for more than a hundred years, the spin Hall effect is orders of magnitude smaller. In 2006 it was also detected at room temperature (i.e. around 300 K) in ZnSe structures.

method

The location-dependent measurement of the spin distribution can be done using Kerr rotation microscopy. This makes use of the fact that certain materials rotate the plane of polarization of incident, linearly polarized light due to their magnetization . Since an accumulation of spin orientation effectively corresponds to magnetization, a map of the spin polarization can be made by scanning the sample. The first evidence by Kato, Awschalom et al. took place via the Kerr rotation.

Technical application

It is hoped that the controlled generation of spin currents will result in significant technical advances in storage media ( MRAM ) and the spin transistor as well as important steps towards the development of a quantum computer , the possibility of which, however, is controversial.

See also

• Spintronics
• Quantum Hall Effect
• Spin-Nernst effect

Individual evidence

1. ↑ S. Murakami, Intrinsic Spin Hall Effect , Adv. Solid State Phys., Volume 45, 2005, pp. 197-209
2. ↑ S. Murakami, N. Nagaosa, S. Zhang, Dissipationless Quantum Spin Current at Room Temperature, Science, Vol 301, 2003, p 1348
3. ↑ Dimitrie Culcer, Q. Niu, NA Sinitsyn, T. Jungwirth, AH MacDonald, J. Sinova: Universal Intrinsic Spin-Hall Effect, Phys. Rev. Lett., Vol. 92, 2004, p. 126603, Arxiv
4. ↑ MI Dyakonov, VI Perel ': Possibility of Orienting Electron Spins with Current . In: JETP Letters . tape 13 , 1971, p. 206 . ( Summary )
5. ↑ ^{a b} Y. K. Kato, RC Myers, AC Gossard, DD Awschalom: Observation of the Spin Hall Effect in Semiconductors . In: Science . tape 306 , no. 5703 , 2004, p. 1910–1913 , doi : 10.1126 / science.1105514 .
6. ↑ T. Kimura, Y. Otani, T. Sato, S. Takahashi, S. Maekawa: Room-Temperature Reversible Spin Hall Effect . In: Physical Review Letters . tape 98 , no. 15 , 2007, p. 156601–156604 , doi : 10.1103 / PhysRevLett.98.156601 .