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Quantum spin Hall effect[edit]
For mercury telluride two dimensional quantum wells with strong spin-orbit coupling, in zero magnetic field, at low temperature, the quantum spin Hall effect has been recently observed.
Anomalous Hall effect[edit]
In ferromagnetic materials (and paramagnetic materials in a magnetic field), the Hall resistivity includes an additional contribution, known as the anomalous Hall effect (or the extraordinary Hall effect), which depends directly on the magnetization of the material, and is often much larger than the ordinary Hall effect. (Note that this effect is not due to the contribution of the magnetization to the total magnetic field.) For example, in nickel, the anomalous Hall coefficient is about 100 times larger than the ordinary Hall coefficient near the Curie temperature, but the two are similar at very low temperatures.[17] Although a well-recognized phenomenon, there is still debate about its origins in the various materials. The anomalous Hall effect can be either an extrinsic (disorder-related) effect due to spin-dependent scattering of the charge carriers, or an intrinsic effect which can be described in terms of the Berry phase effect in the crystal momentum space (k-space).[18]
Hall effect in ionized gases[edit]
The Hall effect in an ionized gas (plasma) is significantly different from the Hall effect in solids (where the Hall parameter is always much less than unity). In a plasma, the Hall parameter can take any value. The Hall parameter, β, in a plasma is the ratio between the electron gyrofrequency, Ωe, and the electron-heavy particle collision frequency, ν:
where
- e is the elementary charge (approximately 1.6×10−19 C)
- B is the magnetic field (in teslas)
- me is the electron mass (approximately 9.1×10−31 kg).
The Hall parameter value increases with the magnetic field strength.
Physically, the trajectories of electrons are curved by the Lorentz force. Nevertheless, when the Hall parameter is low, their motion between two encounters with heavy particles (neutral or ion) is almost linear. But if the Hall parameter is high, the electron movements are highly curved. The current density vector, J, is no longer collinear with the electric field vector, E. The two vectors J and E make the Hall angle, θ, which also gives the Hall parameter:
Spacecraft propulsion[edit]
A Hall-effect thruster (HET) is a device that is used to propel some spacecraft, after it gets into orbit or farther out into space. In the HET, atoms are ionized and accelerated by an electric field. A radial magnetic field established by magnets on the thruster is used to trap electrons which then orbit and create an electric field due to the Hall effect. A large potential is established between the end of the thruster where neutral propellant is fed, and the part where electrons are produced; so, electrons trapped in the magnetic field cannot drop to the lower potential. They are thus extremely energetic, which means that they can ionize neutral atoms. Neutral propellant is pumped into the chamber and is ionized by the trapped electrons. Positive ions and electrons are then ejected from the thruster as a quasineutral plasma, creating thrust. The thrust produced is extremely small, with a very low mass flow rate and a very high effective exhaust velocity/specific impulse. This is achieved at the cost of very high electrical power requirements, on the order of 4 KW for a few hundred millinewtons of thrust.
The Corbino effect[edit]
The Corbino effect is a phenomenon involving the Hall effect, but a disc-shaped metal sample is used in place of a rectangular one. Because of its shape the Corbino disc allows the observation of Hall effect–based magnetoresistance without the associated Hall voltage.
A radial current through a circular disc, subjected to a magnetic field perpendicular to the plane of the disc, produces a "circular" current through the disc.[20]
The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect.
See also[edit]
- Capacitor
- Transducer
- Coulomb potential between two current loops embedded in a magnetic field
- Eddy current
- Eric Fawcett
- List of plasma (physics) articles
- Nernst effect
- Quantum Hall effect
- Fractional quantum Hall effect
- Quantum anomalous Hall effect
- Senftleben–Beenakker effect
- Spin Hall effect
- Thermal Hall effect
https://en.wikipedia.org/wiki/Hall_effect#Hall_effect_in_ionized_gases
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