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TOPIC: Monopole

Blobrana

L

Posts: 131433

Date: Oct 14 21:31 2009

Magnetic monopoles	Permalink

'Magnetic electricity' discovered Researchers have discovered a magnetic equivalent to electricity: single magnetic charges that can behave and interact like electrical ones. The work is the first to make use of the magnetic monopoles that exist in special crystals known as spin ice. Read more __________________

Blobrana

L

Posts: 131433

Date: Sep 4 10:42 2009

RE: Monopole	Permalink

Icy journey finally uncovers magnetic monopole A team, including Oxford University scientists, has found the first evidence that magnetic monopoles - where the 'North' and 'South' poles of magnets are separated - do exist in nature. Scientists from the Institut Laue-Langevin in Grenoble, University College London and Oxford University, report in this week's Science that their investigations have detected disturbances in the magnetism of a spin ice compound that strongly suggest the influence of magnetic monopoles. The monopoles predicted to occur in spin ice are not elementary particles like protons or electrons but are disturbances of the arrangement of spins - similar to ripples on the surface of a pond. Read more __________________

Blobrana

L

Posts: 131433

Date: Jan 4 18:09 2008

Magnetic monopoles	Permalink

`Spin ice could contain magnetic monopoles Materials might lead to high-density magnetic memories Particles carrying isolated north or south magnetic poles, otherwise known as magnetic monopole One environment in which monopoles might pop up is crystalline solids. In a crystal at a low temperature, excitations above the ground state often behave like elementary particles: they carry a quantised amount of energy, momentum, electric charge and spin. In their theoretical study, Castelnovo et al. find the first instance of such an excitation with a non-zero magnetic charge. Under certain conditions, these magnets behave as a gas of independent magnetic poles. There is even a phase transition at which a thin vapour of these monopoles condenses into a dense liquid. Source Nature Title: Magnetic Monopoles in Spin Ice Authors: Claudio Castelnovo, Roderich Moessner, Shivaji L. Sondhi (Version v2) Electrically charged particles, such as the electron, are ubiquitous. By contrast, no elementary particles with a net magnetic charge have ever been observed, despite intensive and prolonged searches. We pursue an alternative strategy, namely that of realising them not as elementary but rather as emergent particles, i.e., as manifestations of the correlations present in a strongly interacting many-body system. The most prominent examples of emergent quasiparticles are the ones with fractional electric charge e/3 in quantum Hall physics. Here we show that magnetic monopoles do emerge in a class of exotic magnets known collectively as spin ice: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles. This enables us to account for a mysterious phase transition observed experimentally in spin ice in a magnetic field, which is a liquid-gas transition of the magnetic monopoles. These monopoles can also be detected by other means, e.g., in an experiment modelled after the celebrated Stanford magnetic monopole search. Read more (305kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jul 30 00:24 2007

Monopole	Permalink

Title: A monopole near a black hole Authors: Claudio Bunster and Marc Henneaux A striking property of an electric charge near a magnetic pole is that the system possesses angular momentum even when both the electric and the magnetic charges are at rest. The angular momentum is proportional to the product of the charges and independent of their distance. We analyse the effect of bringing gravitation into this remarkable system. To this end, we study an electric charge held at rest outside a magnetically charged black hole. We find that even if the electric charge is treated as a perturbation on a spherically symmetric magnetic ReissnerNordstrom hole, the geometry at large distances is that of a magnetic KerrNewman black hole. When the charge approaches the horizon and crosses it, the exterior geometry becomes that of a KerrNewman hole, with electric and magnetic charges and with total angular momentum given by the standard value for a charged monopole pair. Thus, in accordance with the "no-hair theorem," once the charge is captured by the black hole, the angular momentum associated with the charge monopole system loses all traces of its exotic origin and is perceived from the outside as common rotation. It is argued that a similar analysis performed on TaubNUT space should give the same result. Read more (PDF, Subscription) __________________

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