发现磁单极子:统一场理论的前奏?

by Matrix on 九月 6, 2009

最近科学界最热闹的大概是科学家声称探测到磁单极子,这里没有提只好偶这个业余爱好者随便说说了。

上周的《科学》杂志发表了两篇论文

Picture of monopoles

Magnetic Coulomb Phase in the Spin Ice Ho2Ti2O7


T. Fennell 1*, P. P. Deen 1, A. R. Wildes 1, K. Schmalzl 2, D. Prabhakaran 3, A. T. Boothroyd 3, R. J. Aldus 4, D. F. McMorrow 4, S. T. Bramwell 4

Spin ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Their low-temperature magnetic state has been predicted to be a phase that obeys a Gauss’ Law and supports magnetic monopole excitations: in short, a "Coulomb phase." Here, we use polarized neutron scattering to show that the spin ice material Ho2Ti2O7 exhibits an almost perfect Coulomb phase. Our result proves the existence of such phases in magnetic materials and strongly supports the magnetic monopole theory of spin ice.

另一篇

Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7


D. J. P. Morris 1*, D. A. Tennant 2*, S. A. Grigera 3*, B. Klemke 2, C. Castelnovo 4, R. Moessner 5, C. Czternasty 1, M. Meissner 1, K. C. Rule 1, J.-U. Hoffmann 1, K. Kiefer 1, S. Gerischer 1, D. Slobinsky 6, R. S. Perry 7

While sources of magnetic fields—magnetic monopoles—have so far proven elusive as elementary particles, several scenarios have been proposed recently in condensed matter physics of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin ice state is argued to be well-described by networks of aligned dipoles resembling solenoidal tubes—classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defect looks like a magnetic monopole. We demonstrate, by diffuse neutron scattering, the presence of such strings in the spin ice Dy2Ti2O7. This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.

还有两篇预印本值得关注:

Observation of Magnetic Monopoles in Spin Ice

 

Magnetic Charge Transport

 

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