Spin Ice and Monopoles

For those of you like "cool" stuff:

A recent paper---
Title: Observation of Magnetic Monopoles in Spin Ice
Authors: Hiroaki Kadowaki, Naohiro Doi, Yuji Aoki, Yoshikazu Tabata, Taku J.
Sato, Jeffrey W. Lynn, Kazuyuki Matsuhira, Zenji Hiroi
\\
From the symmetry of Maxwell's equations of electromagnetism as well as field
theoretical arguments, magnetic charges or monopoles would be expected to
exist. But magnetic monopoles have never been observed despite longstanding
experimental searches. Recently, attention has turned to condensed matter
systems where tractable analogs of magnetic monopoles might be found, and one
prediction is for an emergent elementary excitation in the spin ice compound,
where the strongly competing magnetic interactions exhibit the same type of
frustration as water ice. We directly probe the monopoles in spin ice using
neutrons, and show that they interact via the magnetic Coulomb force. Specific
heat measurements show that the density of monopoles can be controlled by
temperature and magnetic field, with the density following the expected
Arrhenius law.
\\ ( http://arxiv.org/abs/0908.3568 , 627kb)

More background:
http://www.nature.com/nature/journal/v451/n7174/abs/nature06433.html
http://www.nature.com/nphys/journal/v5/n4/abs/nphys1227.html