Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I know they are not elementary particles but quasi-particles.)

(1) Dirac, P. A. M. Quantised singularities in the electromagnetic field. Proc. R. Soc. A 133, 60–72 (1931)

(2) Castelnovo, C., Moessner, R. & Sondhi, S. Magnetic monopoles in spin ice. Nature 451, 42–45 (2008).

share|improve this question
add comment

1 Answer 1

These are "fake monopoles", in the sense that the north and south poles are not actually separated. They are the ends of thin tubes which behave like Dirac strings - like long thin twisted magnets. The tubes are formed due to geometrical frustration, which forces the magnetic field to be orientated either toward the outside or toward the inside of the tetrahedral cells. The tetrahedral cells end up by having two faces with "spin in" orientation and two faces with "spin out" orientation. Two tetrahedral cells couple one another like tiny magnets, so that tiny magnetic tubes form. The ends seem to be separated north and south magnetic poles, while in fact they are connected through the tube.

Had they been genuine monopoles, they would have indeed modified Gauss's law for magnetism, and Faraday's law of induction, by adding terms corresponding to magnetic charge density and current.

share|improve this answer
1  
Thank you very much for the answer! –  Jeremy Sep 17 '12 at 1:54
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.