tag:blogger.com,1999:blog-2007509643610309350.post938046632994342303..comments2024-01-22T10:47:38.507+05:30Comments on As I Please: Magnetic Monopoles and MagnetricityRahul Basuhttp://www.blogger.com/profile/07751088048215388592noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-2007509643610309350.post-9392397340569745862009-10-24T00:37:50.303+05:302009-10-24T00:37:50.303+05:30I've written a slightly longer take on the thi...I've written a slightly longer take on the thing <a href="http://horadecubitus.blogspot.com/2009/10/magnetic-monopoles-from-classical.html" rel="nofollow">here</a>.Rahul Siddharthanhttps://www.blogger.com/profile/04809667965184094636noreply@blogger.comtag:blogger.com,1999:blog-2007509643610309350.post-64872920070782671612009-10-22T16:11:10.588+05:302009-10-22T16:11:10.588+05:30Slightly edited cut-and-paste of my email, as you ...Slightly edited cut-and-paste of my email, as you requested:<br /><br />There are two other relevant papers: one is by <a href="http://www.sciencemag.org/cgi/content/full/326/5951/411" rel="nofollow">Morris et al.</a>, just published, and both are motivated by <a href="http://www.nature.com/nature/journal/v451/n7174/abs/nature06433.html" rel="nofollow">Castelnovo, Moessner and Sondhi</a>.<br /><br />This is a quick reaction, mainly to the Castelnovo et al paper, which I haven't yet read carefully but I think I get the idea. <br /><br /> is a very neat result, but of course the media (and the authors themselves) overstate the significance. These are not fundamental monopoles, but "things that look like monopoles" -- as will be obvious to many of your readers but perhaps not to the general public. Similarly, there is nothing fundamental about the "magnetic charge" that they measure: it is a property of this system only.<br /><br />More significantly, they are not "quasiparticles" in the quantum-mechanical sense, or "manifestations of the correlations present in a strongly interacting many-body system" (the phrase used by Castelnovo et al). They are a purely classical phenomenon. This material can be described as a system of classical Ising spins that interact primarily via a long-ranged "dipole-dipole" interaction, but with a short-ranged correction due to superexchange. The local structure is tetrahedral, with the tetrahedra linked at corners and the spins sitting at the corners aligned along the centres of the adjoining tetrahedra. In the ground state two spins point in and two point out of each tetrahedron. An excitation would consist of a spin flip, where one tetrahedron has three in and one out, and the neighbouring one has three out and one in. It will superficially look like a "north pole" in one tetrahedron and a "south pole" in another. What Castelnovo showed is that this can propagate via further spin flips, so that the poles get separated by considerable distances, and they examined the dynamics of this process.<br /><br />It is a very neat and elegant idea and, in retrospect, should have occurred to earlier authors (there have been dozens of papers on these systems in the last decade). But if you built a classical model with wires and constrained magnets, with the same geometry, it would behave the same way. So all the buzzwords should be taken with a grain of salt.Rahul Siddharthanhttps://www.blogger.com/profile/04809667965184094636noreply@blogger.comtag:blogger.com,1999:blog-2007509643610309350.post-73118497311063317662009-10-22T15:37:33.054+05:302009-10-22T15:37:33.054+05:30Surely you are aware that Glashow is supposed to h...Surely you are aware that Glashow is supposed to have sent a telegram saying<br />"Roses are red, violets are blue,<br />It is time for monopole two."<br /><br />Strangely by 2009, the story has morphed into Weinberg sending him a letter to this effect. I cannot believe Weinberg (c)would have done something like that.<br /><br />Another folk explanation I found via google is that the Cabrera result was because of some condensed matter flux-pinning effect in his system. Maybe he had discovered spin-ice?Ananthttps://www.blogger.com/profile/12974808252913561726noreply@blogger.com