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"""this is the first time we’ve actually seen a two-dimensional monopole in a naturally occurring magnet ... These monopoles are a collective state of many

by andy99 3y ago

"""this is the first time we’ve actually seen a __two-dimensional__ monopole in a naturally occurring magnet ... These monopoles are a collective state of many spins that twirl around a singularity rather than a single fixed particle, so they emerge through many-body interactions. The result is a tiny, localised stable particle with diverging magnetic field coming out of it,""" So do I take it that there is some kind of superposition of spins that locally, possibly just in a 2D cross section, appears to have a magnetic field with non-zero divergence? Is \nabla\cdot\vec{B} actually violated somewhere? The language seems pretty cagey. Incidentally, I belive Dirac posited that they existence of magnetic monopoles would explain the quantization of charge.

Anon84 3y ago
Yes, it’s a superposition of spins such that the resulting effect is the non-zero divergence
andy99 3y ago
From the other thread where this was discussed: In the "Emergent Magnetic Charge" section, second paragraph: "Finally, we emphasize that the observation of emergent monopoles is fully consistent with the modelling of AFM topological textures in Fig. 2 and does not violate Maxwell’s equation as they are, in fact, sinks and sources of the H^ field." So this is a collective effect of a bunch of magnetic dipoles, and they go on to describe how div B is indeed zero in the material. https://news.ycombinator.com/item?id=38549099 https://news.ycombinator.com/item?id=38549099 So this is not a Maxwell's Equations violation or anything, it's just some 'trick' to make a field that somehow locally looks divergent.
kuchenbecker 3y ago
(not a physicist) Dirac proposed a sufficiently long and narrow solenoid would behave as if each end was a magnetic monopole. If the math says it works, then it should be possible in nature. Please correct my understanding if you know better and I'm wrong.

"""this is the first time we’ve actually seen a __two-dimensional__ monopole in a naturally occurring magnet ... These monopoles are a collective state of many

by andy99 3y ago

Anon84 3y ago

Yes, it’s a superposition of spins such that the resulting effect is the non-zero divergence

andy99 3y ago

From the other thread where this was discussed: In the "Emergent Magnetic Charge" section, second paragraph: "Finally, we emphasize that the observation of emergent monopoles is fully consistent with the modelling of AFM topological textures in Fig. 2 and does not violate Maxwell’s equation as they are, in fact, sinks and sources of the H^ field." So this is a collective effect of a bunch of magnetic dipoles, and they go on to describe how div B is indeed zero in the material. https://news.ycombinator.com/item?id=38549099 https://news.ycombinator.com/item?id=38549099 So this is not a Maxwell's Equations violation or anything, it's just some 'trick' to make a field that somehow locally looks divergent.

kuchenbecker 3y ago

(not a physicist) Dirac proposed a sufficiently long and narrow solenoid would behave as if each end was a magnetic monopole. If the math says it works, then it should be possible in nature. Please correct my understanding if you know better and I'm wrong.