High-Energy Materials Science

Someone I know recently asked me about this recent New Scientist article, and honestly, I’m not sure what to make of it. To summarize the article, ‘string-net condensation‘ (a model in which “electrons are not really elementary, but are formed at the ends of long ’strings’ of other, fundamental particles”) predicts interesting new phases of matter in certain spin models, and recent experiments on the amusingly-named Herbertsmithite may be a signature of one such phase of matter.

The subject matter is definitely interesting, although I am in no position to comment on the actual science (especially the theory, because I don’t understand it - my very little exposure to renormalization group theory so far has been in the context of statistical mechanics). On the experimental side, there is no doubt that recent work studying material properties of this system (such as looking at the specific heat or the temperature-dependence of the magnetic susceptibility, as well as using inelastic neutron scattering) is yielding some very cool physics. And of course on the theory side of things, it is clear that being able to come up with a unified theory from which electrons and photons are emergent is a Big Deal. The problem I have is that while the New Scientist article makes it sound like these measurements are a clear signature of a new phase of matter as predicted by string-net condensation, I can’t really discern the degree to which the link between the theory and experiments is scientifically rigorous, at least from reading the relevant papers. Rather, the article strikes me as being yet another example of really bad sensationalist journalism (see this post by Doug Natelson for more).

However, I find this to be a nice example of how things like high-energy physics theories of string-net condensation or quantum electrodynamics are becoming increasingly important in the study of materials. The ‘hot’ material for this kind of thing these days is obviously graphene, the “new bridge between condensed matter physics and quantum electrodynamics“. Another surprising example of this, for example, is this recent paper connecting SU(2) Yang-Mills theory in the low-temperature phase to nematic liquid crystals (who’d have thought? Certainly not me - I found it amusing that the only equations in the paper I actually understood were 18-20, the ones relating to liquid crystals).

And of course, this Herbertsmithite stuff is an example of another big thing in condensed matter physics - namely, ‘discovering’ new states of matter (at least theoretically). A lot of interesting physics is coming out of this effort, such as this recent work by Shoucheng Zhang at Stanford.