I have a confession to make. I don’t much care for solid-state physics. It bores me to tears. It shouldn’t, but it does.
Yet, once upon a time, I was on a track to build a career around it. While a grad student at the University of Houston, I worked at the Space Vacuum Epitaxy Center developing methods for using ion beam lithography for patterning integrated circuits on superconducting YBCO thin-films with the goal of eventually fabricating and testing SQUIDs and other such superconductor-based devices devices. My biggest challenge at the time I left was trying to modify the ion beam I was using to erode away the unwanted material to be more diffuse, as it was having a tendency to etch a doughnut-shaped pattern on the film as the target rotated on its platform.
But it wasn’t for me.
Yet, there is a specific aspect of solid-state physics which very much interests me, and it intersects closely with the work I was doing (except for the fact that my work wasn’t so much on the theoretical end of things). The mechanisms underlying superconductivity intersect in an unexpected way with theoretical particle physics, specifically with respect to spontaneous symmetry-breaking and the Higgs mechanism.
Reading this article got me started thinking about this, but perhaps it is best that I back up and explain a bit.
The phenomenon of superconductivity has been known for just a hair over a century, but for most of that time, it has eluded widespread practical applications due to the requirement of cooling materials to temperatures approaching absolute zero (generally via liquid helium). The traditional explanation for this phenomenon has been the Bardeen-Cooper-Schrieffer Theory (or BCS Theory, for short, not to be confused with the “Bowl Championship Series”). BCS Theory is a rather complex quantum mechanical model describing electrons within the superconductive material pairing-off in what are called “Cooper pairs.” The Cooper pairs in turn behave as a single particle, no matter how widely they are separated and the collective behavior of all of the Cooper pairs in the material form a condensate which is free to move through the material without encountering electrical resistance. (This is, of course, grotesquely over-simplified.) The key to getting the material in this state is extremely low temperatures, otherwise their is too much thermal energy in the system for the electrons to remain quantum-mechanically correlated as Cooper pairs.
In 1986, superconductivity research received a jolt with the discovery of cupric ceramics that could become conductive at temperatures reachable via liquid nitrogen. Unfortunately, BCS theory does not seem to adequately explain this new generation of high-temperature superconductors, but the breakthrough has spurred a surge in research in the field, with the Holy Grail of the research being the development of room-temperature superconductors. We aren’t nearly there yet, with the highest superconducting temperature achieved yet being 138 K. More recently, in 2008, and entirely new family of iron-based high-temperature superconductors was discovered, and research into the properties of these new materials was the subject of the article I mentioned earlier.
So what does all of this have to do with the Higgs mechanism? Well, first of all, Peter Higgs wasn’t the first to suggest it. He was the first to point out that it might be possible to generate a Higgs boson from the Higgs field. Many researchers contributed to the theoretical development of the Higgs mechanism (in fact, I’m working up a posting about that), but it was Nambu, Goldstone, and Goldstone who caught onto the idea of appropriating some of the key mathematical concepts from BCS theory and applying them to particle physics, and Goldstone, Salam, and Weinberg who figured out how to apply those principles into one of the foundations of the Standard Model, Electroweak Theory. For a nicely detailed look at this, have a look here.
- Bardeen, J., Cooper, L. N. & Schrieﬀer, J. R., “Microscopic Theory of Superconductivity“. Phys. Rev. 106, 162–164 (1957). DOI: 10.1103/PhysRev.106.162
- J. G. Bednorz and K. A. Müller (1986). “Possible high Tc superconductivity in the Ba−La−Cu−O system”. Z. Physik, B 64 (1): 189–193. Bibcode 1986ZPhyB..64..189B.DOI:10.1007/BF01303701.
- Nambu, Y. “Axial Vector Current Conservation in Weak Interactions“, Phys. Rev. Lett. 4, 380–382 (1960).
- Goldstone, J. “Field Theories with Superconductor Solutions“, Nuovo Cim. 19, 154–164 (1961). doi:10.1007/BF02812722.
- Goldstone, J., Salam, A. & Weinberg, S. “Broken Symmetries“, Phys. Rev. 127, 965–970 (1962).
- Ph. Anderson: “Plasmons, gauge invariance and mass.” In: Physical Review. 130, pp. 439–442 (1963).