High Energy Theory Seminar

Many experiments point to a significant transformation in the electronic state of the cuprate superconductors as their density is varied at very low temperature. The critical density is close to the “optimal” density where the superconductivity is present at the highest temperature. Such a transformation is present for both electron and hole doping, although the observed characteristics are rather different. Despite extensive searches, experiments have not displayed any broken symmetry which could serve as an order parameter for a quantum phase transition that can explain the observations. I will describe the observations by transformations of gauge theories between Higgs and confining regimes. These two regimes can be connected either by a smooth crossover, or by a sharp phase transition described by a deconfined critical gauge theory. Symmetry breaking order parameters or topological order can appear as ancillary features in the Higgs regime, and these are also important for interpreting experiments. Ref: arXiv: 1811.04930