Pseudogap temperature along the Widom line of a first-order transition in doped Mott insulators

A state of matter with unusual physical properties, dubbed ``the pseudogap'', appears below a characteristic temperature $T^*$ in hole-doped high-temperature superconductors. In many cases, it is not even clear whether $T^*$ is a crossover or a phase transition. We construct the normal-state phase diagram of the two dimensional Hubbard model using cellular dynamical mean-field theory. We find that $T^*$ is a crossover line above the critical endpoint of a first-order phase transition between two metallic phases, one with a pseudogap and one without. Thus $T^*$ appears in a new light: it is an unexpected example of a phenomenon observed in fluids, namely a sharp crossover between different dynamical regimes along a line of thermodynamic anomalies that appears above a first-order phase transition, the Widom line. Our findings thus suggest that the critical point of a first-order transition, and not a quantum critical point, can be the organizing principle for the rich behavior of the normal state of the cuprates. Refs: G. Sordi et al., PRL 104, 226402 (2010); G. Sordi et al., PRB 84, 075161 (2011); G. Sordi et al., arXiv:1110.1392 (2011).