Abstract. The theoretical description of the anomalous properties of the pseudogap phase in the underdoped region of the cuprate phase diagram lags behind the progress in spectroscopic and other experiments. A phenomenological ansatz, based on analogies to the approach to Mott localization at weak coupling in lower dimensional systems, has been proposed by Yang, Rice and Zhang [Phys. Rev. B 73 (2006),174501]. This ansatz has had success in describing a range of experiments. The motivation underlying this ansatz is described and the comparisons to experiment are reviewed. Implications for a more microscopic theory are discussed together with the relation to theories that start directly from microscopic strongly coupled Hamiltonians.arXiv:1109.0632v1 [cond-mat.str-el]

We have numerically evaluated the energy of the staggered flux phase state (sm), the d-wave resonating valence bond state, and the mixed SFP and d-wave state (sm + d) of the extended 1-3 model at various hole densities (6). The flux per plaquette and the size of the d-wave gap are taken as variational parameters. The calculation includes the kinetic energy, spinenergy, the effectivehole-holeinteraction and the three-sitepair-hoppingterm.