Bottom-up approach to high-temperature superconductivity
  Since the discovery of high-temperature superconductivity in the cuprates a theoretical understanding of their phase diagram has remained one of the major outstanding problems in condensed matter physics. Here we propose an effective low-energy Hamiltonian which produces both d-wave density wave (dDW) and d-wave superconducting (dSC) solutions within the BCS mean-field theory. This model predicts that (a) the observed pseudogap phase is a dDW state, (b) the superconducting phase is a d-wave BCS state, and (c) in the underdoped regime there is a gossamer superconducting state, i.e. dSC in coexistence with dDW. Moreover, this theory naturally explains the Uemura relation, the reduction of the quasiparticle density of states at the Fermi level, and the salient features in the tunneling conductivity measured in underdoped Bi2212. 
Hyekung Won, Stephan Haas, Kazumi Maki