Short coherence length superconductors with anisotropic pairing in 2D

The two models of short coherence length superconductors with anisotropic p airing symmetry are discussed. First, we examine superconducting properties of the extended Hubbard model with intersite attraction on a 2D square lat tice with nearest- and next-nearest-neighbor hopping. The effects of phase fluctuations on the extended s and d(x)(2)-(2)(y)-wave as well as on the mi xed s +/- id state are studied within the Kosterlitz-Thouless scenario. Thi s leads to a new phase with a pseudogap, and the universal linear scaling o f the critical temperature versus zero temperature phase stiffness can occu r on the Uemura type plots due to the separation of scales for pairing and for the phase coherence. The second model is that of local electron pairs a nd itinerant fermions coupled via charge exchange mechanism, which mutually induces superconductivity in both subsystems. The phase diagram of this tw o-component system is presented for anisotropic pairing on a 2D square latt ice.