Metallic conduction and superconductivity in the pseudogap phase

We analyze the t-J model on a square lattice using bosonic spinons and fermionic holons for low density x of holes. Spinons are paired into singlets, which condense below a temperature T*. The condensate evolves out of the Mott phase - preserving its symmetry. For T > T* holons and spinons are confined (by gauge forces), so that there is no coherent charge propagation. Metallic conduction and d-wave superconductivity result from separate, sublattice-preserving, holon hopping processes which originate below T* from a coupling with the condensate. A simple effective Hamiltonian describing these processes is derived and solved. Holons form a charge Fermi liquid, becoming incoherent (confined) above T*. In the superconductor holons hop as pairs, reducing kinetic energy. The two-sublattice property is the glue that connects the three phases; its effect can be seen in various correlation functions. The theory can account for many features of the cuprate superconductors, including the origin of two-dimensional metallicity.Comment: 7 pages 5 Postscript figure

Spin-Charge Separation and Kinetic Energy in the t-J Model

I show that spin-charge separation in 2-D t-J model leads to an increase of kinetic energy. Using a sum rule, I derive an exact expression for the lowest possible KE (E_{bound}) for any state without doubly occupied sites. KE of relevant slave-boson and Schwinger-boson mean-field states -- which exhibit complete spin-charge separation -- are found to be much larger than E_{bound}. Examination of n(k) shows that the large increse in KE is due to excessive depletion of electrons from the bottom of the band (Schwinger boson) and of holes from the top (slave boson). To see whether the excess KE is simply due to poor treatment of the constraints, I solve the constraint problem analytically for the Schwinger boson case in the J = 0 limit. This restores gauge invariance, incorrectly violated in MF theories. The result is a generalized Hartree-Fock state of the Hubbard model, but one that includes spin waves. Even after constraints are imposed correctly, the KE remains much larger than E_{bound}. These results support the notion, advanced earlier [PRB 61, 8663 (2000)] that spin-charge separation in the MF state costs excessive KE, and makes the state unstable toward recombination processes which lead to superconductivity in d = 2 and a Fermi liquid state in higher dimensions.Comment: 13 pages, LateX plus three figures. To appear in Phys Rev B Typos correcte

A theoretical construction of wormhole supported by Phantom Energy

A new solution has been presented for the spherically symmetric space time describing wormholes with Phantom Energy. The model suggests that the existence of wormhole is supported by arbitrarily small quantity of Phantom Energy.Comment: 6 pages, One reference has been correcte