Coulomb repulsion-induced hyperbolic pairing as a mechanism of high-T-c superconductivity

The hyperbolic metric of the dispersion law (the effective mass tensor comp onents of carriers are opposite in sign) in the vicinity of the Fermi conto ur in high-T-c superconducting cuprates in the case of repulsive interactio n gives rise to a superconducting state characterized by the condensate of pairs with a large total momentum (hyperbolic pairing). The gain in the ene rgy of the superconducting state over the normal state is due to the fact t hat a change in the kinetic energy of pairs (because of the negative light component of the effective mass) dominates over the change in the potential energy (corresponding to energy loss). The shift of the chemical potential upon the transition to the superconducting phase is substantial in this ca se. With increasing repulsive interaction, the superconducting gap Delta (K ) increases and the resulting gain in energy changes to an energy loss at a certain critical value of the repulsive potential. The low temperature T-c of the superconducting transition and the large value of Delta (K) in this region of potential values are the reasons for the high value of the 2 Del ta (K)/T-c ratio and for the developed quantum fluctuations that are observ ed in underdoped cuprate superconductors. (C) 2001 MAIK "Nauka/Interperiodi ca".