Relationships between the superconducting gap, pseudogap and transition temperature in high-Tc superconductors

The crossover from superconducting gap to pseudogap is considered, We show that the superconductivity is destroyed at the temperature T-c, with the superconducting gap being smoothly transformed into the pseudoggap. Relations, which are of general interest, between the maximum values of the gap Delta(1), T-c and T* are established. We presents arguments that T* as a function of the doping level X is approximately a straight line that crosses the abscissa at some point X-FC. In the vicinity of this point T* coincides with T-c, and at X = X-FC the fermion condensation quantum phase transition takes place. (C) 2002 Elsevier Science B.V. All rights reserved.