Energy gap evolution over wide temperature and doping ranges in Bi2Sr2CaCu2O8+δ

In this article we report the energy gap evolution in Bi2Sr2CaCu2O8+delta(Bi2212) on the basis of recent tunneling and Raman scattering experiments over wide temperature and hole-doping (p) ranges. It has been demonstrated that in the normal-state electronic excitations, there exist two kinds of pseudogaps (LPG and SPG) with different characteristic energies. The LPG, which is 3 to 4 times larger than the superconducting (SC) gap at T much less than T-c, develops below similar to T-max, where the magnetic susceptibility starts to decrease because of the gradual development of antiferromagnetic spin fluctuations. On the other hand, the SPG, whose magnitude is comparable to the SC gap, develops progressively, in addition to the LPG, below the mean-field characteristic temperature T-co for d-wave superconductors, and then evolves into the SC gap below T, suggesting that it will be some kind of precursor of superconductivity. It has also been demonstrated that the maximal gap Delta(0) or the gap at the positions near (+/-pi, 0) and (0, +/-pi), determined at T much less than T-c by tunneling technique, does not scale with T-c, while the gap around (+/-pi/2,+/-pi/2), determined at T much less than T-c from the coherence peak energy in B-2g Raman spectra, scales with T-c, suggesting that the latter gap will function as an effective SC gap Delta(eff) in determining T-c. Furthermore, we will report that Delta(eff) is given by the product of p and Delta(0); Delta(eff) similar to 5.3pDelta(0) in Bi2212, and discuss some scenarios for the SC transition which is consistent with the present result on the effective SC gap.