Correlation between superconducting gap and pseudogap in high-T-c cuprates

We studied the low-temperature energy gap 2 Delta(o) on Bi2Sr2CaCu2O8-delta (Bi2212) and La2-xSrxCuO4 (La214) systematically over a wide range of dopi ng level p using STS, break junction tunneling spectroscopy, Raman scatteri ng and low-T electronic specific heat data. We have also studied the electr onic specific heat of La214 in the normal state at T > T-c, and confirmed t hat pseudogap behavior appears at around T*, below which the in-plane resis tivity rho and magnetic susceptibility chi tend to be slightly suppressed. Similar suppression appears in rho and chi of Bi2212 below the onset temper ature of pseudogap T*. It is pointed out in the present study that 2 Delta( o) is closely related to T* in both Bi2212 and La214 systems; T* similar to 2 Delta(o)/4.3k(B). It is also pointed out that 2 Delta(o) is in almost li near proportion to k(B)T(max)(<< T*), where T-max is the temperature exhibi ting a broad peak in chi-T curves and k(B)T(max) can be considered to give a measure of the effective antiferromagnetic ex change energy J(eff). The a lpha factors in 2 Delta(o) similar to alpha k(B)T(max) similar to alpha J(e ff) are similar to 1 for La214 and similar to 2 for Bi2212, respectively. W e also report that in both Bi2212 and La214 systems T-c roughly scales with p Delta(o) except in highly doped samples, where T-c proportional to 2 Del ta(o).