INFLUENCE OF SPIN AND CHARGE FLUCTUATIONS ON THE HIGH-T_c SUPERCONDUCTIVITY

In the framework of the weak coupling theory of superconductivity, we have proved that spin and charge fluctuations in the high-T_c superconductors can pro-duce respectively, pair-breaking and pair-forming effects on the superconductivity resulting from the "generalized BCS mechanism". With the coupling constant for spin fluctuations larger than that for charge fluctuations, they combine to produce a temperature-dependent effective pair-breaking effect, which makes T_c decrease more rapidly than \Delta(0), the superconducting gap at T=0, and therefore, enhances the ratio 2\Delta(0)/T_c. This provides a reasonable physical interpretation for the relevant experimental results.