一、引言 自从A15金属型超导体被发现后,人们一直在探索可能导致高温超导转变温度的超导机制。高T_c氧化物超导体Y-Ba-Cu-O、Bi-Sr-Ca-Cu-O和T1-Ba-Ca-Cu-O的相继问世,使人们对这一中心课题更加关注。为了系统地研究探讨超导机制,人们首先注意到传统超导 I. INTRODUCTION Since the discovery of A15 metallic superconductors, superconducting mechanisms have been explored that may lead to high-temperature superconducting transition temperatures. The successive advent of high T_c oxide superconductors Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O and T1-Ba-Ca-Cu-O has drawn more attention to this central subject. In order to systematically study and investigate the superconducting mechanism, people first notice the traditional superconductivity