摘要
Since the initial work done by Bednorz and Müller in 1986, four families of highT<sub>c</sub> oxide superconductor systems have been discovered. They are La<sub>2-x</sub>A<sub>x</sub> Cu O<sub>4</sub>-j) （A= Ca, Sr, Ba）, LnBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-y</sub>,（Ln=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu）,
