High temperature superconducting materials

The epoch-making discovery of superconductivity in doped LaCuO perovskite at temperature 35K leads to discovery of a class of compound (CuO2)a(ABmO1) A=rare earth or Bi, TL Hg and B= Ba, Sr and/or Ca) where the zero-resistance states occurs at much higher temperature ranging from 90K to 165K. These cuprates system are characterized by many unusual features like granularity in superconducting state, pseudogap in energy spectrum, and complex pairing mechanism. Alkali-doped C'" solid is another class of compounds that exhibits super conductivity around 33-40K. By injecting hole from outside to C60 solid, the transition temperature is enhanced to 52K. Recent addition to the list of high temperature superconducting material is MgB2 (Tc=40K) that constitutes boron layer sandwiched between magnesium layer. In these entire system the hole as charge carrier facilities the super conductivity. The common aspects of these superconductors are outlined and possible mechanisms of pairing are traced.