Dalela, S: Electronic Structure Of Cuprate Perovskites: High

After the discovery of superconductivity in mercury by Kamerling Onnes, Meissner effect, Alex Müller and Georg Bednorz, discovered a ceramic LBCO and its Tc is highest then known: 35 K in 1987, and they considered them as High Temperature Superconductors. When Yttrium is substituted for Lanthanum an incredible 92 K Tc is achieved. The world record Tc of 138 K is now held by a mercuric-cuprate perovskites, which under extreme pressure can be coaxed up even higher by 25 to 30 degrees more at 300,000 Pa. All parent compounds of high Tc superconductors are insulator and by substitutional doping of cations they show a transition from insulator to metal/ superconductor. Temperature dependence of the itinerant holes in the superconducting crystals appears to have escaped general attention. A band gap, called pseudogap has been found to open up in these materials at a temperature T*Tc. T* is the temperature at which pseudogap opens. In this book we also report the anomalous temperature dependence of itinerant holes using XAFS technique. The role of the in-plane and out-of-plane carriers i.e. the carriers in the ab-plane and those along the c-axis is very important for superconductivity.