Electronic properties of La sub (2-x) Sr sub x CuO sub 4 High- T sub c superconductors.

The basic macroscopic properties of the high-T sub c superconductors La sub (2-x) Sr sub x CuO sub 4 (x=0.075 - 0.20) with bulk transition temperatures up to 37.5 K were studied. The upper and lower critical fields, specific heat, Meissner effect and electrical resistivity were measured and extreme type-II behavior with large upper critical field slopes is observed. The density of states at E sub F is calculated from three different sets of experimental quantities (gammaBCS = 6+- 1.5 mJ/mole K sup 2). The critical temperatures of (La,Sr) sub 2 CuO sub 4 and Ba(Pb,Bi)0 sub 3 are ~3 times higher than those of other superconductors with comparable values of gamma, which empirically distinguishes them as a sparate class of superconductors.