Superconductivity and Electronic Structure of Sr_xLa_2-xCuO_4-y Prepared under Reducing Condition

Abstract

The compound Sr x La 2- x CuO 4- y ( x ∼0.7, y ∼1.0) with a tetragonal K 2 NiF 4 structure prepared under reducing conditions showed a high superconducting transition temperature ( T c ) of 37.0 K and T co (the onset of T c ) of 54.0 K. Its photomission spectrum showed the existence of a large amount of monovalent Cu ions and a small amount of bivalent Cu ions. The valence band spectrum has a strong resemblance to the semimetallic DOS (the density of states) of ZrC and has a small DOS at the Fermi level. These facts suggest the T c enhancement from a plasmon or exciton origin due to the Cu d-hole creation and anihilation resonating with vibration modes of the CuO 6 and CuO 5 clusters.