Dependence of Superconducting Transition Temperature on Doping and Structural Distortion of the CuO2Planes inLa2−xMxCuO4(M=Nd, Ca, Sr)

Abstract

By comparing structural and superconducting properties of ${\mathrm{La}}_{2-x-y}{\mathrm{Ca}}_x{\mathrm{Nd}}_y{\mathrm{CuO}}_4$ to ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ we have separated the effects of structure and doping on the superconducting $T_c$. At a fixed doping level, the highest $T_c$ is found for flat and square Cu${\mathrm{O}}_2$ planes in the tetragonal structure. $T_c$ is reduced by the structural distortions of the Cu${\mathrm{O}}_2$ planes in the orthorhombic structure. The local minimum of $T_c$ vs doping observed around $x\sim 0.12$ indicates the presence of a weakly split singularity of the electronic density of states for the orthorhombic material.