Thermal Conductivity of La 2- x- yNd ySr xCuO 4

We have measured the thermal conductivity κ of La 2- x - y R y Sr x CuO 4 ( R =Nd, Sm, Eu, Gd) and found that it shows the enhancement below the transition temperature T d2 from the LTO1 (low-temperature orthorhombic-1) to LTT (low-temperature tetragonal) (or LTO2 (low temperature orthorhombic-2)) phase and the magnitude of the enhancement strongly depends on x and y . We propose that the characteristic enhancement of κ below T d2 reflects the nature of the structure below T d2 . From the results that in La 1.875- y Nd y Sr 0.125 CuO 4 , the LTT (or LTO2) phase appears at y >1/8, we propose the pair substitution of Sr 2+ and Nd 3+ ions where the loss of the strain energy is smaller and the local LTT (or LTO2) distortion is more largely enhanced than in the case of the independent substitution. We show that various characteristic properties associated with the LTT (or LTO2) transition could be explained naturally from the stand point that the local lattice distortion induced by the substituted ion plays an...