Anisotropic transport properties of single-crystal La2−x−yNdySrxCuO4: Effect of the structural phase transition

Abstract

We have successfully grown single crystals of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}\mathrm{-}\mathit{y}}$ ${\mathrm{Nd}}_{\mathit{y}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ (x=0,0.12,0.20; y∼0.4) by the traveling-solvent floating-zone method. All of these crystals show a lattice instability to the low-temperature tetragonal (LTT) phase and enable us to investigate the anisotropic transport properties of the LTT phase. For x=0.12, various transport coefficients show a discontinuous jump at the phase transition (evidence for a first-order transition), and superconductivity is suppressed almost completely, while the effects are much reduced for x=0.20, which show a bulk superconductivity with reduced ${\mathit{T}}_{\mathit{c}}$. The result emphasizes the importance of the hole density x∼1/8 coupled with the LTT distortion in the system composed of a two-dimensional ${\mathrm{CuO}}_6$ octahedral array.