Incommensurate lattice distortion in the high temperature tetragonal phase of La(Sr,Ba)CuO

Wakimoto, Shuichi  ; Kimura, Hiroyuki*; Fujita, Masaki*; Yamada, Kazuyoshi*; Noda, Yukio*; Shirane, Gen*; Gu, G.*; Kim, H.*; Birgeneau, R. J.*

We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La(Sr,Ba)CuO with observed by the neutron diffraction technique. For all compositions, a sharp superlattice peak of the low-temperature-orthorhombic (LTO) structure is replaced by a pair of ICD peaks with the modulation vector parallel to the CuO octahedral tilting direction, that is, the diagonal Cu-Cu direction of the CuO plane, above the LTO-HTT transition temperature . The temperature dependences of the incommensurability for all samples scale approximately as , while those of the integrated intensity of the ICD peaks scale as . These observations together with absence of ICD peaks in the non-superconducting sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.