Incommensurate lattice distortion in the high temperature tetragonal phase of La${}_{2-x}$(Sr,Ba)${}_x$CuO${}_4$

Abstract

We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La${}_{2-x}$(Sr,Ba)${}_x$CuO${}_4$ with $0.07\le x\le 0.20$ 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${}_6$ octahedral tilting direction, that is, the diagonal Cu-Cu direction of the CuO${}_2$ plane, above the LTO-HTT transition temperature $T_s$. The temperature dependences of the incommensurability $\delta$ for all samples scale approximately as $T/T_s$, while those of the integrated intensity of the ICD peaks scale as $(T-T_s{)}^{-1}$. These observations together with absence of ICD peaks in the non-superconducting $x=0.05$ sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.

6 pages, 6 figures

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