Studies of phase transitions in PETN at high pressures Original Research Article

Local structure of optimally doped T-(La,Sr)2CuO4 (LSCO) single-crystal thin films grown by molecular-beam epitaxy on LaSrCuO4 and SrTiO3 substrates was studied by the in-plane polarized Cu K-edge extended X-ray absorption fine structure (EXAFS). The results of data analysis show that the local structure (CuO6 octahedra) of LSCO thin films is strained by ca. 5×10−3 in accordance with the crystallographic data. Although the planar and apical oxygen displacements ΔRCuO are related to the critical temperature in a simple relation, the magnitude of strain-induced oxygen displacements (leading to anti-Jahn–Tell or Jahn–Teller distortion) is less than 0.1% of the equilibrium bond length. This suggests that the strain dependence of electronic states involves a different mechanism than a purely electronic model in a homogeneous conducting plane. The fact that LSCO thin films under tensile strain have a large local distortion of planar oxygens indicates that inhomogeneity may affect the critical temperature rather than the apical oxygen displacement.