Low temperature Pmmm and C2/m phases in Sr2CuO3+δ high temperature superconductor**Project supported by the National Basic Research Program of China (Grant Nos. 2012CB922004/3, 2010CB934501, and 2009CB929502), the Funds of Jilin Province, China (Grant No. JJKH20180860KJ), the National Natural Science Foundation of China, and the Fundamental Research Funds for the Central Universities, China (Grant No. WK2310000043). The authors appreciate the beam

Abstract

A new low temperature Pmmm (120 K) phase was found in high temperature superconductor Sr2CuO3+δ, which was indicated as a pure electronic phase by resonant x-ray diffraction at Cu K-edge. As shown by x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) at Cu K-edge, the strong charge density redistribution and local lattice fluctuations around Cu site at the onset of phase transition were due to the occurrence of superconductive coherence, the redistribution and fluctuation finished at Tc. Finally, the electron–lattice interaction was mainly elaborated to understand the superconductivity of Sr2CuO3+δ.