| Investigation of lattice fluctuations is of fundamental and crucial importance to elucidate the puzzling mechanisms of high temperature cuprate superconductors (HTS). Based on the success of the study of the lattice fluctuations in YBCO by the RBS channeling technique, we have applied the same technology and methodology to a simpler structured cuprate superconductor La1.89Sr0.11 CuO4 whose onset temperature of the Meissner effect is 30 K. RBS-channeling angular scans of the sample in the normal state over a wide temperature range, 40--290 K, have been executed. Although we carried out the scan across Tc (30 K), due to the difficulty in the design of experimental procedures at lower temperature, the data taken across T c are not reliable. However, the investigation of structural and electrical properties of FITS in normal state is also of important concern. This is because the revelations of the properties and phenomena of HTS in the normal state are believed to shed light on the conundrum of high temperature superconductivity. The comparison of the measured values and the calculated values of the critical angle Psi1/2 of channeling has revealed the presence of three anomalies in the lattice fluctuations. The first abnormal lattice fluctuations around 230--250 K are found to be due to the structural phase transition from the HTT (high temperature tetragonal) to the LTO (low temperature orthorhombic) phase. The correspondence of our data point to the reference data strongly supports our speculation for the first anomaly. The second anomaly around 175--185 K is believed to be related to the opening of a pseudogap of the sample. This idea originates from the reported fact that a pseudogap develops due to lattice distortion by the Jahn-Teller effect in the CuO2 layer of HTS, and the good agreement of our result with the pseudogap opening temperature dependence of the hole concentration per CuO2 layer. Partial phase transition to LTT (low temperature tetragonal) phase from LTO phase as stripe form would be the cause for the third anomaly around 80--90 K. |
