EVIDENCE FOR ONSET OF CHARGE-DENSITY-WAVE IN THE LA-BASED PEROVSKITE SUPERCONDUCTORS

Recent studies have shown that structural instabilities play a vital r ole in high-T-c superconductivity. We have used a local structural pro be, extended X-ray absorption fine structure (EXAFS), to investigate t he instability of the CuO2 plane in La-based high-T-c perovskite syste ms. Temperature-dependent Cu K-edge EXAFS spectra measured on single c rystals of La1.85Sr0.15CuO4 (LSCO) and La2CuO4.1 (LCO) show a characte ristic temperature (T-ls) where the local structure od the system dive rges from the average one. This temperature coincides with a crossover temperature where the system shows anomalous metal-insulator transiti on in transport measurements. We have discussed the EXAFS results as a n evidence for a particular phase transition of the system with segreg ation of localized and itinerant charge carriers in a short coherence charge density wave (CDW). A phase diagram for this CDW has been propo sed.