Thermal Expansion Anomaly in High Tc La1.85Sr0.15CuO4 Associated with the Superconductivity

Precision lattice parameter in La1.85Sr0.15CuO4 single crystal superconductor has been measured in a wide temperature range between 4.2 K and room temperature by the X-ray Bond’s method. An anomalous lattice contraction associated with the appearance of the superconductivity was found in c-plane. Along c-direction, on the contrary, an anomalous expansion of the lattice was observed. The relative spontaneous change in the lattice parameter in c-plane was 2.3xl0­-5 and that of c-axis was 1.5×l0-5 at 4.2 K. The temperature dependence of the spontaneous lattice change was compared with currently existing theories for high Tc superconductivity.