Abstract
Single-phase sintered YBa2Cu3O6.9 exhibits no anomaly in the attenuation around Tc (90 K). On the other hand, its sound velocity shows an anomalous increase just below Tc. This may come from lattice hardening due to the condensation of holes. To clarify the relation between this anomaly and the superconductivity, measurement under 8 Tesla was performed. Exactly the same anomaly was observed at 90 K and nothing happened around 72 K, which is the critical temperature under 8 Tesla. The hardening may not be directly related to the superconductivity of this material. An ultrasonic study of a single crystal of La2CuO4 is being made to investigate its antiferromagnetic property, which may be a key in understanding the new superconductivity. A small peak in the attenuation at TN and a very small anomaly in the sound velocity were observed at 43 MHz. The result of a study on a single crystal of YBa2Cu3O6.9 will also be presented at the conference.
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