Large ultrasonic attenuation at Tc in YBa2Cu3O7?x

We investigated elastic anomalies of sintered YBa₂Cu₃O_7–x (x=0.35) superconductor around the critical temperature (T_c=60 K). We observed the non-symmetric and large attenuation peak (2 dB/cm at 9.7 MHz) at T_c, which was due to the lattice softening caused by the strong correlation between carriers and local lattice distortion. The rapid decrease of ultrasonic attenuation just below T_c suggested a condensation mechanism. These supported the polaronic condensation in high-T_c superconductivity.