ULTRASONIC EXPERIMENTS ON THE HIGH-Tc-SUPERCONDUCTOR Y2-xBaxCuO4-δ

Abstract

Sound velocity measurements on a mixed-phase sample Y1.2Ba0.8CuO4-δ in high magnetic fields are reported. Like in normal metals, but in contrast to single-phase samples, the material is found to harden on cooling. In the vicinity of 95 K an elastic instability is observed which is referred to a semimetal-metal transition. For B0= 6 T an anomalously large softening of ~ 460 ppm is found at Tc (B0). The importance of internal strains for the elastic behaviour and for the appearance of pronounced hysteresis effects in single-phase samples is discussed.