Separate smectic and nematic melting transitions in YBa 2Cu 3O y

Abstract

For magnetic fields accurately aligned with the CuO-planes in YBa 2Cu 3O y, two peaks in the temperature dependence of the critical current are observed in agreement with the theoretical prediction of two separate melting transitions in the presence of intrinsic pinning. These peaks are assigned to the consecutive softening of the shear and tilt moduli expected at a transition from solid to smectic and from smectic to liquid respectively.