Comment on “Observation of vortex-lattice melting inYBa2Cu3O7<

Abstract

The findings of Ghamlouch et al. ͓Phys. Rev. B 54, 9070 ͑1996͔͒ on the jump in the thermoelectric power of high-T c superconductors below the critical temperature in the presence of large magnetic fields are discussed. The complicated interplay between the vortex lattice thermodynamic transitions and the transport property percolation transitions raises questions on their similarities, differences, and relationships with respect to the ͑B,T͒ phase diagram features and the classical Kosterlitz-Thouless transition. A few comments pertain to the experimental details and others on the relevant role of thermomagnetic transport properties.

The influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y–Ba–Cu–O

“…Such an anomalous peak has been observed previously in measurements of the thermoelectric power and has been explained by superconducting fluctuation effects [64], vortex lattice melting [65] or anisotropy of the thermoelectric power along the a and b directions in the ab plane of the lattice [66]. Extrinsic origins of this peak are either artefacts caused by AC measurement techniques [67,68] or the existence of small inhomogeneities in T c in the YBa 2 Cu 3 O 7−δ superconducting matrix [69,70]. In the present case, the peak is likely to arise from the magnitude of the thermal gradient used in the measurement, which is larger than the width of the superconducting transition (<0.7 K).…”