Abstract
High resolution adiabatic specific heat experiments on YBa2Cu3O7−δ (0≤δ≤0.05) are performed in magnetic fields from 0 to 14 T (B∥c and B⊥c). In a 0.3 gram, twinned crystal with strong pinning, a step is consistently observed at the melting temperature Tm of the vortex solid up to a critical point that depends on δ. The field Bm and step temperature Tm obey the relation Bm=Bmo(δ)(1−Tm/Tc)≈4/3. The anisotropy of Bm and that of the upper critical field Bc2 are found to be equal. Alternatively, in a 18 mg, twinned crystal of high purity with low pinning, first-order-like specific heat peaks are observed on the melting line from 8 to 14 T. The entropy under these peaks is ≈0.5 kB /vortex/bilayer. These characteristic features are attributed to the melting of a vortex glass in the former case and that of a vortex lattice in the latter case.
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Roulin, M., Junod, A., Erb, A. et al. Melting of the flux line lattice observed by specific heat experiments in YBa2Cu3O7−δ . J Low Temp Phys 105, 1099–1104 (1996). https://doi.org/10.1007/BF00753846
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DOI: https://doi.org/10.1007/BF00753846