Abstract
We have determined for the first time the electronic specific heatγ(x, T) of YBa2Cu3O6+x for 0.16≤x≤0.97 from 1.8 to 300 K. Weakly superconducting behavior betweenx=0.4 and 0.8 progresses rapidly to strong coupling BCS-like superconducting and metallic normal state behavior forx> 0.9. However, the continuous development of the entropyS(x, T) withx andT across the entire series suggests a progressive modification of the low-energy spin spectrum with hole doping rather than a simple band model. Fermi statistics andk-space pairing for allx is indicated by the magnitude andT-dependence ofS(x, T). Pseudogap behavior inS(x, T) is observed over a temperature region aboveT c , which increases rapidly with oxygen depletion to around 200 K forx∼0.7. This loss of entropy reflects normal-state correlations apparently unrelated to the superconducting pairing.
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Loram, J.W., Mirza, K.A., Cooper, J.R. et al. Electronic specific heat of YBa2Cu3O6+x from 1.8 to 300 K. J Supercond 7, 243–249 (1994). https://doi.org/10.1007/BF00730405
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DOI: https://doi.org/10.1007/BF00730405