Doping dependence of condensation energy and upper critical field in Y 0.8Ca 0.2Ba 2Cu 3O 7− δ from specific heat measurement

Abstract

The temperature dependence of upper critical field ( H C2 ) is still being understood for high T C cuprates because of strong thermal fluctuations around T C and extremely high H C2 value at lower temperatures. Usin ga high-resolution differential technique, we determined the electronic specific heat of Y 0.8 Ca 0.2 Ba 2 Cu 3 O 7−δ from liquid helium temperature to room temperature in applied magnetic field up to 13T. From the temperature and field dependence of the superconducting free energy density, obtained by integrating the electronic entropy, the magnitude and temperature dependence of H C2 is deduced using the London model. The variation of these quantities with oxygen content is discussed.