We apply Landau-Ott scaling to the reversible magnetization data of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ published by Wang et al. [Phys. Rev. Lett. 95, 247002 (2005)] and find that the extrapolation of the Landau-Ott upper critical field line vanishes at a critical temperature parameter $T_c^{*}$ a few degrees above the zero resistivity critical temperature $T_c$. Only isothermal curves below and near $T_c$ were used to determine this transition temperature. This temperature is associated with the disappearance of the mixed state instead of a complete suppression of superconductivity in the sample.

• Received 30 January 2007

DOI:https://doi.org/10.1103/PhysRevB.76.052504