The model proposed recently by Yeshurun and Malozemoff to explain the "irreversibility line" in high-temperature superconductors is extended to account for the experimentally measured width and shape of the resistive transition in a magnetic field, without invoking material inhomogeneity. It is argues that high $T_c$ and $H_{c2\mathrm{}}$ are necessary, but not sufficient, conditions for such materials to show zero resistance at room temperature in substantial magnetic fields.

• Received 6 July 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1658