Contrasting effects of magnetic field on thermodynamic and resistive transitions in high- Tc cuprates

For a number of high-Tc cuprates it has been observed that the resistive transition reveals an upper critical field with increasingly negative gradient on cooling. However, the λ point of the specific heat scarcely shifts with applied magnetic field. Either phenomenon is highly unusual in itself, but also appears to be irreconcilable with one another under the BCS framework. This Letter offers an explanation of the observed phenomena on the basis of the bipolaron theory.