Characteristic Lengthsλandξof BCS Theory

The calculations of Eilenberger and Büttner are misleading in the regime where $\lambda$ and $\xi$ are complex. We study the regime of validity of linear-response theory in calculating the asymptotic properties of plane boundary and vortex structure. On this basis, it is not possible to predict if a sufficiently clean low-$\kappa$ type-II superconductor such as niobium or vanadium will exhibit field reversal at low temperatures.