Lowest Landau level approximation in strongly type-II superconductors

Abstract

Higher than the lowest Landau level, (LLL) contributions to magnetization and specific heat of superconductors are calculated using the Ginzburg-Landau equation approach. Corrections to the excitation spectrum around the solution of these equations (treated perturbatively) are found. Due to symmetries of the problem leading to numerous cancellations the range of validity of the LLL approximation in the mean held is much wider then a naive range and extends ail the way down to H=H-c2(T)/13. Moreover, the contribution of higher Landau levels (HLL) is significantly smaller compared to LLL than expected naively. Like the LLL part, the lattice excitation spectrum at small quasimomenta is softer than that of the usual acoustic phonons. This enhances the effect of fluctuations. The mean-held calculation extends to third order, while the fluctuation contribution due to HLL is to one leap. This complements the earlier calculation of the LLL part to two-loop order, [S0163-1829(99)03834-5].