On the theory of fluctuations in superconductors in magnetic fields

A contribution to the study of the fluctuations of the superconducting order parameter in a magnetic field is presented within a framework which makes possible an inclusion of field dependent correction effects occurring near the transition point. Calculations of the excess conductivity in the presence of a magnetic field have so far ignored the effect of the fourth order term in the Ginzburg-Landau functional. In this thesis this effect is treated within a functional integral formulation from a transformation first suggested by Hubbard in 1959, which proves to be particularly convenient for this problem. Only the 'Aslamazov-Larkin contribution' is dealt with in detail for the systems considered here; this is justified in relation to recent experiments performed on such systems. The partition function is considered within two approximations. The results are incorporated into the calculation of Q, and the corrected magnetoparaconductivity is given for regimes above and below the transition point for applied magnetic fields perpendicular to the film, and below the transition point for the parallel field case. It is hoped that experiments will be performed close to and on each side of the transition point in connection with these results. The extent to which the theory agrees with some existing experimental data is discussed. (author)