Theory of Nernst effect in high- T_c superconductors

We calculated, using the time-dependent Ginzburg-Landau equation with thermal noise, the transverse thermoelectric conductivity α_xy and the Nernst signal e_N, describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree-Fock utilized by Ullah and Dorsey Phys. Rev. Lett. 65 2066 (1990)]. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The resulting values in two dimensions are significantly lower than the numerical simulation data of the same model but are in reasonably good quantitative agreement with experimental data on La₂SrCuO₄ above the irreversibility line (below the irreversibility line at which α_xy diverges and theory should be modified by including pinning effects). The values of e_N calculated in three dimensions are also in good quantitative agreement with experimental data for temperature close to T_c on YBa₂Cu₃O₇. For each of the materials we consider, the melting and the irreversibility lines are also fitted with the same set of parameters using a recent quantitative Ginzburg-Landau theory.