Determinations of upper critical field in the c-a plane

Within a continuous Ginzburg-Landau model for layered superconductors, two procedures are proposed to determine the upper critical field parallel to the $c$-$a$ crystal plane with an angle $\theta$ tilted from the c-axis. For an intrinsically layered superconductor, the upper critical fields for $\theta \to 90^\circ$, as determined by the two procedures, are consistent with each other and in reasonably good agreement with those determined by similar procedures suited for the parallel upper critical field ($\theta = 90^\circ$). The profile of the order parameter obtained at $B_{c2}$ is Gaussian-like, indicating the plausibility of the procedures proposed.