Anisotropy of Upper Critical Field and Pairing Symmetry

Abstract

We calculate the angular dependence of the upper critical field ${H}_{c2}$, taking account of the effect of the gap anisotropy and nonlocal correction. If the Fermi surface is nearly isotropic in the $a\ensuremath{-}b$ plane, the results show that the angular dependence of the upper critical field for ${\mathrm{LaSrCuO}}_{4}$ in the $a\ensuremath{-}b$ plane is qualitatively explained by an order parameter $\ensuremath{\Delta}$ with the symmetry of the pairing state ${d}_{{x}^{2}{\ensuremath{-}y}^{2}}$, consistent with a recent experiment by Raman spectroscopy.