Anisotropy of Upper Critical Field and Pairing Symmetry

We calculate the angular dependence of the upper critical field $H_{c2\mathrm{}}$, taking account of the effect of the gap anisotropy and nonlocal correction. If the Fermi surface is nearly isotropic in the $a-b$ plane, the results show that the angular dependence of the upper critical field for ${\mathrm{LaSrCuO}}_4$ in the $a-b$ plane is qualitatively explained by an order parameter $\Delta$ with the symmetry of the pairing state $d_{x^2{-y}^2}$, consistent with a recent experiment by Raman spectroscopy.