Is the anisotropy of the upper critical field of Sr2RuO4 consistent with a helical p-wave state?

We calculate the angular and temperature T dependencies of the upper critical field Hc2(θ, ϕ, T) for the C4v point group helical p-wave states, assuming a single uniaxial ellipsoidal Fermi surface, Pauli limiting and strong spin-orbit coupling that locks the spin-triplet d-vectors onto the layers. Good fits to the Sr2RuO4 Hc2,a(θ, T) data of Kittaka et al (2009 Phys. Rev. B 80 174514) are obtained. Helical states with d(k) =kˆxxˆ −kˆyy and kˆyxˆ +kˆxy (or kˆxxˆ +kˆyyˆ and kˆyxˆ -kˆxyˆ ) produce Hc2(90°, ϕ, T) that greatly exceed (or do not exhibit) the fourfold azimuthal anisotropy magnitudes observed in Sr2RuO4 by Kittaka et al and by Mao et al (2000 Phys. Rev. Lett. 84 991), respectively.