Vortex Lattice Anisotropy in Sr2RuO4 with H || a

ABSTRACT We have studied the vortex lattice (VL) in superconducting Sr2RuO4 using spin-polarized small-angle neutron scattering (SP-SANS) and with magnetic fields (H) close to, but not perfectly aligned with, the crystalline basal plane. In this configuration the VL possesses a large transverse field component, due to the large anisotropy of Sr2RuO4, which greatly increases the spin-flip SANS scattered intensity. Bragg reflections indicative of a highly distorted hexagonal VL were observed, and an analysis of the magnitude of the scattering vector yielded an anisotropy of 50 - 60, roughly two times the Hc2 anisotropy. We discuss implications of this result in relation to theoretical predictions of Pauli paramagnetic effects in Sr2RuO4 with H c [K. Machida and M. Ichioka, Phys. Rev. B 77, 184515 (2008)].