Ferromagnetism stabilized by lattice distortion at the surface of the p-wave superconductor Sr2RuO4

Ferromagnetic (FM) spin fluctuations are believed to mediate the spin-tripl et pairing for the rho-wave superconductivity in Sr2RuO4. Our experiments s how that, at the surface, a bulk soft-phonon mode freezes into a static Lat tice distortion associated with an in-plane rotation of the RuO6 octahedron . First-principle calculations confirm this structure and predict a FM grou nd state at the surface. This coupling between structure and magnetism in t he environment of broken symmetry at the surface allows a reconsideration o f the coupling mechanism in the bulk.