Strong spin-orbit coupling effects on the fermi surface of Sr2RuO4 and Sr2RhO4

We present a first-principles study of spin-orbit coupling effects on the Fermi surface of Sr(2)RuO(4) and Sr(2)RhO(4). For nearly degenerate bands, spin-orbit coupling leads to a dramatic change of the Fermi surface with respect to nonrelativistic calculations; as evidenced by the comparison with experiments on Sr(2)RhO(4), it cannot be disregarded. For Sr(2)RuO(4), the Fermi surface modifications are more subtle but equally dramatic in the detail: Spin-orbit coupling induces a strong momentum dependence, normal to the RuO(2) planes, for both orbital and spin character of the low-energy electronic states. These findings have profound implications for the understanding of unconventional superconductivity in Sr(2)RuO(4).