Effect of a staggered spin-orbit coupling on the occurrence of a nematic phase in Sr3Ru2O7

Ultraclean crystals of Sr3Ru2O7 undergo a metamagnetic transition at low temperatures. This transition shows a strong anisotropy in the applied field direction with the critical field H-c ranging from similar to 5.1 T for H perpendicular to c to similar to 8 T for H parallel to c. In addition, studies on ultrapure samples revealed a bifurcation of the metamagnetic line for fields in c direction and it has been argued that a nematic phase emerges between the magnetization jumps. The aim of this study is to explain the field-direction anisotropy of these phenomena. Based on a microscopic tight-binding model, we introduce the metamagnetic transition by means of a Van Hove singularity scenario. We show that the rotation of the O octahedra around the c axis observed in this material introduces a staggered spin-orbit coupling within the planes and naturally leads to an anisotropy in the low-temperature behavior around the metamagnetic transition. In particular, the low-temperature (nematic) phase is affected. We show that uniform in-plane magnetic fields induce a (commensurate) staggered magnetic-moment component which can suppress the low-temperature phase. In contrast, the response to fields along the c axis remains unaffected and thus, also the corresponding low-temperature phase. As a concrete example, we choose a nematic Pomeranchuk instability for the low-temperature phase. An experimentally testable prediction of this work is the occurrence of a staggered magnetic moment in response to a uniform magnetic field perpendicular to the c axis, which should be accessible by neutron scattering.