Enhanced Spin Orbit Interaction in Strongly Correlated Materials

We investigate the effect of many-body interactions on the spin-orbit coupling of anisotropic metals. We use the Underscreened Anderson Lattice Model that was proposed to describe uranium and plutonium compounds. By using a rotationally invariant approximation, we show that Coulomb interactions induce off-diagonal correlations that enhance the components of the spin-orbit coupling. Even modest values of the Coulomb interaction $U$ can enhance the spin-orbit coupling by factors of about 4 and have significant effects on the electronic spectrum, but the enhancements are most pronounced for systems that are on the verge of magnetic instabilities. The enhancement is anisotropic in crystals with non-cubic symmetries and can lead to giant magnetic anisotropies in paramagnetic states.