A First Principles Plus Many-Body Approach to the Correlated Spin Dynamics in SmB₆

The emergent dynamical processes in heavy fermion materials like SmB₆ are highly dependent on the momentum space electronic structure. Here we present a microscopic model to capture these effects by imposing many-body correlations on a high quality single particle description produced by density functional theory. We calculate the low energy spin excitation spectrum within the random phase approximation, and find good agreement with magnetic neutron scattering experiments. We also calculate the mean field magnetic phase diagram, and show the ground state is highly quantum critical with several competing phases. We further find novel interplay between the magnetic ordering and the orbital ordering in the f-levels, which could drive non-trivial topological phase transitions at finite temperatures. Implications of our results in light of recent experiments will be discussed. This work emphasizes the importance of a high quality momentum space description for describing correlation effects in heavy fermion systems.