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Orbital order and Hund's rule frustration in Kondo lattices

We propose and analyze microscopic origin of the Kondo effect-assisted orbital order in heavy-fermion materials. We show that, for periodic two-orbital Anderson model with two local electrons, frustration of local Hund's rule coupling due to Kondo screening leads to an incommensurate spiral orbital and magnetic order, which exists only inside the Kondo (heavy-electron) phase. This spiral state can in principle be observed in neutron and resonant X-ray scattering measurements in U and Pr-based heavy-fermion compounds, and realized in cold atomic gases, e.g. fermionic 173Yb. We discuss the implications of this result for the phase diagram of such systems.