The underscreened anderson lattice: A model for uranium compounds

We first present a model based on the Underscreened Anderson Lattice with two 5f electrons per site to account for the Kondo-ferromagnetism co-existence observed in some actinide compounds. Then, we analyze the physics behind a novel type of phase transition that appears in the spinrotationally invariant form of the Underscreened Anderson Lattice Model. The model exhibits a continuous phase transition and below the critical temperature a pseudo-gap opens in the density of states. The transition is driven by the spin-flip part of the inter-orbital Hund’s rule interaction which produces a novel order parameter and breaks spin-rotational invariance. It is suggested that this order parameter might describe the “Hidden Order” transition found in URu2Si2.