Unified Theory of Hastatic order and Antiferromagnetism in URu$_2$Si$_2$

Abstract

The hidden order phase of URu$_2$Si$_2$ has eluded identification for over thirty-five years. A compelling proposal that explains the Ising heavy-fermion nature of the material is \emph{hastatic order}: a symmetry breaking heavy-Fermi liquid arising from a spinorial microscopic hybridization. The original hastatic proposal cannot microscopically model the pressure induced antiferromagnetic phase; and while it predicts a spinorial order parameter, it does not provide any detectable signatures of the spinorial nature. Here, we present a more realistic microscopic model of hastatic order in URu$_2$Si$_2$ based on two conducting electron bands and explore its phase diagram in detail. Our model non-trivially preserves the Ising heavy-fermion physics of the original, while allowing us to tune between the antiferromagnet and hidden order using pressure analogues and magnetic field. Our model is also consistent with recent phenomenological predictions of not one, but two vector order parameters associated with the spinorial order that provide the first microscopic predictions for detecting the spinorial nature.