Spin and orbital hybridization at specifically nested Fermi surfaces in URu2Si2

Abstract

The Fermi-surface (FS) nesting properties of URu${}_{2}$Si${}_{2}$ are analyzed with particular focus on their implication for the mysterious hidden order phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wave vector ${\mathbit{Q}}_{0}=(0,0,1)$. The corresponding energy dispersions fulfill the relation ${\ensuremath{\epsilon}}_{1}(\mathbit{k})=\ensuremath{-}{\ensuremath{\epsilon}}_{2}(\mathbit{k}\ifmmode\pm\else\textpm\fi{}{\mathbit{Q}}_{0})$ at eight FS hot-spot lines. The spin-orbital characters of the involved $5f$ states are distinct(${j}_{z}=\ifmmode\pm\else\textpm\fi{}5/2$ vs $\ifmmode\pm\else\textpm\fi{}$3/2) and hence the degenerate Dirac crossings are symmetry protected in the nonmagnetic normal state. Dynamical symmetry breaking through an Ising-like spin and orbital excitation mode with $\ensuremath{\Delta}{j}_{z}=\ifmmode\pm\else\textpm\fi{}1$ induces a hybridization of the two states, causing substantial FS gapping. Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking.