Spin and orbital hybridization at specifically nested Fermi surfaces in URu2Si2

The Fermi-surface (FS) nesting properties of URu2Si2 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 Q(0) = (0,0,1). The corresponding energy dispersions fulfill the relation epsilon(1)(k) = -epsilon(2)(k +/- Q(0)) at eight FS hot-spot lines. The spin-orbital characters of the involved 5f states are distinct (j(z) = +/-5/2 vs +/-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 Delta j(z) = +/-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.