Competing magnetic orders and multipolar Weyl fermions in 227 pyrochlore iridates.

Pyrochlore iridates are a class of materials in which the confluence of electronic interactions and emergent topology leads to a plethora of exotic states of matter. In this work, we focus on an effective low-energy Luttinger model accounting for a quadratic band touching (QBT) around the Γ point, and study interaction-induced instabilities of the QBT. In particular, we analyze the impact of a new type of magnetic order transforming under the T_2u irreducible representation of the cubic point group. This magnetic order is of octupolar character. It breaks time-reversal symmetry but is inversion-invariant, and thus for example stabilized quadrupoles of Weyl points on different planes in the Brillouin zone. We detail the regime of critical couplings for which the T_2u order can occur in the phase diagram, and conclude with a discussion of possible experimental verifications.