paper

Orthogonal Magnetization and Symmetry Breaking in Pyrochlore Iridate Eu2Ir2O7

arXiv:1603.08022 · doi:10.1038/nphys4051

Abstract

Electrons in the pyrochore iridates experience a large interaction energy in addition to a strong spin-orbit interaction. Both features make the iridates promising for realizing novel states such as the Topological Mott Insulator. The pyrochlore iridate Eu $_{2}$ Ir $_{2}$ O $_{7}$ shows a metal-insulator transition at $T_{N} \sim$ 120 K below which a magnetically ordered state develops. Using torque magnetometry, we uncover a highly unusual magnetic response. A magnetic field $H$ applied in its $a$ - $b$ plane produces a nonlinear magnetization $M_{⊥}$ orthogonal to the plane. $M_{⊥}$ displays a $d$ -wave field-angle pattern consistent with octupolar order, with a handedness dictated by field cooling, leading to symmetry breaking of the chirality $I ¨ $ . A surprise is that the lobe orientation of the $d$ -wave pattern is sensitive to the direction of the field when the sample is field-cooled below $T_{N}$ , suggestive of an additional order parameter $I^\cdot$ already present at 300 K.

23 pages, 14 figures