Bond Directional Anapole Order in a Spin-Orbit Coupled Mott Insulator Sr${}_2$(Ir${}_{1-x}$Rh${}_x$)O${}_4$

Abstract

An anapole state that breaks inversion and time reversal symmetries with preserving translation symmetry of underlying lattice has aroused great interest as a new quantum state, but only a few candidate materials have been reported. Recently, in a spin-orbit coupled Mott insulator \SIR, the emergence of a possible hidden order phase with broken inversion symmetry has been suggested at $T_{\Omega }$ above the Néel temperature by optical second harmonic generation measurements. Moreover, polarized neutron diffraction measurements revealed the broken time reversal symmetry below $T_{\Omega }$, which was supported by subsequent muon spin relaxation experiments. However, the nature of this mysterious phase remains largely elusive. Here, we investigate the hidden order phase through the combined measurements of the in-plane magnetic anisotropy with exceptionally high-precision magnetic torque and the nematic susceptibility with elastoresistance. A distinct two-fold in-plane magnetic anisotropy along the [110] Ir-O-Ir bond direction sets in below $\sim T_{\Omega }$, providing thermodynamic evidence for a nematic phase transition with broken $C_4$ rotational symmetry. However, in contrast to the even-parity nematic transition reported in other correlated electron systems, the nematic susceptibility exhibits no divergent behavior towards $T_{\Omega }$. These results provide bulk evidence for an odd-parity order parameter with broken rotational symmetry in the hidden order state. We discuss the hidden order in terms of an anapole state, in which polar toroidal moment is induced by two current loops in each IrO${}_6$ octahedron of opposite chirality. Contrary to the simplest loop-current pattern previously suggested, the present results are consistent with a pattern in which the intra-unit cell loop-current flows along only one of the diagonal directions in the IrO${}_4$ square.

11 pages, 10 figures

References in corpus (19)

• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Magnetic order in the pseudogap phase of high-$T_C$ superconductors
• Twisted Hubbard Model for Sr2IrO4: Magnetism and Possible High Temperature Superconductivity
• Nematic and meta-nematic transitions in the iron pnictides
• Fermi Arcs in a Doped Pseudospin-1/2 Heisenberg Antiferromagnet
• Rotational Symmetry Breaking in the Hidden-Order Phase of URu2Si2
• Thermodynamic evidence for nematic phase transition at the onset of pseudogap in YBa${}_2$Cu${}_3$O${}_y$
• Monte Carlo study of an unconventional superconducting phase in Ir-oxide J_{eff}=1/2 Mott insulators induced by carrier doping
• The magnetic and crystal structures of Sr2IrO4: A neutron diffraction study
• Exotic Superconducting States in FeSe-based Materials
• Odd-parity triplet superconductivity in multi-orbital materials with strong spin-orbit coupling: applications to doped Sr2IrO4
• Observation of a ferro-rotational order coupled with second-order nonlinear optical fields
• Spin-orbit tuned metal-insulator transitions in single-crystal Sr2Ir1-xRhxO4 (0\leqx\leq1)
• Neutron scattering study of correlated phase behavior in Sr2IrO4
• Square Lattice Iridates
• A structural distortion induced magneto-elastic locking in Sr${}_2$IrO${}_4$ revealed through nonlinear optical harmonic generation
• No Evidence for Orbital Loop Currents in Charge Ordered YBa${}_2$Cu${}_3$O${}_{6+x}$ from Polarized Neutron Diffraction
• a-b anisotropy of the intra-unit-cell magnetic order in $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.6}$
• Absence of the polar Kerr effect in the helical loop-current model [Phys. Rev. Lett. 111, 047005 (2013)]

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• Three-dimensional Stacking of Canted Antiferromagnetism and Pseudospin Current in Undoped Sr${}_2$IrO${}_4$: Symmetry Analysis and Microscopic Model Realization
• Microscopic model realization of $\mathbf{d}$-wave pseudospin current order in Sr${}_2$IrO${}_4$
• Emergent Inductance from Chiral Orbital Currents in a Bulk Ferrimagnet
• Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La${}_3$Ir${}_3$O${}_{11}$