paper

Cluster Toroidal Multipoles Formed by Electric-Quadrupole and Magnetic-Octupole Trimers: A Possible Scenario for Hidden Orders in CaIrO

arXiv:2302.03818 · doi:10.7566/JPSJ.92.033702

Abstract

Cluster multipole orderings composed of atomic high-rank multipole moments are theoretically investigated with a 5-electron compound CaIrO in mind. CaIrO exhibits two hidden orders: One is an intermediate-temperature phase with time-reversal symmetry and the other is a low-temperature phase without time-reversal symmetry. By performing the symmetry and augmented multipole analyses for a -orbital model under the hexagonal point group , we find that the 120-type ordering of the electric quadrupole corresponds to cluster electric toroidal dipole ordering with the electric ferroaxial moment, which can become the microscopic origin of the intermediate-temperature phase in CaIrO. Furthermore, based on Ir synchrotron-radiation-based Mössbauer spectroscopy, we propose that the low-temperature phase in CaIrO is regarded as a coexisting state with cluster electric toroidal dipole and cluster magnetic toroidal quadrupole, the latter of which is formed by the 120-type ordering of the magnetic octupole and accompanies a small uniform magnetization as a secondary effect. Our results provide a clue to two hidden phases in CaIrO.

6 pages, 4 figures, 1 table, accepted for publication in JPSJ

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