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arXiv · 1912.11229

Quantum versus Classical Spin Fragmentation in Dipolar Kagome Ice Ho3Mg2Sb3O14

Zhiling Dun·Xiaojian Bai·Joseph A. M. Paddison·Emily Hollingworth·Nicholas P. Butch·Clarina D. Cruz·Matthew B. Stone·Tao Hong·Franz Demmel·Martin Mourigal·Haidong Zhou
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Abstract

A promising route to realize entangled magnetic states combines geometrical frustration with quantum-tunneling effects. Spin-ice materials are canonical examples of frustration, and Ising spins in a transverse magnetic field are the simplest many-body model of quantum tunneling. Here, we show that the tripod kagome lattice material Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$ unites an ice-like magnetic degeneracy with quantum-tunneling terms generated by an intrinsic splitting of the Ho$^{3+}$ ground-state doublet, which is further coupled to a nuclear spin bath. Using neutron scattering and thermodynamic experiments, we observe a symmetry-breaking transition at $T^{\ast}\approx0.32$ K to a remarkable state with three peculiarities: a concurrent recovery of magnetic entropy associated with the strongly coupled electronic and nuclear degrees of freedom; a fragmentation of the spin into periodic and ice-like components; and persistent inelastic magnetic excitations down to $T\approx0.12$ K. These observations deviate from expectations of classical spin fragmentation on a kagome lattice, but can be understood within a model of dipolar kagome ice under a homogeneous transverse magnetic field, which we survey with exact diagonalization on small clusters and mean-field calculations. In Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$, hyperfine interactions dramatically alter the single-ion and collective properties, and suppress possible quantum correlations, rendering the fragmentation with predominantly single-ion quantum fluctuations. Our results highlight the crucial role played by hyperfine interactions in frustrated quantum magnets, and motivate further investigations of the role of quantum fluctuations on partially-ordered magnetic states.

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Zhiling Dun, Xiaojian Bai, Joseph A. M. Paddison, Emily Hollingworth, Nicholas P. Butch, Clarina D. Cruz, Matthew B. Stone, Tao Hong, Franz Demmel, Martin Mourigal, Haidong Zhou. 2019-12-24. Quantum versus Classical Spin Fragmentation in Dipolar Kagome Ice Ho3Mg2Sb3O14. https://doi.org/10.1103/physrevx.10.031069

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