Quantum Spin Fragmentation in Kagome Ice Ho3Mg2Sb3O14*

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 Ho3Mg2Sb3O14 unites an ice-like magnetic degeneracy with quantum-tunneling terms generated by an intrinsic splitting of the Ho3+ ground-state doublet, realizing a frustrated transverse Ising model. Using neutron scattering and thermodynamic experiments, we observe a symmetry-breaking transition at 0.32 K to a remarkable quantum spin-fragmented states with strongly reduced ordered/local moment. Using exact diagonalization and mean-field calculation, we demonstrate that whereas the transverse field tends to drive the system into a spin-liquid state with zero on-site moment, the hyperfine interaction helps to stabilize the fragmented local moments. Our results establish that Ho3Mg2Sb3O14 realizes a quantum spin-fragmented state on the kagome lattice.