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  Xu, J.; Benton, O.; Islam, A.T.M.N.; Guidi, T.; Ehlers, G.; Lake, B.: Order out of a Coulomb Phase and Higgs Transition: Frustrated Transverse Interactions of Nd₂Zr₂O₇. Physical Review Letters 124 (2020), p. 097203/1-6

10.1103/physrevlett.124.097203
Open Access Version

Abstract:
The pyrochlore material Nd2Zr2O7 with an “all-in-all-out” (AIAO) magnetic order shows novel quantum moment fragmentation with gapped flat dynamical spin ice modes. The parametrized spin Hamiltonian with a dominant frustrated ferromagnetic transverse term reveals a proximity to a U(1) spin liquid. Here we study the magnetic excitations of Nd2Zr2O7 above the ordering temperature (TN) using high-energy-resolution inelastic neutron scattering. Wefind strong spin ice correlations at zero energy with the disappearance of gapped magnon excitations of the AIAO order. It seems that the gap to the dynamical spin ice closes above TN and the system enters a quantum spin ice state competing with and suppressing the AIAO order. Classical Monte Carlo simulations, molecular dynamics, and quantum boson calculations support the existence of a Coulombic phase above TN. Our findings relate the magnetic ordering of Nd2Zr2O7 with the Higgs mechanism and provide explanations for several previously reported experimental features.