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Continuum of Quantum Fluctuations in a Three-Dimensional S = 1 Heisenberg Magnet



K. W. Plumb, Hitesh J. Changlani, A. Scheie, Shu Zhang, J. W. Krizan, Jose Rodriguez Rivera, Yiming Qiu, B. Winn, R. J. Cava, Collin L. Broholm


Spin liquids are a fundamentally new phase of matter that cannot be described by a broken symmetry and have no order parameter. While the quantum entanglement that characterizes a quantum spin liquid is not directly accessible to any current measurement technique, the spin liquid can reveal itself indirectly through the character of emergent quasi-particles that it may support. A key signature of a spin liquid are deconfined fractionalized excitations that appear as a broad structured continuum in the dynamic structure factor accessible by neutron scattering. In magnetic materials where magnetic interactions are confined to one or two-dimensions this is the celebrated continuum of chargeless fermionic quasiparticles called spinions. So far, such a continuum has not been observed in a three-dimensional magnet. The antiferromagnetic Heisenberg model on a pyrochlore lattice may support a three dimensional spin liquid in the quantum limit, but no suitable model system has been examined with the relevent tools. Here, we provide evidence for fractional magnetic excitations in a new S = 1 Heisenberg antiferromagnet NaCaNi2F7. Through measurements of the magnetic specific heat and dynamic structure factor we show that NaCaNi2F7 realizes the antiferromagnetic Heisenberg model on a pyrochlore lattice. Below T = 3.6 K 10% of the available magnetic spectral weight is frozen leaving the remainder in a quantum fluctuating state. The inelastic neutron scattering measurements reveal a separation of energy scales wherein measurements probing the static spin correlations are sensitive to the glassy physics, while those probing dynamic correlations expose a structured continuum of magnetic excitations that is consistent with fractionalized quasiparticles.
Nature Physics


continuum magnetic excitation, neutron scattering


Plumb, K. , Changlani, H. , Scheie, A. , Zhang, S. , Krizan, J. , Rodriguez Rivera, J. , Qiu, Y. , Winn, B. , Cava, R. and Broholm, C. (2019), Continuum of Quantum Fluctuations in a Three-Dimensional S = 1 Heisenberg Magnet, Nature Physics, [online], (Accessed December 7, 2023)
Created December 31, 2018, Updated October 12, 2021