Experimental signatures of emergent quantum electrodynamics in Pr                         2                         Hf                         2                         O                         7

Romain Sibille; Nicolas Gauthier; Han Yan; Monica Ciomaga Hatnean; Jacques Ollivier; Barry Winn; Uwe Filges; Geetha Balakrishnan; Michel Kenzelmann; Nic Shannon; Tom Fennell

doi:10.1038/s41567-018-0116-x

Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇

Romain Sibille, Nicolas Gauthier, Han Yan, Monica Ciomaga Hatnean, Jacques Ollivier, Barry Winn, Uwe Filges, Geetha Balakrishnan, Michel Kenzelmann, Nic Shannon, Tom Fennell

Direct Geometry

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Abstract

In a quantum spin liquid, the magnetic moments of the constituent electron spins evade classical long-range order to form an exotic state that is quantum entangled and coherent over macroscopic length scales ^1,2 . Such phases offer promising perspectives for device applications in quantum information technologies, and their study can reveal new physics in quantum matter. Quantum spin ice is an appealing proposal of one such state, in which the fundamental ground state properties and excitations are described by an emergent U(1) lattice gauge theory ^3-7 . This quantum-coherent regime has quasiparticles that are predicted to behave like magnetic and electric monopoles, along with a gauge boson playing the role of an artificial photon. However, this emergent lattice quantum electrodynamics has proved elusive in experiments. Here we report neutron scattering measurements of the rare-earth pyrochlore magnet Pr ₂ Hf ₂ O ₇ that provide evidence for a quantum spin ice ground state. We find a quasi-elastic structure factor with pinch points - a signature of a classical spin ice - that are partially suppressed, as expected in the quantum-coherent regime of the lattice field theory at finite temperature. Our result allows an estimate for the speed of light associated with magnetic photon excitations. We also reveal a continuum of inelastic spin excitations, which resemble predictions for the fractionalized, topological excitations of a quantum spin ice. Taken together, these two signatures suggest that the low-energy physics of Pr ₂ Hf ₂ O ₇ can be described by emergent quantum electrodynamics. If confirmed, the observation of a quantum spin ice ground state would constitute a concrete example of a three-dimensional quantum spin liquid - a topical state of matter that has so far mostly been explored in lower dimensionalities.

Original language	English
Pages (from-to)	711-715
Number of pages	5
Journal	Nature Physics
Volume	14
Issue number	7
DOIs	https://doi.org/10.1038/s41567-018-0116-x
State	Published - Jul 1 2018

Funding

We acknowledge the Institut Laue-Langevin (Grenoble, France) for the allocated beamtime. We acknowledge funding from the Swiss National Science Foundation (grant nos 200021_140862; 206021_139082; and 200021_138018). This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The work at ORNL was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC05-00OR22725. The work at the University of Warwick was supported by the EPSRC, UK, through grant EP/M028771/1. Additional neutron scattering experiments were carried out at the continuous spallation neutron source SINQ at the Paul Scherrer Institut at Villigen PSI in Switzerland.

Funders	Funder number
Office of Basic Energy Sciences	DE-AC05-00OR22725
U.S. Department of Energy
Office of Science
Engineering and Physical Sciences Research Council	EP/M028771/1
Japan Society for the Promotion of Science	18J10475
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung	200021_138018, 200021_140862, 206021_139082

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Sibille, R., Gauthier, N., Yan, H., Ciomaga Hatnean, M., Ollivier, J., Winn, B., Filges, U., Balakrishnan, G., Kenzelmann, M., Shannon, N., & Fennell, T. (2018). Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇ Nature Physics, 14(7), 711-715. https://doi.org/10.1038/s41567-018-0116-x

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title = " Experimental signatures of emergent quantum electrodynamics in Pr 2 Hf 2 O 7 ",

abstract = " In a quantum spin liquid, the magnetic moments of the constituent electron spins evade classical long-range order to form an exotic state that is quantum entangled and coherent over macroscopic length scales 1,2 . Such phases offer promising perspectives for device applications in quantum information technologies, and their study can reveal new physics in quantum matter. Quantum spin ice is an appealing proposal of one such state, in which the fundamental ground state properties and excitations are described by an emergent U(1) lattice gauge theory 3-7 . This quantum-coherent regime has quasiparticles that are predicted to behave like magnetic and electric monopoles, along with a gauge boson playing the role of an artificial photon. However, this emergent lattice quantum electrodynamics has proved elusive in experiments. Here we report neutron scattering measurements of the rare-earth pyrochlore magnet Pr 2 Hf 2 O 7 that provide evidence for a quantum spin ice ground state. We find a quasi-elastic structure factor with pinch points - a signature of a classical spin ice - that are partially suppressed, as expected in the quantum-coherent regime of the lattice field theory at finite temperature. Our result allows an estimate for the speed of light associated with magnetic photon excitations. We also reveal a continuum of inelastic spin excitations, which resemble predictions for the fractionalized, topological excitations of a quantum spin ice. Taken together, these two signatures suggest that the low-energy physics of Pr 2 Hf 2 O 7 can be described by emergent quantum electrodynamics. If confirmed, the observation of a quantum spin ice ground state would constitute a concrete example of a three-dimensional quantum spin liquid - a topical state of matter that has so far mostly been explored in lower dimensionalities.",

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Sibille, R, Gauthier, N, Yan, H, Ciomaga Hatnean, M, Ollivier, J, Winn, B, Filges, U, Balakrishnan, G, Kenzelmann, M, Shannon, N & Fennell, T 2018, ' Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇ ', Nature Physics, vol. 14, no. 7, pp. 711-715. https://doi.org/10.1038/s41567-018-0116-x

Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇ . / Sibille, Romain; Gauthier, Nicolas; Yan, Han et al.
In: Nature Physics, Vol. 14, No. 7, 01.07.2018, p. 711-715.

Research output: Contribution to journal › Article › peer-review

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AU - Winn, Barry

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Sibille R, Gauthier N, Yan H, Ciomaga Hatnean M, Ollivier J, Winn B et al. Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇ Nature Physics. 2018 Jul 1;14(7):711-715. doi: 10.1038/s41567-018-0116-x

Experimental signatures of emergent quantum electrodynamics in Pr ₂ Hf ₂ O ₇

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