Wannier states and spin supersolid physics in the triangular antiferromagnet K2Co(SeO3)2

M. Zhu; Leandro M. Chinellato; V. Romerio; N. Murai; S. Ohira-Kawamura; Christian Balz; Z. Yan; S. Gvasaliya; Yasuyuki Kato; C. D. Batista; A. Zheludev

doi:10.1038/s41535-025-00791-2

Wannier states and spin supersolid physics in the triangular antiferromagnet K₂Co(SeO₃)₂

M. Zhu
, Leandro M. Chinellato
, V. Romerio
, N. Murai
, S. Ohira-Kawamura
, Christian Balz
, Z. Yan
, S. Gvasaliya
, Yasuyuki Kato
, C. D. Batista
, A. Zheludev

Direct Geometry

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

6 Scopus citations

Abstract

We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K₂Co(SeO₃)₂ under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.

Original language	English
Article number	74
Journal	npj Quantum Materials
Volume	10
Issue number	1
DOIs	https://doi.org/10.1038/s41535-025-00791-2
State	Published - Dec 2025

Funding

We are grateful to M. E. Zhitomirsky for directing us to relevant prior literature and to A. Läuchli for illuminating discussions. We have incorporated new references to appropriately acknowledge these contributions. The authors are grateful to Hao Zhang for advice on using Sunny.jl. We thank James Neuhaus for the useful discussion in the setup of SmoQyDEAC.jl. This work was Supported by a MINT grant of the Swiss National Science Foundation. Data at J-PARC were collected in Experiment no. 2023B0161. Experiments at the ISIS Pulsed Neutron and Muon Source were supported by a beamtime allocation from the Science and Technology Facilities Council under proposal no. RB2320138. L.M.C. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.

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title = "Wannier states and spin supersolid physics in the triangular antiferromagnet K2Co(SeO3)2",

abstract = "We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K2Co(SeO3)2 under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.",

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AU - Zhu, M.

AU - Chinellato, Leandro M.

AU - Romerio, V.

AU - Murai, N.

AU - Ohira-Kawamura, S.

AU - Balz, Christian

AU - Yan, Z.

AU - Gvasaliya, S.

AU - Kato, Yasuyuki

AU - Batista, C. D.

AU - Zheludev, A.

PY - 2025/12

Y1 - 2025/12

N2 - We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K2Co(SeO3)2 under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.

AB - We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K2Co(SeO3)2 under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.

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Wannier states and spin supersolid physics in the triangular antiferromagnet K₂Co(SeO₃)₂

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