Journal
NATURE COMMUNICATIONS
Volume 12, Issue 1, Pages -Publisher
NATURE RESEARCH
DOI: 10.1038/s41467-021-23851-0
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Funding
- European Research Council under the European Union's Horizon 2020 research and innovation programme [788814]
- Lincoln College
- University of Oxford
- Royal Society University Research Fellowship
- National Science Foundation [NSF PHY-1748958]
- Science and Technology Facilities Council
- European Research Council (ERC) [788814] Funding Source: European Research Council (ERC)
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Recent theoretical proposals suggest that cobaltates with edge-sharing octahedral coordination may have significant bond-dependent exchange couplings, providing a platform to study physics beyond 4d and 5d materials in 3d ions. Experimental data and theoretical analysis in the stacked honeycomb magnet CoTiO3 demonstrate the presence of a spectral gap and bond-dependent anisotropic couplings, suggesting the existence of a quantum order-by-disorder mechanism. Additionally, the observation of a universal winding of scattering intensity in angular scans indicates non-trivial topology of the quasiparticle wavefunction near nodal points in momentum space.
Recent theoretical proposals have argued that cobaltates with edge-sharing octahedral coordination can have significant bond-dependent exchange couplings thus offering a platform in 3d ions for such physics beyond the much-explored realisations in 4d and 5d materials. Here we present high-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO3 revealing the presence of a finite energy gap and demonstrate that this implies the presence of bond-dependent anisotropic couplings. We also show through an extensive theoretical analysis that the gap further implies the existence of a quantum order-by-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations. Our data also provide an experimental observation of a universal winding of the scattering intensity in angular scans around linear band-touching points for both magnons and dispersive spin-orbit excitons, which is directly related to the non-trivial topology of the quasiparticle wavefunction in momentum space near nodal points. It was suggested that some 3d materials display bond-dependent exchange interactions, leading to exotic many-body effects. Here, using inelastic neutron scattering, the authors reveal such interactions in the stacked honeycomb magnet CoTiO3 and show how they induce a spectral gap and affect the Dirac magnon band structure.
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