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Triplet excitations in the frustrated spin ladder Li2Cu2O(SO4)2

Abstract : Magnetic excitations of the recently discovered frustrated spin-1/2 two-leg ladder system Li2Cu2O(SO4)2 are investigated using inelastic neutron scattering, magnetic susceptibility and in-frared absorption measurements. Despite the presence of a magnetic dimerization concomitant with the tetragonal-to-triclinic structural distortion occurring below 125 K, neutron scattering experiments reveal the presence of dispersive triplet excitations above a spin gap of ∆ = 10.6 meV at 1.5 K, a value consistent with the estimates extracted from magnetic susceptibility. The likely detection of these spin excitations in infrared spectroscopy is explained by invoking a dynamic Dzyaloshinskii-Moriya mechanism in which light is coupled to the dimer singlet-to-triplet transition through an optical phonon. These results are qualitatively explained by exact diagonalization and higher-order perturbation calculations carried out on the basis of the dimerized spin Hamiltonian derived from first-principles.
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O. Vaccarelli, A. Honecker, P. Giura, K. Beneut, B. Fåk, et al.. Triplet excitations in the frustrated spin ladder Li2Cu2O(SO4)2. Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2019, 99 (6), pp.064416. ⟨10.1103/PhysRevB.99.064416⟩. ⟨hal-02340199⟩

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