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arXiv · 1902.02798

Triplet excitations in the frustrated spin ladder Li$_2$Cu$_2$O(SO$_4$)$_2$

Ornella Vaccarelli·Andreas Honecker·Paola Giura·Keevin Béneut·Björn Fåk·Gwenaëlle Rousse·Guillaume Radtke
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Abstract

Magnetic excitations of the recently discovered frustrated spin-1/2 two-leg ladder system Li$_2$Cu$_2$O(SO$_4$)$_2$ are investigated using inelastic neutron scattering, magnetic susceptibility and infrared 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 $Δ= 10.6$ 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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Ornella Vaccarelli, Andreas Honecker, Paola Giura, Keevin Béneut, Björn Fåk, Gwenaëlle Rousse, Guillaume Radtke. 2019-02-07. Triplet excitations in the frustrated spin ladder Li$_2$Cu$_2$O(SO$_4$)$_2$. https://doi.org/10.1103/physrevb.99.064416

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