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 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.
@article{arxiv.1902.02798,
title = {Triplet excitations in the frustrated spin ladder Li$_2$Cu$_2$O(SO$_4$)$_2$},
author = {Ornella Vaccarelli and Andreas Honecker and Paola Giura and Keevin Béneut and Björn Fåk and Gwenaëlle Rousse and Guillaume Radtke},
journal= {arXiv preprint arXiv:1902.02798},
year = {2019}
}
Comments
to appear in Phys. Rev. B, 10 pages including 7 figure (supplemental series provided as ancillary files)