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Magnetoelastic coupling and spin excitations in the spin-gap system (VO)$_2$P$_2$O$_7$: A Raman scattering study

M. Grove·P. Lemmens·G. Güntherodt·B. C. Sales·F. Büllesfeld·W. Assmus
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Abstract

Single crystals of the spin-gap system $\rm (VO)_2P_2O_7$ have been investigated by means of Raman scattering. At temperatures below T=75 K~$\approx 2Δ_{01}({\bf k}=0)$, with $Δ_{01}$ the singlet-triplet gap, a shoulder appears at 47 cm$^{-1}$. An analysis of the polarization selection rules and the temperature dependence of the scattering intensity leads to its identification as a singlet bound state with very small binding energy. Therefore in contrast to recent theoretical models the importance of frustration for this compound must be rejected. The observation of a strong anharmonicity of three phonons with energies close to $Δ_{01}$ at the zone boundary and additional quasielastic light scattering, however, both point to a strong spin-phonon coupling in this system. We propose this coupling to be the origin of the second bound triplet state observed in recent neutron scattering experiments.

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M. Grove, P. Lemmens, G. Güntherodt, B. C. Sales, F. Büllesfeld, W. Assmus. 1999-12-03. Magnetoelastic coupling and spin excitations in the spin-gap system (VO)$_2$P$_2$O$_7$: A Raman scattering study. https://doi.org/10.1103/physrevb.61.6126

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