Comment to the paper : Collapse of the vortex-lattice inductance and   shear modulus at the melting transition in untwinned YBa$_2$Cu$_3$O$_7$, by   Matl \QTR{em}{et al.}
  In a recent paper, Matl et al present a high-frequency study of the complex resistivity of a pinned vortex lattice in YBaCuO . They focus on the inductive-to-resistive transition which is investigated as a function of temperature at a constant field $B_0=2$ T, so that the transition is associated with the vanishing of vortex pinning strength. To our view, their conclusions rely on a rather brittle experimental body and the collapse of C66 results from an involved analysis of the finite frequency corrections to $\rho (\omega)$. These corrections are not necessary since the complex frequency spectrum has been previously interpreted by the two modes model, first proposed for low Tc materials. We think that it is more adequate to interpret the present data and should be at least considered. 
A.Pautrat, C. Goupil, Ch. Simon B. Pla\c{c}ais, P. Mathieu