Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned YBa2Cu3O7 -: art. no. 214514

The complex resistivity (ρ) over cap(omega) of the vortex lattice in an untwinned crystal of 93-K YBa2Cu3O7 has been measured at frequencies omega/2pi from 100 kHz to 20 MHz in a 2-T field Hparallel toc, using a four-probe rf transmission technique that enables continuous measurements versus omega and temperature T. As T is increased, the inductance L-s(omega)=Im (ρ) over cap(omega)/omega increases steeply to a cusp at the melting temperature T-m, and then undergoes a steep collapse consistent with vanishing of the shear modulus c(66). We discuss in detail the separation of the vortex-lattice inductance from the "volume" inductance, and other skin-depth effects. To analyze the spectra, we consider a weakly disordered lattice with a low pin density. Close fits are obtained to rho(1)(omega) over 2 decades in omega. Values of the pinning parameter kappa and shear modulus c(66) obtained show that c(66) collapses by over 4 decades at T-m, whereas kappa remains finite.