Evidence for possible interaction between CDW and magnetic vortices in 2H-NbSe2 : comparison with 2H-NbS2

We have performed vibrating reed (f-1 kHz) and ac susceptibility (f-800 kHz, i.e. RF penetration depth) measurements on superconducting 2H-NbSe 2 and 2H-NbS 2 in magnetic fields. For NbSe 2 , a low temperature dissipation peak is correlated with a dip in vibrating reed resonant frequency and peak in ac susceptibility, signifying softening of the flux line lattice; these features are not observed in NbS 2 . We suggest that the softening of the FLL is due to an interaction with the CDW, which does not occur in NbS 2