Dynamical behavior of vortices introduced into a layered superconductor κ-(BEDT-TTF)2Cu(NCS) 2

Vortices penetrating κ-(BEDT-TTF) 2 Cu(NCS) 2 are interesting for its strongly two dimensional character. We investigated the behavior of vortices introduced by a dc-magnetic field through the shielding effect of the ac-magnetic field. For moderately strong ac-fields, we found an anomalous peak in the dc-field dependence of the shielding effect. The temperature dependence of the peak position is expressed as Hp = H 0 (Tc/T-1). It turned out that the peak appears at the dc-field where the effective pinning potential on vortices has its maximum. We have confirmed this by estimating the pinning potential from the relaxation of the shielding effect, which is caused by thermal creep of vortices and depends logarithmically on time.