V-I characteristics in the vicinity of the order-disorder transition in vortex matter -: art. no. 060503

The shape of the V-I characteristics leading to a peak in the differential resistance r(d)=dV/dI in the vicinity of the order-disorder transition in NbSe2 is investigated. r(d) is large when measured by dc current. However, for a small I-ac on a dc bias, r(d) decreases rapidly with frequency, even at a few hertz, and displays a large out-of-phase signal. In contrast, the ac response increases with frequency in the absence of dc bias. These surprisingly opposite phenomena and the peak in r(d) are shown to result from a dynamic coexistence of two vortex matter phases rather than from the commonly assumed plastic depinning.