Large vortex-density fluctuations induced by current in the Corbino-disk

We have studied the vortex dynamics driven by the constant current I in the Meissner phase of a thick amorphous MoxSi1−x film with the Corbino-disk contact geometry. In the certain I region we have observed unusual large voltage pulses that oscillate almost periodically with a period t0 larger than ∼15 s and with the pulse width tw in the range 5-10 s. With increasing I, t0 initially decreases and then increases. Over the whole I region where the oscillation of V(t) is observed, both t0 and tw are much longer than the characteristic time for free vortices to rotate in the circles. At high I a small peak(s) or cusp-like structure exceeding the normal-state voltage appears on the top (plateau) region of the pulses. These results indicate that the observed voltage pulses originate from large vortex-density fluctuations of moving vortices.