Current-driven large density fluctuations of vortices and antivortices in the corbino disk

In the Meissner state just below the transition temperature, vortices and antivortices perpendicular to the sample plane move to the opposite directions in the presence of large transport current. In the Corbino disk (CD), where vortices are rotated in concentric circles by a radial current, one vortex can annihilate only by colliding with another vortex with opposite vorticity and, hence, large vortex-density fluctuations are expected. We have found unusual large voltage pulses that oscillate almost periodically in the Meissner state of thick amorphous MoxSi1-x films with the CD geometry. Both the period and width of the pulse are much larger than the characteristic time for free vortices to rotate in the circles. This result indicates that the voltage oscillation originates from large density fluctuations of vortices and antivortices.