Dynamics of single vortices in grain boundaries: I-V characteristics on the femtovolt scale

Abstract

We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBa 2Cu3O6+δ thin films in the presence of an applied current. Detecting the motion of individual vortices allowed us to probe the current-voltage (I-V) characteristics of the grain boundary with voltage sensitivity below a femtovolt. We find a very sharp onset of dissipation with V ∞ In with an unprecedented high exponent of n≈290 that shows essentially no dependence on temperature or grain boundary angle. Our data have no straightforward explanation within the existing grain boundary transport models. © 2009 American Institute of Physics.