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

TL;DR

This study uses a scanning Hall probe microscope to observe individual vortex motion in YBCO grain boundaries, revealing an extremely sharp dissipation onset with a high voltage-current exponent, challenging existing models.

Contribution

It provides the first direct measurement of single vortex dynamics along grain boundaries with femto-volt sensitivity, uncovering a novel dissipation behavior.

Findings

Sharp dissipation onset with V~I^290

Exponent n~290 independent of temperature and angle

Data inconsistent with current models

Abstract

We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBCO 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 femto-volt. We find a very sharp onset of dissipation with V~I^n 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.