Is there a vortex-glass transition in high-temperature superconductors?

We show that DC voltage versus current measurements of a YBCO micro-bridge in a magnetic field can be collapsed onto scaling functions proposed by Fisher, Fisher, and Huse, as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.