Why can’t experimentalists agree on the superconducting critical exponents?

The scaling analysis of voltage vs. current curves has been an invaluable tool in the study of the normal-superconducting phase transition, both in zero-field and in the vortex–glass transition in a field. However, we have recently shown that the conventional scaling analysis is too flexible to uniquely determine the critical parameters. We have also shown that extrinsic effects such as current noise, small magnetic fields (for the zero-field transition), and finite size effects can obscure and even destroy the three-dimensional phase transition. These factors have led to the wide range of values for the dynamic critical exponent z   and the static critical exponent νν reported in the literature, even for the zero-field transition. We have developed a criterion that removes the flexibility in the scaling analysis and have conducted experiments to eliminate the extrinsic effects described above. Our results show that finite size effects, which obscure the phase transition in thin films, are absent in bulk, untwinned, single crystals.