Do superconductors have zero resistance in a magnetic field?
We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] 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.
Strachan
D R
DR
Center for Superconductivity Research, University of Maryland, College Park, Maryland 20742, USA.
Sullivan
M C
MC
Fournier
P
P
Pai
S P
SP
Venkatesan
T
T
Lobb
C J
CJ