3D XY and lowest Landau level fluctuations in deoxygenated YBa2Cu3O7-delta thin films

Conductivity measurements reflect vortex solid melting in YBa2Cu3O7-delta films. Field-independent glass exponents nu(g) similar or equal to 1.9 and z(g) similar or equal to 4.0 describe the transition T-g(H) for 0 < H less than or equal to 26 T. At low fields, 3D XY exponents nu(XY) similar or equal to 0.63 and z(XY) = 1.25 are also observed, with z(XY) smaller than expected. These compete with glass scaling according to multicritical theory. A predicted power-law form of T-g(H) is observed for 0.5T(c) < T-g < T-c. For T-g < 0.5T(c), 3D XY scaling fails, but a self-consistent lowest Landau level analysis becomes possible, obtaining T-c2(H) with positive curvature.