Scaling of vortex transport properties in high-temperature superconductors

High current-carrying capability in c-axis-oriented superconducting MgB2 thin films

In high-quality c-axis-oriented MgB2 thin films, we observed high critical current densities ( J(c)) of approximately 16 MA/cm(2) at 15 K under self-fields comparable to those of cuprate high-temperature superconductors. The extrapolated value of J(c) at 5 K was estimated to be approximately 40 MA/cm(2). For a magnetic field of 5 T, a J(c) of approximately 0.1 MA/cm(2) was detected at 15 K, suggesting that this compound would be a very promising candidate for practical applications at high temperature and lower power consumption. The vortex-glass phase is considered to be a possible explanation for the observed high current-carrying capability.

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.

Experimental evidence for the vortex glass phase in untwinned, proton irradiated YBa2Cu3O7-delta

We report on magnetoresistance measurements of the effects of 9 MeV proton irradiation on a clean, untwinned single crystal of YBa2Cu3O7-delta. For the first time, evidence for a vortex glass transition is detected in an untwinned single crystal of YBa2Cu3O7-delta with induced pointlike disorder, in which the first order vortex melting transition is completely suppressed after proton irradiation. Our results suggest that a sufficiently high pinning disorder is required in order for the vortex glass phase to be observed.