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We have measured voltage-current characteristics for YBa2Cu3O7 thin films in magnetic fields from 5 T to ambient, including some in the millitesla range. In all cases, the resistivity-current density isotherms can be separated into two classes: those which exhibit upward curbature, and have constant resistivity at low currents, and those which exhibit downward curvature at all currents. These two classes of isotherms are separated by a field-dependent temperture Tg. For each field, the isotherms scale in a manner consistent with a three dimensional vortex-liquid to vortex-glass phase transition. The region that can be scaled is several kelving at 5 T and narrows with decreasing field. The low-current resistivity above Tg varies as |1-T/Tg|^s with s≈7.4 at all fields, but the critical scaling exponentsz z and v become fileld dependent below about 10 mT.


Article published in Physical Review B, 41, pp 6890-6894 (1994).

© 1994 The American Physical Society


DOI: 10.1103/PhysRevB.49.6890

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