A vortex solid-to-liquid transition with fully anisotropic scaling

The vortex solid-to-liquid transition has been studied in heavy ion irradiated untwinned single crystals of YBa₂Cu₃O _7-δ with an inclined applied magnetic field. For magnetic fields tilted at angles about 45° away from the columnar defects, we find that the electric resistivity in the vortex liquid regime approaches zero with power laws in the reduced temperature T - T_c that have different exponents in all three spatial directions. Since the symmetry in the problem has been broken in two non-collinear directions by i) the direction of the columnar defects and ii) the direction of the applied magnetic field, our findings give evidence for a new type of critical behavior with fully anisotropic critical exponents. A possible view of the vortex topology for the transition is also suggested.