Vortex glass and lattice melting transitions in a YNi2B2C single crystal.

Abstract

The mixed state of the weakly disordered superconductor ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ is found to be similar to that of high- ${T}_{c}$ materials due to its large fluctuations. The very sharp resistive transition with a kink and the S-shaped $I\ensuremath{-}V$ curve appear below $H\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}$ 1 T indicating a lattice melting transition. The scaling behavior of the vortex glass transition in $R\ensuremath{-}T$ and $I\ensuremath{-}V$ curves for $H\ensuremath{\ge}2$ T is observed with critical exponents $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.23\ifmmode\pm\else\textpm\fi{}0.02$ and $z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5.46\ifmmode\pm\else\textpm\fi{}0.32$, which are field independent. The vortex solid state changes from the vortex lattice at low fields to the vortex glass at high fields due to a field-enhanced pinning effect. The type of multicriticality is not yet conclusive.