XY-like critical behavior of the thermodynamic and transport properties of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ in magnetic fields near ${\mathit{T}}_{\mathit{c}}$

The heat capacity, magnetization, and electrical conductivity of single-crystal samples of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ have been measured and are shown to support the existence of an intermediate critical regime in the vicinity of ${\mathit{T}}_{\mathit{c}}$, governed by the XY-like critical exponent ν≃2/3. Clear evidence is found for the divergence of the ohmic conductivity along the line ${\mathit{H}}_{\mathit{m}}$(T)∝(1-T/${\mathit{T}}_{\mathit{c}}$ ${)}^{2\nu }$, the vortex melting line. The glass exponents along that line satisfy ${\mathit{z}}_{\mathit{g}}$(${\nu }_{\mathit{g}}$-1)≃6.