  The Vortex Glass phase has been unequivocally identified by analyzing the non
linear magnetic response of type II superconductors. The method here
introduced, more effective than the study of direct transport measurements, is
based on a combined frequency dependence analysis of the real and imaginary
part of the 1st and 3rd harmonics of the AC magnetic susceptibility. The
analysis has been performed by taking into account both the components and the
Cole-Cole plots (i.e. the imaginary part as a function of the real part).
Numerical simulations have been used to individuate the fingerprints of the
magnetic behaviour in the Vortex Glass phase. These characteristics allowed to
distinguish the Vortex Glass phase from the other disordered phases, even those
showing similar electrical properties. Finally, this method has been
successfully applied to detect the Vortex Glass Phase in an YBCO bulk
melt-textured sample.
