Identification of the vortex glass phase by harmonics of the AC magnetic susceptibility

We compared the AC magnetic susceptibility behaviour for the vortex glass phase and for the creep phenomena with an inhomogeneous pinning potential. The temperature dependence of the harmonics of the susceptibility have been numerically simulated with these two models, and we studied them as a function of the frequency, in terms of Cole-Cole plots. From our analysis we show that it is possible to distinguish between the two different phases, because of their clear differences in the Cole-Cole plots behaviour with the frequency.Comment: 8 pages, 2 figures to be published on "The Journal of Physics and Chemistry of Solids

Quantum optics in the phase space - A tutorial on Gaussian states

In this tutorial, we introduce the basic concepts and mathematical tools needed for phase-space description of a very common class of states, whose phase properties are described by Gaussian Wigner functions: the Gaussian states. In particular, we address their manipulation, evolution and characterization in view of their application to quantum information.Comment: Tutorial. 23 pages, 1 figure. Updated version accepted for publication in EPJ - ST devoted to the memory of Federico Casagrand

A new method to detect the vortex glass phase and its evidence in YBCO

The evidence of the vortex glass phase has been obtained by analysing the nonlinear magnetic response of type-II superconductors. The method introduced here 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 identify the fingerprints of the magnetic behaviour in the vortex glass phase. These characteristics allowed the vortex glass phase to be distinguished from the other disordered phases, even those showing similar electrical properties. Finally, this method has been successfully applied to detecting the vortex glass phase in an YBCO bulk melt-textured sample