Fyzikální ústav Akademie věd ČR

The thermally activated quantum turbulence in He II has been studied, in a canal with superfluid holes not allowing the normal component of a finite viscosity to flow through. Thus, the turbulence in the canal was generated by a longitudinal flow of the pure superfluid component. Besides the already in literature described stationary state of the flow, we discovered a new turbulent state in which the density of quantum vortices is proportional to the transport superfluid velocity, with a parabolic velocity profile like in a classical viscous liquid flow.

We have participated in study of electromagnetic properties of topic bulk high-T_c superconductors of the (Nd,Eu,Gd)BaCuO composition in which a tiny doping by Nb, Mo or Ti oxides leads to a substantial critical current density enhancement. In the composite doped by Nb₂O₅ the critical current density, J_c, reached the record values of 925 kA/cm² (65 K), both in the remnant state and at 4.5 T, and 100 kA/cm² at the self-field at 90 K [1].

The developed technique is based on the idea of optimization of earlier known magnetic hysteresis methods. Instead of collecting the usable information from measurement of the classical major hysteresis loop and keeping under surveillance dependence of its traditional parameters (coercive force, remanence, and saturation magnetization) on structural variations, MAT gets its test parameters from the complex set of minor hysteresis loops.