It is carried out in this research work an experimental and theoretical study of a practically unknown phenomenon in high temperature polycrystalline superconductors (SAT): the relaxation in time of critical transport current in presence of magnetic fields. This phenomenon could have relevant consequences for possible applications (mainly of electric power transmission). For this reason, it is important to know it thoroughly. That is why it was created a theoretical phenomenological model based on previous studies carried out by the work group in the last ten years, which explains quantitatively or semi-quantitatively all the experimental results that were obtained. Their precision and rigor are at first level, from both the instrumental point of view, and the used materials' point of view. On one hand, the measuring device --completely created and adjusted in Cuba-- is one of a kind. On the other hand, besides being examined SAT from YBCO system, samples of HgBCCO system are also studied, which has a critical temperature record at world level.

The scientific-social impact is very high and it creates a path in the understanding of an important aspect in high temperature superconductivity of polycrystalline material, with potential relevance for the applications. It is a remarkable contribution of Cuban science. This is demonstrated by its publication in Physical Review B prestigious magazine characterized by a rigorous arbitration, and also because it is mentioned in High Tc Update bulletin, published by the University of Iowa (USA), main reference in the field of superconductivity during the last decade.

The unit and coherence of the results drove to the group of authors to carry out a single publication, instead of dividing the work in two or three parts. However, it should be noticed that this work is, to a large extent, a result obtained after dozens of publications in the subject, some of which appear as references of the same article previously mentioned.