Positron lifetime change effect during YBa2Cu3O7-δ transition in superconducting state and positronium ortho-para conversion in microcavity

Temperature dependence τ(T) in Tc region is investigated using YBa2Cu3O7-δ ceramic samples. It is ascertained that the effect of τ(T) change near Tc in these substances depends on the method of their preparation. Interpretation of this effect based on the application of the Anderson magnetic impurity model is proposed. In this case positronium is under 'magnetic impurity' which means a similar state produced by positron captured by microcavity in the crystal lattice. Such positronium atom interacts actively with the electron medium surrounding the cavity. 45 refs.; 2 figs