2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/18798This is a Comment on an experimental paper by Zhukov et al. on the issue of a lower critical point, seen only in YBCO clean samples, of the first order transition line implying a vortex liquid-freezing. An explanation with a firm theoretical basis of the strange doping dependence of the lower critical point is presented.1 pageSuperconductivitytext