Evolution of vortex matter, phase diagram, and upper critical field in the FeSe<inf>1-x </inf>S<inf>x</inf>system

We present a comprehensive study of vortex matter in the FeSe1-x S x system with various doping degree. The influence of sulphur substitution on peak effect occurrence is studied. Additionally, we study a possible vortex liquid-vortex glass/lattice transition and find an evidence that the vortex liquid-vortex glass phase transition in FeSe1-x S x has a quasi two-dimensional nature. We investigate the upper critical field behaviour in FeSe1-x S x system, and found that the upper critical field is higher than that predicted by the Werthamer-Helfand-Hohenberg (WHH) model, whereas its temperature dependence could be fitted within a two-band framework. Finally, a detailed H-T phase diagram is presented