Hydrostatic pressure-induced huge enhancement of critical current density and flux pinning in Fe1−xCoxSe0.5Te0.5 single crystals

Abstract

We performed a systematic study of the hydrostatic pressure (HP) effect on the supercon-ducting transition temperature (Tc), critical current density (Jc), irreversibility field (Hirr), upper critical field (Hc2), and flux pinning mechanism in un-doped and 3 at.% Co-doped FeSe0.5Te0.5 crystals. We found that Tc is increased from 11.5 to 17 K as HP increases from 0 to 1.2 GPa. Remarkably, the Jc is significantly enhanced by a factor of 3 to 100 for low and high temperature and field, and the Hirr line is shifted to higher fields by HP up to 1.2 GPa. Based on the collective pinning model, the δl pinning associated with charge-carrier mean free path fluctuation is responsible for the pinning mechanism of Fe1−xCoxSe0.5Te0.5 samples with or without pressure. A comprehensive vortex phase diagram in the mixed state is constructed and analysed for the 3 at.% Co-doped sample.