Enhancement of superconducting state properties of Fe_0.994Ni_0.007Te_0.66Se_0.34 single crystal with increasing pressure: a correlation with pressure-induced crystallinity degradation

Abstract

Detailed investigations of Ni substituted Fe 0.94 Ni 0.007 Te 0.66 Se 0.34 and unsubstituted Fe 0.99 Te 0.66 Se 0.34 crystals were performed at ambient and under hydrostatic pressure in order to understand complex relationship between the structure, magnetism, and superconductivity in iron selenides. The investigations aimed at determining structural and superconducting state properties and studying their evolution under pressure up to 11 kbar. Comparison of Fe 0.99 Te 0.66 Se 0.34 , a material with much less developed phase separation, with FeTe 0.5 Se 0.5 , a material exhibiting well pronounced nanoscale phase separation, was also performed. Under ambient pressure the weakening of superconducting state properties was observed in Fe 0.994 Ni 0.007 Te 0.66 Se 0.34 crystal, with disorder introduced by Ni substitution, as compared with those in Fe 0.99 Te 0.66 Se 0.34. For Fe 0.994 Ni 0.007 Te 0.66 Se 0.34 , the X-ray diffraction studies have revealed a degradation of crystal quality under applied elevated pressure. Superconducting state properties of single phase Fe 0.99 Te 0.66 Se 0.34 crystal, such as upper and lower critical

The Impact of Hydrogenation on Structural and Superconducting Properties of FeTe0.65Se0.35 Single Crystals

“…Magnetic impurities may destroy local superconductivity-they can lead to a local decrease in superconducting carrier density and an increase in penetration depth, and thus a reduction of diamagnetic response. We already noticed small decreases of superconducting responses in superconducting FeTe0.5Se0.5, FeTe0.66Se0.34, and Fe0.994Ni0.007Te0.66Se0.34 when a degradation of crystal quality under applied elevated pressure was correlated with significant improvement of superconducting state properties [27]. After treatment with hydrogen at temperature of 250 °C, the Tc bulk decreases to about 9 K. Importantly, the M-H curve for the sample hydrogenated at 250 °C is completely different from that for pristine sample and for the samples hydrogenated at 180 and 200 °C.…”