Structural and optical investigations of Fe_1.03Se_0.5Te_0.5under high pressure

Abstract

Optimally doped iron-chalcogenide superconductor Fe1.03Se0.5Te0.5 has been investigated under high pressures using synchrotron-based x-ray diffraction and mid-infrared reflectance measurements at room temperature. The superconducting transition temperature (Tc) of the same sample has been determined by temperature-dependent resistance measurements up to 10 GPa. The tetragonal phase (P4/nmm) is found to exist in phase-separated states where both the phases have remarkably high compressibility. A first-order structural transition to the orthorhombic phase (Pbnm) is reported above 10 GPa. For the tetragonal phase, a strong correlation is observed between the Fe(Se,Te)4 tetrahedral deformation and the sharp rise of Tc up to ∼ 4 GPa, above which Tc shows marginal pressure dependence at least up to 10 GPa. The evolution with pressure of the optical conductivity shows that with increasing pressure the tetragonal phase approaches towards a conventional metallic state. Above ∼ 6 GPa, the Drude term reduces drastically, indicating poor metallic character of the high-pressure orthorhombic phase.

Superconducting Properties of F e S e 0.5 T e 0.5 Under High Pressure

“…Coherence length also is increased by about 400% at P = 158 MPa. According to our experiments, and others, pressure strongly affect the superconducting parameters and these changes can be attributed not only to increment of T C but to additional factors, as crystal parameters and structural changes, etc [17]. In our investigation, we noticed that the T C , critical fields and su- perconducting parameter are very sensitive to pressure, being a clear sign that this compound presents unconventional superconductivity [37].…”

“…On the other hand, it was observed that F eSe 0.5 T e 0.5 increased its T C to 26 K at P = 2 GPa while higher pressures produces structural transitions to a monoclinic symmetry that decreases T C [13][14][15]. Moreover at P = 11.5 GPa the compound changes into an amorphous phase [16,17]. In a recent report Pietosa et al, studied the pressure effects on the critical fields up to 1.04 GPa founding no important variations on the behavior of the dH C2 /dT , concluding that the observed changes on the upper critical field was related only to changes of T C [18].…”

Enhancement of superconducting state properties of Fe0.994Ni0.007Te0.66Se0.34 single crystal with increasing pressure: a correlation with pressure-induced crystallinity degradation

“…The crystal structure of Fe 0.994 Ni 0.007 Te 0.66 Se 0.34 was identified as that of anti-PbO type, the quality was insufficient for studies of structure details. Identification of this phase is in line with the results of studies using X-ray diffraction [36,37] and other methods [38][39][40],…”

Superconductivity at 25 K under Hydrostatic Pressure for FeTe 0 . 5 Se 0 . 5 Superconductor

“…The FeTe 1-x Se x chalcogenide system has the simplest crystal structure among the other iron-based superconductors that gives the positive discrimination to its experimental and theoretical studies related to on site chemical substitution and the impact of high pressures [15,16]. The impact of high pressure on FeSe 1-x Te x compounds showed that the crystal structure change from tetragonal (P4/nmm) phase to the orthorhombic (Pbnm) at high pressures and low temperatures [17][18][19]. Also the pressure dependent superconducting properties have been studied for the FeTe 0.5 Se 0.5 system, which showed the improvement in T c from 14K to 22K for the pressure of 25.3kbar [20].…”