Pressure-induced effects on the structure of the FeSe superconductor

Abstract

A polycrystalline sample of FeSe, which adopts the tetragonal PbO-type structure (P 4 /nmm) at room temperature, has been prepared using solid state reaction. We have investigated pressure-induced structural changes in tetragonal FeSe at varying hydrostatic pressures up to 0.6 GPa in the orthorhombic (T = 50 K) and tetragonal (T = 190 K) phases using high resolution neutron powder diffraction. We report that the structure is quite compressible with a bulk modulus ≈ 31 GPa to 33 GPa and that the pressure response is anisotropic with a larger compressibility along the c-axis. Key bond angles of the SeFe 4 pyramids and FeSe 4 tetrahedra are also determined as a function of pressure.

Electronic and magnetic phase diagram of β-Fe1.01Se with superconductivity at 36.7 K under pressure

“…The transition to linear resistivity is very sharp in much of the pressure range, but undergoes a change in concavity making precise assignment of the transition temperature at 0.8 GPa difficult. At ambient pressure this change in the resistance, from linear behavior below to normal conductivity above the transition, is accompanied by the change of the structure from tetragonal to orthorhombic symmetry [11,12,17]. Although this may be the case under pressure as well, we currently have no information on this aspect of the pressure dependent behavior of this system.…”

“…These properties suggest that the superconductivity in the iron arsenides is unconventional, with electron pairing possibly mediated by magnetic interactions. More recently, superconductivity has been reported at 8.5 K [9], increasing up to 27 K under pressure [10], in the structurally related material iron selenide [11,12]. Iron selenide and the iron arsenides share a common structural motif, containing Fe 2 X 2 (X=As, Se) layers of edge-shared FeX 4 tetrahedra, suggesting that the mechanism of superconductivity may be the same in both families in spite of the low T c for the selenide.…”

Strain effects on electronic structure and superconductivity in the iron telluride

“…Interestingly, the strain effects on SC in FeSe and FeTe are opposite. In FeSe tensile strain strongly decreases T c [4] but all kinds of compressive strain lead to an increase of its T c [4,5,6,7,8,9,10,11,12,13]. The influence of strain on SC of iron chalcogenides is somewhat related to the changes of tetrahedral coordination of Fe atoms [10,5,12].…”

Magnetic properties of novel FeSe(Te) superconductors

“…Also the large pressure effect on transition temperature was later observed [2][3][4] with T c ≈ 37 K at pressures P ≈ 9 GPa, indicating that FeSe 1−x is actually a high temperature superconductor. Therefore, the superconducting FeSe 1−x compound has attracted considerable attention and is a subject of intensive studies for the last years [5][6][7][8][9][10][11][12] . The structural simplicity of FeSe favors experimental and theoretical studies of chemical substitution and high pressure effects, which are aimed at promoting a better understanding of a mechanism of the superconductivity.…”