The Pressure Effects on Electronic Structure of Iron Chalcogenide Superconductors FeSe_1-xTe_x (original) (raw)
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Iron-chalcogenide superconductor Fe$_{1.03}$Se$_{0.5}$Te$_{0.5}$ has been investigated under high pressure using synchrotron based x-ray diffraction and mid-infrared reflectance measurements at room temperature. Pressure dependence of the superconducting transition temperature (T$_c$) of the same sample has been determined by temperature-dependent resistance measurements up to 10 GPa. Although the high pressure orthorhombic phase ($\textit{Pbnm}$) starts emerging at 4 GPa, structural transition becomes clearly observable above 10 GPa. A strong correlation is observed between the Fe(Se,Te)$_{4}$ tetrahedral deformation in the tetragonal phase ($\textit{P4/nmm}$) and the sharp rise of T$_c$ up to sim\simsim4 GPa, above which T$_c$ is found to be almost pressure independent at least up to 10 GPa. A subtle structural modification of the tetragonal phase is noticed above 10 GPa, suggesting a structural transition with possible Fe$^{2+}$ spin-state transition. The evolution with pressure of t...
The substitution effects on electronic structure of iron selenide superconductors
Intermetallics, 2013
The influence of a partial substitution with S, Te, Co, Ni and Cu atoms on the electronic structure of the FeSe superconductor has been investigated within the density functional theory. The results of the supercell calculations reveal distinct changes of electronic structures of the substituted FeSe systems, which can be responsible for their superconducting properties. The replacement of Se atoms by Te or S ones yields imperfect nesting between the holelike and electronlike Fermi surface (FS) sheets, which enhances magnetic fluctuations responsible for superconducting pairing, thus leading to higher values of the superconducting critical temperatures. Meanwhile, the substitutions with transition-metal atoms for iron sites make more substantial changes of the FSs topology, since the holelike cylinders shrink at the cost of an enlargement of the electronlike ones. Thus, the superconducting pairing, driven by the nesting between these sheets, weakens and superconductivity disappears for a small percentage of dopants. The results support the idea of spin-fluctuation mediated superconductivity in iron chalcogenides. .pl (A. Ciechan), M.Winiarski@int.pan.wroc.pl (M.J. Winiarski), M.Samsel@int.pan.wroc.pl (M. Samsel-Czekała)
Strain effects on the electronic structure of the iron selenide superconductor
EPL (Europhysics Letters), 2012
The influence of various strains on crystal and electronic structures of superconducting FeSe has been studied ab initio. We consider changes in the Fermi surface nesting with a vector Q = (0.5, 0.5) × (2π/a) as crucial for rising superconductivity (SC) mediated by spin-fluctuations (SF). Our results indicate that the c-axis strained FeSe exhibits the most imperfect nesting, which enhances SF and, hence, also SC. In turn, the ab-plane compressive strain slightly weakens this nesting while the tensile strain destroys it completely. These findings are consistent with reported earlier experimental dependencies of superconducting transition temperatures on strain in FeSe thin films.
Physical Review B, 2009
FeSe with the PbO structure is a key member of the family of new high-Tc iron pnictide and chalcogenide superconductors, as while it possesses the basic layered structural motif of edge-sharing distorted FeSe4 tetrahedra, it lacks interleaved ion spacers or charge-reservoir layers. We find that application of hydrostatic pressure first rapidly increases Tc which attains a broad maximum of 37 K at ∼7 GPa (this is one of the highest Tc ever reported for a binary solid) before decreasing to 6 K upon further compression to ∼14 GPa. Complementary synchrotron X-ray diffraction at 16 K was used to measure the low-temperature isothermal compressibility of α-FeSe, revealing an extremely soft solid with a bulk modulus, K0 = 30.7(1.1) GPa and strong bonding anisotropy between inter-and intra-layer directions that transforms to the more densely packed β-polymorph above ∼9 GPa. The non-monotonic Tc(P ) behavior of FeSe coincides with drastic anomalies in the pressure evolution of the interlayer spacing, pointing to the key role of this structural feature in modulating the electronic properties. PACS numbers: 74.70.Dd, 74.25.Ha, 61.05.C-
Strain effects on the electronic structure of the FeSe0.5Te0.5 superconductor
Journal of Alloys and Compounds, 2013
The electronic structure of the strained FeSe 0.5 Te 0.5 superconductor has been investigated from first principles. Our calculation results indicate that the influence of hydrostatic, biaxial or uniaxial compressive stress on the density of states at the Fermi level is insignificant. The overall shape of the Fermisurface (FS) nesting function for FeSe 0.5 Te 0.5 at ambient pressure resembles that of its parent compound, FeSe, but under the ab-plane compressive strain. In these two systems, changes of their FSs under various stress conditions are qualitatively almost the same. However, in FeSe 0.5 Te 0.5 the intensity of the perfect Q = (0.5, 0.5) × (2π/a) nesting vector is more diminished. These findings are in good agreement with former experimental data and support the idea of spin-fluctuation mediated superconductivity in iron chalcogenides.
Reemerging superconductivity at 48 K across quantum criticality in iron chalcogenides
Arxiv preprint arXiv: …, 2011
Pressure plays an essential role in the induction 1 and control 2,3 of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effects has raised the superconducting transition temperature T C to a record high of 55 K in these materials 4,5. Analogous to the bell-shaped curve of T C dependence on chemical doping, pressure-tuned T C typically drops monotonically after passing the optimal pressure 1-3. Here we report the observations of an unexpected phenomenon in superconducting iron chalcogenides that after the T C dropped from the maximum of 32 K at 1 GPa and vanished (< 4 K) above 9.5 GPa, a second superconducting region with considerably higher T C than the first maximum suddenly reemerged above 11.5 GPa. The T C of the reemerging superconducting phase reaches 48.0-48.7 K for Tl 0.6 Rb 0.4 Fe 1.67 Se 2 , K 0.8 Fe 1.7 Se 2 and K 0.8 Fe 1.78 Se 2 , setting a new T C record for iron chalcogenide superconductors. The recent discoveries of superconductivity at 30-32 K in a new family of iron-based chalcogenide superconductors 6-9 A 1-x Fe 2-y Se 2 (A=K, Rb or Cs, with possible Tl substitution) bring new excitement to the field of superconductivity 10. Some of the most striking features of such superconductors include the unusually large magnetic moments up to 3.3 B per Fe atom and the Fe-vacancy ordering in the Fe square lattice 11. How superconductivity with such a high T C can exist on such a strong magnetic background remains perplexing 10. It has been established that the superconductivity in strongly correlated electronic systems can be dictated by their crystallographic structure, electronic charge, as well as orbital and spin degree of freedom, which in turn, can be manipulated by controlling parameters including pressure, magnetic field, and chemical composition 12-15. Pressure is a 'clean' way to tune basic electronic and structural properties without changing the chemistry. High-pressure studies are thus very useful in elucidating mechanisms of superconductivity as well as in searching for new high-T C
Pressure effect on superconductivity in FeSe0.5Te0.5
physica status solidi (b), 2016
Due to the simple layered structure, isostructural FeSe and FeSe 0.5 Te 0.5 are clue compounds for understanding the principal mechanisms of superconductivity in the family of Fe-based superconductors. High-pressure magnetic, structural and Mössbauer studies have been performed on single-crystalline samples of superconducting FeSe 0.5 Te 0.5 with T c = 13.5 K. Susceptibility data have revealed a strong increase of T c up to 19.5 K for pressures up to 1.3 GPa, followed by a plateau in the T c (p) dependence up to 5.0 GPa. Further pressure increase leads to a disappearance of the superconducting state around 7.0 GPa. X-ray diffraction and Mössbauer studies explain this fact by a tetragonal-to-hexagonal structural phase transition. Mössbauer parameters of the non-superconducting high-pressure phase indicate less covalency of Fe-Se bonds. Based on structural and susceptibility data we conclude about a common character of T c (p) diagrams for both FeSe and FeSe 0.5 Te 0.5 superconductors.
Journal of Physics: Condensed Matter, 2013
The local structure and the electronic properties of FeSe under hydrostatic pressure were studied by means of dispersive x-ray absorption measurements at the Fe K-edge. The pressure dependence of the x-ray absorption near edge structure features seems to follow the behavior of the superconducting transition temperature T c . The local structure, that has an important impact on the superconducting properties, appears to fall into two regimes: the pressure dependence of the Fe-Fe bond distance shows a clear change in the compressibility at p ∼ 5 GPa; in contrast, the Fe-Se bond distance decreases continuously with increasing pressure with a lower compressibility than the Fe-Fe bond. The results suggest that the pressure dependent changes in T c of FeSe are closely related to the changes in local structure.
Interrelation of superconductivity and magnetism in FeSe1−xTex compounds. Pressure effects
Low Temperature Physics, 2014
The effect of isotropic pressures P up to 5 kbar on the superconducting transition temperature T c of the FeSe 1Àx Te x system (x ¼ 0, 0.85, 0.88, 0.90) is studied. For the first time, a change in the sign of the effect of pressure on T c on going from FeSe to the tellurium-rich alloys is observed. This makes it possible to specify more precisely the form of the dependence of the pressure derivative dT c /dP on composition in this system. This dependence is compared with first principles calculations of the electron structure and magnetism of FeSe, FeTe, and FeSe 0.5 Te 0.5 as functions of pressure, as well as with our earlier experimental data on the effect of pressure on the magnetic susceptibility of the normal state in FeSe and FeTe. This comparison is indicative of a competitive interrelationship between superconductivity and magnetism in tellurium rich FeSe 1Àx Te x compounds. V C 2014 AIP Publishing LLC.[http://dx.