Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5

Iron-chalcogenide single crystals with the nominal composition FeSe0.5Te0.5 and a transition temperature of Tc�14.6 K were synthesized by the Bridgman method. The structural and anisotropic superconducting properties of those crystals were investigated by means of single crystal x-ray and neutron powder diffraction, superconducting quantum interference device and torque magnetometry, and muon-spin rotation (�SR). Room temperature neutron powder diffraction reveals that 95% of the crystal volume is of the same tetragonal structure as PbO. The structure refinement yields a stoichiometry of Fe1.045Se0.406Te0.594. Additionally, a minor hexagonal Fe7Se8 impurity phase was identified. The magnetic penetration depth � at zero temperature obtained by means of �SR was found to be �ab(0)=491(8) nm in the ab plane and �c(0)=1320(14) nm along the c axis. The zero-temperature value of the superfluid density �s(0)��−2(0) obeys the empirical Uemura relation observed for various unconventional superconductors, including cuprates and iron pnictides. The temperature dependences of both �ab and �c are well described by a two-gap s+s-wave model with the zero-temperature gap values of ΔS(0)=0.51(3) meV and ΔL(0)=2.61(9) meV for the small and the large gap, respectively. The magnetic penetration depth anisotropy parameter ��(T)=�c(T)/�ab(T) increases with decreasing temperature, in agreement with ��(T) observed in the iron-pnictide superconductors. © 2010 The American Physical Society DOI: https://doi.org/10.1103/PhysRevB.81.224520 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-45334 Accepted Version Originally published at: Bendele, M; Weyeneth, S; Puzniak, R; Maisuradze, A; Pomjakushina, E; Conder, K; Pomjakushin, V; Luetkens, H; Katrych, S; Wisniewski, A; Khasanov, R; Keller, H (2010). Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5.PhysicalReview.B, CondensedMatterandMaterialsPhysics, 81(22) : 224520. DOI: https://doi.org/10.1103/PhysRevB.81.224520 PREPRINT (April 7, 2010) Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5 M. Bendele, 2, ∗ S. Weyeneth, R. Puzniak, A. Maisuradze, E. Pomjakushina, K. Conder, V. Pomjakushin, H. Luetkens, S. Katrych, A. Wisniewski, R. Khasanov, and H. Keller Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL-02-668 Warsaw, Poland Laboratory for Developments and Methods, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland Laboratory for Neutron Scattering, ETHZ & PSI, CH-5232 Villigen PSI, Switzerland Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zürich, Switzerland Iron-chalcogenide single crystals with the nominal composition FeSe0.5Te0.5 and a transition temperature of Tc ' 14.6 K were synthesized by the Bridgman method. The structural and anisotropic superconducting properties of those crystals were investigated by means of single crystal X-ray and neutron powder diffraction, SQUID and torque magnetometry, and muon-spin rotation. Room temperature neutron powder diffraction reveals that 95% of the crystal volume is of the same tetragonal structure as PbO. The structure refinement yields a stoichiometry of Fe1.045Se0.406Te0.594. Additionally, a minor hexagonal Fe7Se8 impurity phase was identified. The magnetic penetration depth λ at zero temperature was found to be λab(0) = 491(8) nm in the ab-plane and λc(0) = 1320(14) nm along the c-axis. The zero-temperature value of the superfluid density ρs(0) ∝ λ−2(0) obeys the empirical Uemura relation observed for various unconventional superconductors, including cuprates and ironpnictides. The temperature dependences of both λab and λc are well described by a two-gap s+swave model with the zero-temperature gap values of ∆S(0) = 0.51(3) meV and ∆L(0) = 2.61(9) meV for the small and the large gap, respectively. The magnetic penetration depth anisotropy parameter γλ(T ) = λc(T )/λab(T ) increases with decreasing temperature, in agreement with γλ(T ) observed in the iron-pnictide superconductors. PACS numbers: 74.25.Ha, 74.25.Op, 74.25.Xa, 76.75.+i, 64.05.cp, 61.05.fm