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Robustness of superconducting properties to transition metal substitution and impurity phases in Fe 1 − x V x Se

DOI: 10.1103/PhysRevB.100.094527 DOI Help

Authors: Franziska K. K. Kirschner (University of Oxford) , Daniel N. Woodruff (University of Oxford) , Matthew J. Bristow (University of Oxford) , Franz Lang (University of Oxford) , Peter J. Baker (ISIS Facility) , Simon J. Clarke (University of Oxford) , Stephen J. Blundell (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 100

State: Published (Approved)
Published: September 2019
Diamond Proposal Number(s): 13284 , 18786

Abstract: We have performed transverse- and zero-field muon spin rotation/relaxation experiments, as well as magnetometry measurements, on samples of Fe 1 − x V x Se and their Li + NH 3 intercalates Li 0.6 ( NH 2 ) 0.2 ( NH 3 ) 0.8 Fe 1 − x V x Se . We examine the low vanadium substitution regime: x = 0.005 , 0.01, and 0.02. The intercalation reaction significantly increases the critical temperature ( T c ) and the superfluid stiffness for all x . The nonintercalated samples all exhibit T c ≈ 8.5 K while the intercalated samples all show an enhanced T c > 40 K. Vanadium substitution has a negligible effect on T c , but seems to suppress the superfluid stiffness for the nonintercalated samples and weakly enhance it for the intercalated materials. The optimal substitution level for the intercalated samples is found to be x = 0.01 , with T c ≈ 41 K and λ a b ( 0 ) ≈ 0.18 μ m . The nonintercalated samples can be modeled with either a single d -wave superconducting gap or with an anisotropic gap function based on recent quasiparticle imaging experiments, whereas the intercalates display multigap nodal behavior which can be fitted using s + d - or d + d -wave models. Magnetism, likely from iron impurities, appears after the intercalation reaction and coexists and competes with the superconductivity. However, it appears that the superconductivity is remarkably robust to the impurity phase, providing an avenue to stably improve the superconducting properties of transition metal substituted FeSe.

Journal Keywords: Superconductivity; Iron-based superconductors; Muon spin relaxation & rotation; Susceptibility measurements

Subject Areas: Materials, Physics


Instruments: I11-High Resolution Powder Diffraction