Weak superconducting pairing and a single isotropic energy gap in stoichiometric LiFeAs

Abstract

We report superconducting (SC) properties of stoichiometric LiFeAs (Tc = 17 K) studied by small-angle neutron scattering (SANS) and angle-resolved photoemission (ARPES). Although the vortex lattice exhibits no long-range order, well-defined SANS rocking curves indicate better ordering than in chemically doped 122-compounds. The London penetration depth of 210 nm, determined from the magnetic field dependence of the form factor, is compared to that calculated from the ARPES band structure with no adjustable parameters. Its temperature dependence is best described by a single isotropic SC gap of 3.0 meV, which agrees with the ARPES value of 3.1 meV and corresponds to the ratio 2Delta/kTc = 4.1, approaching the weak-coupling limit predicted by the BCS theory. This classifies LiFeAs as a weakly coupled single-gap superconductor, similar to conventional metals.

4 pages, 4 figures

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• Time of life as it is in LiFeAs
• Microwave Surface Impedance Measurements of LiFeAs Single Crystals
• An ARPES view on the high-Tc problem: phonons vs spin-fluctuations
• Small anisotropy of the lower critical field and $s_{\pm }$-wave two-gap feature in single crystal LiFeAs
• Single crystal growth and superconducting properties of LiFeAs