Author:

Keywords:

Science & Technology, Technology, Physical Sciences, Materials Science, Multidisciplinary, Physics, Applied, Physics, Condensed Matter, Materials Science, Physics, PENETRATION DEPTH, PHASE-DIAGRAM, FLUX JUMPS, ANISOTROPY, cond-mat.supr-con, 02 Physical Sciences, 03 Chemical Sciences, 09 Engineering, Fluids & Plasmas, 34 Chemical sciences, 40 Engineering, 51 Physical sciences

Abstract:

We investigate the temperature dependence of the lower critical field Hc1(T ) of a high-quality FeSe single crystal under static magnetic fields H parallel to the c axis. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods and the corresponding Hc1(T ) was deduced by taking into account demagnetization factors. A pronounced change in the Hc1(T) curvature is observed, which is attributed to anisotopic s-wave or multiband superconductivity. The London penetration depth λab(T ) calculated from the lower critical field does not follow an exponential behavior at low temperatures, as it would be expected for a fully gapped clean s-wave superconductor. Using either a two-band model with s-wave-like gaps of magnitudes 1 = 0.41 ± 0.1 meV and 2 = 3.33 ± 0.25 meV or a single anisotropic s-wave order parameter, the temperature dependence of the lower critical field Hc1(T ) can be well described. These observations clearly show that the superconducting energy gap in FeSe is nodeless.