Field-dependent superfluid density in the optimally doped SmFeAsO_1-xF_y superconductor

¹ Physik-Institut der Universität Zürich - Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
² Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute - CH-5232 Villigen PSI, Switzerland
³ Institute of Physics, Polish Academy of Sciences - Aleja Lotników 32/46, PL-02-668 Warsaw, Poland
⁴ Max-Planck-Institut für Festkörperforschung - Heisenbergstrasse 1, D-70569 Stuttgart, Germany
⁵ Laboratory for Solid State Physics, ETH Zurich - Schafmattstrasse 16, CH-8093 Zurich, Switzerland
⁶ Department of Physics, Tbilisi State University - Chavchavadze 3, GE-0128 Tbilisi, Georgia

^a wstephen@physik.uzh.ch

Received: 10 June 2010
Accepted: 5 August 2010

Abstract

The magnetic-field dependence of the in-plane magnetic penetration depth λ_ab for optimally doped SmFeAsO_1−xF_y was investigated by combining torque magnetometry, SQUID magnetometry, and muon-spin rotation. The results obtained from these techniques show all a pronounced decrease of the superfluid density ρ_s∝λ_ab^{− 2} as the field is increased to 1.4 T. This behaviour of ρ_s is analysed within a two-band model with self-consistently derived coupled gaps and ρ_s=ρ_s1+ρ_s2, where ρ_s1 related to the larger gap is field independent, and ρ_s2 related to the smaller gap is strongly suppressed with increasing field.