High-Field Pauli-Limiting Behavior and Strongly Enhanced Upper Critical Magnetic Fields near the Transition Temperature of an Arsenic-Deficient ${\mathrm{LaO}}_{0.9}{\mathbf{F}}_{0.1}{\mathrm{FeAs}}_{1\ensuremath{-}\ensuremath{\delta}}$ Superconductor

High-Field Pauli-Limiting Behavior and Strongly Enhanced Upper Critical Magnetic Fields near the Transition Temperature of an Arsenic-Deficient ${LaO}_{0.9} F_{0.1} {FeAs}_{1 - δ}$ Superconductor

G. Fuchs, S.-L. Drechsler, N. Kozlova, G. Behr, A. Köhler, J. Werner, K. Nenkov, R. Klingeler, J. Hamann-Borrero, C. Hess, A. Kondrat, M. Grobosch, A. Narduzzo, M. Knupfer, J. Freudenberger, B. Büchner, and L. Schultz

Phys. Rev. Lett. 101, 237003 – Published 4 December 2008; Erratum Phys. Rev. Lett. 101, 249901 (2008)

Abstract

We report upper critical field $B_{c 2} (T)$ data for disordered (arsenic-deficient) ${LaO}_{0.9} F_{0.1} {FeAs}_{1 - δ}$ in a wide temperature and magnetic field range up to 47 T. Because of the large linear slope of $B_{c 2} \approx - 5.4$ to $- 6.6 T / K$ near $T_{c} \approx 28.5 K$ , the $T$ dependence of the in-plane $B_{c 2} (T)$ shows a flattening near 23 K above 30 T which points to Pauli-limited behavior with $B_{c 2} (0) \approx 63 - 68 T$ . Our results are discussed in terms of disorder effects within conventional and unconventional superconducting pairings.