title: Possible unconventional superconductivity in substituted BaFe2As2 revealed by magnetic pair-breaking studies.
abstract: The possible existence of a sign-changing gap symmetry in BaFe2As2-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe1.9M0.1As2 (M = Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for M = Cu and Mn compounds, which display very low SC transition temperature (Tc) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of Tc cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials.
authors.affiliation: 1] Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil [2] University of California, Irvine, California 92697-4574, USA.
authors.forename: P F S
authors.initials: PF
authors.lastname: Rosa
authors.affiliation: Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil.
authors.forename: C
authors.initials: C
authors.lastname: Adriano
authors.affiliation: Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil.
authors.forename: T M
authors.initials: TM
authors.lastname: Garitezi
authors.affiliation: 1] Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil [2] Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany.
authors.forename: M M
authors.initials: MM
authors.lastname: Piva
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Mydeen
authors.affiliation: University of California, Irvine, California 92697-4574, USA.
authors.forename: T
authors.initials: T
authors.lastname: Grant
authors.affiliation: University of California, Irvine, California 92697-4574, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Fisk
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Nicklas
authors.affiliation: Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil.
authors.forename: R R
authors.initials: RR
authors.lastname: Urbano
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Fernandes
authors.affiliation: Instituto de Física "Gleb Wataghin", UNICAMP, Campinas-SP, 13083-859, Brazil.
authors.forename: P G
authors.initials: PG
authors.lastname: Pagliuso