Simultaneous evidence for Pauli paramagnetic effects and multiband superconductivity in KFe 2 As 2 by small-angle neutron scattering studies of the vortex lattice

Iron-based superconductors, where the Cooper pairing is theorized to arise from magnetic interactions, have emerged as very good model systems for studies of the interplay between superconductivity and magnetism. Superconducting vortices, introduced by an applied magnetic field, can serve as a sensitive probe of the superconducting state in the host material. The authors have used small-angle neutron scattering to study the vortex lattice in KFe${}_{2}$As${}_{2}$, and perform a comprehensive characterization of the effects of multiband superconductivity and Pauli paramagnetism in this material. In particular, they have succeeded in separating orbital and paramagnetic contributions to the vortex lattice field modulation, and obtain a quantitative measure of the Pauli paramagnetic effects deep within the superconducting phase.