title: Infrared Study of the Spin Reorientation Transition and Its Reversal in the Superconducting State in Underdoped Ba(1-x)K(x)Fe(2)As(2).
abstract: With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba(1-x)K(x)Fe(2)As(2). In agreement with the predicted transition from a single-Q to a double-Q AF structure, we found that a distinct spin density wave develops in the t-AF phase. The pair breaking peak of this spin density wave acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity. We also observed additional phonon modes in the t-AF phase which likely arise from a Brillouin-zone folding that is induced by the double-Q magnetic structure with two Fe sublattices exhibiting different magnitudes of the magnetic moment.
authors.affiliation: University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland.
authors.forename: B P P
authors.initials: BP
authors.lastname: Mallett
authors.affiliation: University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Marsik
authors.affiliation: University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Yazdi-Rizi
authors.affiliation: Institute of Solid State Physics, Karlsruhe Institute of Technology, Postfach 3640, Karlsruhe 76021, Germany.
authors.forename: Th
authors.initials: T
authors.lastname: Wolf
authors.affiliation: Institute of Solid State Physics, Karlsruhe Institute of Technology, Postfach 3640, Karlsruhe 76021, Germany.
authors.forename: A E
authors.initials: AE
authors.lastname: Böhmer
authors.affiliation: Institute of Solid State Physics, Karlsruhe Institute of Technology, Postfach 3640, Karlsruhe 76021, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Hardy
authors.affiliation: Institute of Solid State Physics, Karlsruhe Institute of Technology, Postfach 3640, Karlsruhe 76021, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Meingast
authors.affiliation: Department of Condensed Matter Physics, Faculty of Science and Central European Institute of Technology, Masaryk University, Kotlářska 2, 61137 Brno, Czech Republic.
authors.forename: D
authors.initials: D
authors.lastname: Munzar
authors.affiliation: University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Bernhard