Close correlation between magnetic properties and the soft phonon mode of the structural transition in BaFe2As2 and SrFe2As2

D. Parshall, L. Pintschovius, J. L. Niedziela, J.-P. Castellan, D. Lamago, R. Mittal, Th. Wolf, and D. Reznik
Phys. Rev. B 91, 134426 – Published 27 April 2015

Abstract

Parent compounds of Fe-based superconductors undergo a structural phase transition from a tetragonal to an orthorhombic structure. We investigated the temperature dependence of the frequencies of TA phonons that extrapolate to the shear vibrational mode at the zone center, which corresponds to the orthorhombic deformation of the crystal structure at low temperatures in BaFe2As2 and SrFe2As2. We found that acoustic phonons at small wave vectors soften gradually towards the transition from high temperatures, tracking the increase of the size of slowly fluctuating magnetic domains. On cooling below the transition to base temperature the phonons harden, following the square of the magnetic moment (which we find is proportional to the anisotropy gap). Our results provide evidence for close correlation between magnetic and phonon properties in Fe-based superconductors.

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  • Received 7 November 2014
  • Revised 25 March 2015

DOI:https://doi.org/10.1103/PhysRevB.91.134426

©2015 American Physical Society

Authors & Affiliations

D. Parshall1,*, L. Pintschovius2, J. L. Niedziela3, J.-P. Castellan2,4, D. Lamago2, R. Mittal5, Th. Wolf2, and D. Reznik6

  • 1National Institute of Standards and Technology, NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA
  • 2Institut für Festkörperphysik, Karlsruhe Institut für Technologie, P.O. Box 3640, D-76021 Karlsruhe, Germany
  • 3Instrument and Source Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 4Laboratoire Léon Brillouin, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France
  • 5Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
  • 6Department of Physics, University of Colorado, Boulder, Colorado 80309, USA

  • *parshall@nist.gov

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Vol. 91, Iss. 13 — 1 April 2015

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