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Publication Detail
Pressure dependence of phonon modes across the tetragonal to collapsed-tetragonal phase transition in CaFe2As2
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Article
  • Authors:
    Mittal R, Heid R, Bosak A, Forrest TR, Chaplot SL, Lamago D, Reznik D, Bohnen KP, Su Y, Kumar N, Dhar SK, Thamizhavel A, Ruegg C, Krisch M, McMorrow DF, Brueckel T, Pintschovius L
  • Publisher:
    AMER PHYSICAL SOC
  • Publication date:
    01/04/2010
  • Journal:
    PHYS REV B
  • Volume:
    81
  • Issue:
    14
  • Print ISSN:
    1098-0121
  • Language:
    EN
  • Addresses:
    Mittal, R
    Forschungszentrum Julich
    Juelich Ctr Neutron Sci
    IFF
    Outstn FRM 2
    D-85747
    Garching
    Germany

    CEA Saclay
    Lab Leon Brillouin
    F-91191
    Gif Sur Yvette
    France

    Univ Colorado
    Dept Phys
    Boulder
    CO
    80309
    USA

    Forschungszentrum Julich
    Inst Festkorperphys
    D-52425
    Julich
    Germany
Abstract
The pressure dependence of a large number of phonon modes in CaFe2As2 with energies covering the full range of the phonon spectrum has been studied using inelastic x-ray and neutron scatterings. The pressure range was large enough to cover the first-order phase transition into the so-called collapsed phase where the c-axis contracts by about 6% whereas a and b axes expand by about 1.5%. Our main result is that pressure-induced phonon frequency shifts are well explained by the changes in relevant bond lengths throughout the pressure range, including those associated with the first-order phase transition. Specifically, the frequencies of phonons polarized in the ab plane as well as the Fe-As bond lengths change little across the phase transition. On the other hand, the transverse-acoustic phonons propagating along the c direction stiffen very significantly in response to the large contraction of the bonds along the c axis. Nonmagnetic density-functional calculations describe the frequencies in both the zero pressure and in the collapsed phase in a satisfactory way if based on the respective experimental crystal structures. This suggests that there is no need to invoke changes in magnetic moments on Fe atoms to explain the pressure-induced frequency shifts.
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