Journal Article

PreJuSER-9354

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Pressure dependence of phonon modes across the tetragonal to collapsed tetragonal phase transition in CaFe2As2

Mittal, R. ; Heid, R. ; Bosak, A. ; Forrest, T. R. ; Chaplot, S. L. ; Lamago, D. ; Reznik, D. ; Bohnen, K. P. ; Su, Y.FZJ* ; Kumar, C. M. N.FZJ* ; Dhar, S. K. ; Thamizhavel, A. ; Rueegg, C. ; Krisch, M. ; McMorrow, D. F. ; Brückel, T.FZJ* ; Pintschovius, L.

2010
APS College Park, Md.

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Please use a persistent id in citations: http://hdl.handle.net/2128/10991  doi:10.1103/PhysRevB.81.144502

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.

Keyword(s): J

Note: Record converted from VDB: 12.11.2012

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Contributing Institute(s):

1. Streumethoden (IFF-4)
2. Neutronenstreuung (IFF-5)
3. JCNS (Jülich Centre for Neutron Science JCNS (JCNS) ; JCNS)
4. Jülich-Aachen Research Alliance - Fundamentals of Future Information Technology (JARA-FIT)

Research Program(s):

1. BioSoft: Makromolekulare Systeme und biologische Informationsverarbeitung (P45)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)

Appears in the scientific report 2010

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