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Title: Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.

Abstract

Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in threemore » '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.« less

Authors:
; ; ;  [1]
  1. Materials Science Division
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1009337
Report Number(s):
ANL/MSD/JA-67969
Journal ID: 0921-4534; TRN: US201106%%532
DOE Contract Number:  
DE-AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Physica C
Additional Journal Information:
Journal Volume: 469; Journal Issue: 9-12 ; Mar. 20, 2009
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; ANISOTROPY; COPPER OXIDES; CRYSTAL STRUCTURE; ENERGY GAP; EXCHANGE INTERACTIONS; FERMIONS; FLUCTUATIONS; IRON; IRON ARSENIDES; MAGNETISM; MONOCRYSTALS; NEUTRONS; ORDER PARAMETERS; PHONONS; SCATTERING; SPIN; SPIN WAVES; SUPERCONDUCTIVITY; SUPERCONDUCTORS; SYMMETRY; TRANSITION TEMPERATURE

Citation Formats

Osborn, R, Rosenkranz, S, Goremychkin, E A, Christianson, A D, and ORNL). Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.. United States: N. p., 2009. Web. doi:10.1016/j.physc.2009.03.036.
Osborn, R, Rosenkranz, S, Goremychkin, E A, Christianson, A D, & ORNL). Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.. United States. doi:10.1016/j.physc.2009.03.036.
Osborn, R, Rosenkranz, S, Goremychkin, E A, Christianson, A D, and ORNL). Fri . "Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.". United States. doi:10.1016/j.physc.2009.03.036.
@article{osti_1009337,
title = {Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.},
author = {Osborn, R and Rosenkranz, S and Goremychkin, E A and Christianson, A D and ORNL)},
abstractNote = {Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.},
doi = {10.1016/j.physc.2009.03.036},
journal = {Physica C},
number = 9-12 ; Mar. 20, 2009,
volume = 469,
place = {United States},
year = {2009},
month = {3}
}