Phonon anomalies in <i>AE</i>Fe<sub>2</sub>As<sub>2</sub> (<i>AE </i>= Ca, Sr and Ba)
ORAL
Abstract
The infrared vibrational properties of AEFe2As2 (AE = Ca, Sr and Ba) have been measured above and below the structural and magnetic transition at TN = 172, 195 and 138 K [1], and compared to ab initio calculations of the frequency and atomic character at the center of the Brillouin zone. In the Ca compound both of the infrared-active Eu modes split below TN. However, while the low-frequency mode splits in the Sr compound, the high-frequency mode appears to only have a lower branch which displays an anomalous increase in strength below TN. In the Ba compound, the high-frequency mode again fails to split and the oscillator strength increases dramatically below TN [2]; furthermore, there is a net decrease in the strength of the low-frequency modes at low temperature. Ab initio calculations indicate that the nature of the high-frequency mode does not change across this series of compounds. The presence of SDW order along the b axis below TN suggests the nature of the bonding has been altered due to orbital ordering, possibly explaining the lack of splitting and the increase in strength of the high-frequency mode.
[1] Y. M. Dai et al., Phys. Rev. B 94, 195142 (2016).
[2] A. Akrap et al., Phys. Rev. B 80, 180502(R) (2009).
[1] Y. M. Dai et al., Phys. Rev. B 94, 195142 (2016).
[2] A. Akrap et al., Phys. Rev. B 80, 180502(R) (2009).
*Supported by DOE-BES under DE-AC02-07CH11358 and DE-SC0012704.
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Presenters
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Christopher Homes
- Condensed Matter Physics and Materials Science, Brookhaven National Laboratory
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory
- condense matter physic and material science, Brookhaven National Lab
- CMPMS, Brookhaven Natl Lab