Phonon spectra in CaFe2As2 and Ca0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison with ab-initio and shell model calculations

R. Mittal; S. Rols; M. Zbiri; Y. Su; H. Schober; S. L. Chaplot; M. Johnson; M. Tegel; T. Chatterji; S. Matsuishi; H. Hosono; D. Johrendt; Th. Brueckel

doi:10.1103/physrevb.79.144516

arXiv · 0902.4590

Phonon spectra in CaFe2As2 and Ca0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison with ab-initio and shell model calculations

R. Mittal·S. Rols·M. Zbiri·Y. Su·H. Schober·S. L. Chaplot·M. Johnson·M. Tegel·T. Chatterji·S. Matsuishi·H. Hosono·D. Johrendt·Th. Brueckel

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Abstract

We report the pressure and temperature dependence of the phonon density-of-states in superconducting Ca0.6Na0.4Fe2As2 (Tc=21 K) and the parent compound CaFe2As2, using inelastic neutron scattering. We observe no significant change in the phonon spectrum for Ca0.6Na0.4Fe2As2 at 295 K up to pressures of 5 kbar. The phonon spectrum for CaFe2As2 shows softening of the low-energy modes by about 1 meV when decreasing the temperature from 300 K to 180 K. There is no appreciable change in the phonon density of states across the structural and anti-ferromagnetic phase transition at 172 K. These results, combined with our earlier temperature dependent phonon density of states measurements for Ca0.6Na0.4Fe2As2, indicate that the softening of low-energy phonon modes in these compounds may be due to the interaction of phonons with electron or short-range spin fluctuations in the normal state of the superconducting compound as well as in the parent compound. The phonon spectra are analyzed with ab-initio and empirical model calculations giving partial densities of states and dispersion relations.

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R. Mittal, S. Rols, M. Zbiri, Y. Su, H. Schober, S. L. Chaplot, M. Johnson, M. Tegel, T. Chatterji, S. Matsuishi, H. Hosono, D. Johrendt, Th. Brueckel. 2009-02-26. Phonon spectra in CaFe2As2 and Ca0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison with ab-initio and shell model calculations. https://doi.org/10.1103/physrevb.79.144516

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