Ultrafast transient response and electron-phonon coupling in the iron-pnictide superconductor Ba(Fe1−xCox)2As2

Barbara Mansart 1 Davide Boschetto 2 A. Savoia 2 F. Rullier-Albenque 3 F. Bouquet 1 E. Papalazarou 1 A. Forget 3 D. Colson 3 Antoine Rousse 2 M. Marsi 1
1 LPS - Laboratoire de Physique des Solides
2 LOA - Laboratoire d'optique appliquée
3 SPEC - UMR3680 - Service de physique de l'état condensé
Abstract : The transient response of Ba(Fe1−xCox)2As2, x=0.08 was studied by pump-probe optical reflectivity. After ultrafast photoexcitation, hot electrons were found to relax with two different characteristic times, indicating the presence of two distinct decay channels: a faster one, of less than 1 ps in the considered pump fluence range and a slower one, corresponding to lattice thermalization and lasting ≅6 ps. Our analysis indicates that the fast relaxation should be attributed to preferential scattering of the electrons with only a subset of the lattice-vibration modes with a second moment of the Eliashberg function λ⟨ω^2⟩≅64 meV^2. The simultaneous excitation of a strong fully symmetric A1g optical phonon corroborates this conclusion and makes it possible to deduce the value of λ≅0.12. This small value for the electron-phonon coupling confirms that a phonon-mediated process cannot be the only mechanism leading to the formation of superconducting pairs in this family of pnictides.
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Submitted on : Wednesday, March 2, 2011 - 8:40:20 AM
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Barbara Mansart, Davide Boschetto, A. Savoia, F. Rullier-Albenque, F. Bouquet, et al.. Ultrafast transient response and electron-phonon coupling in the iron-pnictide superconductor Ba(Fe1−xCox)2As2. Physical Review B : Condensed matter and materials physics, American Physical Society, 2010, 82 (2), pp.024513. ⟨10.1103/PhysRevB.82.024513⟩. ⟨hal-00572659⟩

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