Abstract
The transient response of , 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 . 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 . The simultaneous excitation of a strong fully symmetric optical phonon corroborates this conclusion and makes it possible to deduce the value of . 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.
- Received 14 June 2010
DOI:https://doi.org/10.1103/PhysRevB.82.024513
©2010 American Physical Society