Abstract
We systematically investigate the photoexcited (PE) quasiparticle (QP) relaxation and low-energy electronic structure in electron doped Ba(FeCo)As single crystals as a function of Co doping, . The evolution of the photoinduced reflectivity transients with proceeds with no abrupt changes. In the orthorhombic spin-density-wave (SDW) state, a bottleneck associated with a partial charge-gap opening is detected, similar to previous results in different SDW iron pnictides. The relative charge gap magnitude decreases with increasing . In the superconducting (SC) state, an additional relaxational component appears due to a partial (or complete) destruction of the SC state proceeding on a sub-0.5-picosecond timescale. From the SC component saturation behavior the optical SC-state destruction energy, K/Fe, is determined near the optimal doping. The subsequent relatively slow recovery of the SC state indicates clean SC gaps. The dependence of the transient reflectivity amplitude in the normal state is consistent with the presence of a pseudogap in the QP density of states. The polarization anisotropy of the transients suggests that the pseudogap-like behavior might be associated with a broken fourfold rotational symmetry resulting from nematic electronic fluctuations persisting up to K at any . The second moment of the Eliashberg function, obtained from the relaxation rate in the metallic state at higher temperatures, indicates a moderate electron phonon coupling, , that decreases with increasing doping.
4 More- Received 29 July 2011
DOI:https://doi.org/10.1103/PhysRevB.86.024519
©2012 American Physical Society