Doping dependence of femtosecond quasiparticle relaxation dynamics in Ba(Fe,Co)2As2 single crystals: Evidence for normal-state nematic fluctuations

L. Stojchevska, T. Mertelj, Jiun-Haw Chu, Ian R. Fisher, and D. Mihailovic
Phys. Rev. B 86, 024519 – Published 19 July 2012

Abstract

We systematically investigate the photoexcited (PE) quasiparticle (QP) relaxation and low-energy electronic structure in electron doped Ba(Fe1xCox)2As2 single crystals as a function of Co doping, 0x0.11. The evolution of the photoinduced reflectivity transients with x 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 2Δ(0)/kBTs decreases with increasing x. 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, Up/kB=0.3 K/Fe, is determined near the optimal doping. The subsequent relatively slow recovery of the SC state indicates clean SC gaps. The T 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 T200 K at any x. 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, λ0.3, that decreases with increasing doping.

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  • Received 29 July 2011

DOI:https://doi.org/10.1103/PhysRevB.86.024519

©2012 American Physical Society

Authors & Affiliations

L. Stojchevska1, T. Mertelj1, Jiun-Haw Chu2,3, Ian R. Fisher2,3, and D. Mihailovic1

  • 1Complex Matter Deptartment, Jozef Stefan Institute, Jamova 39, Ljubljana, SI-1000, Ljubljana, Slovenia
  • 2Geballe Laboratory for Advanced Materials and Department of Applied Physics, Stanford University, Stanford, California 94305, USA
  • 3Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

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Vol. 86, Iss. 2 — 1 July 2012

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