Coherent excitations and electron phonon coupling in Ba/EuFe_2As_2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy

Abstract

We employed femtosecond time- and angle-resolved photoelectron spectroscopy to analyze the response of the electronic structure of the 122 Fe-pnictide parent compounds Ba/EuFe_2As_2 and optimally doped BaFe_{1.85}Co_{0.15}As_2 near the Γpoint to femtosecond optical excitation. We identify pronounced changes of the electron population within several 100 meV above and below the Fermi level, which we explain as combination of (i) coherent lattice vibrations, (ii) a hot electron and hole distribution, and (iii) transient modifications of the chemical potential. The response of the three different materials is very similar. In the Fourier transformation of the time-dependent photoemission intensity we identify three modes at 5.6, 3.3, and 2.6 THz. While the highest frequency mode is safely assigned to the A_{1g} mode, the other two modes require a discussion in comparison to literature. The time-dependent evolution of the hot electron distribution follows a simplified description of a transient three temperature model which considers two heat baths of lattice vibrations, which are more weakly and strongly coupled to transiently excited electron population. Still the energy transfer from electrons to the strongly coupled phonons results in a rather weak, momentum-averaged electron-phonon coupling quantified by values for λ<ω^2> between 30 and 70 meV^2. The chemical potential is found to present a transient modulation induced by the coherent phonons. This change in the chemical potential is particularly strong in a two band system like in the 122 Fe-pnictide compounds investigated here due to the pronounced variation of the electrons density of states close to the equilibrium chemical potential.

10 pages, 6 figures

References in corpus (16)

• Is LaO${}_{1-x}$F${}_x$FeAs an electron-phonon superconductor ?
• Ultrafast transient generation of spin-densitywave order in the normal state of BaFe2As2 driven by coherent lattice vibrations
• Anisotropy of the Optimally-Doped Iron Pnictide Superconductor Ba(Fe0.926Co0.074)2As2
• Laser ARPES, the sudden approximation, and quasiparticle-like peaks in Bi2Sr2CaCu2O8+delta
• Electrical Resistivity and Specific Heat of EuFe2As2 Single Crystals: Magnetic homologue of SrFe2As2
• Effects of magnetism and doping on the electron-phonon coupling in BaFe${}_2$As${}_2$
• Evidence for Strong Itinerant Spin Fluctuations in the Normal State of CeFeAsO(0.89)F(0.11) Iron-Oxypnictides
• Ultrafast transient response and electron-phonon coupling in the iron-pnictide superconductor Ba(Fe(1-x)Co(x))2As2
• Raman scattering study of (K${}_x$Sr${}_{1-x}$)Fe${}_2$As${}_2$ ($x$ = 0.0, 0.4)
• Electronic Structure and Electron Correlation in LaFeAsO_{1-x}F_x and LaFePO_{1-x}F_x
• Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for studying phonons in BaFe2As2: Effect of structural phase transition, structural relaxation and magnetic ordering
• Non-perturbative improvement of stout-smeared three flavour clover fermions
• Lattice and electronic anomalies of CaFe_2As_2 studied by Raman spectroscopy
• On the electronic structure of electron doped LaOFeAs as seen by X-ray absorption spectroscopy
• Electron-phonon coupling and charge gap in spin-density-wave iron-pnictides from quasiparticle relaxation dynamics
• Electronic Structure of CeFeAsO1-xFx (x=0, 0.11/x=0.12) compounds