Rullier-Albenque, Alloul, and Tourbot Reply: Openov [1] agrees that the Abrikosov-Gor'kov (AG) theory for d-wave superconductivity does not apply to our accurate data on the T c depression induced by controlled disorder [2]. He suggests that inclusion of an s-wave contribution can explain the quasilinear decrease of our data. As already detailed in the references 8, 12, and 13 of [2], the AG theory fails to explain the initial slope of the T c decay. This slope is fixed by the value of the plasma frequency ! p and a consensus is now well established from the numerous optical data for ! p 1:2 0:2 eV for YBCO 7 [3]. To obtain a quasilinear decay one needs to introduce a significant s-wave component which is maintained when the d-wave one has been killed, assuming a weak spin scattering. Although the orthorhombic structure of YBCO 7 favors s d wave admixture, the upper limit of the s-wave component quoted is 20% [4] (corresponding to 0:93). Thus to get 0:9, Openov is forced to use a value of ! p smaller than that given by optical data. Obviously, it is possible to play again with such mathematical fits to also explain the data for YBCO 6:6 . But, as the fraction of s-wave component should be reduced for this hole content, it seems to us even more difficult to find for YBCO 6:6 a set of physically sound parameters compatible with those taken above and resulting as well in a quasilinear decrease of T c .Therefore alternative approaches must be considered in the case of cuprates. Let us mention that, as nonmagnetic impurities induce a magnetic response [5], the relative contributions of spin and potential scattering in these correlated electron systems cannot be treated classically. Also, as noted in [2], the upturns in the ab T curves is not taken into account in the AG approach.Let us come now to the final point of Openov, who doubts the actual validity of our analysis of the transition width T c , which is a good estimate of the macroscopic homogeneity of the samples. For a chemical substitution such as Zn, T c increases much faster [6] than in [2] (see the inset of Fig. 1). This is natural, as increasing Zn content brings us towards the solubility limit, hence a macroscopic inhomogeneity of the sample. For our electron irradiation experiment, as explained in [2], the spatial distribution of defects is particularly homogeneous. We proposed that the width of the transition is given by T c ÿa ab dT c =d ab [7]. Openov questions our model as, for him, the T c maximum is not compatible with the linear variation of T c with ab . He probably overlooked our data which do curve slightly when T c approaches zero. The two data sets are totally consistent since as shown in [2] the Emery-Kivelson (EK) equation (Ref. 10 in [2]) fits reasonably both variations of T c and T c with ab :. We demonstrate in Fig. 1 this consistency without any model for T c ab , just by integrating numerically the data for T c , using the equation above with the single adjustable parameter a 0:06.

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We present a comprehensive angle-resolved photoemission study of the three-dimensional electronic structure of Ba(Fe 1-x Co x ) 2 As 2 . The wide range of dopings covered by this study, x=0 to x=0.3, allows to extract systematic features of the electronic structure. We show that there are three different hole pockets around the Γ point, the two inner ones being nearly degenerate and rather two dimensional, the outer one presenting a strong three dimensional character. The structure of the electron pockets is clarified by studying high doping contents, where they are enlarged. They are found to be essentially circular and two dimensional. From the size of the pockets, we deduce the number of holes and electrons present at the various dopings. We find that the net number of carriers is in good agreement with the bulk stoichiometry, but that the number of each species (holes and electrons) is smaller than predicted by theory. Finally, we discuss the quality of nesting in the different regions of the phase diagram. The presence of the third hole pocket significantly weakens the nesting at x=0, so that it may not be a crucial ingredient in the formation of the Spin Density Wave. On the other hand, superconductivity seems to be favored by the coexistence of two-dimensional hole and electron pockets of similar sizes.

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The negative Hall constant R(H) measured all over the phase diagram of Ba(Fe(1-x) Co(x))(2)As(2) allows us to show that electron carriers always dominate the transport properties. The evolution of R(H) with x at low doping (x<2%) indicates that important band structure changes happen for x<2% prior to the emergence of superconductivity. For higher x, a change with T of the electron concentration is required to explain the low T variations of R(H), while the electron scattering rate displays the T(2) law expected for a Fermi liquid. The T=0 residual scattering is affected by Co disorder in the magnetic phase, but is rather dominated by incipient disorder in the paramagnetic state.

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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 ∼ = 6ps. 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. PACS numbers: 74.70.Xa; 78.47.J-; 74.25.KcThe discovery of high temperature superconductivity in iron pnictide compounds in 2008(Refs. 1 and 2 ) has raised a lot of questions about the nature of this phenomenon. One of these questions concerns the role of electron-phonon (e-ph) coupling, which is at the heart of conventional Bardeen-Cooper-Shrieffer (BCS) superconductivity 3 .For unconventional superconductors, electron-lattice interaction mechanisms have been extensively studied in cuprates; these materials present some similarities with pnictides, such as the bidimensionality of the crystallographic structure with Cu-O planes instead of Fe-As ones and the presence of a magnetic phase in the underdoped part of the phase diagram 4,5 . While the electron pairing mechanism is still controversial in superconducting cuprates, some elements are today accepted: first, their high critical temperatures are not compatible with a BCS scheme; second, the e-ph interaction is anisotropic, as theoretically predicted 6 and verified by means of time-resolved experiments 7-11 ; indeed, the e-ph coupling constant is strongly mode-selective, and ranges from λ ∼ = 0.13 to λ ∼ = 0.55. This selectivity is linked to the marked bidimensional layered structure of cuprates, leading to a preferential coupling between electrons coming from a specific k-direction of the Fermi surface and one particular phonon mode 6,8 .Much less information is available on e-ph coupling in pnictides. Theoretical works on the 1111 family (LaFeAsO 1−x F x ), employing Density Functionnal perturbation theory, predicted an isotropic coupling, equally distributed for the whole phonon population, and too small to be responsible for superconductivity through a BCS type mechanism 5,12 . On the other hand, a very strong coupling (λ ∼ = 1) between electrons and the A 1g mode (consisting of a breathing movement of As atoms) was predicted by a model in which the electronic polarization of As atoms involve e-ph interaction 13 . For 122 compounds (doped AF e 2 As 2 , A=Ba, Sr, Ca) spin f...