We study with Angle Resolved PhotoElectron Spectroscopy (ARPES) the evolution of the electronic structure of Sr2IrO4, when holes or electrons are introduced, through Rh or La substitutions. At low dopings, the added carriers occupy the first available states, at bottom or top of the gap, revealing an asymmetric gap of 0.7eV, in good agreement with STM measurements. At further doping, we observe a reduction of the gap and a transfer of spectral weight across the gap, although the quasiparticle weight remains very small. We discuss the origin of the in-gap spectral weight as a local distribution of gap values.PACS numbers: 71.30.-h, 71.27.-a, 79.60.-i The reaction of an insulator to doping can reveal many things on its underlying structure. For a band insulator, a simple shift of the chemical potential into bands that were previously completely filled or empty can be expected. If more complex electronic correlations are involved, the formation of in-gap states and/or large transfer of spectral weight across the gap could occur 1,2 . This problem received a lot of attention in the case of cuprates 3,4 . It is very interesting to investigate this in Sr 2 IrO 4 , whose insulating nature is not completely understood. The idea driving the field for a few years is that strong spin-orbit coupling reshapes the electronic structure in a way that enhances correlations 5 . Especially, a narrow half-filled band of J=1/2 character forms at the Fermi level, which could be split by correlations to form a Mott insulator. The exact role of the antiferromagnetic (AF) ordering observed below 240 K 6 in the insulating nature is still debated 7,8 . On the other hand, applying pressure, even up to 55 GPa, was not able to close the gap 9 , which is surprising for a Mott insulator. In this context, it would be interesting to know more about the electronic structure of doped phases, which exhibit metallic-like behaviors even for rather low doping rates 10-13 .Recently, a few Angle Resolved Photoemission (ARPES) studies of doped iridate phases were reported, but they lead to quite a confusing picture. For Rh substitutions, which results in effective hole doping 13 , a metallic-like state was observed, albeit with residual pseudogaps instead of well defined quasiparticles (QP) peaks 14 . Another kind of metallic state was observed by evaporating K on the surface of Sr 2 IrO 4 , which presumably dopes electrons into it 15 . In this case, well defined QP were observed, with strong momentum and temperature dependences that resemble those found in the cuprates and even possible signs of superconductivity 16,17 . Very recently, results similar to intermediate K coverage were reproduced in La doped Sr 2 IrO 4 18 . In these cases, a large Fermi Surface (FS) containing ∼ 1±x electrons was apparently observed (x is the number of added carriers), although the spectral weight along it could be strongly modulated. In contrast, La doping in Sr 3 Ir 2 O 7 apparently produces a small FS containing only the added x electrons 19 with a progressive reduct...

Despite extensive work on high-temperature superconductors, the critical behavior of an incipient condensate has so far been studied exclusively under equilibrium conditions. Here, we excite Bi(2)Sr(2)CaCu(2)O(8+δ) with a femtosecond laser pulse and monitor the subsequent nonequilibrium dynamics of the midinfrared conductivity. Our data allow us to discriminate temperature regimes where superconductivity is either coherent, fluctuating or vanishingly small. Above the transition temperature T(c), we make the striking observation that the relaxation to equilibrium exhibits power-law dynamics and scaling behavior, both for optimally and underdoped superconductors. Our findings can in part be modeled using time-dependent Ginzburg-Landau theory, and they provide strong indication of universality in systems far from equilibrium.

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International audienceWe perform time-resolved photoelectron spectroscopy measurements of optimally doped Bi2Sr2CaCu2O8+δ(Bi-2212) and Bi2Sr2−xLaxCuO6+δ (Bi-2201). The electron dynamics shows that inelastic scattering by nodalquasiparticles decreases when the temperature is lowered below the critical value of the superconductingphase transition. This drop in electronic dissipation is astonishingly robust and survives to photoexcitationdensities much larger than the value sustained by long-range superconductivity. The unconventional behavior ofquasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to theinelastic path. Our measurements indicate that strongly driven superconductors enter in a regime without phasecoherence but finite pairing amplitude. The latter vanishes near to the critical temperature and has no evident linkto the pseudogap observed by angle-resolved photoelectron spectroscopy