Quasiparticle dynamics in high-temperature superconductors far from equilibrium: An indication of pairing amplitude without phase coherence

Abstract

We 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 nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop in electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude. The latter vanishes near to the critical temperature and has no evident link to the pseudogap observed by angle-resolved photoelectron spectroscopy.