Signatures of superconductivity and pseudogap formation in nonequilibrium nodal quasiparticles revealed by ultrafast angle-resolved photoemission

We use time- and angle-resolved photoemission to measure the nodal nonequilibrium electronic states in various dopings of Bi₂Sr₂CaCu₂O_8+δ. We find that the initial pump-induced transient signal of these ungapped states is strongly affected by the onset of the superconducting gap at Tc, superconducting pairing fluctuations at Tₚ, and the pseudogap at T*. Moreover, Tₚ marks a suggestive threshold in the fluence-dependent transient signal, with the appearance of a critical fluence below Tₚ that corresponds to the energy required to break apart all Cooper pairs. These results challenge the notion of a nodal-antinodal dichotomy in cuprate superconductors by establishing a link between nodal quasiparticles and the cuprate phase diagram.