Competition between the pseudogap and superconducting states of Bi ₂Sr₂Ca_0.92Y_0.08Cu₂O _8+δ single crystals revealed by ultrafast broadband optical reflectivity

Ultrafast broadband transient reflectivity experiments are performed to study the interplay between the nonequilibrium dynamics of the pseudogap and the superconducting phases in Bi₂Sr₂Ca_0.92Y _0.08Cu₂O_8+δ. Once superconductivity is established, the relaxation of the pseudogap proceeds ∼2 times faster than in the normal state, and the corresponding transient reflectivity variation changes sign after ∼0.5 ps. The results can be described by a set of coupled differential equations for the pseudogap and for the superconducting order parameter. The sign and strength of the coupling term suggest a remarkably weak competition between the two phases, allowing their coexistence.