Study of pseudogap and superconducting quasiparticle dynamics in Bi2Sr2CaCu2O8+δ by time resolved optical reflectivity

Abstract The relation between pseudogap (PG) and superconducting (SC) gap, whether PG is a precursor of SC or they coexist or compete, is a long-standing controversy in cuprate high-temperature supercondutors. Here, we report ultrafast time-resolved optical reflectivity investigation of the dynamic densities and relaxations of PG and SC quasiparticles (QPs) in the underdoped Bi2Sr2CaCu2O 8 + δ (Tc = 82 K) single crystals. We find evidence of two distinct PG components in the positive reflectivity changes in the PG state, characterized by relaxation timescales of τfast  ≈  0.2 ps and τslow  ≈  2 ps with abrupt changes in both amplitudes Afast and Aslow at the PG-opening temperature T*. The former presents no obvious change at Tc and coexists with the SC QP. The latter’s amplitude starts decreasing at the SC phase fluctuation Tp and vanishes at Tc followed by a negative amplitude signifying the emergence of the SC QP, therefore suggesting a competition with superconductivity.