Quasiparticle dynamics in overdoped Bi_(1.4)Pb_(0.7)Sr_(1.9)CaCu₂O_(8+δ): Coexistence of superconducting gap and pseudogap below T_(c)

Photoexcited quasiparticle relaxation dynamics in overdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ ($T_{c}$=65~K, hole doping $p$=0.22) single crystal is investigated as a function of temperature. We provide evidence of a $\sim$22~meV pseudogap ($T^{\ast}$$\approx$100~K) at this doping level. Our data support the scenario where both the superconducting gap and pseudogap coexist in the superconducting state. Our results also suggest an increased scattering rate between electrons and spin fluctuations as the sample enters the pseudogap phase.