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${}_{8+\delta }$ (T_c = 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 τ_fast ≈ 0.2 ps and τ_slow ≈ 2 ps with abrupt changes in both amplitudes A_fast and A_slow at the PG-opening temperature T*. The former presents no obvious change at T_c and coexists with the SC QP. The latter’s amplitude starts decreasing at the SC phase fluctuation T_p and vanishes at T_c followed by a negative amplitude signifying the emergence of the SC QP, therefore suggesting a competition with superconductivity.

伪间隙（PG）和超导（SC）间隙之间的关系，无论PG是SC的前体，还是它们共存或竞争，在铜酸盐高温超导体中一直存在争议。在这里，我们报告超快时间分辨光学反射率调查的动态密度和PG和SC准粒子（QPs）在掺杂不足Bi ₂ Sr ₂ CaCu ₂ O中的弛豫${}_{8+\delta }$（T _c = 82 K）单晶。我们发现两种不同的PG组分的证据在PG状态的正反射率的变化，其特征在于，松弛时间尺度τ_快≈0.2皮秒和τ_减缓≈2 PS与在两个振幅突然变化甲_快速和甲_慢在PG-开口温度T *。前者在T _c处无明显变化，与SC QP共存。后者的振幅在SC相位波动T _p处开始减小，在T _c处消失。 其次是负振幅，表示SC QP的出现，因此表明存在超导性竞争。