Figure 1

$\Delta R/R$ signal (solid lines) as a function of delay time at different temperatures (from 95 to 38 K) on a Y-Bi2212 overdoped single crystal. The dashed lines are the fits to the experimental curves (see the fitting function in the text). The black line represents the $\Delta R/R$ trace at $T$${}_c$. In the inset we report the fit parameters of the SCS, i.e., decay time ${\tau }_B$ (red circles) and amplitude $B$ (black circles). The error bars obtained from the fit procedure are displayed for all the data. The high uncertainty on the decay time above $T$${}_c$ led us to plot just the error bar and not the data point. The black arrow on the temperature axis of the inset shows the superconducting transition amplitude of the sample.Reuse & Permissions

Figure 2

(a) Excitation density for both thermal and photoinduced QPs, respectively $n_T$ and $n_{\mathrm{ph}}$ (solid lines), and their sum $N_{\mathrm{tot}}$ (dashed line) as a function of temperature. For the thermal QP we assumed Eq. (2) and a $d$-wave-like $\Delta (T)$ dependence and we compared the predicted value with the one obtained through Eq. (3) from the experimental $B(T)$ amplitude (inset of Fig. 1). On the right axis we report the experimental decay rate obtained from the fit in Fig. 1. (b) $\gamma /T^2$ as a function of the reduced temperature in a double-logarithmic plot. The long-dashed line represents the $(1-T/T_c){}^{1/2}$ power-law dependence. In the inset we show the result of the numerical integration of the $d$-wave BCS gap equation as a function of temperature compared to the $(1-T/T_c){}^{1/2}$ dependence (Ref. 36). In all the panels the vertical dashed lines divide the low- from the high-temperature regime (see text). In (b) the error bars are within the black circles’ size.Reuse & Permissions

Figure 3

$\Delta R/R$ signal, solid lines in (a) and (b), at 10 K at different pump fluences. The fits to the experimental curves are shown with dashed lines. The fit parameters (decay time ${\tau }_B$ and amplitude $B$) are reported in (c) as a function of pump fluence. In (a) the low-intensity regime is shown, corresponding to $\Phi <{\Phi }_C$ in (c). The short-dashed line in (c) is the linear fit in the low-fluence regime. (b) and (c) for $\Phi >{\Phi }_C$ correspond to the high-excitation regime. The long-dashed line in (c) represents the saturation value. The error bars in (c) are within the circles’ size.Reuse & Permissions

Figure 4

$|\Delta R/R|$ traces in logarithmic scale at several pump fluences at $T$ $=$ 10 K, where the exponential $A$ component has been subtracted. The dashed lines represent the exponential fit of the decay. The solid line refers to the curve at $\Phi =77$ $\mu$J/cm${}^2$.Reuse & Permissions

Figure 5

$|\Delta R/R|$ of the SCS at $\Phi =26$ $\mu$J/cm${}^2$ and the corresponding fit (solid line) obtained with the numerical solutions of the time-dependent Rothwarf-Taylor equations [Eqs. (7) and (8)] considering a $d$-wave gap symmetry. The $a$ optimal value is ($1.0\pm 0.2$)$\times$10${}^{-20}$ cm${}^3$. For comparison we also show the fits when the parameter $a$ is fixed to the values $a=2.45\times {10}^{-20}$ cm${}^3$ (short-dashed line) and $a=0$ (long-dashed line), which is equivalent to the time-independent RT model. In the inset we show the corresponding function $[{\gamma }_{\mathrm{esc}}(t)]{}^{1/2}$, which is proportional to the nonequilibrium superconducting gap $\Delta (t)$ [Eq. (9)]. We normalized the gap to the low-fluence value.Reuse & Permissions

Figure 6

(a) Experimental decay rate extracted by the fit of the $|\Delta R/R|$ traces at different pump fluences (see Fig. 3). The dashed line is the linear fit obtained in the low-intensity limit. The error bars are within the circles’ size. (b) $\delta$ as a function of $|\Delta R/R|$. We normalized the value to the zero-fluence limit, which correspond to the equilibrium gap $\Delta (T,0)$. The error bars account both for the 30$\%$ uncertainty in the determination of $\alpha$ and for the difference between the results obtained within the analytic and the numerical solutions of the RT equations (see text). On the same graph (right and upper axes) we show the analytical results of the $\mu$* model for the superconducting gap $\Delta$ as a function of QP density $n_{\mathrm{ph}}$ as reported in Ref. 2 for both $s$-wave and $d$-wave cases. The threshold values are calculated numerically within the $\mu$* model (Ref. 2) at a finite temperature corresponding to 10 K in our experiment.Reuse & Permissions