Figure 1

Measurement-apparatus temporal accuracy checks. (a) $V(t)$ and $I(t)$ (multiplied by a constant $R=62\Omega$) for a test resistor in place of a superconducting sample. (b) $dI(t)/dt$ and $V(t)$ (divided by a constant $L=15\mathrm{nH}$) for a test inductor in place of a superconducting sample. The voltages across the purely resistive and inductive loads are seen to track their respective current and current-derivative functions with subnanosecond accuracy.Reuse & Permissions

Figure 2

Time dependencies of voltage and current in niobium meanders at $T=3.84\mathrm{K}$. Panels (a) and (b) represent $V(t)$ and $dI/dt$ (scaled by a constant $L$) for samples A and B, respectively. Panels (c) and (d) show the corresponding $I(t)$ functions, which rise steadily during the voltage plateaus of the panels above; the time axes for panels (a) and (c) and for panels (b) and (d) are the same.Reuse & Permissions

Figure 3

(a) Measured total inductance, $L(t)=V(t).dt/dI(t)$, versus time for sample A. The curves correspond to the temperatures (from top to bottom): $T=6.10$, 5.91, 5.54, 5.17, 4.73, 4.10, and 3.78 K. (Each plot symbol on these curves corresponds to separately measured digital voltage sample. The period between samples is 100 ps.) (b) A similar $L(t)$ plot for sample B. For this panel, the temperatures (from top to bottom) are: $T=6.51$, 6.4, 6.22, 6.02, 5.84, 5.24, 4.64, and 3.84 K. Panels (c) and (d) show the temperature dependencies of the above measured $L$ values (taken on the plateaus around $t\sim 11\mathrm{ns}$) for samples A and B, respectively. The symbols show the experimental data and the solid line represents the least-squares fit to the two-parameter function $L(T)=L_g+L_k(0)/[1-(T/T_c{)}^2]$ as discussed in the text.Reuse & Permissions