Figure 1

(Color online) Speedup and latching of nanowire detectors with increased load impedance. (a) electrical model of detector operation. A hotspot is nucleated by absorption of a photon, producing a resistance $R_n$ in series with the wire’s kinetic inductance $L$. (b) Experimental circuit, including series resistor $R_S$, bias tee, and impedance of current source $R_{\text{dc}}$. (c) and (d) Averaged pulse shapes for $R_S=0,250\Omega$ $\left(L\sim 50\text{nH}\right)$; dashed lines are predictions with no free parameters. (e) $I_{\text{switch}}$ vs $R_S$. As $R_S$ is increased, $I_{\text{switch}}$ decreases, becoming less than $I_c$. (f) DE at $I_0=0.975I_{\text{switch}}$ vs $R_S$ (open squares). Also shown (crosses) are the expected DEs assuming that latching affects DE simply by limiting $I_0$ (obtained from DE vs $I_0$ at $R_S=0$).Reuse & Permissions

Figure 2

(Color online) Hotspot stability measurements. (a) Device schematic; two ground-signal-ground probes perform a high-impedance three-point measurement of $R_n$, with $R_L$ determined by probe position. (b) Equivalent electrical circuit. (c) and (d) Example $V\text{−}I$ curves, with $L=60\text{nH}$ and $L=605\text{nH}$, respectively. (e) and (f) Inferred $I_d$ and $R_n/R_L$ for the data shown in (d). In (e) the relaxation oscillations in the region $I_c<I_0<I_{\text{latch}}$ are shown schematically. Dashed lines show (e) $I_d=I_c$ and $I_d=I_{\text{ss}}$. (f) $R_{\text{ss}}=R_L\left(I_0/I_{\text{ss}}-1\right)$.Reuse & Permissions

Figure 3

(Color online) Summary of hotspot stability results. Data are shown from three different chips (indicated by different colors). Circles, squares, and triangles are data for $L=6–12$, 15–60, and 120–600 nH, respectively. In the ${\tau }_e⪢{\tau }_a$ limit (where NS domain-wall motion dominates the feedback), the data approach the dashed line, which is the prediction based on Eq. (1). The solid curves are obtained from Eq. (8) with a phase margin of $30°$; each curve corresponds to a fixed $L$ in the set (6,15,30,60,600) nH and spans the range of $R_L$ in the data. The dotted lines extend these predictions over a wider range of $R_L$. For ${\tau }_e⪡{\tau }_{\text{th}}$ the NS domain walls are effectively fixed and the temperature feedback dominates. In this regime the feedback is always unstable when $R_n\lesssim R_L$ (or equivalently, $I_0\lesssim 2I_{\text{ss}}$), as shown in the inset; the minimum stable $R_n$ are all above the dashed-dotted line $\left(R_n=R_L\right)$.Reuse & Permissions