Self-heating hotspots in superconducting nanowires cooled by phonon black-body radiation.

Controlling thermal transport is important for a range of devices and technologies, from phase change memories to next-generation electronics. This is especially true in nano-scale devices where thermal transport is altered by the influence of surfaces and changes in dimensionality. In superconducting nanowire single-photon detectors, the thermal boundary conductance between the nanowire and the substrate it is fabricated on influences all of the performance metrics that make these detectors attractive for applications. This includes the maximum count rate, latency, jitter, and quantum efficiency. Despite its importance, the study of thermal boundary conductance in superconducting nanowire devices has not been done systematically, primarily due to the lack of a straightforward characterization method. Here, we show that simple electrical measurements can be used to estimate the thermal boundary conductance between nanowires and substrates and that these measurements agree with acoustic mismatch theory across a variety of substrates. Numerical simulations allow us to refine our understanding, however, open questions remain. This work should enable thermal engineering in superconducting nanowire electronics and cryogenic detectors for improved device performance.

Large-Area Superconducting Nanowire Single-Photon Detectors for Operation at Wavelengths up to 7.4 µm.

The optimization of superconducting thin-films has pushed the sensitivity of superconducting nanowire single-photon detectors (SNSPDs) to the mid-infrared (mid-IR). Earlier demonstrations have shown that straight tungsten silicide nanowires can achieve unity internal detection efficiency (IDE) up to λ = 10 µm. For a high system detection efficiency (SDE), the active area needs to be increased, but material nonuniformity and nanofabrication-induced constrictions make mid-IR large-area meanders challenging to yield. In this work, we improve the sensitivity of superconducting materials and optimize a high-resolution nanofabrication process to demonstrate large-area SNSPDs with unity IDE at 7.4 µm. Our approach yields large-area meanders down to 50 nm width, with average line-width roughness below 10%, and with a lower impact from constrictions compared to previous demonstrations. Our methods pave the way to high-efficiency SNSPDs in the mid-IR band with potential impacts on astronomy, imaging, and physical chemistry.