New constraints on dark matter from superconducting nanowires

Superconducting nanowires, a mature technology originally developed for quantum sensing, can be used as a target and sensor with which to search for dark matter interactions with electrons. Here we report on a 180-hour measurement of a tungsten silicide superconducting nanowire device with a mass of 4.3 nanograms. We use this to place new constraints on dark matter–electron interactions, including the strongest terrestrial constraints to date on sub-MeV (sub-eV) dark matter that interacts with electrons via scattering (absorption) processes.

Figure 1

SEM images of the prototype WSi SNSPD device taken at different magnifications. Left: the entire device with two contact pads and active area of $400\mathrm{\mu }\mathrm{m}$ by $400\mathrm{\mu }\mathrm{m}$. Top right: view of the detector area in the center. Bottom right: several individual nanowires.

Figure 2

Schematic cross section of a single nanowire. Layers are not drawn to scale.

Figure 3

Sketch of the experimental setup. The prototype device was embedded in a light-tight box and cooled to a temperature of 0.3 K. The high-frequency signal was carried out of the cryostat though a low-noise cryogenic amplifier to the readout, while the dc path was connected to a low-noise voltage source. A low-temperature bias tee decoupled the high-frequency path from the dc bias path at the 3 K stage.

Figure 4

New constraints and updated expected reach for DM–electron scattering in SNSPDs via light (left panel) and heavy (right panel) mediators at 95% CL as a function of DM mass. The shaded blue region indicates the new bound placed by our prototype device with 4.3 ng exposed for 180 hours with four dark counts observed. The dot-dashed blue curve indicates results from our previous run [24] with an exposure of 10000 seconds, now updated to include in-medium effects. Other curves show the projected reach for WSi, NbN, or Al targets with the indicated exposures and thresholds, assuming that sources of dark counts are eliminated. Solid curves conservatively neglect thin-layer enhancements. Dashed curves include these enhancements following Ref. [70]. Dotted curves conservatively include estimated effects of dissipation in neighboring layers (see text). The $177\mathrm{\mu }\mathrm{g}$ exposure corresponds to a $10\mathrm{cm}\times 10\mathrm{cm}$ area of NbN at 4 nm thickness and a 50% fill factor, and 248 (124) meV threshold corresponds to a $5(10)\mathrm{\mu }\mathrm{m}$ wavelength. In shaded gray we show the existing constraints from SENSEI [49], SuperCDMS HVeV [51], DAMIC [47], Xenon10 [14], DarkSide-50 [43], and Xenon1T [48].

Figure 5

New constraints and updated expected reach for DM absorption in SNSPDs as a function of DM mass, for a relic kinetically mixed dark photon. As in Fig. 4, the shaded blue region indicates the new bound at 95% CL, and other solid curves indicate projections for future experiments, neglecting possible geometric effects. The shaded gray region shows existing terrestrial constraints from Xenon data [75], SuperCDMS [42], DAMIC [47], EDELWEISS [50], FUNK [76] and SENSEI [49], while the yellow region indicates model-dependent stellar bounds [75, 77, 78].