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Superconductor-ferromagnet thermoelectric detector (SFTED) is a novel ultrasensitive radiation detector based on the giant thermoelectric effect in superconductor-ferromagnet tunnel junctions. This type of detector can be operated without the need of additional bias lines, and is predicted to provide a performance rivaling transition-edge sensors and kinetic inductance detectors. Here we report our numerical studies on the SFTED noise equivalent power, energy resolution and time constant, and the feasibility of a SQUID readout in both bolometric and calorimetric regimes, with the goal to provide practical design parameters for the detector fabrication and the readout circuitry implementation.

Periodic hole array phononic crystals (PnC) can strongly modify the phonon dispersion relations, and have been shown to influence thermal conductance coherently, especially at low temperatures where scattering is suppressed. One very important parameter influencing this effect is the period of the structure. Here, we measured the sub-Kelvin thermal conductance of nanofabricated PnCs with identical hole filling factors, but three different periodicities, 4, 8, and 16 µm, using superconducting tunnel junction thermometry. We found that all the measured samples can suppress thermal conductance by an order of magnitude, and have a lower thermal conductance than the previously measured smaller period, 1 µm and 2.4 µm structures. The 8 µm period PnC gives the lowest thermal conductance of all the samples above, and has the lowest specific conductance/unit heater length observed to date in PnCs. In contrast, coherent transport theory predicts that the longest period should have the lowest thermal conductance. Comparison to incoherent simulations suggests that diffusive boundary scattering is likely the mechanism behind the partial breakdown of the coherent theory.

Direct laser writing (DLW) lithography using two‐photon absorption is a powerful technique mostly used for the fabrication of complex structures in micro‐ and nanoscale, by photopolymerizing a negative‐tone resist. In contrast, herein, it is demonstrated that DLW is also well suited for fabricating nano‐ to microscale metallic structures using liftoff and a positive‐tone photoresist. It is shown first that versatile, fast, and large‐area fabrication is possible on flat 2D insulating substrates, and an expression for how the line width varies with the scanning speed is derived, with excellent agreement with the experiments. Even more interestingly, a unique application for the DLW lift‐off process is demonstrated, by fabricating submicron scale metallic wiring on uneven substrates with sloping elevation changes as high as 20 μm. Such fabrication is practically impossible with more standard lithographic techniques.