纳米薄 NbTi 超导细丝中能隙弛豫与热逃逸的特征时间：厚度依赖性与衬底效应
Characteristic times for gap relaxation and heat escape in nanothin NbTi superconducting filaments: thickness dependence and effect of substrate
AI总结：
本文通过测量不同厚度 NbTi 超导细丝的瞬态电压响应并结合含时 Ginzburg-Landau 理论，揭示了能隙弛豫时间随厚度线性变化及衬底界面对其的显著影响，为优化单光子探测器等超导传感技术提供了关键依据。
摘要：
我们测量了具有不同纳米尺度厚度的 NbTi 超导细丝在阶跃电流脉冲作用下的时间电压响应，这些脉冲会诱导由热点机制主导的非平衡超导态。这种检测到的电压在延迟时间 td 之后出现，td 与能隙弛豫时间和热逃逸时间密切相关。通过采用含时 Ginzburg-Landau 理论将延迟时间与施加电流联系起来，我们确定能隙弛豫时间与薄膜厚度呈线性关系，这与超导-衬底界面处声子透射的声学失配理论一致。由此我们发现，在抛光蓝宝石衬底上的 NbTi 薄膜，其能隙弛豫时间为每纳米厚度 104 ps。我们进一步表明，与衬底的界面相互作用显著影响能隙弛豫时间，在 T = 5.75 K 时，对于 50 nm 厚的 NbTi 条带，在 SiOx 上观测到的值为 9 ns，在熔融石英上为 6.8 ns，在蓝宝石上为 5.2 ns。这些见解对于优化超导传感技术具有重要价值，特别是对于工作在纳米薄超导桥和细丝瞬态区间的单光子探测器。
英文摘要：
We measured the temporal voltage response of NbTi superconducting filaments with varied nanoscale thicknesses to step current pulses that induce non-equilibrium superconducting states governed by a hot-spot mechanism. Such detected voltage emerges after a delay time td, which is intimately connected to the gap relaxation and heat escape times. By employing time-dependent Ginzburg-Landau theory to link the delay time to the applied current, we determined that the gap relaxation time depends linearly on film thickness, aligning with the acoustic mismatch theory for phonon transmission at the superconductor-substrate interface. We thereby find a gap relaxation time of 104 ps per nm of thickness for NbTi films on polished sapphire. We further show that interfacial interaction with the substrate significantly impacts the gap relaxation time, with observed values of 9 ns on SiOx, 6.8 ns on fused silica, and 5.2 ns on sapphire for a 50 nm thick NbTi strip at T = 5.75 K. These insights are valuable for optimizing superconducting sensing technologies, particularly the single-photon detectors that operate in the transient regime of nanothin superconducting bridges and filaments
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