Harrabi Khalil, Mekki Abdelkrim, Milošević Milorad V
Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
Interdisciplinary Research Center (RC) for Intelligent Secure Systems, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia.
Nanomaterials (Basel). 2024 Sep 30;14(19):1585. doi: 10.3390/nano14191585.
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.
我们测量了具有不同纳米尺度厚度的铌钛（NbTi）超导细丝对阶跃电流脉冲的时间电压响应，这些电流脉冲会诱导由热点机制控制的非平衡超导态。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。通过采用含时金兹堡 - 朗道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，这与超导体 - 衬底界面处声子传输的声学失配理论相符。由此我们发现，在抛光蓝宝石上的NbTi薄膜，每纳米厚度的能隙弛豫时间为104皮秒。我们进一步表明，与衬底的界面相互作用对能隙弛豫时间有显著影响，在T = 5.75 K时，对于50纳米厚的NbTi条带，在氧化硅（SiOx）上观察到的值为9纳秒，在熔融石英上为6.8纳秒，在蓝宝石上为5.2纳秒。这些见解对于优化超导传感技术非常有价值，特别是对于在纳米级超导桥和细丝的瞬态区域工作的单光子探测器。
