Optical and Tunneling Studies of Energy Gap in Superconducting Niobium Nitride Films
Optical and Tunneling Studies of Energy Gap in Superconducting Niobium Nitride Films
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超导氮化铌薄膜能隙的光学和隧道研究
DOI：
10.1007/s10909-019-02324-1
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发表时间：
2020
影响因子：
2
通讯作者：
and Z. Wang
中科院分区：
文献类型：
--
作者：
Y. Uzawa;S. Saito;W. Qiu;K. Makise;T. Kojima;and Z. Wang
我们已经制备了一个外延氮化铌（NbN）薄膜和NbN/AlN/NbN隧道结来研究能隙。通过太赫兹时域光谱测量了临界温度（TC）约为14 K的41 nm厚薄膜的电导率谱，得到了约为1.2 THz的差距频率。一个不明确的差距，建议由于加宽的开始吸收的温度升高。另一方面，隧道结的电流-电压曲线测量显示，随着温度升高，在差距电压为5.6 mV（对应于1.4 THz）时，电流以模糊的形状上升。我们发现，这两个间隙加宽可以解释通过引入一个温度依赖的虚能隙部分的超导能隙，对应于一个有限的准粒子寿命的NbN膜。
We have prepared an epitaxial niobium nitride (NbN) film and NbN/AlN/NbN tunnel junctions to investigate the energy gaps. By measuring the optical conductivity spectrum of a 41-nm-thick film with the critical temperature (TC) of about 14 K by terahertz time-domain spectroscopy, we obtained the gap frequency of about 1.2 THz. An ill-defined gap was suggested due to the broadening of the onset of absorption as the temperature increases. On the other hand, the current–voltage curve measurement of the tunnel junctions showed the current rise at the gap voltage of 5.6 mV (corresponding to 1.4 THz) with a smeared shape as the temperature increases. We found that both gap broadenings can be explained by introducing a temperature-dependent imaginary energy gap part into the superconducting energy gap, corresponding to a finite quasi-particle lifetime in the NbN films.