Dynamic fluctuations in the superconductivity of NbN films from microwave conductivity measurements
Dynamic fluctuations in the superconductivity of NbN films from microwave conductivity measurements
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DOI：
10.1103/physrevb.73.174522
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发表时间：
2006-05-01
影响因子：
3.7
通讯作者：
Fujimaki, Akira
中科院分区：
文献类型：
--
作者：
Ohashi, Takeyoshi;Kitano, Haruhisa;Fujimaki, Akira
我们用微波宽带技术测量了NbN薄膜在0.1 ~ 10 GHz零磁场中的复交流电导率σ（Ω）= σ（1）（Ω）-i σ（2）（Ω）随频率和温度的变化。在超导临界温度Tc附近，由于超导涨落效应，σ（1）（Ω）和σ（2）（Ω）都表现出低频极限的快速增加。对于薄于300 nm的薄膜，波动电导率σ（fl）（Ω，T）的频率和温度依赖性被成功地缩放到一个缩放函数，这是符合Aslamazov和Larkin模型的二维（2D）的情况下。对于较厚的膜，sigma（fl）（omega，T）数据不能按比例缩放，但表明当温度从上方接近T-c时，发生从三维到2D的尺寸交叉。这为目前感兴趣的更奇特的超导体的交流涨落电导率提供了一个很好的参考。
We have measured the frequency and temperature dependences of complex ac conductivity, sigma(omega)=sigma(1)(omega)-i sigma(2)(omega), of NbN films in zero magnetic fields between 0.1 and 10 GHz using a microwave broadband technique. In the vicinity of superconducting critical temperature T-c both sigma(1)(omega) and sigma(2)(omega) showed a rapid increase in the low frequency limit owing to the fluctuation effect of superconductivity. For the films thinner than 300 nm, frequency and temperature dependences of fluctuation conductivity sigma(fl)(omega,T) were successfully scaled onto one scaling function, which was consistent with the Aslamazov and Larkin model for two-dimensional (2D) cases. For thicker films, sigma(fl)(omega,T) data could not be scaled, but indicated that the dimensional crossover from three dimensions to 2D occurred as the temperature approached T-c from above. This provides a good reference of ac fluctuation conductivity for more exotic superconductors of current interest.