超导材料NbS2上临界磁场的理论分析

根据两带Ginzburg-Landau 理论计算了层状超导材料NbS₂的上临界磁场, 以及上临界磁场各向异性参数随温度的变化情况, 并将NbS₂与MgB₂, NbSe₂上临界磁场的各向异性进行比较. 所得计算结果与已有实验数据符合得很好, 充分说明了NbS₂的超导电性具有两能隙特征. NbS₂上临界磁场各向异性参数在5.0 K附近逐渐变小, 这与MgB₂和NbSe₂有相似之处. 但NbS₂的上临界磁场各向异性参数大约为7.3, 明显大于MgB₂和NbSe₂. 计算结果还表明, NbS₂较大能隙所对应能带的有效质量比约为54, 另一能带的有效质量基本为各向同性.

Theoretical analysis on the upper critical field of superconductor NbS2

From the two-band Ginzburg-Landau theory, we study the temperature dependence of upper critical field on the layered superconductor NbS₂. The temperature dependence of the anisotropic parameter for upper critical filed is also obtained. All the results fit the experimental data well in a broad temperature range. Thus our results show strong evidence that two-gap scenario is better to account for the superconductivity of NbS₂. The anisotropic parameter of the upper critical field for NbS₂ starts to decrease from 5.0 K, and this behavior is similar to those of MgB₂ and NbSe₂. However for NbS₂ this number is about 7.3, which is much greater than the ones in MgB₂ and NbSe₂. The results also show that the band with the larger gap exhibits that the effective mass ratio between the in-plane and out-of-plane direction is about 54, and the other band indicates that the effective mass ratio is almost isotropic.