Identifying the form of superconducting order parameter is still a controversial problem for the iron-based superconductor FeSe. Based on anisotropic two-component Ginzburg–Landau theory, we study the temperature dependence of upper critical field and London penetration depth for FeSe. Without including the spin paramagnetic effect, all of our theoretical calculations fit the experimental data well in a broad temperature range. Our results thus show that FeSe is a two-gap s-wave superconductor. And the anisotropy of effective masses in the band with larger (or smaller) gap can be estimated as about 10 (or 2) respectively.

中文翻译：

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超导体FeSe的磁性的理论研究

对于铁基超导体FeSe来说，确定超导阶数参数的形式仍然是一个有争议的问题。基于各向异性的两分量Ginzburg-Landau理论，我们研究了FeSe的上临界场和伦敦穿透深度的温度依赖性。在不包括自旋顺磁效应的情况下，我们所有的理论计算都可以在较宽的温度范围内很好地拟合实验数据。因此，我们的结果表明，FeSe是两间隙的s波超导体。间隙较大（或较小）的带中有效质量的各向异性可以分别估计为约10（或2）。