Theoretical study on the magnetic properties of the superconductor FeSe

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