Applicability of two-band Ginzburg–Landau theory in 112-type iron-based superconductors

Abstract

Experiments show that the 112-type iron-based superconductor Ca1−xLaxFeAs2 (x ∼ 0.2) has two-band superconducting properties. Previous reports have shown that the two-band and spin paramagnetic effects are responsible for the inter-plane (H//c) and in-plane (H//ab) upper critical field behaviors of the 112-type iron-based superconductor Ca1−xLaxFeAs2 (x ∼ 0.2) respectively. With the effective mass anisotropy, the present paper suggests that the two-band Ginzburg–Landau theory may be applicable to study the magnetic properties of 112-type iron-based superconductors in arbitrary direction. The theoretical calculations on the upper critical fields fit well with the experimental results over a wide range of temperature. In addition, the upper critical field increases with the increase of the directional angle, which is similar to the result for MgB2. By comparing the upper critical fields of Ca1−xLaxFeAs2 and Ca1−xLaxFe0.98Co0.02As2, we also analyze how impurities affect the physical properties of 112-type iron-based superconductors.