Observation of a bi-critical point between antiferromagnetic and superconducting phases in pressurized single crystal Ca0.73La0.27FeAs2

Angular-dependent magnetoresistance study in Ca0.73La0.27FeAs2: a 'parent' compound of 112-type iron pnictide superconductors

We report a study of angular-dependent magnetoresistance (AMR) with the magnetic field rotated in the plane perpendicular to the current on a Ca_0.73La_0.27FeAs₂ single crystal, which is regarded as a 'parent' compound of 112-type iron pnictide superconductors. A pronounced AMR with twofold symmetry is observed, signifying the highly anisotropic Fermi surface. By further analyzing the AMR data, we find that the Fermi surface above the structural/antiferromagnetic (AFM) transition (T _s/T _N) is quasi-two-dimensional (quasi-2D), as revealed by the 2D scaling behavior of the AMR, Δρ/ρ(0) (H, θ)  =  Δρ/ρ(0) (µ ₀ Hcosθ), θ being the magnetic field angle with respect to the c axis. While such 2D scaling becomes invalid at temperatures below T _s/T _N, the three-dimensional (3D) scaling approach by inclusion of the anisotropy of the Fermi surface is efficient, indicating that the appearance of the 3D Fermi surface contributes to anisotropic electronic transport. Compared with other experimental observations, we suspect that the additional 3D hole pocket (generated by the Ca d orbital and As1 p _z orbital) around the Γ point in CaFeAs₂ will disappear in the heavily electron doped regime, and moreover, the Fermi surface should be reconstructed across the structural/AFM transition. Besides, a quasi-linear in-plane magnetoresistance with H//ab is observed at low temperatures and its possible origins are also discussed. Our results provide more information to further understand the electronic structure of 112-type IBSs.