Possible Phase Separation and Transport Properties in Large Superconducting Ca0.77La0.18Fe0.90As2 Crystals

We synthesized large superconducting single crystal Ca0.77La0.18Fe0.90As2 ('112' type) of 2 millimeter size. Scanning electron microscopy (SEM) measurements revealed that bright and dark stripes alternately spread on the surface of crystals, indicating possible existence of intrinsic phase separation. Temperature (T) -dependent resistivity, Hall effect and magneto-resistance (MR) were measured with magnetic field (H) applied to different directions of crystal. The upper critical field (Hc2) anisotropy was estimated with a moderate value around 2.8. Positive Hall coefficient (RH) and anisotropic MR were found and showed strong T-dependent feature. Below T about 100 K, abnormal behaviors appear simultaneously in resistivity derivative, Hall coefficient and MR, which indicates that other scattering mechanisms more than conventional multiband effect may exist.