Different resistivity response to spin-density wave and superconductivity at 20 K in Ca1-xNaxFe2As2

We report intrinsic transport and magnetic properties and their anisotropy in high-quality single-crystal CaFe2As2. The resistivity anisotropy (rho(c)/rho(ab)) is similar to 50, less than the 150 of BaFe2As2, which arises from the strong coupling along the c-axis due to an apparent contraction of about 0.13 nm compared to BaFe2As2. In sharp contrast to the case of parent compounds ROFeAs (R = rare earth) and MFe2As2 (M = Ba and Sr), spin-density-wave (SDW) ordering (or structural transition) leads to a steep increase of resistivity in CaFe2As2. Such a different resistivity response to SDW ordering is helpful to understand the role played by SDW ordering in Fe-based high-T-c superconductors. The susceptibility behavior is very similar to that observed in single-crystal BaFe2As2. A linear temperature-dependent susceptibility occurs above the SDW transition of about 165 K. Partial substitution of Na for Ca suppresses the SDW ordering (anomaly in resistivity) and induces superconductivity at similar to 20 K.