Transport and anisotropy in single-crystalline SrFe2As2 and A0.6K0.4Fe2As2 (A=Sr, Ba) superconductors

We have successfully grown high-quality single crystals of SrFe2As2 and A(0.6)K(0.4)Fe(2)As(2)(A=Sr, Ba) using flux method. The resistivity, specific heat, and Hall coefficient have been measured. For parent compound SrFe2As2, an anisotropic resistivity with rho(c)/rho(ab) as large as 130 is obtained at low temperatures. A sharp drop in both in-plane and out-plane resistivities due to the spin-density-wave (SDW) instability is observed below 200 K. The angular dependence of in-plane magnetoresistance shows twofold symmetry with field rotating within ab plane below SDW transition temperature. This is consistent with a stripe-type spin ordering in SDW state. In K-doped A(0.6)K(0.4)Fe(2)As(2)(A=Sr, Ba), the SDW instability is suppressed and the superconductivity appears with T-c above 35 K. The rather low anisotropy in upper critical field between H parallel to ab and H parallel to c indicates that interplane coupling plays an important role in hole-doped Fe-based superconductors.