Superconductivity at 32 K and anisotropy in Tl 0.58 Rb 0.42 Fe 1.72 Se 2 crystals

Tl 0.58 Rb 0.42 Fe 1.72 Se 2 single crystals were successfully synthesized with the Bridgeman method. The physical properties are characterized by electrical resistivity, magnetization and Hall resistivity. Tl 0.58 Rb 0.42 Fe 1.72 Se 2 undergoes a superconducting transition at T c onset =32 K and T c zero =31.4 K. Extrapolation of the upper critical field H c 2 at T c to zero temperature gives a large value of H c 2 (0) ( H c 2 (0)=221 T for H ∥ ab and H c 2 (0)=44.2 T for H ∥ c ). The Hall coefficient changes sign upon cooling down, indicating a possible multi-band behavior. The normal-state magnetic susceptibility decreases with decreasing temperature, suggesting strong antiferromagnetic (AFM) spin fluctuations, which might be related to the superconductivity (SC).