The superconductor KxSr1- xFe2As2: normal state and superconducting properties

The normal state and superconducting properties are investigated in the phase diagram of KxSr1- xFe2As2 for 0⩽x⩽1. The ground state upper critical field, Hc2(0), is extrapolated from magnetic field-dependent resistivity measurements. Hc2(0) scales with the critical temperature, Tc, of the superconducting transition. In the normal state, the Seebeck coefficient is shown to experience a dramatic change near a critical substitution of x≃0.3. This is associated with the formation of a spin density wave state above the superconducting transition temperature. The results provide strong evidence for the reconstruction of the Fermi surface with the onset of magnetic order.