Anisotropic characteristics and critical behaviors in Mn doped K0.8Fe2Se2 single crystal

• We report the superconducting properties of K0.8Fe1.97Mn0.03Se2 crystal as containing two new phases with Tc > 32 K.
• The upper critical fields μ0Hc2 (T) were discriminated by magnetotransport measurements.
• The μ0Hc2 (0) values are estimated to be above 100 T for H ∥ ab and 50 T for H ∥ c.
• The pinning potential and critical current density were evaluated and discussed.

We report the anisotropic superconducting properties of nominal K0.8Fe1.97Mn0.03Se2 single crystal. The phase separation is characterized by X-ray diffraction and scanning electron microscopy techniques. The experimental crystal has three superconducting transitions at Tc1mag=31.9K for the first, Tc2mag=36.8K for second, Tc3mag=42.5K for third superconducting phase as seen from magnetic susceptibility measurements. We can discriminate the anisotropic upper critical fields between the second and third superconducting phase by magnetotransport measurements. The upper critical field at T = 0 K are estimated to be μ0Hc2∥ab(0)=137.4T and μ0Hc2∥c(0)=51.8T for the second, μ0Hc2∥ab(0)=178.4T and μ0Hc2∥c(0)=52.6T for third superconducting phase, respectively. We also discuss the vortex pinning in framework of thermally activated flux flow model, by which the pinning potential U0 of the second superconducting phase is derived to be U0∥c=5.1×103K and U0∥ab=6.1×103K at μ0H = 0.25 T, respectively. Finally, we will evaluate the total critical current density, which shows moderate values Jc(0) ∼ 103 − 104 A/cm2 at T = 3 K.