Possible Superconductivity above 25 K in Single-Crystalline Co-Doped BaFe2As2

Abstract

We present the superconducting properties of single-crystalline Ba(Fe 0.9 Co 0.1 ) 2 As 2 by measuring its magnetization, resistivity, upper critical field, Hall coefficient, and magneto-optical images. The magnetization measurements reveal a fish-tail hysteresis loop at high temperatures and a relatively high critical current density above J c = 10 5 A/cm 2 at low temperatures. The upper critical field determined by resistive transition is anisotropic with an anisotropic parameter of ∼3.5. Hall effect measurements indicate that Ba(Fe 0.9 Co 0.1 ) 2 As 2 is a multiband system and that the mobility of electrons is dominant. Magneto-optical imaging reveals a prominent Bean-like penetration of vortices, although there is a slight inhomogeneity in a sample. Moreover, we observe distinct superconductivity above 25 K, which leads us to speculate that a higher transition temperature can be realized by fine-tuning the Co-doping level.