Tuning of Anisotropy by Controlling Excess Fe Concentration in FeyTe0.6Se0.4

We have grown single crystals of FeTe0.6Se0.4 and Fe0.95Te0.6Se0.4 by a conventional self-flux method. The superconducting properties were investigated by magnetization measurements. We found that the anisotropy of the superconducting state for FeTe0.6Se0.4 was clearly higher than that for Fe0.95Te0.6Se0.4. This indicates that the excess Fe concentration can tune the anisotropy of FeyTe0.6Se0.4.