Weak Superconducting Fluctuations and Small Anisotropy of the Upper Critical Fields in an Fe1.05Te0.85Se0.15 Single Crystal

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We have investigated the temperature dependence of the resistive upper critical fields [$\mu_{0}H_{\text{c2}}(T)$] for an Fe1.05Te0.85Se0.15 single crystal, which exhibits superconductivity at $T_{\text{c}} \sim 14$ K, in magnetic fields of up to 55 T. Two-dimensional feature and superconducting fluctuations of the samples are found to be weak, because the resistive broadening effect on applied magnetic fields of up to 14 T is small. The Pauli paramagnetic effect is obviously evidenced by the strong suppression of the $\mu_{0}H_{\text{c2}}^{ab}(T)$ ($H \parallel ab$) curve and nearly isotropic $\mu_{0}H_{\text{c2}}(0) \approx 47$ T is seen for both $H \parallel ab$ and $H \parallel c$. This fact is almost identical to the results of Fe1+yTe0.6Se0.4 single crystals reported previously. We have discussed that the small anisotropy of the upper critical field at low temperatures in Fe1+y(Te,Se) systems against the variation of the Te/Se ratio.
2010-07-15