Weak superconducting fluctuations and small anisotropy of the upper critical fields in an Fe_(1:05)Te_(0:85)Se_(0:15) single crystal

摘要

We have investigated the temperature dependence of the resistive upper critical fields [_(μ0)H_(c2)(T)] for an Fe _(1:05)Te_(0:85)Se_(0:15) single crystal, which exhibits superconductivity at T_c ～ 14K, 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_(μ0)H~(ab)_(c2) (T) (H || ab) curve and nearly isotropic_(μ0)H _(c2)(0) ≈ 47T is seen for both H || ab and H || c. This fact is almost identical to the results of Fe_(1+y)Te_(0:6)Se _(0:4) single crystals reported previously. We have discussed that the small anisotropy of the upper critical field at low temperatures in Fe _(1+y)(Te,Se) systems against the variation of the Te/Se ratio.