Weak superconducting fluctuations and small anisotropy of the upper critical fields in an Fe1.05Te0.85Se0.15 single crystal

摘要

We have investigated the temperature dependence of the resistive uppercritical fields ($\mu_{0}H_{\rm c2}(T)$) for anFe$_{1.05}$Te$_{0.85}$Se$_{0.15}$ single crystal, which exhibitsuperconductivity at $T_{\rm c} \sim 14 K, in magnetic fields of up to 55 T.Two-dimensional feature and superconducting fluctuations of the samples arefound to be weak, because the resistive broadening effect on applied magneticfields of up to 14 T is small. The Pauli paramagnetic effect is obviouslyevidenced by the strong suppression of the $\mu_{0}H_{\rm c2}^{ab}(T)$ ($H\parallel ab$) curve and nearly isotropic $\mu_{0}H_{\rm c2}(0) \approx 47 T isseen for both $H \parallel ab$ and $H \parallel c$. This fact is almostidentical to the results of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystalsreported previously. We have discussed that the small anisotropy of the uppercritical field at low temperatures in Fe$_{1+y}$(Te,Se) systems against thevariation of the Te/Se ratio.