Superconductivity and vortex pinning in Fe _1.04 Te _0.60 Se _0.40 single crystal

Abstract

Measurements of specific heat, resistivity, and magnetic hysteresis loop were performed on high-quality Fe1.04Te0.60Se0.40 single crystal. The exponential decay of the specific heat of the sample can be well described by the BCS-weak coupling theory. The resistive upper critical fields Hc2 were extracted with the zero-resistance criteria. The slopes dHc2ab /dT and dHc2c /dT collected from the existing data in the iron chalcogenide family are roughly scaled by the relation dHc2 /dT∝Tc for both H∥c and H∥ab configurations, which can be interpreted in terms of a pair-breaking effect. Comparing the AFe2As2 superconductors, the second magnetization peak observed in the magnetic hysteresis loops for H∥c is strongly broadened for the Fe1.04Te0.60Se0.40 single crystal. We demonstrate that the δTc pinning associated with spatial fluctuations of the transition temperatures gives rise to the broadening of the second peak.