Superconductivity atTc∼14 Kin single-crystallineFeTe0.61

Abstract

Single crystalline FeTe0.61Se0.39 with a sharp superconducting transition at Tc ∼ 14 K is synthesized via slow furnace cooling followed by low-temperature annealing. The effect of annealing on the chemical and superconducting inhomogeneities is carefully characterized. We also report resistivity, magnetization, and magneto-optical images of this crystal. Based on the Bean model, critical current density is estimated to exceed 1 × 10 5 A/cm 2 below 5 K under zero field. Weak fish-tail effect is identified at lower temperatures.

Iron chalcogenide superconductors at high magnetic fields

“…For example in (Ba,K)Fe 2 As 2 the J c (0) reaches 1 × 10 4 A cm −2 at 4.2 K [89]. But it should be noted that the J c for both iron chalcogenide and iron arsenic superconducting wires fabricated using PIT method are much smaller than those of single crystals [48,63,74], implying that the texturing of grains in wires is important due to the GB weak-link effect. Coated conductor technique has been successfully developed for the YBCO coated conductors (secondgeneration HTS wires) to overcome the weak-link effect [61].…”

Effects of Iodine Annealing on Fe1+yTe0.6Se0.4

“…Figure 3(c) summarizes the evolution of T c and the self-field J c (2 K) with the molar ratio of iodine. T c reaches the highest value of 14.5 K when annealing in 6.7% iodine and J c is up to 5×10 5 A/cm 2 after annealing in 5.6% iodine under a self-field at 2 K, which is larger than those reported for Fe(Te,Se) [10,[21][22][23][24][25][26] and similar to the highest reported value for oxygen-annealed Fe 1+y Te 0.6 Se 0.4 [13,27]. It has been proved that such a large J c cannot be obtained from the superconductivity only near the surface [13], which indicates that the sample maintaining such a large J c obtained in our experiment must be a bulk superconductor.…”

“…However, the excess iron that is located at the interstitial site in the Te/Se layer [7] has strong magnetism and acts as pair a breaker and suppresses superconductivity [8,9]. Thus, the as-grown Fe 1+y Te 1-x Se x single crystals only show filamentary superconductivity [10,11].…”

Effect of spacer layer on flux-pinning properties of iron-based superconductors

“…These data provide further support to the stronger pinning in the 1111 family with respect to the samples of the 11 family, that should be related to the presence of the spacer layer and controlled disorder in the ac-tive layer. An additional evidence of higher flux-pinning in the 1111 system is provided by the critical current measurements with high DC magnetic field on single crystal samples of SmFeAsO 0.7 F 0.25 [62] and FeTe 0.61 Se 0.39 [63]. Finally the Figures 3a and 4a show a further effect: the flux pinning produced by controlled-disorder due to strain/stress by 'space layer' and/or by doping can be optimized even within the same Fe-HTSC family, that is, some compounds show a better matching between FLL and flux pinning.…”