2013/12/22 by Maria Roslova, S. A. Kuzmichev, Roslova, Maria +24
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Rare-earth and actinide compounds #Semiconductor materials and interfaces #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.1312.6441
27 pages, 11 figures
arxiv created 2014/03/03 · arxiv updated 2014/03/04
Using the self-flux technique we grew superconducting (K1-zNaz)xFe2-ySe2 (z = 0.3) single crystals. The EDX mapping revealed the uniform elements distribution on the crystal surface while the XRD measurements indicate that the crystals are compositionally inhomogenous on nanoscale. The physical properties of the as-prepared sample are characterized by electrical resistivity, magnetization and specific heat measurements. Resistivity measurements show the onset of the superconducting transition at 33 K and zero resistivity at 31.7 K. The large upper critical field Hc2(0) was estimated as high as about of 140 T for the in-plane field and 38 T for the out-of-plane field. The anisotropy of Hc2ab(0)/Hc2c(0) and coherence lengths ξab(0)/ξc(0) was found to be around 3.7. The pioneer studies by multiple Andreev reflections effect spectroscopy ("break-junction" technique) revealed the presence of two anisotropic superconducting gaps ΔL = (9.3±1.5) meV, ΔS = (1.9±0.4) meV, and provided measuring of the ΔL(T) temperature dependence. The BCS-ratio for the large gap 2ΔL/kBTcbulk ≈ 6.3 points to a strong electron-boson coupling in the "driving" condensate characterized by ΔL order parameter.