Tuning Superconductivity in Superconducting Nanocomposites
Min Kai Lee1,2*, E. V. Charnaya2,3, L. J. Chang2, Yu. A. Kumzerov4
1MOST Instrument Center At NCKU, National Cheng Kung University, Tainan, Taiwan
2Department of Physics, National Cheng Kung University, Tainan, Taiwan
3Institute of Physics, St. Petersburg State University, St. Petersburg, Petrodvorets, Russian Federation
4A. F. Ioffe Physico-Technical Institute RAS, St. Petersburg, Russian Federation
* presenting author:Min Kai Lee, email:anion3143@hotmail.com
In this study, we investigate superconducting nanocomposites (SCNCs) to elucidate superconductivity in nanostructured superconductor. In the first part, we demonstrate that the geometry of template influence the superconductivity of type I superconductor embedded into nanoconfinement. Exotic phase diagrams in the opal SCNCs magnetism studies reveal an enhanced upper critical field (Hc2(0)) and curvature crossover of upper critical field line. Additionally, according to the field dependence of Ua(H), curvature crossover of the upper critical field line can occur, owing to vortex phase transition. Moreover, a universal value of crossover field Hco~1/2 Hc2(0) is found for opal SCNCs. Results of this study demonstrate a universal superconducting behavior for SCNCs with nearly the same nanostructure. Such an exotic superconductivity is attributed to a geometrical effect in the nanometer regime. In the second part, we utilize the property of eutectic alloys and the Holm-Meissner effect to tune the vortex dynamic and superconductivity in SCNCs. We mix 99.99% pure Gallium and Indium for four different weight %, i.e. 96:4, 94:6, 90:10, 15:85 and embed these GaIn eutectic alloys into porous glasses with average pore size 7 nm. The GaIn eutectic alloys exhibit phase separation during solidification and introduce superconductor-normal metal-superconductor junctions into the mesoscopic network. Our transport measurements show that the curvature crossover of upper critical field line of SCNCs depressed by increasing Indium doping ratio. Such variation indicate distinct behaviors of type I and type II superconducting mesoscopic network.

Keywords: superconductivity, eutectic, nanocomposites