Magnetization studies of soft superconducting metals embedded into opal matrices
M. K. Lee1,2*, E. V. Charnaya1,3, L. J. Chang1, Yu. A. Kumzerov4
1Department of Physics, National Cheng Kung University, Tainan, Taiwan
2MOST Instrument Center At NCKU, National Cheng Kung University, Tainan, Taiwan
3Institute of Physics, St. Petersburg State University, St. Petersburg, Russian Federation
4A. F. Ioffe Physico-Technical Institute RAS, St. Petersburg, Russian Federation
* presenting author:Min Kai Lee,
In this study, we investigate superconducting nanocomposites (SCNCs) to elucidate superconductivity in nanostructured type I superconductor. Indium (In), tin (Sn) and mercury (Hg) are loaded into opal matrices by high pressure up to 10kbar, in which introducing superconducting metals into templates preserves their own 3D nanostructures. The opal matrices is adopted because it is a well-developed nanoconfinement and widely used in the studies of photonic crystal due to its periodically-superlatticed nanoporous structure. The SCNCs are then measured by Quantum Design® MPMS 3, in which temperature dependences of DC magnetization using zero fielded cooling (ZFC) and fielded cooling (FCC) protocols under different external magnetic fields reveal the field dependences of Tc and irreversibility temperature (Tirr). Next, AC susceptibility measurements of SCNCs are taken by Quantum Design® PPMS with the ACMS option, in which temperature variations of AC susceptibility with FCC procedure under different external DC fields, amplitudes of AC driving field and frequencies of AC driving field can determine grain coupling, vortex dynamics and field dependence of activation barrier (Ua) as well as Tc. Additionally, the phase diagrams of these SCNCs are analyzed to study superconductivity for a system with similar nanogeometry. Exotic phase diagrams in the opal SCNC 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. Importantly, results of this study demonstrate a universal superconducting behavior for SCNCs with nearly the same nanostructure.

Keywords: Superconductivity