Nanostructured superconductors: from granular through wire towards high-T<SUB align=right>c nanotubular 2D composites

Abstract

Superconductivity in nanostructured materials, nanowires, nanotubes and their 2D crystals is briefly reviewed. Experimental data show both the decrease of a critical superconducting temperature Tc under transition from polycrystalline to nanogranular ceramics, and the increase of Tc under transition to one-dimensional (1D) nanowires, nanotubes and their 2D crystals. Theoretical requirements for ideal room-Tc superconductor is shown to point out on 2D crystals built from noncarbon nanotubes of superconducting layered material as the ideal media. Analysis of superconductivity in MgBE2 is presented which point out on a key role of E2g-vibrations of boron ions resulted in the mechanism of two-gap two-phonon superconductivity. Connected with the author's concept of nanotubular superconductivity, this model lay off a bridge for the novel joint model of a nanotubular multi-phonon multi-gap room-Tc superconductivity on base of gallery of whispering circular zero-points phonon modes (twistons, rotons), in particular E2g-mode, resulting in resonant electron-phonon coupling. From a structural engineering point of view, a novel route in high-Tc and room-Tc superconductivity is advanced based on 2D crystals built from noncarbon MgB2, NbSe2, Sn, Bi or other superconducting nanotubes with expected record Tc. The suggested original model is in accordance with some recent experimental data confirming the effect of nanotubular superconductivity. Recent progress in synthesis of 2D nanochannel membrane and nanowire-brush templates, aligned nanotube arrays and nanotubular crystals are briefly reviewed as promising routes to fabricate these record nanotubular superconductors.