Superconducting properties of indium nanostructured in pores of thin films of SiO$_{2}$ microspheres

Samples of a superconducting indium nanocomposite based on a thin-film porous dielectric matrix prepared by the Langmuir–Blodgett method are obtained for the first time, and their low-temperature electrophysical and magnetic properties are studied. Films with thickness $b\le$ 5 $\mu$m were made from silicon dioxide spheres with diameter $D$ = 200 and 250 nm; indium was introduced into the pores of the films from the melt at a pressure of $P\le$ 5 kbar. Thus, a three-dimensional weakly ordered structure of indium nanogranules was created in the pores, forming a continuous current-conducting grid. Measurements of the temperature and magnetic field dependences of the resistance and magnetic moment of the samples showed an increase in the critical parameters of the superconductivity state of nanostructured indium (critical temperature $T_c\le$ 3.62 K and critical magnetic field $H_c$ at $T$ = 0 K $H_c(0)\le$ 1700 Oe) with respect to the massive material ($T_c$ = 3.41 K, $H_c(0)$ = 280 Oe). In the dependence of the resistance on temperature and the magnetic field, a step transition to the superconductivity state associated with the nanocomposite structure was observed. A pronounced hysteresis $M(H)$ is observed in the dependence of the magnetic moment $M$ of the nanocomposite on the magnetic field at $T<T_c$, caused by the multiply connected structure of the current-conducting indium grid. The results obtained are interpreted taking into account the dimensional dependence of the superconducting characteristics of the nanocomposite.