Dear Mohamed Lamine Tounsi: we know since almost sixty years that the xenon and some other gas call “inert” has valence and bonds properties see “Chernick C.L., Rec. Chem. Prog., 24, 139-155, (1962)”. As a result, in superconductors as La2-xBaxCuO4 where the bivalent barium replace the trivalent lanthanum it is possible to consider that the xenon shell of Ba or La contributes to the valance, see “From Ln valence to that of 3d”. The substitution of La by Ba introduces break in the bond allowing the electrical conduction in a similar way to that of the semiconductors see “Conductivity and statistic: an alternative view”.

Thus to achieve superconductivity at the highest temperature you have to consider the valence properties of the rare earths and to also to reconsider the mechanism of the electrical conduction.

Dear Mohamed Lamine Tounsi ;

Recent theoretical predictions have shown that a new class of materials of superconducting hydrides could pave the way for higher-temperature superconductivity. Researchers at the Max Planck Institute for Chemistry in Germany teamed up with the University of Chicago researchers to create one of these materials, called lanthanum superhydrides. more details in the following reference;

https://phys.org/news/2019-05-scientists-highest-temperature-superconductor.html

Dear Mohamed Lamine Tounsi

The field of superconductivity is a wonderland, that keeps amazing us with its magics. For several decades, the general rationale was that the BCS theory only applies to low-temperature superconductors, and thus, to find a high-Tc superconductor one must go beyond it and search for materials with unconventional Cooper pairing mechanism. However, the discovery of 203 K superconductivity in pressurized sulfur hydride systems in 2015 (https://www.nature.com/articles/nature14964) and a following report of 260 K superconductivity in ultra-pressurized lanthanum decahydrides in 2019 (Article Evidence for Superconductivity above 260 K in Lanthanum Supe...

Dear Mohamed, the article “Coexistence of Diamagnetism and Vanishingly Small Electrical Resistance at Ambient Temperature and Pressure in Nanostructures” ( https://arxiv.org/ftp/arxiv/papers/1807/1807.08572.pdf ) shows the main way to room temperature SC, that is the local electron pairing.   In the research Tc is tuned by the disorder density and defect nature in nanostructure (NS), containing 3 fractions: Au, Ag, unknown insulating fraction. The disorder causes consequences A and B: A. The carrier trapping, reducing the free electron density relative to the density in pure metals. So the Fermi energy (EF) of NS is lower than EF of pure metals and may be close to a Brillouin zone edge. EF (Ag) ≈ EF (Au) ≈ 5.5 eV, the highest Brillouin zone edge in direction [110] is 4.5 eV. Thus the trapping and the insulating fraction should reduce EF by only 1 eV (plausible scenario for nano-disordered metals). B. The disorder (FIG. S2) provides new local electron states on the Fermi surface; this locality (like standing waves) reduces the length of electronic wave packets, what enhances the singlet bond (exchange energy is strongest locally). 

Note 1: the result reasonably combines the locality with the Bose-Einstein Condensation. Using the link between the temperature of Bose-Einstein Condensation (TBEC) and bosonic density (Nb), we can estimate the length of electron localization (L): L ≤ (Nb)^-1/3 ; L ≤ [3.31·ћ^2/(TBEC·2·me·kB) ]^ 0.5 ,     at TBEC= 286 K we have  L ≤ 2.3 nm 

At FIG. S2 the average distance between neighboring defects is ≈ 2 nm. Assuming that each localization is pinned to one or a few defect points, the BEC formation at 286 K is reasonable. So Tc grows with the decreasing Au-fraction, since the disorder density is inversely related to the Au-fraction (FIG.5a). The final BE-condensate is no longer local, since the BEC is a macroscopic coherent state of all pairs. Note 2: in pure metals at 300 K is impossible to combine the locality and a high Fermi level (a few eV), therefore Tc is low. The  insulating fraction in NS plays a crucial role, since it strongly affects the localization. The biggest problem for the Tc reproducibility is the reproduction of this unknown insulating fraction. 

The approach is described in the article “Formation of Cooper Pairs as a Consequence of Exchange Interaction” in https://arxiv.org/ftp/arxiv/papers/1501/1501.04978.pdf .

Kind regards Stanislav.