Superconductivity in $LaH_{10}$: a new twist of the story

We study the high-pressure chemistry of the La-H system and superconducting properties of the predicted lanthanum hydrides. A $Fmbar{3}m$-$LaH_{10}$+$3H_2$$to$$P6/mmm$-$LaH_{16}$ reaction leading to a new superconducting superhydride $LaH_{16}$ with critical temperature ($T_C$) of 219-243 K, upper critical field $H_C(0)sim50 T$ and superconducting gap up to 53 meV was found at pressures over 200 GPa. Besides $LaH_{16}$, in the framework of Bardeen-Cooper-Schrieffer theory we analyzed in details superconducting properties of $LaH_{10}$ recently studied by Drozdov et al. [1] and Somayazulu et al. [2], where $T_C$ was estimated to be 215-245 K. For better agreement between theory and experiment in $LaH_{10}$ a Coulomb pseudopotential $μ^*$ should be more than 0.2-0.28. Upper critical field in $LaH_{10}$ was evaluated as 76-100 T, isotopic coefficient $β$ was calculated to be 0.41-0.46 and $T_C$($LaD_{10}$) is 156-184 K. The difference between experimental data may be alternatively explained by the existence of $Fmbar{3}m$ and $Rbar{3}m$ allotrope modifications of $LaH_{10}$ with far different superconducting temperatures.