Stability Analysis of Superconductivity in $\text{P6/mmm}$-LaSc${}_2$H${}_{24}$ and its Experimental Reproducibility from La-Sc Alloys

Abstract

In this work, we analyze the feasibility of room-temperature superconductivity in the lanthanum-scandium hydride $\text{P6/mmm}$-LaSc${}_2$H${}_{24}$. We demonstrate that the electron-phonon coupling calculations performed using the $\sigma$-broadening of the double $\delta$-function at the Fermi surface lead to a very strong dependence of $\textit{T$_c$}(σ)$ on the arbitrary $\sigma$, whereas the tetrahedral method for the electron-phonon interaction is free from this drawback and leads to $\textit{T$_c$}$ > 300 K at 300 GPa in agreement with previous predictions. By analyzing the stability of the metallic state of LaSc${}_2$H${}_{24}$ at 250-300 GPa, we show that this compound is at the edge of the stability region ($\xi$ = 0.54), similar to $\text{fcc}$ LaH${}_{10}$ at 140-150 GPa. Seven experimental attempts to synthesize LaSc${}_2$H${}_{24}$ at 250-280 GPa starting from the (La,Sc${}_2$) alloy are unsuccessful and indicate the absence of even traces of superconductivity at 245-300 K in all the resulting La-Sc-H hydrides. The method for preparing the precursor by simultaneous deposition of La and Sc metals may be a key factor for the successful synthesis of LaSc${}_2$H${}_{24}$.

The 2nd version includes three additional experiments conducted by Z.W., as well as a detailed characterization of the starting precursor (La-Sc alloy) for the synthesis