High-$T_c$ superconducting hydrides formed by LaH$_{24}$ and YH$_{24}$ cage structures as basic blocks

TL;DR

This study investigates the stability and superconducting properties of various high-$T_c$ hydride structures formed by LaH$_{24}$ and YH$_{24}$, discovering new stable phases with potential for high-temperature superconductivity around 140 K at high pressure.

Contribution

The paper identifies new stable crystal structures of La-Y hydrides and evaluates their superconducting properties, expanding understanding of high-$T_c$ hydrides beyond previously known phases.

Findings

$Cmmm$-LaYH$_{12}$ shows a $T_c$ of about 140 K at 200 GPa.

New stable structures like $Rar{3}c$-LaYH$_{12}$ and $Rar{3}$-LaY$_3$H$_{24}$ were discovered.

Superconductivity depends on the phase's density of states and electron-phonon coupling.

Abstract

Based on recent studies regarding high-temperature (high-$T_c$) La-Y ternary hydrides (e.g., $P{\bar{1}}$-La$_2$YH$_{12}$, $Pm{\bar{3}}m$-LaYH$_{12}$, and $Pm{\bar{3}}m$-(La,Y)H$_{10}$ with a maximum $T_c \sim 253$ K), we examined the phase and structural stabilities of the (LaH$_6$)(YH$_6$)$_y$ series as high-$T_c$ ternary hydride compositions using a genetic algorithm and $\it ab$ $\it initio$ calculations. Our evaluation showed that the $Pm\bar{3}m$-LaYH$_{12}$ reported in the previous study was unstable during decomposition into $R\bar{3}c$-LaH$_{6}$ + $Im\bar{3}m$-YH$_{6}$. We also discovered new crystal structures, namely $Cmmm$-LaYH$_{12}$ ($y=1$), $R\bar{3}c$-LaYH$_{12}$ ($y=1$), $Cmmm$-LaY$_3$H$_{24}$ ($y=3$), and $R\bar{3}$-LaY$_3$H$_{24}$ ($y=3$), showing stability against such decomposition. While $R\bar{3}c$ ($y=1$) and $R\bar{3}$ ($y=3$) did not exhibit superconductivity owing to the extremely low density of states at the Fermi level, $Cmmm$ phases exhibited a $T_{c}$ of approximately 140~K at around 200~GPa owing to the extremely high electron--phonon coupling constant ($\lambda$ = 1.876 for LaYH$_{12}$). By the twice longer stacking for $Cmmm$-LaY$_3$H$_{24}$, the coupling constant increased owing to the chemical pressure of Y, leading to a slightly increased $T_{c}$.