Metal Atom (Dis)Order and Superconductivity in YCaH$_{n}$ ($n=8-20$) High-Pressure Superhydrides

TL;DR

This study uses density functional theory to explore metal atom disorder and doping effects on superconductivity in YCaH$_{n}$ superhydrides under high pressure, revealing how atomic arrangements influence critical temperatures.

Contribution

It provides new insights into the structural stability, disorder, and doping effects on $T_c$ in YCaH$_{n}$ superhydrides at high pressure, with detailed predictions of superconducting properties.

Findings

YCaH$_8$ exhibits nearly isoenthalpic phases with different metal atom arrangements.

Doping and atomic disorder can significantly alter $T_c$, ranging from mild to drastic changes.

YCaH$_{12}$, YCaH$_{18}$, and YCaH$_{20}$ show specific stable structures with high predicted $T_c$ values.

Abstract

High-pressure superhydrides have attracted much attention due to their high superconducting critical temperatures ($T_\text{c}$s). Herein, density functional theory (DFT) calculations are used to study the structures and properties, including potential for metal atom disorder and doping-enhanced $T_\text{c}$, within Y-Ca superhydrides with YCaH$_{n}$ ($n=8-20$) compositions. For YCaH$_8$ numerous phases that differed in the arrangement of the metal atoms were found to be nearly isoenthalpic, suggesting the importance of configurational entropy on stability. The equimolar ratio of the two metal atoms brought the Fermi level to a peak in the density of states, enhancing $T_\text{c}$ to 149~K and 170~K for $P4/mmm$ and $Cmmm$ YCaH$_{8}$, respectively, at 180~GPa within the isotropic Eliashberg formalism. YCaH$_{12}$ was also predicted to be disordered, however the $T_\text{c}$s of the ordered variants spanned a wide range from 105-253~K at 200~GPa, showing that doping could either mildly enhance or drastically reduce $T_\text{c}$ from that of the parent compounds. For YCaH$_{18}$ and YCaH$_{20}$, only a single dynamically stable superhydride was predicted, which we attribute to the differences in the structures of the stable binary parents.