Underlying mechanism of charge transfer in Li-doped MgH$_{16}$ at high pressure

TL;DR

This study uses first-principles calculations to uncover how Li dopants in MgH16 facilitate charge transfer via electride behavior, stabilizing H cages and leading to high-temperature superconductivity.

Contribution

It reveals the electride nature of Li dopants as crucial for charge transfer and high-Tc in Li-doped MgH16 under high pressure, providing new mechanistic insights.

Findings

Li dopants create excess electrons in interstitial regions.

Electrons stabilize H cage structures, enhancing superconductivity.

Electride behavior of Li is key to charge transfer mechanism.

Abstract

A lithium-doped magnesium hydride Li$_2$MgH$_{16}$ was recently reported [Y. Sun $et$ $al$., Phys. Rev. Lett. {\bf 123}, 097001 (2019)] to exhibit the highest ever predicted superconducting transition temperature $T_{\rm c}$ under high pressure. Based on first-principles density-functional theory calculations, we reveal that the Li dopants locating in the pyroclore lattice sites give rise to the excess electrons distributed in interstitial regions. Such loosely bound anionic electrons are easily captured to stabilize a clathrate structure consisting of H cages. This addition of anionic electrons to H cages enhances the H-derived electronic density of states at the Fermi level, thereby leading to a high-$T_{\rm c}$ superconductivity. We thus propose that the electride nature of Li dopants is an essential ingredient in the charge transfer between Li dopants and H atoms. Our findings offer a deeper understanding of the underlying mechanism of charge transfer in Li$_2$MgH$_{16}$ at high pressure.