Hole-Doping Effect on Superconductivity in Compressed CeH$_{9}$ at High Pressure

TL;DR

This study shows that hole doping in compressed CeH$_9$ significantly increases its superconducting transition temperature by shifting the Fermi level towards a van Hove singularity, with potential implications for other hydrides.

Contribution

It reveals how hole doping and band topology interplay to enhance superconductivity in CeH$_9$, providing a new mechanism for increasing $T_c$ in hydrides.

Findings

Hole doping raises $T_c$ from 74 K to 136 K at 100 GPa.

Electronic states of Ce 4$f$ and H 1$s$ form topologically nontrivial Dirac nodal lines.

The mechanism can be applied to other hydrides like LaH$_{10}$.

Abstract

The experimental realization of high-temperature superconductivity in compressed hydrides H$_3$S and LaH$_{10}$ at high pressures over 150 GPa has aroused great interest in reducing the stabilization pressure of superconducting hydrides. For cerium hydride CeH$_9$ recently synthesized at 80$-$100 GPa, our first-principles calculations reveal that the strongly hybridized electronic states of Ce 4$f$ and H 1$s$ orbitals produce the topologically nontrivial Dirac nodal lines around the Fermi energy $E_F$, which are protected by crystalline symmetries. By hole doping, $E_F$ shifts down toward the topology-driven van Hove singularity to significantly increase the density of states, which in turn raises a superconducting transition temperature $T_c$ from 74 K up to 136 K at 100 GPa. The hole-doping concentration can be controlled by the incorporation of Ce$^{3+}$ ions with varying their percentages, which can be well electronically miscible with Ce atoms in the CeH$_9$ matrix because both Ce$^{3+}$ and Ce behave similarly as cations. Therefore, the interplay of symmetry, band topology, and hole doping contributes to enhance $T_c$ in compressed CeH$_9$. This mechanism to enhance $T_c$ can also be applicable to another superconducting rare earth hydride LaH$_{10}$.