# Tunable localization in an s-electron Kondo system at room temperature

## TL;DR

This paper demonstrates that metal hydrides exhibit strong electron correlations at room temperature, potentially enabling high-temperature superconductivity through tunable localization similar to Kondo systems.

## Contribution

It reveals room-temperature electron localization and Kondo-like behavior in metal hydrides, suggesting a new pathway for high-temperature superconductivity in hydrogen-rich compounds.

## Key findings

- Strong electron correlations observed at room temperature in metal hydrides.
- Divergence of carrier mass indicates proximity to Mott transition.
- Signatures of a correlated metallic Kondo lattice at ambient conditions.

## Abstract

To achieve room-temperature superconductivity, a mechanism is needed that provides heavy quasiparticles at room temperature. In heavy fermion systems such localization is prototypically present only at liquid helium temperatures. In these $f$-electron Kondo systems, conduction electrons magnetically couple to localized moments, enhancing their mass and scatting time. These quasiparticles may form Cooper pairs and cause unconventional superconductivity with a critical temperature $T_c$ of the order of the Fermi energy $\varepsilon_F$. In relative terms, this $T_c$ is much larger than in cuprate or BCS superconductors for which $T_c\ll \varepsilon_F$. This suggests that Kondo systems in general have the potential to be high-temperature superconductors. For this to occur, strong correlations that cause electron localization need to take place at much larger temperatures. Here we show that metal hydrides manifest strong electron correlations in a single $3d_{x^2-y^2}$ band at the Fermi level, similar to the cuprates but at room temperature. Hole doping of this band, by varying the hydrogen content, causes divergence of the carrier mass and suggests the approach of an ordered Mott transition with signatures of a correlated metallic Kondo lattice. These room-temperature phenomena are expected to be widespread across hydrogen-rich compounds, and offer a promising novel ground to encounter unconventional superconductivity in the class of the metallic hydrides.