# Pressure induced Hydrogen-Hydrogen interaction in metallic FeH revealed by NMR

## TL;DR

This study uses NMR to reveal pressure-induced hydrogen-hydrogen interactions in FeH up to 200 GPa, challenging previous assumptions about their occurrence only at extremely high pressures and suggesting new pathways for high-temperature superconductor discovery.

## Contribution

First experimental NMR evidence of pressure-induced H-H interactions in FeH at accessible pressures, supported by ab-initio calculations showing electronic structure changes.

## Key findings

- H-H interactions occur between 64 and 110 GPa
- Formation of an intercalating electron density sublattice
- Enhanced hydrogen contribution to electronic density of states

## Abstract

Knowledge of the behavior of hydrogen in metal hydrides is the key for understanding their electronic properties. So far, no experimental methods exist to access these properties beyond 100 GPa, where high-Tc superconductivity emerges. Here, we present an 1H-NMR study of cubic FeH up to 200GPa. We observe a distinct deviation from the ideal metallic behavior between 64 and 110 GPa that suggests pressure-induced H-H interactions. Accompanying ab-initio calculations support this interpretation, as they reveal the formation of an intercalating sublattice of electron density, which enhances the hydrogen contribution to the electronic density of states at the Fermi level. This study shows that pressure induced H-H interactions can occur in metal hydrides at much lower compression and larger H-H distances than previously thought and stimulates an alternative pathway in the search for novel high-temperature superconductors.