Abstract
Knowledge of the behavior of hydrogen in metal hydrides is the key for understanding their electronic properties. Here, we present an study of cubic FeH up to 202 GPa. 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 result, 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.
- Received 4 March 2019
- Revised 13 May 2019
DOI:https://doi.org/10.1103/PhysRevX.9.031008
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The key to room-temperature superconductivity may come from metal hydrides, compounds in which a metal is bonded to hydrogen. Recent experiments have shown that these materials become superconductive at temperatures of 260 K and pressures of hundreds of gigapascals in diamond anvil cells. Further progress requires a deeper understanding of the electronic properties of hydrogen atoms, which is limited to theoretical predictions because of the lack of spectroscopic probes that can be used in these extreme conditions. Here, we use a novel high-pressure nuclear magnetic resonance method to investigate the electronic properties of hydrogen atoms in iron hydride.
We load samples of iron hydride into diamond anvil cells and ratchet the pressure up to 202 GPa. We then probe the electronic properties of the sample using nuclear magnetic resonance, which induces nuclear spin transitions via radio-frequency irradiation under an external magnetic field. We find that the application of pressure leads to the formation of a sublattice of free-electron gas connecting all hydrogen atoms, raising their ability to contribute to the electronic density of states, which is a prerequisite for high-temperature superconductivity. These interactions are found at distances between hydrogen atoms that are significantly longer than expected from theoretical predictions and might lead to a novel approach for the search of new high-temperature superconductors.
This research lays the foundation for the investigation of exotic hydrogen-rich superhydrides, which are believed to hold the key to room-temperature superconductivity.