Hydrogen Vacancy Induced Superconductivity Collapse in A15 Lanthanum Hydride

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• Hydrogen-rich materials are key to achieving high-temperature superconductivity under pressure.
• The relationship between composition and superconducting properties in lanthanum hydrides remains underexplored.

Purpose of the Study:

• To systematically investigate the interplay between composition, structure, and superconductivity in A15-type lanthanum hydrides.
• To explore the stability and tunability of the A15 framework under varying hydrogen content and pressure.

Main Methods:

• Experimental synthesis and characterization of lanthanum hydrides at high pressures.
• Computational studies to model structural and electronic properties.
• In-situ measurements of superconducting transition temperature (T_c) and hydrogen content.

Main Results:

• A15-type LaH_{5.75-x} exhibits high-T_c superconductivity (98 K at 94 GPa) when hydrogen fully occupies interstitial sites.
• A superconductor-to-insulator transition occurs upon decompression, driven by hydrogen depopulation below LaH_5.
• The A15 framework remains stable from 120 GPa down to 4 GPa, with reversible hydrogen content changes.

Conclusions:

• The A15 framework in lanthanum hydrides offers exceptional stability and tunability.
• Compositional tuning via hydrogen content is a critical factor in modulating superconductivity in these materials.
• This provides a unique platform for studying the fundamental links between structure, composition, and superconductivity.