Superhydrides on the way to ambient pressure: weak localization and persistent X-ray photoconductivity in BaSiH$_{8}$

TL;DR

This study synthesizes BaSiH8 superhydride at high pressures, demonstrates its stability at ambient conditions, and explores its electronic properties, including superconductivity and persistent photoconductivity, advancing hydrogen storage research.

Contribution

It reports the high-pressure synthesis and ambient stability of BaSiH8, a superhydride with unique electronic properties, addressing key challenges in superhydride stability and practical application.

Findings

BaSiH8 remains stable upon decompression to ambient conditions.

BaSiH8 exhibits superconductivity at 9 K under high pressure.

Weak localization and persistent photoconductivity observed in BaSiH8 at lower pressures.

Abstract

Reducing the stabilization pressure of superhydrides represents one of the most important challenges in hydrogen-saturated compound chemistry. Moving in this direction, we studied the Ba-Si-H system at 0-142 GPa using transport measurements, 1H nuclear magnetic resonance, single-crystal and powder X-ray diffraction in the temperature range of 4-317 K. We synthesized the previously predicted cubic BaSiH$_{8}$ at pressures of 18-31 GPa. Remarkably, we demonstrate that BaSiH$_8$ remains stable upon decompression to ambient conditions and can be recovered from the diamond anvil cell. Obtained Ba-Si polyhydrides exhibit metallic and superconducting properties ($\textit{T$_c$}$ = 9 K, $\textit{B$_{c2}$}$(0)=13-16 T) at 142 GPa. However, at pressures below 50 GPa, these hydrides behave as degenerate semiconductors (bandgap < 0.4 meV) or poor metals with weak electron localization, negative magnetoresistance, photovoltaic effect, and persistent photoconductivity in the X-ray and visible range. Our work demonstrates the high-pressure synthesis of Ba-Si polyhydrides that remain stable upon decompression to ambient conditions, overcoming a critical bottleneck in superhydride chemistry and establishing a foundation for practical applications in hydrogen storage.