High Pressure Superconducting Transition in Dihydride BiH_{2} with Bismuth Open-Channel Framework

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• Metal hydrides (MHₓ, x≤2) with low hydrogen content are generally not expected to exhibit high-temperature superconductivity (high-T<0xE1><0xB5><0x84>).
• This is due to limited hydrogen contribution to electronic density of states and electron-phonon coupling strength.

Purpose of the Study:

• To report the synthesis and superconductivity of a novel bismuth dihydride, Cmcm-BiH₂.
• To investigate the structural and electronic properties contributing to superconductivity in this new material.

Main Methods:

• High-pressure synthesis of Cmcm-BiH₂ at approximately 150 GPa.
• Measurement of superconductivity via resistivity drop and magnetic field response at 163 GPa.
• Analysis of structural stability and electronic properties using theoretical calculations.

Main Results:

• Successful synthesis of Cmcm-BiH₂, a novel superconductor among MH₂-type metal dihydrides.
• Discovery of superconductivity with T<0xE1><0xB5><0x84> ≈ 62 K at 163 GPa, evidenced by sharp resistivity drop and critical field dependence.
• Cmcm-BiH₂ exhibits a unique host-guest structure with metallic bismuth channels, contributing significantly (≈51%) to electron-phonon coupling (λ).
• The material demonstrates stability down to 97 GPa upon decompression, with a calculated dynamic stability limit of 10 GPa.

Conclusions:

• Cmcm-BiH₂ represents the first superconductor in the MH₂-type metal dihydrides, challenging previous theoretical limitations.
• The study highlights the crucial role of non-hydrogen elements, specifically the bismuth framework, in achieving high-T<0xE1><0xB5><0x84> superconductivity.
• These findings open new avenues for designing and optimizing high-temperature hydride superconductors by focusing on structural diversity and the contribution of host elements.