High temperature superconductivity in the candidate phases of solid hydrogen

Area of Science:

• Condensed matter physics
• Materials science
• Quantum mechanics

Background:

• Understanding the phase diagram of hydrogen under high pressure is key to discovering new quantum materials.
• Solid hydrogen is theoretically predicted to become metallic and exhibit high-temperature superconductivity at extreme pressures (400-500 GPa).
• Experimental evidence suggests metallization occurs, but disagreements persist regarding the exact mechanisms and resulting crystal phases.

Purpose of the Study:

• To computationally determine the superconducting properties of candidate solid hydrogen phases (Cmca-12, Cmca-4, and I41/amd-2).
• To investigate the influence of anharmonic effects on superconductivity in these phases.
• To provide data that can help distinguish between different crystal structures in future high-pressure experiments.

Main Methods:

• Utilized a Wannier function-based approach with dense k-point and q-point sampling.
• Calculated superconducting transition temperatures (Tc) for Cmca-12, Cmca-4, and I41/amd-2 phases.
• Incorporated anharmonic effects into the calculations for greater accuracy.

Main Results:

• The Cmca-12 phase exhibits a significant increase in Tc from 86 K at 400 GPa to 212 K at 500 GPa.
• The Cmca-4 and I41/amd-2 phases show less pressure-dependent Tc values, ranging from 74-94 K and 307-343 K, respectively.
• Calculated superconducting properties offer a way to experimentally differentiate between these predicted hydrogen phases.

Conclusions:

• The studied crystal phases of hydrogen display a wide range of superconducting transition temperatures under high pressure.
• The Cmca-12 phase shows particularly promising behavior for high-temperature superconductivity as pressure increases.
• These findings are vital for guiding experimental efforts and understanding superconductivity in pure hydrogen and related hydrides.