Phonon localization by mass disorder in dense hydrogen-deuterium binary alloy

Area of Science:

• Condensed matter physics
• Materials science
• Quantum mechanics

Background:

• High-pressure physics studies the behavior of matter under extreme conditions.
• Hydrogen and deuterium are fundamental elements with unique quantum properties.
• Understanding phase transitions in hydrogen-rich systems is crucial for planetary science and fusion energy.

Purpose of the Study:

• To investigate the high-pressure phase behavior of hydrogen-deuterium mixtures.
• To characterize the structural and vibrational properties of these mixtures at extreme conditions.
• To elucidate the role of mass in quantum solids.

Main Methods:

• Raman spectroscopy was employed to probe vibrational modes.
• Density functional theory (DFT) calculations were used to model the system.
• Experiments were conducted on dense hydrogen-deuterium mixtures at varying concentrations, temperatures (300 K and above), and pressures (above 200 GPa).

Main Results:

• Hydrogen-deuterium mixtures transform into a disordered binary alloy, designated as phase IV.
• This phase exhibits six localized intramolecular vibrational (vibrons) modes and four delocalized low-frequency modes (<1200 cm⁻¹).
• A purely mass-induced localization effect was observed, where chemical bonding remains isotope-independent despite a twofold variation in mass.

Conclusions:

• High-pressure hydrogen-deuterium mixtures form a unique quantum solid with distinct vibrational properties.
• The observed phenomenon highlights a purely mass-driven localization effect in quantum solids.
• These findings contribute to the understanding of hydrogen isotopes under extreme conditions and their implications for fundamental physics.