Novel Valence Transition in Elemental Metal Europium around 80 GPa

Area of Science:

• Condensed Matter Physics
• Materials Science
• High-Pressure Physics

Background:

• Valence transitions in rare-earth elements are complex due to localized 4f electron interactions.
• The specific valence transition mechanism in elemental europium (Eu) under pressure remains debated.
• Understanding these transitions is key to predicting properties like magnetism and superconductivity.

Purpose of the Study:

• To investigate the valence and structural transitions in europium (Eu) under high pressure.
• To elucidate the underlying physics of pressure-induced valence changes in Eu.
• To provide insights into the electrodynamics, magnetism, and superconductivity of Eu.

Main Methods:

• Utilizing resonant x-ray emission scattering to probe 4f electron states.
• Employing x-ray diffraction to determine structural phase transitions.
• Subjecting Eu metal to pressures up to 160 GPa.

Main Results:

• Providing compelling evidence for a valence transition in Eu around 80 GPa.
• Observing a concurrent structural transition from monoclinic (C2/c) to orthorhombic (Pnma) phase at approximately 80 GPa.
• Demonstrating that the valence transition is linked to the pressure-dependent energy gap between 4f and 5d electrons approaching the Coulomb interaction.

Conclusions:

• The study confirms a pressure-induced valence transition in europium (Eu) at 80 GPa.
• The valence transition is intrinsically coupled with a structural phase change.
• This research is crucial for understanding Eu's electronic properties, including its magnetic and superconducting behaviors under extreme conditions.