Lifshitz transition from valence fluctuations in YbAl₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Mixed-valent Kondo lattice systems exhibit complex electronic behaviors due to interactions between localized and delocalized electrons.
• Understanding how valence fluctuations impact momentum-space electronic structure is crucial for explaining emergent properties in these materials.

Purpose of the Study:

• To investigate the relationship between valence fluctuations and electronic structure changes in Ytterbium Aluminum 3 (YbAl3).
• To elucidate the impact of these fluctuations on Fermi surface topology and electronic band structure.

Main Methods:

• Utilized molecular beam epitaxy for material synthesis.
• Employed in situ angle-resolved photoemission spectroscopy (ARPES) to probe electronic structure.

Main Results:

• Demonstrated that valence fluctuations in YbAl3 cause significant alterations in Fermi surface topology, including a Lifshitz transition.
• Observed temperature-dependent changes: electron pockets become unoccupied, and Ytterbium (Yb) 4f states become more itinerant with decreasing temperature.
• Yb 4f states showed increased spectral weight, longer lifetimes, and well-defined dispersions at lower temperatures.

Conclusions:

• Established a unified framework connecting local valence fluctuations to momentum-space concepts like band filling and Fermi surface topology.
• Highlighted the profound influence of local chemical environment on the electronic structure of mixed-valence systems.