Tuning orbital-selective phase transitions in a two-dimensional Hund's correlated system

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Hund's coupling (J) is crucial for understanding quantum phases in multi-orbital materials.
• Orbital occupancy significantly influences these phases, but experimental control is challenging due to chemical inhomogeneities.
• Investigating orbital-selective phenomena requires methods that decouple orbital tuning from chemical changes.

Purpose of the Study:

• To develop and demonstrate an experimental method to study the role of orbital occupancy in Hund's coupling (J) phenomena without introducing chemical inhomogeneities.
• To investigate the impact of gradually tuned crystal field splitting and orbital degeneracy on the electronic properties of two-dimensional (2D) ruthenates.
• To observe and characterize the resulting electronic phase transitions and orbital differentiation.

Main Methods:

• Growing SrRuO3 monolayers on various substrates with symmetry-preserving interlayers to tune crystal field splitting.
• Gradually varying the orbital degeneracy and occupancy of Ru t2g orbitals in 2D ruthenates.
• Utilizing in-situ angle-resolved photoemission spectroscopy (ARPES) to probe electronic structure changes.

Main Results:

• Successfully tuned orbital occupancies in 2D SrRuO3 without chemical inhomogeneity.
• Observed a progressive metal-insulator transition (MIT) as orbital occupancy was varied.
• Identified orbital differentiation during the MIT, with a band insulating gap in the dxy band and a Mott gap in the dxz/yz bands.

Conclusions:

• The study presents an effective experimental strategy for investigating orbital-selective phenomena in multi-orbital materials.
• The findings highlight the critical role of orbital occupancy in dictating electronic phases driven by Hund's coupling.
• This method allows for precise control over orbital degrees of freedom, paving the way for deeper understanding of complex electronic states.