Direct Observation of Orbital Driven Strong Interlayer Coupling in Puckered Two-Dimensional PdSe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Interlayer coupling is crucial for tuning properties of 2D materials.
• Strong interlayer interactions in materials like black phosphorus lead to layer-dependent characteristics.
• Understanding the electronic origins of these interactions is key for novel 2D material exploration.

Purpose of the Study:

• To directly observe and characterize interlayer coupling in puckered 2D Palladium Diselenide (PdSe2).
• To investigate the electronic structure origins of strong interlayer interactions in 2D PdSe2.
• To elucidate the role of interlayer coupling in the layer-dependent band gap of 2D PdSe2.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES) for electronic band structure measurement.
• X-ray absorption spectroscopy (XAS) for elemental and electronic state analysis.
• Density functional theory (DFT) calculations for theoretical modeling of electronic structure and bonding.

Main Results:

• Direct observation of a highly dispersive single electronic band along the interlayer (kz) direction in 2D PdSe2.
• Remarkably large kz-direction band dispersion near the Fermi level, exceeding in-plane dispersion.
• Identification of strong interlayer coupling originating from directional Pd 4d orbital bonding in an unusual Pd 4d9 configuration.

Conclusions:

• The observed kz-dispersive band serves as an experimental signature of strong interlayer coupling in 2D PdSe2.
• The unique Pd 4d orbital bonding is the primary source of strong interlayer interactions.
• These strong interactions decisively influence the layer-dependent band gap of 2D PdSe2, highlighting its unique electronic properties.