Spin-Dependent ππ^{*} Gap in Graphene on a Magnetic Substrate.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Graphene on magnetic substrates exhibits unique electronic and magnetic properties.
• Understanding interfacial effects is crucial for designing novel electronic devices.
• Europium (Eu) intercalation can modify interface characteristics.

Purpose of the Study:

• To investigate the electronic properties of graphene intercalated with Europium on a Nickel(111) substrate.
• To analyze the impact of Eu on graphene's Dirac cones and spin properties.
• To characterize the topological nature of the observed electronic band structure.

Main Methods:

• Angle- and spin-resolved photoemission spectroscopy (ARPES and SR-PES).
• Ab initio theoretical calculations.
• Analysis of electronic band structure and Dirac cone dispersions.

Main Results:

• Eu intercalation opens a gap in the freestanding ππ* Dirac cones at the K point.
• Spin degeneracy of Dirac cones is lifted due to graphene-Eu state mixing.
• A large spin-dependent topological gap emerges, featuring significant Berry curvature.
• A spin-polarized Van Hove singularity near the Fermi level induces a polaronic band.

Conclusions:

• Europium intercalation fundamentally alters graphene's electronic properties at the Ni(111) interface.
• The observed topological gap and polaronic band offer new avenues for spintronics and topological electronics.
• This study highlights the potential of controlled interface engineering for novel quantum materials.