Ubiquitous defect-induced density wave instability in monolayer graphene.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Quantum materials exhibit sensitivity to environmental perturbations, leading to competing ground states.
• Graphene displays competing phases, including a bond density wave instability known as Kekulé distortion, which affects electron coupling and lattice symmetry.

Purpose of the Study:

• To investigate the onset and characteristics of the Kekulé distortion in graphene.
• To determine the influence of dilute surface adsorbates on graphene's electronic and structural properties.

Main Methods:

• Utilized angle-resolved photoemission spectroscopy (ARPES) for momentum-sensitive electronic structure analysis.
• Employed low-energy electron diffraction (LEED) to probe lattice symmetry and structural ordering.
• Investigated graphene systems with extremely low concentrations of adsorbed surface atoms.

Main Results:

• Observed a ubiquitous Kekulé distortion across various graphene systems.
• Demonstrated that less than three adsorbed atoms per 1000 graphene unit cells can induce a global Kekulé density wave phase.
• Confirmed the presence of the density wave phase and observed the opening of an energy gap using ARPES and LEED.

Conclusions:

• Graphene exhibits remarkable sensitivity to dilute surface disorder.
• Adsorbed atoms can self-assemble to trigger novel quantum phases in two-dimensional materials.
• This provides a new pathway for designing and controlling quantum phases in graphene and similar materials.