Quantum Interference and Localization in Disordered Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Anderson localization describes the suppression of wave function propagation in disordered systems.
• Graphene's unique electronic properties make it a promising material for studying quantum phenomena.
• Thermoelectric materials convert heat energy into electrical energy and vice versa.

Purpose of the Study:

• To provide direct experimental evidence of Anderson localization in single-layer graphene.
• To investigate the role of controlled disorder in inducing localization.
• To explore the impact of localization on thermoelectric performance.

Main Methods:

• Controlled argon ion (Ar+) irradiation to introduce defects in graphene.
• Raman spectroscopy to quantify disorder (ID/IG ratio) and determine interdefect distance (LD).
• Time-resolved reflectivity measurements to study carrier relaxation dynamics.
• Tight-binding simulations to model electronic transport and localization.
• Electrical resistivity and Seebeck coefficient measurements to assess thermoelectric properties.

Main Results:

• A critical localization threshold (LD* ≈ 20 nm) was identified, where transport and spectroscopic signatures converged.
• Carrier relaxation times peaked at the localization threshold, indicating the formation of localized states.
• Electrical resistivity increased exponentially, and Seebeck coefficients saturated below the threshold, consistent with hopping transport.
• Significant enhancement of the thermoelectric power factor (S²/ρ) and figure of merit (zT) was observed near the localization threshold.

Conclusions:

• Controlled disorder in graphene can drive Anderson localization, validating theoretical predictions.
• Localization effects, particularly sharp energy filtering at mobility edges, can enhance thermoelectric performance in 2D Dirac systems.
• Graphene serves as an excellent model system for fundamental studies of disorder-driven transport and localization phenomena.