Quantum Interference and Localization in Disordered Graphene

We report direct experimental evidence for Anderson localization driven by quantum interference in disordered single-layer graphene induced via controlled Ar + ion irradiation. By systematically introducing defects and quantifying the disorder using the Raman I D / I G ratio, we map the interdefect distance L D and uncover a critical localization threshold near L D * ≈ 20 nm, where multiple transport and spectroscopic signatures converge. Time-resolved reflectivity measurements reveal a nonmonotonic dependence of the carrier relaxation times τ 1,2, peaking at L D *, indicating the emergence of spatially localized states. Tight-binding simulations confirm this threshold as the crossover between delocalized and exponentially localized regimes, satisfying the Ioffe−Regel condition k F l ≈ 1. Electrical resistivity increases exponentially below L D *, while Seebeck coefficients saturate, consistent with hopping-dominated transport. Notably, the power factor S 2 /ρ and the thermoelectric figure of merit zT exhibit pronounced maxima near L D *, corroborating theoretical predictions that localization can enhance thermoelectric performance by introducing sharp energy filtering at mobility edges. While graphene’s intrinsic zT remains low due to high thermal conductivity, these results establish graphene as a model system for probing disorder-driven transport, offering the most direct experimental validation to date of localization-enhanced thermopower in two-dimensional Dirac systems.