Quantum Interference and Localization in Disordered Graphene.
basic_science · Level V
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- Also identified by DOI 10.1021/acsnano.5c13512.
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Abstract
We report direct experimental evidence for Anderson localization driven by quantum interference in disordered single-layer graphene induced via controlled Ar<sup>+</sup> ion irradiation. By systematically introducing defects and quantifying the disorder using the Raman <i>I</i><sub><i>D</i></sub>/<i>I</i><sub><i>G</i></sub> ratio, we map the interdefect distance <i>L</i><sub><i>D</i></sub> and uncover a critical localization threshold near <i>L</i><sub><i>D</i></sub><sup>*</sup> ≈ 20 nm, where multiple transport and spectroscopic signatures converge. Time-resolved reflectivity measurements reveal a nonmonotonic dependence of the carrier relaxation times τ<sub>1,2</sub>, peaking at <i>L</i><sub><i>D</i></sub><sup>*</sup>, 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 <i>k</i><sub><i>F</i></sub> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>l</mi></math> ≈ 1. Electrical resistivity increases exponentially below <i>L</i><sub><i>D</i></sub><sup>*</sup>, while Seebeck coefficients saturate, consistent with hopping-dominated transport. Notably, the power factor <i>S</i><sup>2</sup>/ρ and the thermoelectric figure of merit <i>zT</i> exhibit pronounced maxima near <i>L</i><sub><i>D</i></sub><sup>*</sup>, corroborating theoretical predictions that localization can enhance thermoelectric performance by introducing sharp energy filtering at mobility edges. While graphene's intrinsic <i>zT</i> 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.