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Register a new userUniversal voltage scaling due to self-averaging of the quantum corrections in graphene
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The differential conductance of graphene is shown to exhibit a zero-bias anomaly at low temperatures, arising from a suppression of the quantum corrections due to weak localization and electron interactions. A simple rescaling of these data, free of any adjustable parameters, shows that this anomaly exhibits a universal, temperature- ($T$) independent form. According to this, the differential conductance is approximately constant at small voltages ($V<k_BT/e$), while at larger voltages it increases logarithmically with the applied bias, reflecting a quenching of the quantum corrections. For theoretical insight into the origins of this behavior, we formulate a model for weak-localization in the presence of nonlinear transport. According to this, the voltage applied under nonequilibrium induces unavoidable dephasing, arising from a self-averaging of the diffusing electron waves responsible for transport. By establishing the manner in which the quantum corrections are suppressed in graphene, our study will be of broad relevance to the investigation of nonequilibrium transport in mesoscopic systems in general. This includes systems implemented from conventional metals and semiconductors, as well as those realized using other two-dimensional semiconductors and topological insulators.
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In this theoretical study, we explore the manner in which the quantum correction due to weak localization is suppressed in weakly-disordered graphene, when it is subjected to the application of a non-zero voltage. Using a nonequilibrium Green function approach, we address the scattering generated by the disorder up to the level of the maximally crossed diagrams, hereby capturing the interference among different, impurity-defined, Feynman paths. Our calculations of the charge current, and of the resulting differential conductance, reveal the logarithmic divergence typical of weak localization in linear transport. The main finding of our work is that the applied voltage suppresses the weak localization contribution in graphene, by introducing a dephasing time that decreases inversely with increasing voltage.
It is well known that conductivity of disordered metals is suppressed in the limit of low frequencies and temperatures by quantum corrections. Although predicted by theory to exist up to much higher energies, such corrections have so far been experimentally proven only for $lesssim$80 meV. Here, by a combination of transport and optical studies, we demonstrate that the quantum corrections are present in strongly disordered conductor MoC up to at least $sim$4 eV, thereby extending the experimental window where such corrections were found by a factor of 50. The knowledge of both, the real and imaginary parts of conductivity, enables us to identify the microscopic parameters of the conduction electron fluid. We find that the conduction electron density of strongly disordered MoC is surprisingly high and we argue that this should be considered a generic property of metals on the verge of disorder-induced localization transition.
The near-field interaction between fluorescent emitters and graphene exhibits rich physics associated with local dipole-induced electromagnetic fields that are strongly enhanced due to the unique properties of graphene. Here, we measure emitter lifetimes as a function of emitter-graphene distance d, and find agreement with a universal scaling law, governed by the fine-structure constant. The observed energy transfer- rate is in agreement with a 1/d^4 dependence that is characteristic of 2D lossy media. The emitter decay rate is enhanced 90 times (transfer efficiency of ~99%) with respect to the decay in vacuum at distances d ~ 5 nm. This high energy-transfer rate is mainly due to the two-dimensionality and gapless character of the monoatomic carbon layer. Graphene is thus shown to be an extraordinary energy sink, holding great potential for photodetection, energy harvesting, and nanophotonics.
The combination of field tunable bandgap, topological edge states, and valleys in the band structure, makes insulating bilayer graphene a unique localized system, where the scaling laws of dimensionless conductance g remain largely unexplored. Here we show that the relative fluctuations in ln g with the varying chemical potential, in strongly insulating bilayer graphene (BLG) decay nearly logarithmically for channel length up to L/${xi}$ ${approx}$ 20, where ${xi}$ is the localization length. This marginal self averaging, and the corresponding dependence of <ln g> on L, suggest that transport in strongly gapped BLG occurs along strictly one-dimensional channels, where ${xi}$ ${approx}$ 0.5${pm}$0.1 ${mu}$m was found to be much longer than that expected from the bulk bandgap. Our experiment reveals a nontrivial localization mechanism in gapped BLG, governed by transport along robust edge modes.
We study sample-to-sample fluctuations in a critical two-dimensional Ising model with quenched random ferromagnetic couplings. Using replica calculations in the renormalization group framework we derive explicit expressions for the probability distribution function of the critical internal energy and for the specific heat fluctuations. It is shown that the disorder distribution of internal energies is Gaussian, and the typical sample-to-sample fluctuations as well as the average value scale with the system size $L$ like $sim L lnln(L)$. In contrast, the specific heat is shown to be self-averaging with a distribution function that tends to a $delta$-peak in the thermodynamic limit $L to infty$. While previously a lack of self-averaging was found for the free energy, we here obtain results for quantities that are directly measurable in simulations, and implications for measurements in the actual lattice system are discussed.
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