77 research outputs found
Crossover from quantum to Boltzmann transport in graphene
We compare a fully quantum mechanical numerical calculation of the
conductivity of graphene to the semiclassical Boltzmann theory. Considering a
disorder potential that is smooth on the scale of the lattice spacing, we find
quantitative agreement between the two approaches away from the Dirac point. At
the Dirac point the two theories are incompatible at weak disorder, although
they may be compatible for strong disorder. Our numerical calculations provide
a quantitative description of the full crossover between the quantum and
semiclassical graphene transport regimes.Comment: 4 pages, 4 figures; published versio
Gate-tunable coherent perfect absorption of terahertz radiation in graphene
Perfect absorption of radiation in a graphene sheet may play a pivotal role
in the realization of technologically relevant optoelectronic devices. In
particular, perfect absorption of radiation in the terahertz (THz) spectral
range would tremendously boost the utility of graphene in this difficult range
of photon energies, which still lacks cheap and robust devices operating at
room temperature. In this work we show that unpatterned graphene flakes
deposited on appropriate substrates can display gate-tunable coherent perfect
absorption (CPA) in the THz spectral range. We present theoretical estimates
for the CPA operating frequency as a function of doping, which take into
account the presence of common sources of disorder in graphene samples.Comment: To appear in 2D Material
Equivalence of Effective Medium and Random Resistor Network models for disorder-induced unsaturating linear magnetoresistance
A linear unsaturating magnetoresistance at high perpendicular magnetic
fields, together with a quadratic positive magnetoresistance at low fields, has
been seen in many different experimental materials, ranging from silver
chalcogenides and thin films of InSb to topological materials like graphene and
Dirac semimetals. In the literature, two very different theoretical approaches
have been used to explain this classical magnetoresistance as a consequence of
sample disorder. The phenomenological Random Resistor Network model constructs
a grid of four-terminal resistors, each with a varying random resistance. The
Effective Medium Theory model imagines a smoothly varying disorder potential
that causes a continuous variation of the local conductivity. Here, we
demonstrate numerically that both models belong to the same universality class
and that a restricted class of the Random Resistor Network is actually
equivalent to the Effective Medium Theory. Both models are also in good
agreement with experiments on a diverse range of materials. Moreover, we show
that in both cases, a single parameter, i.e. the ratio of the fluctuations in
the carrier density to the average carrier density, completely determines the
magnetoresistance profile.Comment: 6 pages, 5 figure
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