11 research outputs found
Voltage-driven quantum oscillations in graphene
We predict unusual (for non-relativistic quantum mechanics) electron states
in graphene, which are localized within a finite-width potential barrier. The
density of localized states in the sufficiently high and/or wide graphene
barrier exhibits a number of singularities at certain values of the energy.
Such singularities provide quantum oscillations of both the transport (e.g.,
conductivity) and thermodynamic properties of graphene - when increasing the
barrier height and/or width, similarly to the well-known Shubnikov-de-Haas
(SdH) oscillations of conductivity in pure metals. However, here the SdH-like
oscillations are driven by an electric field instead of the usual
magnetically-driven SdH-oscillations.Comment: 4 pages, 4 figure
Electrostatic deposition of graphene in a gaseous environment: A deterministic route to synthesize rolled graphenes?
The synthesis of single-wall carbon nanotubes (SWCNTs) of desired diameters
and chiralities is critical to the design of nanoscale electronic devices with
desired properties.1-6 The existing methods are based on self-assembly, 7-16
therefore lacking the control over their diameters and chiralities. The present
work reports a direct route to roll graphene. Specifically, we found that the
electrostatic deposition of graphene yielded: (i) flat graphene layers under
high vacuum (10-7 Torr), (ii) completely scrolled graphene under hydrogen
atmosphere, (iii) partially scrolled graphene under nitrogen atmosphere, and
(iv) no scrolling for helium atmospheres. Our study shows that the application
of the electrostatic field facilitates the rolling of graphene sheets exposed
to appropriate gases and allows the rolling of any size graphene. The technique
proposed here, in conjunction with a technique that produces graphene
nanoribbons (GNRs) of uniform widths, will have significant impact on the
development of carbon nanotube based devices. Furthermore, the present
technique may be applied to obtain tubes/scrolls of other layered materials
Symmetry Breaking in Few Layer Graphene Films
Recently, it was demonstrated that the quasiparticle dynamics, the
layer-dependent charge and potential, and the c-axis screening coefficient
could be extracted from measurements of the spectral function of few layer
graphene films grown epitaxially on SiC using angle-resolved photoemission
spectroscopy (ARPES). In this article we review these findings, and present
detailed methodology for extracting such parameters from ARPES. We also present
detailed arguments against the possibility of an energy gap at the Dirac
crossing ED.Comment: 23 pages, 13 figures, Conference Proceedings of DPG Meeting Mar 2007
Regensburg Submitted to New Journal of Physic
Cyclotron motion in graphene
We investigate cyclotron motion in graphene monolayers considering both the
full quantum dynamics and its semiclassical limit reached at high carrier
energies. Effects of zitterbewegung due to the two dispersion branches of the
spectrum dominate the irregular quantum motion at low energies and are obtained
as a systematic correction to the semiclassical case. Recent experiments are
shown to operate in the semiclassical regime.Comment: 6 pages, 1 figure include
Tunneling of Dirac electrons through spatial regions of finite mass
We study the tunneling of chiral electrons in graphene through a region wherethe electronic spectrum changes from the usual linear dispersion to a hyperbolic dispersion,due to the presence of a gap. It is shown that contrary to the tunneling through a potentialbarrier, the transmission of electrons is, in this case, smaller than one for normal incidence.This mechanism may be useful for designing electronic devices made of grapheneinfo:eu-repo/semantics/publishedVersio
Dirac-point engineering and topological phase transitions in honeycomb optical lattices
We study the electronic structure and the phase diagram of non-interacting
fermions confined to hexagonal optical lattices. In the first part, we compare
the properties of Dirac points arising in the eigenspectrum of either honeycomb
or triangular lattices. Numerical results are complemented by analytical
equations for weak and strong confinements. In the second part we discuss the
phase diagram and the evolution of Dirac points in honeycomb lattices applying
a tight-binding description with arbitrary nearest-neighbor hoppings. With
increasing asymmetry between the hoppings the Dirac points approach each other.
At a critical asymmetry the Dirac points merge to open an energy gap, thus
changing the topology of the eigenspectrum. We analyze the trajectory of the
Dirac points and study the density of states in the different phases.
Manifestations of the phase transition in the temperature dependence of the
specific heat and in the structure factor are discussed.Comment: Published version 10 pages, 5 figure
Dirac electrons in graphene-based quantum wires and quantum dots
In this paper we analyse the electronic properties of Dirac electrons in
finite-size ribbons and in circular and hexagonal quantum dots made of
graphene.Comment: Contribution for J. Phys.: Cond. Mat. special issue on graphene
physic
Electronic properties of bilayer and multilayer graphene
We study the effects of site dilution disorder on the electronic properties
in graphene multilayers, in particular the bilayer and the infinite stack. The
simplicity of the model allows for an easy implementation of the coherent
potential approximation and some analytical results. Within the model we
compute the self-energies, the density of states and the spectral functions.
Moreover, we obtain the frequency and temperature dependence of the
conductivity as well as the DC conductivity. The c-axis response is
unconventional in the sense that impurities increase the response for low
enough doping. We also study the problem of impurities in the biased graphene
bilayer.Comment: 36 pages, 42 figures, references adde
Magnetometry of low-dimensional electron and hole systems
Copyright © 2009 Institute of PhysicsThe high-magnetic-field, low-temperature magnetic properties of low-dimensional electron and hole systems reveal a wealth of fundamental information. Quantum oscillations of the thermodynamic equilibrium magnetization yield the total density of states, a central quantity in understanding the quantum Hall effect in 2D systems. The magnetization arising from non-equilibrium circulating currents reveals details, not accessible with traditional measurements, of the vanishingly small longitudinal resistance in the quantum Hall regime. We review how the technique of magnetometry has been applied to these systems, the most important discoveries that have been made, and their theoretical significance