1,075 research outputs found
A cosmological model for corrugated graphene sheets
Defects play a key role in the electronic structure of graphene layers flat
or curved. Topological defects in which an hexagon is replaced by an n-sided
polygon generate long range interactions that make them different from
vacancies or other potential defects. In this work we review previous models
for topological defects in graphene. A formalism is proposed to study the
electronic and transport properties of graphene sheets with corrugations as the
one recently synthesized. The formalism is based on coupling the Dirac equation
that models the low energy electronic excitations of clean flat graphene
samples to a curved space. A cosmic string analogy allows to treat an arbitrary
number of topological defects located at arbitrary positions on the graphene
plane. The usual defects that will always be present in any graphene sample as
pentagon-heptagon pairs and Stone-Wales defects are studied as an example. The
local density of states around the defects acquires characteristic modulations
that could be observed in scanning tunnel and transmission electron microscopy.Comment: Proceedings of the Graphene Conference, MPI PKS Dresden, September
200
Chiral sound waves in strained Weyl semimetals
We show that a strained wire of a Weyl semimetal supports a new type of
gapless excitation, the chiral sound wave (CSW). It is a longitudinal charge
density wave analog to the chiral magnetic wave predicted in the quark-gluon
plasma but driven by an elastic axial pseudo-magnetic field. It involves the
axial-axial-axial contribution to the chiral anomaly which couples the chiral
charge density to the elastic axial gauge field. The chiral sound is
unidirectional: it propagates along the elastic magnetic field and not in the
opposite direction. The CSW may propagate for long distances as it does not
couple directly to quickly dissipating electromagnetic plasmons, while its
damping is controlled by the slow chirality flip rate. We propose an
experimental setup to directly detect the chiral sound, which is excited by
mechanical vibrations of the crystal lattice in the GHz frequency range. Our
findings contribute to a new trend, the chiral acoustics, in strained Weyl
semimetals.Comment: 5 pages, 3 figures; v2: minor changes, published versio
Renormalization group analysis of electrons near a Van Hove singularity.
A model of interacting two dimensional electrons near a Van Hove singularity
is studied, using renormalization group techniques. In hole doped systems, the
chemical potential is found to be pinned near the singularity, when the
electron-electron interactions are repulsive. The RG treatment of the leading
divergences appearing in perturbation theory give rise to marginal behavior and
anisotropic superconductivity.Comment: 4 Latex pages + 5 postcript figure
Thermoelectric relations in the conformal limit in Dirac and Weyl semimetals
In the Fermi liquid description of metals, electrical and thermoelectric
transport coefficients are linked by robust relations which can be challenged
by strong interactions or when the electron liquid enters a different regime.
These relations have been very powerful in the characterisation of novel
materials. We show that Dirac and Weyl semimetals at zero doping and zero
temperature (the conformal limit) have a very singular behavior due to a
quantum anomaly. Away from this point, a Mott relation can be established
Gauge fields in graphene
The physics of graphene is acting as a bridge between quantum field theory
and condensed matter physics due to the special quality of the graphene
quasiparticles behaving as massless two dimensional Dirac fermions. Moreover,
the particular structure of the 2D crystal lattice sets the arena to study and
unify concepts from elasticity, topology and cosmology. In this paper we
analyze these connections combining a pedagogical, intuitive approach with a
more rigorous formalism when required.Comment: Update of the manuscript published on-line in Physics Reports. 43
pages, 18 figure
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