3,666 research outputs found
Generalized Lifshitz-Kosevich scaling at quantum criticality from the holographic correspondence
We characterize quantum oscillations in the magnetic susceptibility of a
quantum critical non-Fermi liquid. The computation is performed in a strongly
interacting regime using the nonperturbative holographic correspondence. The
temperature dependence of the amplitude of the oscillations is shown to depend
on a critical exponent nu. For general nu the temperature scaling is distinct
from the textbook Lifshitz-Kosevich formula. At the `marginal' value nu = 1/2,
the Lifshitz-Kosevich formula is recovered despite strong interactions. As a
by-product of our analysis we present a formalism for computing the amplitude
of quantum oscillations for general fermionic theories very efficiently.Comment: 18 pages, pdftex, 1 figure. v2: figure and few comments adde
Trigonal warping and Berry’s phase Npi in ABC-stacked multilayer graphene.
The electronic band structure of ABC-stacked multilayer graphene is studied within an effective mass approximation. The electron and hole bands touching at zero energy support chiral quasiparticles characterized by Berry’s phase Nπ for N-layers, generalizing the low-energy band structure of monolayer and bilayer graphene. We investigate the trigonal-warping deformation of the energy bands and show that the Lifshitz transition, in which the Fermi circle breaks up into separate parts at low energy, reflects Berry’s phase Nπ. It is particularly prominent in trilayers, N = 3, with the Fermi circle breaking into three parts at a relatively large energy that is related to next-nearestlayer coupling. For N = 3, we study the effects of electrostatic potentials which vary in the stacking direction, and find that a perpendicular electric field, as well as opening an energy gap, strongly enhances the trigonal-warping effect. In magnetic fields, the N = 3 Lifshitz transition is manifested as a coalescence of Landau levels into triply-degenerate levels
Casimir Force between a Small Dielectric Sphere and a Dielectric Wall
The possibility of repulsive Casimir forces between small metal spheres and a
dielectric half-space is discussed. We treat a model in which the spheres have
a dielectric function given by the Drude model, and the radius of the sphere is
small compared to the corresponding plasma wavelength. The half-space is also
described by the same model, but with a different plasma frequency. We find
that in the retarded limit, the force is quasi-oscillatory. This leads to the
prediction of stable equilibrium points at which the sphere could levitate in
the Earth's gravitational field. This seems to lead to the possibility of an
experimental test of the model. The effects of finite temperature on the force
are also studied, and found to be rather small at room temperature. However,
thermally activated transitions between equilibrium points could be significant
at room temperature.Comment: 16 pages, 5 figure
Magnetic spectrum of trigonally warped bilayer graphene - semiclassical analysis, zero modes, and topological winding numbers
We investigate the fine structure in the energy spectrum of bilayer graphene
in the presence of various stacking defaults, such as a translational or
rotational mismatch. This fine structure consists of four Dirac points that
move away from their original positions as a consequence of the mismatch and
eventually merge in various manners. The different types of merging are
described in terms of topological invariants (winding numbers) that determine
the Landau-level spectrum in the presence of a magnetic field as well as the
degeneracy of the levels. The Landau-level spectrum is, within a wide parameter
range, well described by a semiclassical treatment that makes use of
topological winding numbers. However, the latter need to be redefined at zero
energy in the high-magnetic-field limit as well as in the vicinity of saddle
points in the zero-field dispersion relation.Comment: 17 pages, 16 figures; published version with enhanced discussion of
experimental finding
Thermal van der Waals Interaction between Graphene Layers
The van de Waals interaction between two graphene sheets is studied at finite
temperatures. Graphene's thermal length controls
the force versus distance as a crossover from the zero temperature
results for , to a linear-in-temperature, universal regime for
. The large separation regime is shown to be a consequence of the
classical behavior of graphene's plasmons at finite temperature. Retardation
effects are largely irrelevant, both in the zero and finite temperature
regimes. Thermal effects should be noticeable in the van de Waals interaction
already for distances of tens of nanometers at room temperature.Comment: enlarged version, 9 pages, 4 figures, updated reference
Quantum Hall effects of graphene with multi orbitals: Topological numbers, Boltzmann conductance and Semi-classical quantization
Hall conductance as the Chern numbers of the Berry connection
in the magnetic Brillouin zone is calculated for a realistic multi band
tight-band model of graphene with non-orthogonal basis. It is confirmed that
the envelope of coincides with a semi-classical result when
magnetic field is sufficiently small.
The Hall resistivity from the weak-field Boltzmann theory also
explains the overall behaviour of the if the Fermi surface is
composed of a single energy band. The plateaux of are explained
from semi-classical quantization and necessary modification is proposed for the
Dirac fermion regimes.Comment: 5pages, 3figure
Surface-atom force out of thermal equilibrium and its effect on ultra-cold atoms
The surface-atom Casimir-Polder-Lifshitz force out of thermal equilibrium is
investigated in the framework of macroscopic electrodynamics. Particular
attention is devoted to its large distance limit that shows a new, stronger
behaviour with respect to the equilibrium case. The frequency shift produced by
the surface-atom force on the the center-of-mass oscillations of a harmonically
trapped Bose-Einstein condensate and on the Bloch oscillations of an ultra-cold
fermionic gas in an optical lattice are discussed for configurations out of
thermal equilibrium.Comment: Submitted to JPA Special Issue QFEXT'0
Magnetic double refraction in piezoelectrics
A new type of magneto-optical effect in piezoelectrics is predicted. A low
frequency behavior of Faraday effect is found.Comment: 2 pages, to be published in Europhys. Lett
Traversable wormhole in the deformed Ho\v{r}ava-Lifshitz gravity
Asymptotically flat wormhole solutions are found in the deformed
Ho\v{r}ava-Lifshitz gravity. It turns out that higher curvature terms can not
play the role of exotic matters which are crucial to form a traversable
wormhole, and external exotic sources are still needed. In particular, the
exotic matter behaves like phantom energy if Kehagias-Sfetsos vacuum is
considered outside the wormhole. Interestingly, the spherically symmetric
setting makes the matter and the higher curvature contribution satisfy
four-dimensional conservation of energy in the covariant form.Comment: 13 pages, 2 figures, version published in Phys. Rev.
A generalized Kramers-Kronig transform for Casimir effect computations
Recent advances in experimental techniques now permit to measure the Casimir
force with unprecedented precision. In order to achieve a comparable precision
in the theoretical prediction of the force, it is necessary to accurately
determine the electric permittivity of the materials constituting the plates
along the imaginary frequency axis. The latter quantity is not directly
accessible to experiments, but it can be determined via dispersion relations
from experimental optical data. In the experimentally important case of
conductors, however, a serious drawback of the standard dispersion relations
commonly used for this purpose, is their strong dependence on the chosen
low-frequency extrapolation of the experimental optical data, which introduces
a significant and not easily controllable uncertainty in the result. In this
paper we show that a simple modification of the standard dispersion relations,
involving suitable analytic window functions, resolves this difficulty, making
it possible to reliably determine the electric permittivity at imaginary
frequencies solely using experimental optical data in the frequency interval
where they are available, without any need of uncontrolled data extrapolations.Comment: 10 pages, 6 encapsulated figures. A few typos corrected, some
references added. The new version matches the one accepted for publication on
Phys. Rev.
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