637 research outputs found
Lifting of the Landau level degeneracy in graphene devices in a tilted magnetic field
We report on transport and capacitance measurements of graphene devices in
magnetic fields up to 30 T. In both techniques, we observe the full splitting
of Landau levels and we employ tilted field experiments to address the origin
of the observed broken symmetry states. In the lowest energy level, the spin
degeneracy is removed at filling factors and we observe an enhanced
energy gap. In the higher levels, the valley degeneracy is removed at odd
filling factors while spin polarized states are formed at even . Although
the observation of odd filling factors in the higher levels points towards the
spontaneous origin of the splitting, we find that the main contribution to the
gap at , and is due to the Zeeman energy.Comment: 5 pages, 4 figure
Photonic Clusters
We show through rigorous calculations that dielectric microspheres can be
organized by an incident electromagnetic plane wave into stable cluster
configurations, which we call photonic molecules. The long-range optical
binding force arises from multiple scattering between the spheres. A photonic
molecule can exhibit a multiplicity of distinct geometries, including
quasicrystal-like configurations, with exotic dynamics. Linear stability
analysis and dynamical simulations show that the equilibrium configurations can
correspond with either stable or a type of quasi-stable states exhibiting
periodic particle motion in the presence of frictional dissipation.Comment: 4 pages, 3 figure
Spin current and polarization in impure 2D electron systems with spin-orbit coupling
We derive the transport equations for two-dimensional electron systems with
spin-orbit interaction and short-range spin-independent disorder. In the limit
of slow spatial variations of the electron distribution we obtain coupled
diffusion equations for the electron density and spin. Using these equations we
calculate electric-field induced spin accumulation in a finite-size sample for
arbitrary ratio between spin-orbit energy splitting and elastic scattering
rate. We demonstrate that the spin-Hall conductivity vanishes in an infinite
system independent of this ratio.Comment: 5 pages, 1 figure; revised version according to referee's commment
Infrared absorption and Raman scattering on coupled plasmon--phonon modes in superlattices
We consider theoretically a superlattice formed by thin conducting layers
separated spatially between insulating layers. The dispersion of two coupled
phonon-plasmon modes of the system is analyzed by using Maxwell's equations,
with the influence of retardation included. Both transmission for the finite
plate as well as absorption for the semi-infinite superlattice in the infrared
are calculated. Reflectance minima are determined by the longitudinal and
transverse phonon frequencies in the insulating layers and by the density-state
singularities of the coupled modes. We evaluate also the Raman cross section
from the semi-infinite superlattice.Comment: 20 pages,14 figure
Chaotic hysteresis in an adiabatically oscillating double well
We consider the motion of a damped particle in a potential oscillating slowly
between a simple and a double well. The system displays hysteresis effects
which can be of periodic or chaotic type. We explain this behaviour by
computing an analytic expression of a Poincar'e map.Comment: 4 pages RevTeX, 3 PS figs, uses psfig.sty. Submitted to Phys. Rev.
Letters. PS file also available at
http://dpwww.epfl.ch/instituts/ipt/berglund.htm
Optimal interactions of light with magnetic and electric resonant particles
This work studies the limits of far and near-field electromagnetic response
of sub-wavelength scatterers, like the unitary limit and of lossless
scatterers, and the ideal absorption limit of lossy particles. These limit
behaviors are described in terms of analytic formulas that approximate finite
size effects while rigorously including radiative corrections. This analysis
predicts the electric and/or magnetic limit responses of both metallic and
dielectric nanoparticles while quantitatively describing near-field
enhancements.Comment: 9 pages, 8 figures, 2 table
Competition between excitonic gap generation and disorder scattering in graphene
We study the disorder effect on the excitonic gap generation caused by strong
Coulomb interaction in graphene. By solving the self-consistently coupled
equations of dynamical fermion gap and disorder scattering rate ,
we found a critical line on the plane of interaction strength and
disorder strength . The phase diagram is divided into two regions: in the
region with large and small , and ; in the
other region, and for nonzero . In particular, there
is no coexistence of finite fermion gap and finite scattering rate. These
results imply a strong competition between excitonic gap generation and
disorder scattering. This conclusion does not change when an additional contact
four-fermion interaction is included. For sufficiently large , the
growing disorder may drive a quantum phase transition from an excitonic
insulator to a metal.Comment: 8 pages, 1 figur
Light scattering by an elongated particle: spheroid versus infinite cylinder
Using the method of separation of variables and a new approach to
calculations of the prolate spheroidal wave functions, we study the optical
properties of very elongated (cigar-like) spheroidal particles. A comparison of
extinction efficiency factors of prolate spheroids and infinitely long circular
cylinders is made. For the normal and oblique incidence of radiation, the
efficiency factors for spheroids converge to some limiting values with an
increasing aspect ratio a/b provided particles of the same thickness are
considered.
These values are close to, but do not coincide with the factors for infinite
cylinders. The relative difference between factors for infinite cylinders and
elongated spheroids (a/b \ga 5) usually does not exceed 20 % if the following
approximate relation between the angle of incidence and
the particle refractive index m=n+ki takes the place: \alpha \ga 50 |m-1| + 5
where 1.2 \la n \la 2.0 and k \la 0.1. We show that the quasistatic
approximation can be well used for very elongated optically soft spheroids of
large sizes.Comment: 12 pages, 7 figures, Accepted by Measurement Science and Technology
(special OPC issue
Disentangling the electronic and phononic glue in a high-Tc superconductor
Unveiling the nature of the bosonic excitations that mediate the formation of
Cooper pairs is a key issue for understanding unconventional superconductivity.
A fundamen- tal step toward this goal would be to identify the relative weight
of the electronic and phononic contributions to the overall frequency (\Omega)
dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on
Bi2212 crystals with simultaneous time- and frequency-resolution; this
technique allows us to disentangle the electronic and phononic contributions by
their different temporal evolution. The strength of the interaction
({\lambda}~1.1) with the electronic excitations and their spectral distribution
fully account for the high critical temperature of the superconducting phase
transition.Comment: 9 pages, 4 figure
Unbroken supersymmetry in the Aharonov-Casher effect
We consider the problem of the bound states of a spin 1/2 chargless particle
in a given Aharonov-Casher configuration. To this end we recast the description
of the system in a supersymmetric form. Then the basic physical requirements
for unbroken supersymmetry are established. We comment on the possibility of
neutron confinement in this system
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