2,350 research outputs found
Non-relativistic limit in the 2+1 Dirac Oscillator: A Ramsey Interferometry Effect
We study the non-relativistic limit of a paradigmatic model in Relativistic
Quantum Mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a
novel kind of Zitterbewegung which persists in this non-relativistic regime,
and leads to an observable deformation of the particle orbit. This effect can
be interpreted in terms of a Ramsey Interferometric phenomenon, allowing an
insightful connection between Relativistic Quantum Mechanics and Quantum
Optics. Furthermore, subsequent corrections to the non-relativistic limit,
which account for the usual spin-orbit Zitterbewegung, can be neatly understood
in terms of a Mach-Zehnder interferometer.Comment: RevTex4 file, color figures, submitted for publicatio
Measuring topology in a laser-coupled honeycomb lattice: From Chern insulators to topological semi-metals
Ultracold fermions trapped in a honeycomb optical lattice constitute a
versatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.
61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be
engineered through laser-induced methods, explicitly breaking time-reversal
symmetry. This potentially opens a bulk gap in the energy spectrum, which is
associated with a non-trivial topological order, i.e., a non-zero Chern number.
In this work, we consider the possibility of producing and identifying such a
robust Chern insulator in the laser-coupled honeycomb lattice. We explore a
large parameter space spanned by experimentally controllable parameters and
obtain a variety of phase diagrams, clearly identifying the accessible
topologically non-trivial regimes. We discuss the signatures of Chern
insulators in cold-atom systems, considering available detection methods. We
also highlight the existence of topological semi-metals in this system, which
are gapless phases characterized by non-zero winding numbers, not present in
Haldane's original model.Comment: 30 pages, 12 figures, 4 Appendice
Lithium-doped silk fibroin films for application in electrochromic devices
Silk fibroin (SF) is a commonly available natural biopolymer produced in specialized glands of arthropods,
with a long history of use in textile production and also in health cares. The exceptional intrinsic properties
of these fibers, such as self-assembly, machinability, biocompatibility, biodegradation or non-toxicity, offer a
wide range of exciting opportunities [1].
It has long been recognized that silk can be a rich source of inspiration for designing new materials with
tailored properties, enhanced performance and high added value for targeted applications, opening exciting
new prospects in the domain of materials science and related technological fields, including bio-friendly
integration, miniaturization and multifunctionalization. In recent years it has been demonstrated that fibroin
is an excellent material for active components in optics and photonics devices. Progress in new technological
fields such as optics, photonics and electronics are emerging [2,3].
The incorporation of polymer electrolytes as components of various devices (advanced batteries, smart
windows, displays and supercapacitors) offers significant advantages with respect to traditional electrolytes,
including enhanced reliability and improved safety. SF films are particularly attractive in this context. They
have near-perfect transparency across the VIS range, surface flatness (together with outstanding mechanical
robustness), ability to replicate patterned substrates and their thickness may be easily tailored from a few
nanometers to hundreds of micrometers through spin-casting of a silk solution into subtract. Moreover,
fibroin can be added to other biocomponents or salts in order to modify the biomaterial properties leading to
optimized and total different functions.
Preliminary tests performed with a prototype electrochromic device (ECD) incorporating SF films doped
with lithium triflate and lithium tetrafluoroborate (LiTFSI and LiBF4, respectively) as electrolyte and WO3 as
cathodic electrochromic layer, are extremely encouraging. Aiming to evaluate the performance of the ion
conducting SF membranes doped with LiTFSI and LiBF4 (SF-Li), small ECDs with
glass/ITO/WO3/SF-Li/CeO2-TiO2/ITO/glass configuration were assembled and characterized. The device
exhibited, after 4500 cycles, the insertion of charge at -3.0 V reached –1.1 mC.cm-2
in 15 s. After 4500 cycles
the window glass-staining, glass/ITO/WO3/Fibrin-Li salts electrolyte/CeO2-TiO2/ITO/glass configuration
was reversible and featured a T 8 % at λ = 686 n
Reconstruction and thermal stability of the cubic SiC(001) surfaces
The (001) surfaces of cubic SiC were investigated with ab-initio molecular
dynamics simulations. We show that C-terminated surfaces can have different
c(2x2) and p(2x1) reconstructions, depending on preparation conditions and
thermal treatment, and we suggest experimental probes to identify the various
reconstructed geometries. Furthermore we show that Si-terminated surfaces
exhibit a p(2x1) reconstruction at T=0, whereas above room temperature they
oscillate between a dimer row and an ideal geometry below 500 K, and sample
several patterns including a c(4x2) above 500 K.Comment: 12 pages, RevTeX, figures 1 and 2 available in gif form at
http://irrmawww.epfl.ch/fg/sic/fig1.gif and
http://irrmawww.epfl.ch/fg/sic/fig2.gi
Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical gauge fields
We introduce a scheme that combines photon-assisted tunneling by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t _ J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the photon-assisted tunneling scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field
NACO/SAM observations of sources at the Galactic Center
Sparse aperture masking (SAM) interferometry combined with Adaptive Optics
(AO) is a technique that is uniquely suited to investigate structures near the
diffraction limit of large telescopes. The strengths of the technique are a
robust calibration of the Point Spread Function (PSF) while maintaining a
relatively high dynamic range. We used SAM+AO observations to investigate the
circumstellar environment of several bright sources with infrared excess in the
central parsec of the Galaxy. For our observations, unstable atmospheric
conditions as well as significant residuals after the background subtraction
presented serious problems for the standard approach of calibrating SAM data
via interspersed observations of reference stars. We circumvented these
difficulties by constructing a synthesized calibrator directly from sources
within the field-of-view. When observing crowded fields, this novel method can
boost the efficiency of SAM observations because it renders interspersed
calibrator observations unnecessary. Here, we presented the first NaCo/SAM
images reconstructed using this method.Comment: 8 pages, 10 figures, proceedings of the conference "Astrophysics at
High Angular Resolution" (AHAR-2011
Polymer electrolytes for electrochromic devices
Polymer electrolytes are currently the focus of much attention as potential electrolytes in electrochemical devices such as batteries, display devices and sensors. Generically, solid polymer electrolytes (SPEs) are mixtures of salts with soft polar polymers. SPEs have many advantages including high energy density, no risk of leakage, no issues related to the presence of solvent, wide electrochemical stability windows, simplified processability and light weight. With the goal of developing a new family of environmentally friendly multifunctional biohybrid materials displaying high ionic conductivity we have produced in the present work, flexible films based on different polymers or hybrids incorporating different salts.
The polymer electrolytes studied here have been characterized by means of Differential Scanning Calorimetry, Thermogravimetric Analysis, X-ray diffraction, Polarized Optical Microscopy, complex impedance spectroscopy and cyclic voltammetry. An evaluation of the performance of the sample with the highest conductivity as electrolyte in all solid-state ECDs was performed
Edge states of graphene bilayer strip
The electronic structure of the zig-zag bilayer strip is analyzed. The
electronic spectra of the bilayer strip is computed. The dependence of the edge
state band flatness on the bilayer width is found. The density of states at the
Fermi level is analytically computed. It is shown that it has the singularity
which depends on the width of the bilayer strip. There is also asymmetry in the
density of states below and above the Fermi energy.Comment: 9 page
Surface and electronic structure of MOCVD-grown Ga(0.92)In(0.08)N investigated by UV and X-ray photoelectron spectroscopies
The surface and electronic structure of MOCVD-grown layers of
Ga(0.92)In(0.08)N have been investigated by means of photoemission. An
additional feature at the valence band edge, which can be ascribed to the
presence of In in the layer, has been revealed. A clean (0001)-(1x1) surface
was prepared by argon ion sputtering and annealing. Stability of chemical
composition of the investigated surface subjected to similar ion etching was
proven by means of X-ray photoemission spectroscopy.Comment: 13 pages, 6 figure
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