353 research outputs found
Theory of the plasma-wave photoresponse of a gated graphene sheet
The photoresponse of graphene has recently received considerable attention.
The main mechanisms yielding a finite dc response to an oscillating radiation
field which have been investigated include responses of photovoltaic,
photo-thermoelectric, and bolometric origin. In this Article we present a fully
analytical theory of a photoresponse mechanism which is based on the excitation
of plasma waves in a gated graphene sheet. By employing the theory of
relativistic hydrodynamics, we demonstrate that plasma-wave photodetection is
substantially influenced by the massless Dirac fermion character of carriers in
graphene and that the efficiency of photodetection can be improved with respect
to that of ordinary parabolic-band electron fluids in semiconductor
heterostructures.Comment: 11 pages, 3 figures, 1 appendi
Generation and morphing of plasmons in graphene superlattices
Recent experimental studies on graphene on hexagonal Boron Nitride (hBN) have
demonstrated that hBN is not only a passive substrate that ensures superb
electronic properties of graphene's carriers, but that it actively modifies
their massless Dirac fermion character through a periodic moir\'e potential. In
this work we present a theory of the plasmon excitation spectrum of massless
Dirac fermions in a moir\'e superlattice. We demonstrate that graphene-hBN
stacks offer a rich platform for plasmonics in which control of plasmon modes
can occur not only via electrostatic gating but also by adjusting e.g. the
relative crystallographicComment: 10 pages, 12 figures, 3 appendice
Electrical plasmon injection in double-layer graphene heterostructures
It is by now well established that high-quality graphene enables a
gate-tunable low-loss plasmonic platform for the efficient confinement,
enhancement, and manipulation of optical fields spanning a broad range of
frequencies, from the mid infrared to the Terahertz domain. While
all-electrical detection of graphene plasmons has been demonstrated, electrical
plasmon injection (EPI), which is crucial to operate nanoplasmonic devices
without the encumbrance of a far-field optical apparatus, remains elusive. In
this work, we present a theory of EPI in double-layer graphene, where a
vertical tunnel current excites acoustic and optical plasmon modes. We first
calculate the power delivered by the applied inter-layer voltage bias into
these collective modes. We then show that this system works also as a
spectrally-resolved molecular sensor.Comment: 10 pages, 6 figure
Non-local transport and the hydrodynamic shear viscosity in graphene
Motivated by recent experimental progress in preparing encapsulated graphene
sheets with ultra-high mobilities up to room temperature, we present a
theoretical study of dc transport in doped graphene in the hydrodynamic regime.
By using the continuity and Navier-Stokes equations, we demonstrate
analytically that measurements of non-local resistances in multi-terminal Hall
bar devices can be used to extract the hydrodynamic shear viscosity of the
two-dimensional (2D) electron liquid in graphene. We also discuss how to probe
the viscosity-dominated hydrodynamic transport regime by scanning probe
potentiometry and magnetometry. Our approach enables measurements of the
viscosity of any 2D electron liquid in the hydrodynamic transport regime.Comment: 12 pages, 4 multi-panel figure
fea integration in the tolerance analysis using skin model shapes
Abstract Many research works on tolerance analysis have been carried out in the last thirty years. In this paper, a new idea is proposed, aiming to investigate the effect of form error and mechanical behavior of parts on the stack-up result by combining the recent novelties on the tolerance analysis of rigid and flexible bodies. The real parts are simulated considering the non-nominal Skin Model Shape and the mechanical properties in order to simulate the assembly of a realistic case study. A manufacturing signature model to generate the features with geometric deviations and Finite Element Analysis (FEA) are used
Computer-Aided Techniques for Geometry Assurance
Geometry assurance can be described as a number of activities, all contributing to minimize the effect of geometrical variation in a final product. This work aims to introduce a new type of comparison between a computer-aided technique for geometry assurance and some models proposed by the literature. In particular, the aim of this work is to solve, through a computer-aided technique, some case studies that were already solved by different methods of the literature. The different case studies that have been introduced and solved in this paper aim to highlight the potentialities and the limits in using a computer-aided technique for geometry assurance. Because this type of comparison is not present in the literature yet, this work wants to place the emphasis on the fact that till now there is not a unique approach to solve problems of geometry assurance and no approach can be defined as better than another, in terms of results
Electron density distribution and screening in rippled graphene sheets
Single-layer graphene sheets are typically characterized by long-wavelength
corrugations (ripples) which can be shown to be at the origin of rather strong
potentials with both scalar and vector components. We present an extensive
microscopic study, based on a self-consistent Kohn-Sham-Dirac
density-functional method, of the carrier density distribution in the presence
of these ripple-induced external fields. We find that spatial density
fluctuations are essentially controlled by the scalar component, especially in
nearly-neutral graphene sheets, and that in-plane atomic displacements are as
important as out-of-plane ones. The latter fact is at the origin of a
complicated spatial distribution of electron-hole puddles which has no evident
correlation with the out-of-plane topographic corrugations. In the range of
parameters we have explored, exchange and correlation contributions to the
Kohn-Sham potential seem to play a minor role.Comment: 13 pages, 13 figures, submitted. High-quality figures can be
requested to the author
Charger-mediated energy transfer for quantum batteries: an open system approach
The energy charging of a quantum battery is analyzed in an open quantum
setting, where the interaction between the battery element and the external
power source is mediated by an ancilla system (the quantum charger) that acts
as a controllable switch. Different implementations are analyzed putting
emphasis on the interplay between coherent energy pumping mechanisms and
thermalization
Transport and optical properties of an electron gas in a Sierpinski carpet
Recent progress in the design and fabrication of artificial two-dimensional
(2D) materials paves the way for the experimental realization of electron
systems moving on plane fractals. In this work, we present the results of
computer simulations for the conductance and optical absorption spectrum of a
2D electron gas roaming on a Sierpinski carpet, i.e. a plane fractal with
Hausdorff dimension intermediate between one and two. We find that the
conductance is sensitive to the spatial location of the leads and that it
displays fractal fluctuations whose dimension is compatible with the Hausdorff
dimension of the sample. Very interestingly, electrons in this fractal display
a broadband optical absorption spectrum, which possesses sharp "molecular"
peaks at low photon energies.Comment: 6 pages, 5 figures; comments are very welcom
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