2,691 research outputs found
Theory of non-retarded ballistic surface plasma waves in metal films
We present a theory of surface plasma waves in metal films with arbitrary
electronic collision rate . Both \textit{tangential} and \textit{normal}
modes are investigated. A universal self-amplification channel for these waves
is established as a result of the unique interplay between ballistic electronic
motions and boundary effects. The channel is shown to be protected by a general
principle and its properties independent of . The effects of film
thickness and surface roughness are also calculated. Experimental implications,
such as Ferrel radiation, are discussed.Comment: 14 pages, 3 figs. arXiv admin note: text overlap with
arXiv:1701.0106
A Theory of Electrodynamic Responses for Bounded Metals: Surface Capacitive Effects
We report a general macroscopic theory for the electrodynamic response of
semi-infinite metals (SIMs). The theory includes the hitherto overlooked
capacitive effects due to the finite spatial extension of a surface. The basic
structure of this theory is independent of the particulars of electron
dynamics. Analytical expressions have been obtained of the charge
density-density response function, which is naturally parsed into two parts.
One of them represents a bulk property while the other a pure surface property.
We apply the theory to study the responses according to several electronic
dynamics models and provide a unified view of their validity and limitations.
The models studied include the local dielectric model (DM), the dispersive
hydrodynamic model (HDM) and specular reflection model (SRM), as well as the
less common semi-classical model (SCM) based on Boltzmann's transport equation.
We show that, in terms of their basic equations, the SRM is an extension of the
HDM, just as the HDM is an extension of the DM. The SCM improves over the SRM
critically through the inclusion of translation symmetry breaking and surface
roughness effects. We then employ the response function to evaluate the
so-called dynamical structure factor, which plays an important role in particle
scattering. As expected, this factor reveals a peak due to the excitation of
surface plasma waves (SPWs). Surprisingly, however, the peak is shown to be
considerably sharper in the SCM than in other models, indicating an incipient
instability of the system according to this model. We also study the
distribution of charges induced by a charged particle grazing over a SIM
surface at constant speed. This distribution is shown to contain model-specific
features that are of immediate experimental interest.Comment: 24 pages, 10 figures, a few more references are added and discussed,
abstract and introduction modified to improve presentation over older
versions, more experimental aspects are discusse
A universal macroscopic theory of surface plasma waves and their losses
Recently, we have revealed an intrinsic instability of metals due to surface
plasma waves (SPWs) and raised the prospect of using it to create lossless
SPWs. The counter-intuitive nature of this finding prompts one to ask, why had
not this instability been disclosed before, given the long history of this
subject? If this instability does exist, how far is it from reality? The
present work is devoted to answering these questions. To this end, we derive a
unified macroscopic theory of SPWs that applies to any type of electron
dynamics, be they local or non-local, classical or quantum-mechanical. In light
of this theory, we analyze the behaviors of SPWs according to several electron
dynamics models, including the widely used local dielectric model (DM), the
hydrodynamic model (HDM) and the specular reflection model (SRM), in addition
to the less common semi-classical model (SCM). We find that, in order to unveil
the instability, one must (i) self-consistently treat surface effects without
any of the usually imposed auxiliary conditions and (ii) include translation
symmetry breaking effects in electron dynamics. As far as we are concerned,
none existing work had fulfilled both (i) and (ii). To assess the possibility
of realizing the instability, we analyze two very important factors: the
dielectric interfacing the metal and inter-band transitions, which both were
ignored in our recent work. Whereas inter-band absorption -- together with
Landau damping -- is shown adverse to the instability, a dielectric brings it
closer to occurrence. One may even attain it in common plasmonic materials such
as silver under not so tough conditions.Comment: 16 pages, 6 figures, title changed, rewrite of the Introduction and
abstract, restructuring, Fig. 2 deleted, Appendix B added, more references
added, material in Sec. VI has some overlap with arXiv:1706.03404 (not to be
submitted
Helical Topological Edge States in a Quadrupole Phase
Topological electric quadrupole is a recently proposed concept that extends
the theory of electric polarization of crystals to higher orders. Such a
quadrupole phase supports topological states localized on both edges and
corners. In this work, we show that in a quadrupole phase of honeycomb lattice,
topological helical edge states and pseudo-spin-polarized corner states appear
by making use of a pseudo-spin degree of freedom related to point group
symmetry. Furthermore, we argue that a general condition for emergence of
helical edge states in a (pseudo-)spinful quadrupole phase is mirror or
time-reversal symmetry. Our results offers a way of generating topological
helical edge states without spin-orbital couplings
Identifying Calcium-Binding Sites and Predicting Disulfide Connectivity
Most questions in proteomics require complex answers. Yet graph theory, supervised learning, and statistical model have decomposed complex questions into simple questions with simple answers. The expertise in the field of protein study often address tasks that demand answers as complex as the questions. Such complex answers may consist of multiple factors that must be weighed against each other to arrive at a globally satisfactory and consistent solution to the question. In the prediction of calcium binding in proteins, we construct a global oxygen contact graph of a protein, then apply a graph algorithm to find oxygen clusters with the fixed size of four, finally employ a geometry algorithm to judge if the oxygen clusters are calcium-binding sites or not. Additionally, we can predict the locations of those sites. Furthermore, we construct a global oxygen contact graph including oxygen-bonded carbon atoms of a protein, then apply a graph algorithm to find local biggest oxygen clusters, finally design another geometric filter to exclude the non-calcium binding oxygen clusters. In addition, we apply observed chemical properties as a chemical filter to recognize some non-calcium binding oxygen clusters. In order to explore the characteristics of calcium-binding sites in proteins, we conduct a statistic survey on four datasets derived from 1994 to 2005 about the geometric parameters and chemical properties of calcium-binding sites. In the prediction of disulfide bond connectivity, we analyze protein sequences to predict the folding of proteins relative to the cystines using nearest neighboring methods. we extend a new pattern-wise method to all available template proteins, and find global pattern of pairing cysteines with a new descriptor of cysteine separation profile on protein secondary structure
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