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 $\tau$. 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 $\tau$. 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

THREE CENTURIES OF INEQUALITY IN BRITAIN AND AMERICA

Income and wealth inequality rose over the first 150 years of U.S. history. They may have risen at times in Britain before 1875. The first half of this century equalized pre-fisc incomes more in Britain than in America. From the 1970s to the 1990s inequality rose in both countries, reversing some of the previous equalization. Government redistribution explains part but not all of the reversals in inequality trends. Factor-market forces and economic growth would have produced a similar chronology of rises and falls in income inequality even without shifts in the progressivity of redistribution through government. For economies starting from highly unequal property ownership, the development process lowers inequality. History suggests, however, that this may happen only once. Redistribution toward the poor tends to happen least in those times and polities where it would seem most justified by the usual goals of welfare policy.

Fermi-surface reconstruction in a smectic phase of a high temperature superconductor

It is shown that, in the presence of a moderately strong C_4 symmetry breaking (which could be produced either by lattice orthorhombicity or the presence of an electron nematic phase), a weak, period 4, unidirectional charge density wave ("charge stripe") order can reconstruct the Fermi surface of a typical hole-doped cuprate to produce a small electron pocket. This form of charge density wave order is consistent with that adduced from recent high field NMR experiments in YBCO. The Fermi pocket has an area and effective mass which is a rough caricature of those seen in recent high field quantum oscillation experiments.Comment: 4 pages, 2 figures, minor change