Current injection by coherent one- and two-photon excitation in graphene and its bilayer

Coherent control of optically-injected carrier distributions in single and bilayer graphene allows the injection of electrical currents. Using a tight-binding model and Fermi's golden rule, we derive the carrier and photocurrent densities achieved via interference of the quantum amplitudes for two-photon absorption at a fundamental frequency, $\omega$, and one-photon absorption at the second harmonic, $2\omega$. Strong currents are injected under co-circular and linear polarizations. In contrast, opposite-circular polarization yields no net current. For single-layer graphene, the magnitude of the current is unaffected by the rotation of linear-polarization axes, in contrast with the bilayer and with conventional semiconductors. The dependence of the photocurrent on the linear-polarization axes is a clear and measurable signature of interlayer coupling in AB-stacked multilayer graphene. We also find that single and bilayer graphene exhibit a strong, distinct linear-circular dichroism in two-photon absorption.Comment: 9 pages, 8 figure

Alien Registration- Rioux, Arthur J. (Limestone, Aroostook County)

https://digitalmaine.com/alien_docs/35185/thumbnail.jp

On the extent of re-entitlement effects in unemployment compensation

We analyze the implications of two-tier unemployment compensation systems with nonautomatic eligibility in an equilibium matching model with Nash bargaining. As eligibility for UI does not automatically follow from employment, the two types of unemployed workers have different threat points, which delivers equilibrium wage dispersion. The parameters of the model are estimated for France, and the model is also calibrated for Denmark and the U.S. Re-entitlement effects are shown to be sizeable for all three countries. For France, reentitlement effects lower by 15% the rise in the wage and by 25% the rise in unemployment following a 10% increase in the benefit level. Finally, we show that in all three countries the optimal compensation system is characterized by time-decreasing unemployment benefits and non-automatic eligibility for UI, with higher levels of both UI and UA benefits, a smaller decrease in benefits over time, and a longer employment duration required for UI eligibility than in the current system

Ethics Of Tax Law Compliance: An Interdisciplinary Perspective

The first semester Tax I student seems to be interested in the ethical issue of why citizens should report their income and only take legitimate tax deductions when it is unlikely that anyone will ever know. This paper addresses this issue from an interdisciplinary approach of accounting, philosophy, and political science. The accounting perspective discusses the issue from the expectations of the tax preparer and the Internal Revenue Service (IRS). The philosophical perspectives provides background of a citizen who might want to “do the right thing” for the sake of the common good. The political science perspective explores the political nature of the individual and corporate citizen and their approach to civic virtue

Type‐Preserving CPS Translation of Σ and Π Types is Not Not Possible

International audienceDependently typed languages like Coq are used to specify and prove functional correctness of source programs,but what we ultimately need are guarantees about correctness of compiled code. By preserving dependenttypes through each compiler pass, we could preserve source-level specifications and correctness proofs intothe generated target-language programs. Unfortunately, type-preserving compilation of dependent types isnontrivial. In 2002, Barthe and Uustalu showed that type-preserving CPS is not possible for languages likeCoq. Specifically, they showed that for strong dependent pairs (Σ types), the standard typed call-by-name CPSis not type preserving. They further proved that for dependent case analysis on sums, a class of typed CPStranslations—including the standard translation—is not possible. In 2016, Morrisett noticed a similar problemwith the standard call-by-value CPS translation for dependent functions (Π types). In essence, the problem isthat the standard typed CPS translation by double-negation, in which computations are assigned types of theform (A → ⊥) → ⊥, disrupts the term/type equivalence that is used during type checking in a dependentlytyped language.In this paper, we prove that type-preserving CPS translation for dependently typed languages is not notpossible. We develop both call-by-name and call-by-value CPS translations from the Calculus of Constructionswith both Π and Σ types (CC) to a dependently typed target language, and prove type preservation andcompiler correctness of each translation. Our target language is CC extended with an additional equivalencerule and an additional typing rule, which we prove consistent by giving a model in the extensional Calculus ofConstructions. Our key observation is that we can use a CPS translation that employs answer-type polymorphism,where CPS-translated computations have type ∀α.(A → α) → α. This type justifies, by a free theorem,the new equality rule in our target language and allows us to recover the term/type equivalences that CPStranslation disrupts. Finally, we conjecture that our translation extends to dependent case analysis on sums,despite the impossibility result, and provide a proof sketch

Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial Graphene from Polarization Dependent Coherently Controlled Photocurrent Generation

Most experimental studies to date of multilayer epitaxial graphene on C-face SiC have indicated that the electronic states of different layers are decoupled as a consequence of rotational stacking. We have measured the third order nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer electronic coupling, by studying THz emission from coherently controlled photocurrents as a function of the optical pump and THz beam polarizations. We find that the polarization dependence of the coherently controlled THz emission expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not observed. We hypothesize that the observed angular dependence arises from weak coupling between the layers; a model calculation of the angular dependence treating the multilayer structure as a stack of independent bilayers with variable interlayer coupling qualitatively reproduces the polarization dependence, providing evidence for coupling.Comment: submitted to Nano Letter