Bipolar electron waveguides in two-dimensional materials with tilted Dirac cones

This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this recordData availability statement: No new data were created or analysed in this study.We show that the (2+1)-dimensional massless Dirac equation, which includes a tilt term, can be reduced to the biconfluent Heun equation for a broad range of scalar confining potentials, including the well-known Morse potential. Applying these solutions, we investigate a bipolar electron waveguide in 8--$Pmmn$ borophene, formed by a well and barrier, both described by the Morse potential. We demonstrate that the ability of two-dimensional materials with tilted Dirac cones to localize electrons in both a barrier and a well can be harnessed to create pseudogaps in their electronic spectrum. These pseudogaps can be tuned through varying the applied top-gate voltage. Potential opto-valleytronic and terahertz applications are discussed.NATOEuropean Union Horizon 2020Engineering and Physical Sciences Research Council (EPSRC)URC

Guided modes and terahertz transitions for two-dimensional Dirac fermions in a smooth double-well potential

This is the final version. Available from the American Physical Society via the DOI in this recordThe double-well problem for the two-dimensional Dirac equation is solved for a family of quasi-one-dimensional potentials in terms of confluent Heun functions. We demonstrate that for a double well separated by a barrier, both the energy level splitting associated with the wavefunction overlap of well states, and the gap size of the avoided crossings associated with well and barrier state repulsion, can be controlled via the parameters of the potential. The transitions between the two states comprising a doublet, as well as transitions across the pseudo-gaps are strongly allowed, highly anisotropic, and for realistic graphene devices can be tuned to fall within the highly desirable terahertz frequency range.European Union Horizon 2020URCOMinistry of Science and Higher Education of the Russian Federation, Goszadani

Publisher Correction: Two-dimensional Dirac particles in a Pöschl-Teller waveguide

This is the final version. Available on open access from Nature Research via the DOI in this recordThis is a correction the article published in Scientific Reports on 14 September 2017: Hartmann, R.R., Portnoi, M.E. Two-dimensional Dirac particles in a Pöschl-Teller waveguide. Sci Rep 7, 11599 (2017). https://doi.org/10.1038/s41598-017-11411-wThe article to which this is the correction is available in ORE at http://hdl.handle.net/10871/2945

Bipolar electron waveguides in graphene

This is the final version. Available from the American Physical Society via the DOI in this record. We show analytically that the ability of Dirac materials to localize an electron in both a barrier and a well can be utilized to open a pseudogap in graphene’s spectrum. By using narrow top gates as guiding potentials, we demonstrate that graphene bipolar waveguides can create a nonmonotonous one-dimensional dispersion along the electron waveguide, whose electrostatically controllable pseudoband gap is associated with strong terahertz transitions in a narrow frequency range.European Union Horizon 2020URCOMinistry of Science and Higher Education of Russian Federatio

Quasi-exact solutions for guided modes in two-dimensional materials with tilted Dirac cones

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: This study did not generate any new data. The datasets used and analysed in this study are available from the corresponding author upon request.We show that if the solutions to the (2+1)-dimensional massless Dirac equation for a given 1D potential are known, then they can be used to obtain the eigenvalues and eigenfunctions for the same potential, orientated at an arbitrary angle, in a 2D Dirac material possessing tilted, anisotropic Dirac cones. This simple set of transformations enables all the exact and quasi-exact solutions associated with 1D quantum wells in graphene to be applied to the confinement problem in tilted Dirac materials such as 8-Pmmn borophene. We also show that smooth electron waveguides in tilted Dirac materials can be used to manipulate the degree of valley polarization of quasiparticles travelling along a particular direction of the channel. We examine the particular case of the hyperbolic secant potential to model realistic top-gated structures for valleytronic applications.European Union Horizon 2020DOST-SEI ASTHRDPEngineering and Physical Sciences Research Council (EPSRC)NATOURCORussian Science Foundatio

Terahertz transitions in finite carbon chains

This is the final version. Available from the American Physical Society via the DOI in this record. We predict an optical effect associated with systems, which exhibit topologically protected states separated by a finite distance. We develop a tight-binding model to calculate the optical selection rules in linear chains of atoms of different lengths, and show the crucial importance of edge states. For long enough molecules the interband transitions involving these edge states are in the highly sought-after THz frequency range. Although we have specifically considered finite carbon chains terminated by gold nanoparticles, the main results of our paper can be generalized to various systems, which exhibit topologically protected states separated by a finite distance.European CommissionURCORussian Science FoundationWestlake UniversityLeading Innovative and Entrepreneur Team Introduction Program of ZhejiangMinistry of Science and Higher Education of the Russian Federatio

The pH of the skin surface and its impact on the barrier function

The `acid mantle' of the stratum corneum seems to be important for both permeability barrier formation and cutaneous antimicrobial defense. However, the origin of the acidic pH, measurable on the skin surface, remains conjectural. Passive and active influencing factors have been proposed, e. g. eccrine and sebaceous secretions as well as proton pumps. In recent years, numerous investigations have been published focusing on the changes in the pH of the deeper layers of the stratum corneum, as well as on the influence of physiological and pathological factors. The pH of the skin follows a sharp gradient across the stratum corneum, which is suspected to be important in controlling enzymatic activities and skin renewal. The skin pH is affected by a great number of endogenous factors, e. g. skin moisture, sweat, sebum, anatomic site, genetic predisposition and age. In addition, exogenous factors like detergents, application of cosmetic products, occlusive dressings as well as topical antibiotics may influence the skin pH. Changes in the pH are reported to play a role in the pathogenesis of skin diseases like irritant contact dermatitis, atopic dermatitis, ichthyosis, acne vulgaris and Candida albicans infections. Therefore, the use of skin cleansing agents, especially synthetic detergents with a pH of about 5.5, may be of relevance in the prevention and treatment of those skin diseases. Copyright (c) 2006 S. Karger AG, Base

Towards a large-scale quantum simulator on diamond surface at room temperature

Strongly-correlated quantum many-body systems exhibits a variety of exotic phases with long-range quantum correlations, such as spin liquids and supersolids. Despite the rapid increase in computational power of modern computers, the numerical simulation of these complex systems becomes intractable even for a few dozens of particles. Feynman's idea of quantum simulators offers an innovative way to bypass this computational barrier. However, the proposed realizations of such devices either require very low temperatures (ultracold gases in optical lattices, trapped ions, superconducting devices) and considerable technological effort, or are extremely hard to scale in practice (NMR, linear optics). In this work, we propose a new architecture for a scalable quantum simulator that can operate at room temperature. It consists of strongly-interacting nuclear spins attached to the diamond surface by its direct chemical treatment, or by means of a functionalized graphene sheet. The initialization, control and read-out of this quantum simulator can be accomplished with nitrogen-vacancy centers implanted in diamond. The system can be engineered to simulate a wide variety of interesting strongly-correlated models with long-range dipole-dipole interactions. Due to the superior coherence time of nuclear spins and nitrogen-vacancy centers in diamond, our proposal offers new opportunities towards large-scale quantum simulation at room temperatures

How are gender equality and human rights interventions included in sexual and reproductive health programmes and policies: A systematic review of existing research foci and gaps

The importance of promoting gender equality and human rights in sexual and reproductive health (SRH) programmes and policies has been affirmed in numerous international and regional agreements, most recently the 2030 Agenda for Sustainable Development. Given the critical role of research to determine what works, we aimed to identify research gaps as part of a broader priority setting exercise on integrating gender equality and human rights approaches in SRH programmes and policies. A systematic literature review of reviews was conducted to examine the question: what do we know about how research in the context of SRH programmes and policies has addressed gender equality and human rights and what are the current gaps in research. We searched three databases for reviews that addressed the research question, were published between 1994-2014, and met methodological standards for systematic reviews, qualitative meta-syntheses and other reviews of relevance to the research question. Additional grey literature was identified based on expert input. Articles were appraised by the primary author and examined by an expert panel. An abstraction and thematic analysis process was used to synthesize findings. Of the 3,073 abstracts identified, 56 articles were reviewed in full and 23 were included along with 10 from the grey literature. The majority focused on interventions addressing gender inequalities; very few reviews explicitly included human rights based interventions. Across both topics, weak study designs and use of intermediate outcome measures limited evidence quality. Further, there was limited evidence on interventions that addressed marginalized groups. Better quality studies, longer-term indicators, and measurement of unintended consequences are needed to better understand the impact of these types of interventions on SRH outcomes. Further efforts are needed to cover research on gender equality and human rights issues as they pertain to a broader set of SRH topics and populations.Scopu