Minimum Conductivity and Evidence for Phase Transitions in Ultra-clean Bilayer Graphene

Bilayer graphene (BLG) at the charge neutrality point (CNP) is strongly susceptible to electronic interactions, and expected to undergo a phase transition into a state with spontaneous broken symmetries. By systematically investigating a large number of singly- and doubly-gated bilayer graphene (BLG) devices, we show that an insulating state appears only in devices with high mobility and low extrinsic doping. This insulating state has an associated transition temperature Tc~5K and an energy gap of ~3 meV, thus strongly suggesting a gapped broken symmetry state that is destroyed by very weak disorder. The transition to the intrinsic broken symmetry state can be tuned by disorder, out-of-plane electric field, or carrier density

Spatially Resolved On-Chip Picosecond Pulse Detection Using Graphene

We present an on-chip time domain terahertz (TD-THz) system in which picosecond pulses are generated in low-temperature-grown gallium arsenide (LT-GaAs) and detected in graphene. The detected pulses were found to vary in amplitude, full width at half maximum (FWHM), and DC offset when sampled optically at different locations along a 50-μm-long graphene photoconductive (PC) detector. The results demonstrate the importance of detection location and switch design in graphene-based on-chip PC detectors

Atomically thin boron nitride: a tunnelling barrier for graphene devices

We investigate the electronic properties of heterostructures based on ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between two layers of graphene as well as other conducting materials (graphite, gold). The tunnel conductance depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Exponential behaviour of I-V characteristics for graphene/BN/graphene and graphite/BN/graphite devices is determined mainly by the changes in the density of states with bias voltage in the electrodes. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field; it offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.Comment: 7 pages, 5 figure

How close can one approach the Dirac point in graphene experimentally?

The above question is frequently asked by theorists who are interested in graphene as a model system, especially in context of relativistic quantum physics. We offer an experimental answer by describing electron transport in suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with the onset of Landau quantization occurring in fields below 5 mT. The observed charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state with a few charge carriers per entire micron-scale device. Above liquid helium temperatures, the electronic properties of such devices are intrinsic, being governed by thermal excitations only. This yields that the Dirac point can be approached within 1 meV, a limit currently set by the remaining charge inhomogeneity. No sign of an insulating state is observed down to 1 K, which establishes the upper limit on a possible bandgap

MECHANISMS FOR ENSURING SUSTAINABLE DEVELOPMENT AND FOOD SECURITY OF A SOVEREIGN COUNTRY

The social and climatic factors that affect the global and regional food systems of states and regions have been highlighted in the article. The importance of ensuring food security and balanced nutrition of the population at a time of economic hardship to reduce the vulnerability of the economy and strengthen the political stability of the Russian Federation, to build capacity to withstand the crisis and rapid recovery from it has been noted. The problems of food security and tasks aimed at preventing internal and external threats, sustainable development of domestic production sufficient to ensure food independence and state sovereignty have been considered

Quantum electrodynamics with anisotropic scaling: Heisenberg-Euler action and Schwinger pair production in the bilayer graphene

We discuss quantum electrodynamics emerging in the vacua with anisotropic scaling. Systems with anisotropic scaling were suggested by Horava in relation to the quantum theory of gravity. In such vacua the space and time are not equivalent, and moreover they obey different scaling laws, called the anisotropic scaling. Such anisotropic scaling takes place for fermions in bilayer graphene, where if one neglects the trigonal warping effects the massless Dirac fermions have quadratic dispersion. This results in the anisotropic quantum electrodynamics, in which electric and magnetic fields obey different scaling laws. Here we discuss the Heisenberg-Euler action and Schwinger pair production in such anisotropic QEDComment: 5 pages, no figures, JETP Letters style, version accepted in JETP Letter

The Scientific Advisory board resolution: Implementation of intermittently scanned Continuous Glucose monitoring in clinical practice to improve glycemic control

The Scientific Advisory Board chaired by Academician of the Russian Academy of Sciences, Peterkova V.A. was held 26 of November in Moscow to discuss the possibilities of continuous glucose monitoring technology (CGM) implementation into routine clinical practice in Russia in order to improve glycemic control in patients with diabetes mellitus (DM).The main aims for Advisory board were to determine the most significant indicators and parameters for CGM to be implemented in practice from a practical point of view of LMWH, necessary for implementation in clinical practice, for different patients groups with diabetes.The following questions and topics were raised within the discussion: the importance of additional indicators beyond glycated hemoglobin (HbA1c) for glycemic control assessment in diabetes patients, CGM positioning in International and Russian clinical guidelines, the accuracy of CGM devises and approaches to its assessment, the role of education programs for diabetic patients, including trainings in correct use and data interpretation and analysis of CGM data obtained, clinical evidence analysis for CGM in randomized trials and real world evidence

Возможности использования амплитудно-угловых характеристик поверхностных и подповерхностных волн для контроля материалов с поверхностно упрочнённым неоднородным слоем

Improving the efficiency of ultrasonic control of hardened surface layers of metal products with a heterogeneous structure obtained using different technologies is a pressing problem of industrial production. The purpose of this work was to investigate the possibilities of measuring the depth of the surface inhomogeneous layer of steel objects on the basis of the use of amplitude and amplitude-angle characteristics of surface and subsurface transverse waves.The analysis of ultrasonic methods of control of physical and mechanical properties of metals by using surface and subsurface waves and experimentally investigated amplitude-angular characteristics of surface waves, the maximum angle of which increases by 3° at change of dimensionless layer depth hλ from zero to0.82. For the first time, the ratio of normalized amplitudes of surface waves taken at certain angles on theamplitude-angle characteristic curve obtained in the echo mode was proposed to be used as correlating parameters with the depth of the hardened layer. As a result of this research, the possibility of using a phased array transducers to solve the above problems.The effect of the hardened layer depth varying from zero to five in the working frequency range of 1.8– 10 MHz on the peculiarities of the refraction effect (including interference) and dependence of the subsurface wave amplitude on the acoustic base has been studied, making it possible to establish conditions that provide for the determination of the hardened layer depth.Circuit solutions have been offered in order to increase the efficiency of control of properties of the surface layers of metal articles on the basis of utilization of small-aperture transducers and ultrasonic reflectors making it possible to form fields of surface waves of different directional pattern. Повышение эффективности ультразвукового контроля упрочненных поверхностных слоев металлоизделий с неоднородной структурой, полученных по различным технологиям, является актуальной проблемой опытно-промышленного производства. Целью данной работы являлось исследование возможностей измерения глубины поверхностного неоднородного слоя стальных объектов на основе использования амплитудных и амплитудно-угловых характеристик поверхностных и подповерхностных поперечных волн.Проведён анализ ультразвуковых методов контроля физико-механических свойств металлов с использованием поверхностных и подповерхностных волн и экспериментально исследованы амплитудно-угловые характеристики поверхностных волн, максимальный угол которых увеличивается на 3°при изменении безразмерной глубины слоя hλ от нуля до 0,82. Впервые предложено использовать в качестве коррелирующих параметров с глубиной упрочнённого слоя отношение нормированных амплитуд поверхностных волн, взятых под определёнными углами на кривой амплитудно-угловой характеристики, полученной в эхо-режиме. В результате проведённых исследований была выявлена возможностьиспользования преобразователей с фазированной решёткой для решения вышеуказанных задач.Исследовано влияние глубины упрочнённого слоя, изменяющейся от нуля до пяти в рабочем диапазоне частот 1,8–10 МГц, на особенности эффекта преломления (в том числе интерференции) и импенданса амплитуды подповерхностной волны на акустической базе, что позволило установить условия, обеспечивающие определение глубины упрочнённого слоя.Предложены схемные решения для повышения эффективности контроля свойств поверхностных слоев металлических изделий на основе использования малоапертурных преобразователей и ультразвуковых отражателей, позволяющих формировать поля поверхностных волн различной направленности

Time dependence of the proton flux measured by PAMELA during the July 2006 - December 2009 solar minimum

The energy spectra of galactic cosmic rays carry fundamental information regarding their origin and propagation. These spectra, when measured near Earth, are significantly affected by the solar magnetic field. A comprehensive description of the cosmic radiation must therefore include the transport and modulation of cosmic rays inside the heliosphere. During the end of the last decade the Sun underwent a peculiarly long quiet phase well suited to study modulation processes. In this paper we present proton spectra measured from July 2006 to December 2009 by PAMELA. The large collected statistics of protons allowed the time variation to be followed on a nearly monthly basis down to 400 MV. Data are compared with a state-of-the-art three-dimensional model of solar modulation.Comment: 17 pages, 5 figures, 1 table, to appear in Astrophysical Journal. Corrected two elements of Table