Signature of Fermi arc surface states in Andreev reflection at the WTe2_2 Weyl semimetal surface

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.Comment: 5 pages, some misprints has been correcte

Обеспечение безопасности при эксплуатации беспилотных летательных аппаратов на объектах транспортной инфраструктуры

Unmanned aerial vehicles (UAV), also known as drones, are gaining more and more practical application in modern society, particularly as the tools of implementation of the concepts of «smart city», «smart health care», «smart industries», Internet of Things, 3D mapping, digital transport. But currently it is impossible to use of UAV at certain objects, comprising objects of transport infrastructure (OTI), primarily, airports, because of existing restrictions due to security threats arising during the UAV flight.The authors of the present work have set a goal to offer a solution that allows to start operating UAV at transport infrastructure facilities that are currently prohibited for UAV flights. To achieve the objective of the work, using analysis and synthesis, comparison and generalization, factors and conditions for safe use of UAV at OTI have been formulated, a method for increasing security of UAV flight has been developed, followed by the suggestion on the UAV route control system.The proposed system makes it possible to safely use UAVs at OTI by restraining their flight area strictly to the designated corridor, which eliminates a threat of a collision of UAV with other vehicles operated at OTI, dangerous elements of OTI, as well as with people at the object.The system does not need electric power feeding, which makes it possible to implement the system without creating an auxiliary power supply infrastructure.The practical application of the proposed system and, as a consequence, implementation of a greater number of opportunities for the use of UAV, are capable to generate fundamentally new technological processes and structures at transport facilities, which is one of the directions for creating the next generation transport infrastructure based on IoT and artificial intelligence.Беспилотные летательные аппараты (БПЛА), также известные как дроны или беспилотники, получают всё большее практическое применение в современном обществе, в том числе как инструменты реализации концепций «умного города», «умного здравоохранения», «умной индустрии», Интернета вещей, 3D‑картографии, цифрового транспорта. Но, в настоящий момент, применение БПЛА на определённых объектах, в том числе и транспортной инфраструктуры (ОТИ), в первую очередь, в аэропортах, невозможно в силу существующих ограничений, вызванных угрозами безопасности, возникающими при полёте БПЛА.Авторами в данной работе была поставлена цель предложить решение, позволяющее начать эксплуатацию беспилотных летательных аппаратов на объектах транспортной инфраструктуры, в настоящий момент закрытых для полётов БПЛА.Для достижения цели работы, с применением анализа и синтеза, сравнения и обобщения, сформулированы факторы и условия безопасного применения БПЛА на ОТИ, с учётом которых разработаны метод повышения безопасности движения беспилотных летательных аппаратов и реализующая его система контроля маршрутов беспилотных летательных аппаратов.Предложенная система делает возможным безопасно применять БПЛА на ОТИ за счёт ограничения зоны их полёта строго в обозначенном коридоре, что позволяет исключить угрозу столкновения БПЛА с другими транспортными средствами (ТС), эксплуатируемыми на ОТИ, опасными элементами ОТИ, людьми и т.д.Для функционирования системы не требуется электроэнергия, что позволяет внедрять систему без создания вспомогательной энергообеспечивающей инфраструктуры.Практическое применение предложенной системы и, как следствие, внедрение большего количества возможностей, возникающих при применении БПЛА, способно генерировать на объектах транспорта принципиально новые технологические процессы и структуры, что является одним из направлений создания транспортной инфраструктуры следующего поколения, основанной на IoT и искусственном интеллекте

Magnetically stable zero-bias anomaly in Andreev contact to the magnetic Weyl semimetal Co3_3Sn2_2S2_2

Being encouraged by the interplay between topology, superconductivity and magnetism, we experimentally investigate charge transport through the interface between the Nb superconductor and the time-reversal symmetry breaking Weyl semimetal Co$_3$Sn$_2$S$_2$. In addition to the proximity induced superconducting gap, we observe several subgap features, among which the most interesting is the prominent subgap zero-bias anomaly, absolutely stable against external magnetic fields up to the critical field of Nb. As the promising scenario for the zero-bias anomaly to appear in transport characteristics, we consider the proximity induced zero-energy Andreev bound states interfaced with the half-metallic Co$_3$Sn$_2$S$_2$ and influenced by the strong spin-orbit coupling and large Zeeman splitting

Stability of quantized conductance levels in memristors with copper filaments: toward understanding the mechanisms of resistive switching

Memristors are among the most promising elements for modern microelectronics, having unique properties such as quasi-continuous change of conductance and long-term storage of resistive states. However, identifying the physical mechanisms of resistive switching and evolution of conductive filaments in such structures still remains a major challenge. In this work, aiming at a better understanding of these phenomena, we experimentally investigate an unusual effect of enhanced conductive filament stability in memristors with copper filaments under the applied voltage and present a simplified theoretical model of the effect of a quantum current through a filament on its shape. Our semi-quantitative, continuous model predicts, indeed, that for a thin filament, the "quantum pressure" exerted on its walls by the recoil of charge carriers can well compete with the surface tension and crucially affect the evolution of the filament profile at the voltages around 1V. At lower voltages, the quantum pressure is expected to provide extra stability to the filaments supporting quantized conductance, which we also reveal experimentally using a novel methodology focusing on retention statistics. Our results indicate that the recoil effects could potentially be important for resistive switching in memristive devices with metallic filaments and that taking them into account in rational design of memristors could help achieve their better retention and plasticity characteristics.Comment: version accepted for publication in Phys. Rev. Applied, including improved statistic

Signature of Fermi arc surface states in Andreev reflection at the WTe2_2 Weyl semimetal surface

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.Comment: 5 pages, some misprints has been correcte

Capture into Rydberg states and momentum distributions of ionized electrons

The yield of neutral excited atoms and low-energy photoelectrons generated by the electron dynamics in the combined Coulomb and laser field after tunneling is investigated. We present results of Monte-Carlo simulations built on the two-step semiclassical model, as well as analytic estimates and scaling relations for the population trapping into the Rydberg states. It is shown that mainly those electrons are captured into bound states of the neutral atom that due to their initial conditions (i) have moderate drift momentum imparted by the laser field and (ii) avoid strong interaction ("hard" collision) with the ion. In addition, it is demonstrated that the channel of capture, when accounted for in semiclassical calculations, has a pronounced effect on the momentum distribution of electrons with small positive energy. For the parameters that we investigated its presence leads to a dip at zero momentum in the longitudinal momentum distribution of the ionized electrons.Comment: 9 pages, 8 figures in one zip-archiv

Тенденции современного терроризма на метрополитене

[For the English abstract and full text of the article please see the attached PDF-File (English version follows Russian version)].ABSTRACT The issue of anti-terrorist protection of subways in recent decades has significantly worsened. This is due to the general growth of the terrorist threat in the world - a number of terrorist acts have been committed in subways of various countries of the world, including Russia, the United States, Britain, Japan and France. For effective measures to counteract such acts, it is necessary to clearly know the trends of modern terrorism, particularly on the basis of systematization and analysis of statistical data on the terrorist acts committed in the metro with the subsequent formation of a matrix of trends, which in this case was done by the authors of the article. The proposed matrix helps to assess terrorist threats for Russian subways and can be used to develop measures to ensure their transport security. Keywords: subway, station, terrorist act, statistics, threat trends, transport safety.Текст аннотации на англ. языке и полный текст статьи на англ. языке находится в прилагаемом файле ПДФ (англ. версия следует после русской версии).Вопрос антитеррористической защиты метрополитенов в последние годы значительно обострился. Это обусловлено общим ростом террористической угрозы в мире - целый ряд терактов совершён в метрополитенах различных стран: России, США, Великобритании, Японии, Франции. Для эффективных мер противодействия подобным актам необходимо чётко знать тенденции современного терроризма. В том числе на основе систематизации и анализа статистических данных, что в данном случае и проделано авторами статьи. Предложенная ими матрица помогает оценить террористические угрозы для метрополитенов России и может применяться при разработке способов обеспечения их транспортной безопасности