133 research outputs found
Local Border Traffic as a Form of Visa Liberalisation and Territorial Development
This article addresses the issue of visa liberalisation between Russia and the European Union, which constitutes a key aspect of the partiesâ diplomatic cooperation. This work sets out to identify the main results of Russia/EU cooperation. The authors have conducted a brief historical analysis of this area of relations. The visa âregionalisationâ is considered in the context of identifying the key actors of the EU â Russia negotiations: the Kaliningrad region, Germany, Poland, and Lithuania. In their analysis, the authors rely mostly on primary sources: intergovernmental agreements on simplified border traffic, border-crossing statistics for the Kaliningrad region in the framework of the local border traffic, expert interviews, and related analytic reports. Specifically, local border traffic is viewed as the most effective form of interaction in the field of visa regime simplification and border territory development. An assessment of the positions of key negotiators shows that local border traffic between the Kaliningrad region of Russia and the Polish border voivodeships is a success, which stresses the need for a prompt transition to a visa-free regime with the EU
The military and political situation in the Baltic region in the late 20th/early 21st centuries: the prospects of âuneasy peace
In this article, we consider the development of international relations in the Baltic region in the late 20th/early 21st centuries. This study aims to analyse the security prospects of the Baltic region in view of the changes in the overall geopolitical situation in Europe and in the relations between Russia and its closest neighbours and the leading NATO countries. We examine the ideas and forecasts of international and Russian experts relating to the state and dynamics of military security in the region at the first stage of the Balticsâ memberÂship in NATO. Another focus is on changes in the strategy of the NATO leadership for the Baltic region as a priority zone of potential warfare and, thus, for the presence of the alliance in the area. We stress that the steps taken by the NATO leadership prompted the Russian side to assign a special role in the countryâs foreign policy to the Kaliningrad region and to take practical steps to ensure peace and security in the region
Detecting topological currents in graphene superlattices
This is the author accepted manuscript. The final version is available from AAAS via the DOI in this record.Topological materials may exhibit Hall-like currents flowing transversely to the applied electric field even in the absence of a magnetic field. In graphene superlattices, which have broken inversion symmetry, topological currents originating from graphene's two valleys are predicted to flow in opposite directions and combine to produce long-range charge neutral flow. We observed this effect as a nonlocal voltage at zero magnetic field in a narrow energy range near Dirac points at distances as large as several micrometers away from the nominal current path. Locally, topological currents are comparable in strength with the applied current, indicating large valley-Hall angles. The long-range character of topological currents and their transistor-like control by means of gate voltage can be exploited for information processing based on valley degrees of freedom.This work was supported by the European Research Council, the Royal Society, the National Science
Foundation (STC Center for Integrated Quantum Materials, grant DMRâ1231319), Engineering & Physical Research Council (UK), the Office of Naval Research and the Air Force Office of Scientific Research
Detecting Topological Currents in Graphene Superlattices
Topological materials may exhibit Hall-like currents flowing transversely to
the applied electric field even in the absence of a magnetic field. In graphene
superlattices, which have broken inversion symmetry, topological currents
originating from graphene's two valleys are predicted to flow in opposite
directions and combine to produce long-range charge neutral flow. We observe
this effect as a nonlocal voltage at zero magnetic field in a narrow energy
range near Dirac points at distances as large as several microns away from the
nominal current path. Locally, topological currents are comparable in strength
to the applied current, indicating large valley-Hall angles. The long-range
character of topological currents and their transistor-like control by gate
voltage can be exploited for information processing based on the valley degrees
of freedom.Comment: 19 pgs, 9 fg
High-temperature quantum oscillations caused by recurring Bloch states in graphene superlattices
Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties. Cryogenic temperatures are usually required to observe these oscillations. We show that graphene superlattices support a different type of quantum oscillations that do not rely on Landau quantization. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few T. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell. Our work points at unexplored physics in Hofstadter butterfly systems at high temperatures
Edge currents shunt the insulating bulk in gapped graphene
An energy gap can be opened in the spectrum of graphene reaching values as large as 0.2âeV in the case of bilayers. However, such gaps rarely lead to the highly insulating state expected at low temperatures. This long-standing puzzle is usually explained by charge inhomogeneity. Here we revisit the issue by investigating proximity-induced superconductivity in gapped graphene and comparing normal-state measurements in the Hall bar and Corbino geometries. We find that the supercurrent at the charge neutrality point in gapped graphene propagates along narrow channels near the edges. This observation is corroborated by using the edgeless Corbino geometry in which case resistivity at the neutrality point increases exponentially with increasing the gap, as expected for an ordinary semiconductor. In contrast, resistivity in the Hall bar geometry saturates to values of about a few resistance quanta. We attribute the metallic-like edge conductance to a nontrivial topology of gapped Dirac spectra
Electronic properties of graphene encapsulated with different two-dimensional atomic crystals.
Hexagonal boron nitride is the only substrate that has so far allowed graphene devices exhibiting micrometer-scale ballistic transport. Can other atomically flat crystals be used as substrates for making quality graphene heterostructures? Here we report on our search for alternative substrates. The devices fabricated by encapsulating graphene with molybdenum or tungsten disulfides and hBN are found to exhibit consistently high carrier mobilities of about 60â000 cm(2) V(-1) s(-1). In contrast, encapsulation with atomically flat layered oxides such as mica, bismuth strontium calcium copper oxide, and vanadium pentoxide results in exceptionally low quality of graphene devices with mobilities of âŒ1000 cm(2) V(-1) s(-1). We attribute the difference mainly to self-cleansing that takes place at interfaces between graphene, hBN, and transition metal dichalcogenides. Surface contamination assembles into large pockets allowing the rest of the interface to become atomically clean. The cleansing process does not occur for graphene on atomically flat oxide substrates.This work was supported by the European Research Council, Graphene Flagship, Engineering
and Physical Sciences Research Council (UK), the Royal Society, US Office of Naval Research, US
Air Force Office of Scientific Research, US Army Research Office
Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals
Hexagonal boron nitride is the only substrate that has so far allowed
graphene devices exhibiting micron-scale ballistic transport. Can other
atomically flat crystals be used as substrates for making quality graphene
heterostructures? Here we report on our search for alternative substrates. The
devices fabricated by encapsulating graphene with molybdenum or tungsten
disulphides and hBN are found to exhibit consistently high carrier mobilities
of about 60,000 cmVs. In contrast, encapsulation with
atomically flat layered oxides such as mica, bismuth strontium calcium copper
oxide and vanadium pentoxide results in exceptionally low quality of graphene
devices with mobilities of ~ 1,000 cm Vs. We attribute the
difference mainly to self-cleansing that takes place at interfaces between
graphene, hBN and transition metal dichalcogenides. Surface contamination
assembles into large pockets allowing the rest of the interface to become
atomically clean. The cleansing process does not occur for graphene on
atomically flat oxide substrates.Comment: 19 pages, 11 figures, 1 table including Supporting Informatio
Unintentional high density p-type modulation doping of a GaAs/AlAs core-multi-shell nanowire
Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of
considerable technological importance but remains a challenge due to the
amphoteric behavior of the dopant atoms. Here we show that placing a narrow
GaAs quantum well in the AlAs shell effectively getters residual carbon
acceptors leading to an \emph{unintentional} p-type doping. Magneto-optical
studies of such a GaAs/AlAs core multi-shell NW reveal quantum confined
emission. Theoretical calculations of NW electronic structure confirm quantum
confinement of carriers at the core/shell interface due to the presence of
ionized carbon acceptors in the 1~nm GaAs layer in the shell.
Micro-photoluminescence in high magnetic field shows a clear signature of
avoided crossings of the Landau level emission line with the Landau
level TO phonon replica. The coupling is caused by the resonant hole-phonon
interaction, which points to a large 2D hole density in the structure.Comment: just published in Nano Letters
(http://pubs.acs.org/doi/full/10.1021/nl500818k
- âŠ