Impurity center in a semiconductor quantum ring in the presence of a radial electric field

The problem of an impurity electron in a quantum ring (QR) in the presence of a radially directed strong external electric field is investigated in detail. Both an analytical and a numerical approach to the problem are developed. The analytical investigation focuses on the regime of a strong wire-electric field compared to the electric field due to the impurity. An adiabatic and quasiclassical approximation is employed. The explicit dependencies of the binding energy of the impurity electron on the electric field strength, parameters of the QR and position of the impurity within the QR are obtained. Numerical calculations of the binding energy based on a finite-difference method in two and three dimensions are performed for arbitrary strengths of the electric field. It is shown that the binding energy of the impurity electron exhibits a maximum as a function of the radial position of the impurity that can be shifted arbitrarily by applying a corresponding wire-electric field. The maximal binding energy monotonically increases with increasing electric field strength. The inversion effect of the electric field is found to occur. An increase of the longitudinal displacement of the impurity typically leads to a decrease of the binding energy. Results for both low- and high-quantum rings are derived and discussed. Suggestions for an experimentally accessible set-up associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure

Long-term variability of Atlantic water temperature in the Svalbard fjords in conditions of past and recent global warming

Within last decades, the climate of our planet has underwent remarkable changes. The most notable are those called "Arctic amplification." is the changes comprise a decrease in the area of ​​multi-years ice in 2007 and 2012 in polar regions of the Northern hemisphere, accompanied by the temperature rise of intermediate Atlantic waters, increasing surface temperature. In this paper, an analysis of long-term variability of temperature transformed Atlantic waters (TAW) in the fjords of the West-Spitsbergen island (Isfjorden, Grnfjorden, Hornsund and Kongsfjorden) in the first period (1920–1940) and modern (1990–2009) warming in the Arctic is reported. It is shown that the instrumental observation data corresponds to the periods of rise in temperature in the layer of the TAW and surface air temperature (SAT) for the area of ​​the Svalbard

Changes in thermohaline system on the west Spitsbergen shelf since 1950 to present time

The west Spitsbergen shelf is the principal region for the Atlantic water pass and it is very dynamic area, which has been changing a lot in the last two centuries. Herein, the analysis results of long-term variability of thermohaline characteristics of West-Spitsbergen current (WSC) and Coastal current (CC) are presented for the period from 1950 to present time based on the in-situ oceanographic data from the “Nordic Seas” database created in the Arctic and Antarctic Research Institute (AARI). Water temperature and salinity of WSC and CC were measured at 10 points and analyzed. It was concluded that the temperature and salinity in the study region were exposed to quasicyclic changes with common periods of about 5-6 and 10 years. Positive trends of water temperature for all points in the both currents were estimated (1.2°C per 60 years for WSC, and 2°C for CC, respectively). Correlation coefficients were calculated to describe the linear relationship between air temperature, atmospheric circulation indexes, the Atlantic multidecadal oscillation index, and water temperature in the region of the western shelf of the Spitsbergen

Environmental pollution impact on radiation properties of atmosphere, snow and ice cover: Study from Barentsburg (Spitsbergen Archipelago)

The value of the albedo of snow and ice surface is associated with the texture and structure of the surface layer of snow or ice (sea ice, glaciers), the peculiarities of the vertical redistribution of contaminations in this layer (mineral or organic particles of various concentrations, the size and shape), temperature regime of the surface layer of the atmosphere. Identifying links with the albedo characteristics of natural and artificial contamination is very important. For example, the results of mathematic modeling the evolution of ice sheets, sea ice and snow cover demonstrate the high sensitivity of the model to this parameter. Original results in the framework of this problem were obtained by researches from AARI and St. Petersburg State University during the 2010-2012 years on Svalbard in the vicinity of the Russian mining settlement Barentsburg. We present original results showing the relationship of "albedo-contaminations" and the influence of anthropogenic factors. The estimation of solar radiation that penetrates deep into the snow, and the impact of contamination on its redistribution in the snow thickness were obtained

Spin-Hall nanooscillator based on an antiferromagnetic domain wall

We propose here a high-frequency spin-Hall nano-oscillator based on a simple magnetic texture, such as a domain wall, located in an antiferromagnet with easy-axis anisotropy type. We show that the spin current, polarized along the anisotropy axis, excites a conical precession of the N\'eel vector in such a domain wall, which allows obtaining a robust ac output signal, -- contrary to the planar precession in an uniform uniaxial antiferromagnet, where ac output is hard to achieve. The frequency of the auto-oscillations is easily tunable by the applied current up to the THz range, and the threshold current vanishes for pure uniaxial antiferromagnet. By micro-magnetic simulations, we demonstrate that the pinning of the domain wall is crucial for the oscillator design, which can be achieved in nano-constriction layout of the free layer.Comment: 7 pages, 5 figures. Brief explanation of the dynamics near the threshold is added at P.

Antiferromagnetic droplet soliton driven by spin current

We demonstrate that a spin current flowing through a nano-contact into a uniaxial antiferromagnet with first- and second-order anisotropy can excite a self-localized dynamic magnetic soliton, known as a spin-wave droplet in ferromagnets. The droplet nucleates at a certain threshold current with the frequency of the N\'eel vector precession laying below the antiferromagnetic resonance. The frequency exhibits nonlinear behavior with the increasing of applied current. At the high value of applied torque, the soliton mode transforms, and the oscillator emits spin waves propagating in the antiferromagnetic layer.Comment: 6 pages, 5 figure

Comparative analysis of Russian and Norwegian precipitation gauges, measurements in Barentsburg, Western Spitsbergen

Comparative analysis of records of two gauges with different wind shields (Tretyakov gauge and Geonor T200-B) were done, based on time series of parallel measurement in Barentsburg settlement, Svalbard, during two winter times in period from September 2014 to July 2016. All collected data of solid precipitation were divided into two ranges with different wind speed conditions. As it was known from earlier papers, Tretyakov gauge measurements tend to underestimate solid precipitation in case when precipitation is not intensive and wind speed is less than 5 m s-1. Opposite results were obtained for blizzard conditions (wind speed is more than 6 m s-1): Tretyakov gauge shows greater values for amount of solid precipitation than Norwegian sensor. Preliminary results in Barentsburg cannot be described as conclusive ones. Estimation of solid precipitation on Spitsbergen measured by different gauges needs further and more detailed research, which includes fieldwork in Barentsburg in spring, such as detailed snow surveys in the settlement