Reduced leakage current in Josephson tunnel junctions with codeposited barriers

Josephson junctions were fabricated using two different methods of barrier formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the first two layers were epitaxial. The oxide barrier was formed either by exposing the Al surface to O2 or by codepositing Al in an O2 background. The codeposition process yielded junctions that showed the theoretically predicted subgap current and no measurable shunt conductance. In contrast, devices with barriers formed by thermal oxidation showed a small shunt conductance in addition to the predicted subgap current.Comment: 3 pages, 4 figure

Fiske Steps and Abrikosov Vortices in Josephson Tunnel Junctions

We present a theoretical and experimental study of the Fiske resonances in the current-voltage characteristics of "small" Josephson junctions with randomly distributed misaligned Abrikosov vortices. We obtained that in the presence of Abrikosov vortices the resonant interaction of electromagnetic waves, excited inside a junction, with the ac Josephson current manifests itself by Fiske steps in a current-voltage characteristics even in the absence of external magnetic field. We found that the voltage positions of the Fiske steps are determined by a junction size, but the Fiske step magnitudes depend both on the density of trapped Abrikosov vortices and on their misalignment parameter. We measured the magnetic field dependence of both the amplitude of the first Fiske step and the Josephson critical current of low-dissipative small $Nb$ based Josephson tunnel junctions with artificially introduced Abrikosov vortices. A strong decay of the Josephson critical current and a weak non-monotonic decrease of the first Fiske step amplitude on the Abrikosov vortex density were observed. The experimentally observed dependencies are well described by the developed theory.Comment: 21 pages, 7 figures, submitted to Physical Review

Single-dopant resonance in a single-electron transistor

Single dopants in semiconductor nanostructures have been studied in great details recently as they are good candidates for quantum bits, provided they are coupled to a detector. Here we report coupling of a single As donor atom to a single-electron transistor (SET) in a silicon nanowire field-effect transistor. Both capacitive and tunnel coupling are achieved, the latter resulting in a dramatic increase of the conductance through the SET, by up to one order of magnitude. The experimental results are well explained by the rate equations theory developed in parallel with the experiment.Comment: 16 pages, 8 figure

Dynamical correlations in electronic transport through a system of coupled quantum dots

Current auto- and cross-correlations are studied in a system of two capacitively coupled quantum dots. We are interested in a role of Coulomb interaction in dynamical correlations, which occur outside the Coulomb blockade region (for high bias). After decomposition of the current correlation functions into contributions between individual tunneling events, we can show which of them are relevant and lead to sub-/supper-Poissonian shot noise and negative/positive cross-correlations. The results are differentiated for a weak and strong inter-dot coupling. Interesting results are for the strong coupling case when electron transfer in one of the channel is strongly correlated with charge drag in the second channel. We show that cross-correlations are non-monotonic functions of bias voltage and they are in general negative (except some cases with asymmetric tunnel resistances). This is effect of local potential fluctuations correlated by Coulomb interaction, which mimics the Pauli exclusion principle

Phase Modulated Thermal Conductance of Josephson Weak Links

We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference ($\phi$) of the superconducting leads. Branch conversion processes, low-energy Andreev bound states near the contact and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature and disorder, on the phase modulation of the conductance are reported. For high-transmission weak links, $D\to 1$, the formation of an Andreev bound state at $\epsilon_{\text{\tiny b}}=\Delta\cos(\phi/2)$ leads to suppression of the density of states for the continuum excitations that transport heat, and thus, to a reduction in the conductance for $\phi\simeq\pi$. For low-transmission ($D\ll 1$) barriers resonant scattering at energies $\epsilon\simeq(1+D/2)\Delta$ leads to an increase in the thermal conductance as $T$ drops below $T_c$ (for phase differences near $\phi=\pi$).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for Ricatti amplitude

Penetration of the magnetic field into the twinning plane in the type I and II superconductors

It is demonstrated that in the type I and II superconductors with low-transparent twinning planes (TP) the penetration of external parallel magnetic field into the region of the twinning plane can be energetically favorable. In the type I superconductors the twinning planes become similar to Josephson junctions and the magnetic field penetrates into the center of the TP in the form of soft Josephson-like vortices. This leads to increase in the critical magnetic field values. The corresponding phase diagram in the parameter plane "temperature - magnetic field" essentially differs from the one obtained without taking the finite value of the magnetic field near the TP into account. Comparison between obtained phase diagrams and experimental data for different type I superconductors can allow to estimate the value of the TP transparency, which is the only fitting parameter in our theory.Comment: 5 pages, 2 figure

Зв’язок між виробничими функціями на підприємствах побутового обслуговування

В сучасних умовах актуальною науковою і практичною проблемою стає дослідження ролі і місце підприємств побутового обслуговування в процесах модернізації та інновації розвитку на регіональному рівні. Роль підприємств побутового обслуговування в економіці України і її регіонів, а також їх соціальне значення є досить вагомим. Ці підприємства надають можливість створювати нові робочі місця навіть під час економічної кризи, що знижує соціальну напругу і навантаження на ринок праці. Інтенсивному розвитку підприємств побутового обслуговування сприяє зростаючий споживацький попит на побутові послуги, що обумовлює необхідність ефективного управління підприємствами побутового обслуговування в стратегічному аспекті. Метою статті є дослідження зв’язку між виробничими функціями підприємств сфери обслуговування. Розглянуто функціонування малого підприємства, яке складається з двох ланок: хімчистка і пральня. В залежності від ефективності діяльності функціонування одного з двох підприємств аналітично побудовані виробничі функції. Використовуючи апарат економіко-математичного моделювання інвестиційної діяльності підприємства в роботі проаналізовані характеристики, які впливають на динаміку розвитку підприємства в цілому, на стратегію інвестування, яка відображає процеси самофінансування підприємства. Наведені рисунки показують різні моделі розвитку підприємств і дають можливість проаналізувати економічні показники функціонування підприємства що необхідно враховувати при побудові системи показників ефективності функціонування підприємств, які задіяні в побутовому секторі. Ця система повинна характеризувати ступінь результативності виробництва і здійснювати оцінку динаміки економічного ефекту при залученні додаткових ресурсів. Також необхідно забезпечити співвідношення економічних коефіцієнтів, які відповідають за інвестиції таким чином, щоб функціонування підприємства не зазнавало регресії чи стагнації, а працювало в оптимальному режимі в залежності від власних потужностей, соціальних потреб регіону тощо.Nowadays, the role and place of consumer services enterprises in the processes of modernization and development innovations at the regional level is becoming a topical scientific and practical problem. The role of household services in the economy of Ukraine and its regions, as well as their social significance, is quite important. These enterprises provide the opportunity to create new work places even during the economic crisis, which reduces social tension and the burden on the labour market. The intensive development of consumer services is supported by the growing consumer demand for domestic services, which necessitates the effective management of household services in the strategic aspect. The purpose of the article is to investigate the connection between the production functions of the service sector enterprises. We investigated the functioning of a small enterprise, which consists of two parts: dry cleaning and laundry. Depending on the functioning efficiency of one of the two companies, analytical production functions are built. Using the apparatus of economic-mathematical modelling of investment activity of the enterprise, were analysed the characteristics that affect the dynamics of the enterprise as a whole, on the investment strategy, which reflects the processes of self-financing of the enterprise. The given figures show different models of enterprise development and give an opportunity to analyse economic indicators of the functioning of an enterprise that need to be taken into account when constructing a system of indicators of the efficiency of functioning of enterprises that are involved in the domestic sector. This system should characterize the degree of performance of production and assess the dynamics of the economic effect of attracting additional resources. It is also necessary to ensure a ratio of economic coefficients that are responsible for the investment in such a way that the operation of the enterprise would not be subjected to regression or stagnation, but worked in the optimal mode depending on their own capacities, social needs of the region, etc