Supercurrent reversal in quantum dots

When two superconductors become electrically connected by a weak link a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of Shapiro steps in Josephson junctions under microwave irradiation and in the magnetic flux periodicity of h/2e in superconducting quantum interference devices. Several different materials have been used to weakly couple superconductors, such as tunnel barriers, normal metals, or semiconductors. Here, we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Due to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, i.e. in a normal or a pi-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions

Charge tunneling rates in ultrasmall junctions

1.1. Ultrasmall tunnel junctions With the advances of microfabrication techniques in recent years it has become possible to fabricate tunnel junctions of increasingly smaller dimensions and thereby decreasing capacitance C. Nowadays one can study tunnel junctions in a regime wher

Asymptotics of the frequency of a surface wave trapped by a slightly inclined barrier in a liquid layer

A two-dimensional statement of the scattering problem for an oblique incident surface wave by an obstacle in the form of a submerged barrier is considered. If the barrier is vertical, the discrete spectrum of the problem is shown to be empty, but for an inclined barrier an eigenvalue appears below the threshold of the continuous spectrum and the corresponding trapped mode decays exponentially in the direction perpendicular to the obstacle. The behaviour of the eigenvalue is analyzed for small values of the angle of inclination from the vertica

Economic Consequences of Current Precarious Employment, Alignment Paths and Development Trends

The economic crisis associated with the epidemiological situation in the other countries and in Russia in particular has a powerful impact on the level of employment now, and further, according to analysts, the situation will worsen. The unemployment rate is rising, along with the level of employment falling. The role of small business is not only to maintain balance in the labor market, create new jobs and absorb excess labor, but also to develop the economy and ensure the revenue of the state budget. However, to optimize their costs, employers go into the shadows. This problem has always existed; tax control measures have made it possible to solve it for the formal sector of the economy, though it still remains among small businesses. There is a need to develop, improve the efficiency of employment as well as research and optimization of precarious employment. The paper analyzes the category of “precarious employment” conducting a study of both employment and precarious employment in various businesses, identifies promising areas against precarization of employment. Proposals have been made to determine the category of precarious employment in small businesses, to increase the level of employment in certain sectors over the long term