Localization of superconductivity in superconductor-electromagnet hybrids

We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magnetic field generated by a current-carrying Nb wire, perpendicularly oriented and located underneath the strip. The inhomogeneous magnetic field, induced by the Nb wire, produces a spatial modulation of the critical temperature T_c, leading to a controllable localization of the superconducting order parameter (OP) wave function. We demonstrate that close to the phase boundary T_c(B_ext) the localized OP solution can be displaced reversibly by either applying an external perpendicular magnetic field B_ext or by changing the amplitude of the inhomogeneous field.Comment: 10 pages, 6 figure

Mesoscopic cross-film cryotrons: Vortex trapping and dc-Josephson-like oscillations of the critical current

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the superconducting strip. It is well known that the critical current of the superconducting strip, Ic, in such cryotron--like system can be tuned by changing the current in the control wire, Iw. We demonstrated that the discrete change in the number of the pinned vortices/antivortices inside the narrow and long strip nearby the current-carrying wire results in a peculiar oscillatory dependence of Ic on Iw.Comment: 8 pages, 8 figure

Abnormal phenomena in a one-dimensional periodic structure containing left-handed materials

The explicit dispersion equation for a one-dimensional periodic structure with alternative layers of left-handed material (LHM) and right-handed material (RHM) is given and analyzed. Some abnormal phenomena such as spurious modes with complex frequencies, discrete modes and photon tunnelling modes are observed in the band structure. The existence of spurious modes with complex frequencies is a common problem in the calculation of the band structure for such a photonic crystal. Physical explanation and significance are given for the discrete modes (with real values of wave number) and photon tunnelling propagation modes (with imaginary wave numbers in a limited region).Comment: 10 pages, 4 figure

Glory Oscillations in the Index of Refraction for Matter-Waves

We have measured the index of refraction for sodium de Broglie waves in gases of Ar, Kr, Xe, and nitrogen over a wide range of sodium velocities. We observe glory oscillations -- a velocity-dependent oscillation in the forward scattering amplitude. An atom interferometer was used to observe glory oscillations in the phase shift caused by the collision, which are larger than glory oscillations observed in the cross section. The glory oscillations depend sensitively on the shape of the interatomic potential, allowing us to discriminate among various predictions for these potentials, none of which completely agrees with our measurements

The model of dynamo with small number of modes and magnetic activity of T Tauri stars

The model that describes operation of dynamo in fully convective stars is presented. It is based on representation of stellar magnetic field as a superposition of finite number of poloidal and toroidal free damping modes. In the frame of adopted low of stellar differential rotation we estimated minimal value of dynamo number D, starting from which generation of cyclic magnetic field in stars without radiative core is possible. We also derived expression for period of the cycle. It was found that dynamo cycles of fully convective stars and stars with thin convective envelopes differ in a qualitative way: 1) distribution of spots over latitude during the cycle is different in these stars; 2) the model predicts that spot formation in fully convective stars should be strongly suppressed at some phases of the cycle. We have analyzed historical lightcurve of WTTS star V410 Tau and found that long term activity of the star is not periodic process. Rather one can speak about quasi cyclic activity with characteristic time of $\sim 4$ yr and chaotic component over imposed. We concluded also that redistribution of cool spots over longitude is the reason of long term variations of V410 Tau brightness. It means that one can not compare directly results of photometric observations with predictions of our axially symmetric (for simplicity) model which allows to investigate time evolution of spot's distribution over latitude. We then discuss what kind of observations and in which way could be used to check predictions of the dynamo theory.Comment: 18 pages, 5 figures, accepted to Astron. Let

Theoretical Insights into Vinyl Derivatives Adsorption on a Cu(100) Surface

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b06142Here, we present a thorough theoretical study of the adsorption of acrolein (ACO), acrylonitrile (ACN), and acrylamide (ACA) on Cu(100) surface. For this purpose, we have used the density functional theory, imposing periodic boundary conditions to have a correct description of the electronic band structure of the metal and including dispersion forces through two different schemes: the D2 method of Grimme and the vdW-DF. We have found several adsorption geometries. In all of them, the vinyl group together with the amide (in ACA), ciano (in ACN), and carbonyl (in ACO) groups, is highly involved. The highest adsorption energy is found for acrylamide, followed by acrolein and the lowest for acrylonitrile (depending on the level of theory employed ∼1.2, 1.0, and 0.9 eV, respectively). We show that a strong coupling between the π electronic system (both occupied and virtual orbitals) and the electronic levels of the metal is mainly responsible of the chemisorption. As a consequence, electronic density is transferred from the surface to the molecule, whose carbon atoms acquire a partial sp3 hybridization. Lone-pair orbitals of the cyano, amide, and carbonyl groups also play a role in the interaction. The simulations and following analysis allow to disentangle the nature of the interaction, which can be explained on the basis of a simple chemical picture: donation from the occupied lone pair and π orbitals of the molecule to the surface and backdonation from the surface to the π∗ orbital of the molecule (π-backbonding)This work was partially supported by the project CTQ2016-76061-P of the Spanish Ministerio de Economı́a y Competitividad (MINECO). F.A.G. acknowledges the FPI grant associated with the project CTQ2013-43698-P (MINECO). Financial support from the MINECO through the “Marı́a de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0377) is also acknowledge