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1

Enhancement of the Critical Temperature Induced by the Quantum Size Effect in Superconducting Nanofilms

100%

Wójcik P.

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vol. 126

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issue 4a

A-130-A-133

EN

The interplay between the quantum size effect and superconductivity in the metallic Al nanofilms has been studied with the use of the self-consistent numerical solutions of the Bogoliubov-de Gennes equations. We have shown that the critical temperature of the metallic nanofilm oscillates as a function of the nanofilm thickness. This phenomenon results from the quasi-particle energy quantization induced by the confinement of electrons in the direction perpendicular to the film. For the ultrathin nanofilms with thickness 1-2 nm we have found that the critical temperature increases up to value several times higher as compared to the one measured in the bulk.

2

Signatures of Majorana States in Electron Transport through a Quantum Dot Coupled to a Topological Wire

100%

Stefański P.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

198-200

EN

We consider theoretically a system composed of a quantum dot coupled to a topological superconducting wire. The dot, being in Coulomb blockade (CB) regime is additionally coupled to the normal leads. The topological wire hosts Majorana states, which, as we show, characteristically modifies conductance through the dot. An unpaired Majorana state in the wire causes a unique temperature dependence of zero bias conductance vs. gate voltage. It decreases in-between CB peaks and on the sides of the peaks from the plateau at ~ e²/2h when temperature increases. At the same time conductance increases at the CB peak positions. It is accompanied by zero bias anomaly in differential conductance. For finite overlap of Majorana states in the wire the zero bias anomaly disappears. Instead, two characteristic Fano resonances of opposite symmetry appear, positioned mirror-symmetrically with respect to zero bias.

3

d-Wave Superconductivity in a System with Open Boundary Conditions

100%

Pisarski P., Harań G.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

721-725

EN

We discuss the d-wave superconductivity in confined geometry by imposing open boundary conditions on the attractive Hubbard model. Within the Bogoliubov-de Gennes approach we evaluate the order parameter and charge density distribution in the system.

4

Probing Fractional Josephson Junction with a Quantum Dot

100%

Stefański P.

Acta Physica Polonica A

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2016

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vol. 130

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issue 2

554-557

EN

We consider theoretically a junction between two topological superconducting wires, mediated by a quantum dot. The wires are modelled by the Kitaev chains tuned into topological phase, which possess unpaired Majorana states at their ends. We derive the low energy Hamiltonian of the model. The Majorana states closer to the dot convert into the Dirac fermion inside the dot, forming fractional Josephson junction. The dot is additionally weakly coupled to the normal tunneling probe allowing transport measurement through the dot. When the topological wires are short, the unpaired Majorana end-states can hybridize inside the wire forming an extended Dirac fermionic state. It yields the destruction of the extended state in the dot. We discuss the dependence of the spectral density of the dot and its conductance on superconducting phase. We show that the conservation of parity of the junction, crucial for successful measurement of the fractional effect, can be assured by the gate voltage manipulation of the dot level position and that in case of an unpaired Majorana state in the junction a half conductance quantum can be observed.

5

Interplays between Mesoscopic Josephson Junctions and the Harper Equation

100%

Papp E., Micu C., Bica I.

Acta Physica Polonica A

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2009

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vol. 116

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issue 4

486-488

EN

Proofs are given that by resorting to the discretization of the superconducting phase variable leads to the conversion of the eigenvalue equation of a mesoscopic Josephson junction under a dc voltage into a generalized version of the Harper equation with anisotropy parameter. A full conversion proceeds, however, in terms of selected parameters. Classical limits and further generalizations are also shortly discussed.

6

The Multiple Phase Slip Phenomena in the Narrow Superconducting Channels

100%

Baranov V., Balanov A., Kabanov V.

Acta Physica Polonica A

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2012

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vol. 121

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issue 5-6

1038-1041

EN

The current-voltage characteristic of the narrow superconducting channel is investigated by direct numerical integration of the time-dependent Ginzburg-Landau equations. We have demonstrated that the steps in the current-voltage characteristic correspond to a number of different bifurcation points of the time-dependent Ginzburg-Landau equations. We have analytically estimated the period and the averaged voltage of the oscillating solution for the relatively small currents. We have also found the range of currents where the system transforms to the chaos.

7

Size Modification of Nanographite System of Activated Carbon Fibers Studied by EPR

88%

Kempiński M., Kempiński W., Śliwińska-Bartkowiak M.

Acta Physica Polonica A

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2005

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vol. 108

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issue 2

339-343

EN

We report results of EPR measurements of activated carbon fibers. Experiments made for pristine activated carbon fibers and activated carbon fibers with adsorbed molecules (CCl_4, C_6H_5NO_2, and H_2O) confirmed the localized character of paramagnetic centers observed in the system. Pristine activated carbon fibers are characterized by single Lorentzian line. Broader component of EPR signal appears when guest molecules are adsorbed in nanopores. The strongest localization is observed for water-filled activated carbon fibers nanopores (with hydrophobic pore walls) where changes in distance between nanographite particles were monitored by the g-shift to higher values. This process is related to stronger spin-orbit interaction of electrons trapped at nanographite particles compressed by guest molecules.

8

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines

63%

Prikhna T., Gawalek W., Savchuk Y., Sergienko N., Moshchil V., Sokolovsky V., Vajda J., Tkach V., Karau F., Weber H., Eisterer M., Joulain A., Rabier J., Chaud X., Wendt M., Dellith J., Danilenko N., Habisreuther T., Dub S., Meerovich V., Litzkendorf D., Nagorny P., Kovalev L., Schmidt C., Melnikov V., Shapovalov A., Kozyrev A., Sverdun V., Kosa J., Vlasenko A.

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issue 1

7-14

EN

Materials of the Y-Ba-Cu-O (melt-textured YBa_{2}Cu_{3}O_{7-δ}-based materials or MT-YBCO) and Mg-B-O (MgB_{2}-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogeneities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800°C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB_{2}-based materials allowed us to attain high superconductive (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 μm^{-1}), prevention of macrocracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB_{2}-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogeneities as well as inclusions of higher borides with near-MgB_{12} stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high T_{c} (37 K) and critical current densities in materials with MgB_{12} matrix (with 95% of shielding fraction as calculated from the resistant curve).

Refine search results

Enhancement of the Critical Temperature Induced by the Quantum Size Effect in Superconducting Nanofilms

Signatures of Majorana States in Electron Transport through a Quantum Dot Coupled to a Topological Wire

d-Wave Superconductivity in a System with Open Boundary Conditions

Probing Fractional Josephson Junction with a Quantum Dot

Interplays between Mesoscopic Josephson Junctions and the Harper Equation

The Multiple Phase Slip Phenomena in the Narrow Superconducting Channels

Size Modification of Nanographite System of Activated Carbon Fibers Studied by EPR

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines