Electron-electron interactions of the multi-Cooper-pairs in the 1D limit and their role in the formation of global phase coherence in quasi-one-dimensional superconducting nanowire arrays

Nanostructuring of superconducting materials to form dense arrays of thin parallel nanowires with significantly large transverse Josephson coupling has proven to be an effective way to increase the upper critical field of superconducting elements by as much as two orders of magnitude as compared to the corresponding bulk materials and, in addition, may cause considerable enhancements in their critical temperatures. Such materials have been realized in the linear pores of mesoporous substrates or exist intrinsically in the form of various quasi-1D crystalline materials. The transverse coupling between the superconducting nanowires is determined by the size-dependent coherence length E0. In order to obtain E0 over the Langer-Ambegaokar- McCumber-Halperin (LAMH) theory, extensive experimental fitting parameters have been required over the last 40 years. We propose a novel Monte Carlo algorithm for determining E0 of the multi-Cooper pair system in the 1D limit. The concepts of uncertainty principle, Pauli-limit, spin flip mechanism, electrostatic interaction, thermal perturbation and co-rotating of electrons are considered in the model. We use Pb nanowires as an example to monitor the size effect of E0 as a result of the modified electron-electron interaction without the need for experimental fitting parameters. We investigate how the coherence length determines the transverse coupling of nanowires in dense arrays. This determines whether or not a global phase-coherent state with zero resistance can be formed in such arrays. Our Monte Carlo results are in very good agreement with experimental data from various types of superconducting nanowire array

Quantum-Classical Molecular Simulation of the Linear-Chained Carbon Synthesis on Silicon Substrate

The aim of this work is the molecular dynamics simulation of the linear-chained carbon synthesis. Comparison of quantum-classical molecular dynamics methods: Simple, Force-based and Electrostatic

Low-Temperature Luminescence of Lead Silicate Glass

The temperature quenching of intrinsic luminescence of a lead silicate glass of the 20PbO · 80SiO2 composition has been investigated in the temperature range 7-200 K. It has been found that the temperature behavior of the intensity of intrinsic luminescence does not obey the well-known Mott's law for intracenter quenching of luminescence but is adequately described by the empirical Street's formula. It has been dem-onstrated that, with allowance made for the disorder of the atomic structure, the experimental temperature dependence of the luminescence intensity of the glass can be represented as a superposition of Mott's depen-dences for an ensemble of local luminescence centers. The obtained distribution of luminescence centers over the activation energies of quenching has an asymmetric form with prevailing low-energy states. It has been assumed that this feature has a general character and, at low temperatures, determines the specificity of the processes of nonradiative relaxation of the electronic subsystem for many oxide glasses. © Pleiades Publishing, Ltd., 2010.This study was supported by the Russian Foundation for Basic Research (project nos. 09-02-00493 and 08-02-01072)

THE RAMAN SPECTRA FEATURES OF LINEAR-CHAINED CARBON FILMS ON A PLATINUM SUBSTRATE

The aim of this work is an ab initio study of the features of the Raman spectra for linear-chained carbon (LCC) films on a platinum. The obtained spectra, calculated by the DFT method, can be used for control during the synthesis of LCC films

A theoretical quest for high temperature superconductivity on the example of low-dimensional carbon structures

Abstract High temperature superconductivity does not necessarily require correlated electron systems with complex competing or coexisting orders. Instead, it may be achieved in a phonon-mediated classical superconductor having a high Debye temperature and large electronic density of states at the Fermi level in a material with light atoms and strong covalent bonds. Quasi-1D conductors seem promising due to the Van Hove singularities in their electronic density of states. In this sense, quasi-1D carbon structures are good candidates. In thin carbon nanotubes, superconductivity at ~15 K has been reported, and it is likely the strong curvature of the graphene sheet which enhances the electron-phonon coupling. We use an ab-initio approach to optimize superconducting quasi-1D carbon structures. We start by calculating a T c of 13.9 K for (4.2) carbon nanotubes (CNT) that agrees well with experiments. Then we reduce the CNT to a ring, open the ring to form chains, optimize bond length and kink structure, and finally form a new type of carbon ring that reaches a T c value of 115 K

Application of Metadynamics to Accelerate Modeling of the Synthesis of Chain Structures

Application of metadynamics for simulation Ar+ ionstimulated plasma deposition of hy-drocarbons for synthesis chains structures in LAMMPS programs. Collective variables, pa-rameters of metadynamics were studied to accelerate the formation of structures with sphybridization