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Korol A.N.,National Food Technology University | Korol A.N.,Laboratory on Quantum Theory in Linkoping
Low Temperature Physics | Year: 2014

The energy spectra of a Thue-Morse superlattice based on monolayer graphene containing a band gap are studied. The lattice consists of rectangular barriers located along the x axis. It is proposed that aperiodic Thue-Morse modulation be produced by a difference in the gap width in different elements of the superlattice. It is shown that effective splitting of the allowed bands (and, thereby, the formation of a series of gaps) under the influence of the aperiodic factor can be observed with both oblique and normal incidence of an electron wave on the superlattice. The spectra have periodicity that depends on the potential barrier height. In some segments of the spectrum, band splitting follows the Fibonacci inflation rule in each new generation. As in periodic graphene-based superlattices, a gap associated with a superlattice Dirac point is formed in all Thue-Morse generations. Its width depends substantially on the parameters of the problem; at the same time the position of this band on the energy axis depends weakly on the mass term in the hamiltonian and is independent of the superlattice period. The spectra have little dependence on the angle of incidence of the electron wave. © 2014 AIP Publishing LLC. Source


Korol A.M.,Laboratory on Quantum Theory in Linkoping | Korol A.M.,National University of Food Technologies | Litvynchuk S.I.,National University of Food Technologies | Bagliuk S.V.,National University of Food Technologies | Lazarenko M.V.,National University of Food Technologies
Low Temperature Physics | Year: 2016

We discuss and analyze the dependence spectra of the transmission coefficient T on the quasiparticle energy E of one variety of graphene-based Fibonacci superlattices (SL). The SL is built from armchair graphene nanoribbons (GNR), and the quasi-periodicity is produced by metal-like (MGNR) and semiconductor (SCGNR) ribbons, placed along the lattice growth axis in accordance with the Fibonacci sequence, which are used as individual SL elements. It is shown that the difference in the values of quantized transverse quasi-momentum of electrons in MGNR and SCGNR is enough to form an effective quasi-periodic modulation in the examined structure (no additional factors required), and the optimal nanoribbon width range for this purpose is determined. We also analyzed the dependence of the spectral properties of the test structure on the geometric parameters of the superlattice, and the external electrostatic potential. We paid particular attention to the fact that each Fibonacci generation had a Dirac superlattice band gap. The results of the study can be useful in the determination of optimal parameters for graphene-based nanoelectronic devices. © 2016 AIP Publishing LLC. Source


Onipko A.,Laboratory on Quantum Theory in Linkoping | Malysheva L.,Laboratory on Quantum Theory in Linkoping | Malysheva L.,NASU Bogolyubov Institute for Theoretical Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

There is an enormous amount of literature on molecular-size circuits. However, no common regularities have ever been reported regarding the embedding of Y-like or, more generally, starlike molecular junctions into circuits. At the same time, connections of several wires are unavoidable components of any circuit. We show that in star junctions of N identical molecular wires, which are equally coupled to the feeding leads, the branched current is inversely proportional to N2. It is also proved that, independently of molecular structure, the minimal resistance that is associated with the terminal-to-terminal current through such junctions is equal to hN2/8e2. In words, it is divided by eight von Klitzing resistance times N2. These predictions rule the performance of quantum wire junctions and provide useful references for studies of complex multiterminal molecular devices. The current-voltage dependence predicted for the circuits that contain a star junction of molecular wires is compared with I-V characteristics of constructively similar junctions of conventional resistors, where the Ohm law prescribes the proportionality of branched current to 1/N. The newly derived basic formulas include the exact solution of Lippman-Schwinger equation for a general model of multiterminal, rigid (coherent) scatterer, and also, a new and general trace formula for multiterminal transmission. © 2012 American Physical Society. Source


Malysheva L.,NASU Bogolyubov Institute for Theoretical Physics | Malysheva L.,Laboratory on Quantum Theory in Linkoping | Onipko A.,Laboratory on Quantum Theory in Linkoping | Onipko A.,Linkoping University
Physica Status Solidi (B) Basic Research | Year: 2011

We consider coherent transport in an arbitrary molecular complex functioning as N-terminal conductor. The matrices that enter Datta's trace formula for the transmission function T(E) are represented in terms of free-molecule Green's function matrix elements referring exclusively to molecular atoms perturbed by the lead-molecule interaction. Explicit expressions of transmission function are obtained for a commonly used model of multiterminal molecular devices, where the molecule is coupled with each lead via a single bond. In the particular cases of connection of molecular wires via a single atom and a benzene ring, this gives the analytical expressions of T(E). Physical implications of the derived formulas are briefly discussed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Malysheva L.,NASU Bogolyubov Institute for Theoretical Physics | Malysheva L.,Laboratory on Quantum Theory in Linkoping | Onipko A.,Laboratory on Quantum Theory in Linkoping | Fyrner T.,Linkoping University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2012

Two series of oligo(ethylene glycol) (OEG) thiol compounds HS-(CH 2CH 2O) nR, with R = CH 3, H and n = 5, 6, 7, have been synthesized and used to form self-assembled monolayers (SAMs) on gold. The data from null ellipsometry, infrared reflection-absorption spectroscopy, and ab initio calculations of this type of OH- and CH 3-terminated OEG SAMs are used to examine the rarely addressed in-SAM orientation of oligo(ethylene glycols) and to provide detailed assignments of infrared bands in the fingerprint and CH-stretching regions. On the basis of these results, a new spectral band has been observed at 2947 cm -1 and identified by the first-principle calculations as localized vibrations that are specific for hydrogen-terminated OEG thiolate SAMs. This band can be used as an indicator of a high crystalline-like ordering. It is furthermore stressed that theory agrees with the experimentally obtained CH-stretching spectra remarkably well if, and only if, the OEG helix axis within studied SAMs is tilted by about 20° with respect to the surface normal. © 2012 American Chemical Society. Source

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