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Transport Properties of Rippled Graphene

100%
Zwierzycki M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1246-1249
EN
It is common to describe graphene as ideally flat plane, however there exists both theoretical and experimental evidence that it is most usual to find it in a rippled state. The ripples can be either induced by the substrate or formed spontaneously in suspended graphene. The lateral size of such features ranges between several and tens of nanometers with the height of up to 1 nm. It has been suggested that the presence of ripples could be one of the factors ultimately limiting mobility of carriers and that it may be also responsible, by introducing an effective gauge field, for the lack of weak localization observed in certain graphene samples. In the present contribution the transport properties of the rippled graphene are studied theoretically starting with the simple case of one-dimensional modulation. Using either single-band or the full sp^3 tight-binding Hamiltonians we compare and discuss the importance of two ripple-related mechanisms of scattering: the variation of interatomic distances and hybridization between π and σ bands of graphene.
2
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Magnetic Properties of Hexagonal Graphene Nanomeshes

63%
Zwierzycki M., Ryndyk D.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
830-832
EN
Graphene nanomeshes are the nanostructures consisting of graphene flake with a regular pattern of antidots (holes) punched through it. Thanks to the energy gaps opening in electronic spectrum, nanomesh-based transistors offer improved I_{on}/I_{off} ratio of the collector current while supporting up to 100 larger driving currents than nanoribbon-based devices. In this paper the electronic and magnetic structure of graphene nanomeshes with hexagonally shaped antidots was studied. It has been found that the internal zigzag edges support magnetic moments and that lowest energy magnetic configuration is antiferromagnetic. The density of states calculated for ground state configuration exhibit the energy gap which can be substantially reduced upon switching (e.g. by external magnetic field) to ferromagnetic configuration. Based on this we predict that the structure will exhibit magnetoresistive effect, which makes graphene nanomeshes of this kind relevant for spintronic applications.
3
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The Overlapping Muffin-Tin Approximation

63%
Zwierzycki M., Andersen O.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
64-68
EN
We present the formalism and demonstrate the use of the overlapping muffin-tin approximation. This fits a full potential to a superposition of spherically symmetric short-ranged potential wells plus a constant. For one-electron potentials of this form, the standard multiple-scattering methods can solve Schrödingers' equation correctly to 1st order in the potential overlap. Choosing an augmented-plane-wave method as the source of the full potential, we illustrate the procedure for diamond-structured Si. First, we compare the potential in the Si-centered overlapping muffin-tin approximation with the full potential, and then compare the corresponding overlapping muffin-tin approximation N-th order muffin-tin orbital and full-potential linear augmented plane wave band structures. We find that the two latter agree qualitatively for a wide range of overlaps and that the valence bands have a root mean squared deviation of 20 meV/electron for 30% radial overlap. Smaller overlaps give worse potentials and larger overlaps give larger 2nd-order errors of the multiple-scattering method. To further remove the mean error of the bands for small overlaps is simple.
4
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Ab Initio Study of the Edge States of Graphene Nanoribbons in the Presence of Electrodes

63%
Zwierzycki M., Krompiewski S.
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EN
Thanks to its outstanding electronic properties, like very high mobility of carriers, graphene has emerged in recent years as exciting candidate for use in new electronic devices. When it is patterned in the form of ribbons with widths in the range of nanometers, its transport properties become strongly influenced by the presence of the states localized at the edges of the ribbon. Using first principles calculations we study the properties of these states for both isolated ribbons and in the presence of metallic electrodes. The calculations were performed for end contacted geometry i.e. for graphene sheets at right angle to the electrodes. Both para- and ferromagnetic electrodes were considered.
5
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Perpendicular and Parallel Transport, and Interlayer Exchange Coupling in Magnetic Trilayers with Extra Cap-Layers

63%
Krompiewski S., Zwierzycki M.
Acta Physica Polonica A
|
2000
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vol. 97
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issue 3
555-558
EN
Oscillations of Magnetoresistance and Interlayer Exchange Coupling Vs. both Non-magnetic Spacer and Cap-layer Thicknesses Are Studied Within the Framework of the S-d Model. the Studies Are Carried Out by Means of the Kubo Formula and a Green Function Recursion Technique. Transport Calculations Concern Multilayers (sandwiched Between Two Semi-infinite Ideal Lead Wires) Oriented Either Parallel Or Perpendicular To the Current Direction. the Considered Structures for the Above Mentioned Two Basic Geometries, Are Cubic Grains Identical In: (i) Size, (ii) Number of Sublayers, and (iii) Thicknesses of Particular Sublayers, Which Makes It Possible To Compare, in a Direct and Reliable Way, the Corresponding Magnetoresistances. the Current-in-plane Magnetoresistance Is Found To Be Usually Lower Than the Current-perpendicular-to-plane One, But Both of Them Show Oscillatory Behaviours Mutually Correlated, and Related To the Fermi Surface Callipers. moreover, the Current-perpendicular-to-plane Giant Magnetoresistance for Structures in a Form of Infinite in Layer-plane Trilayers Capped with An Extra Bilayer (ferromagnet/paramagnet) Is Also Discussed.
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