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Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Condensed Matter Physics Laboratory, Heinrich-Heine-Universität, Düsseldorf, Germany.
Condensed Matter Physics Laboratory, Heinrich-Heine-Universität, Düsseldorf, Germany.
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 16, 161407- p.Article in journal (Refereed) Published
Abstract [en]

We study the effect of the edge disorder on the conductance of the graphene nanoribbons (GNRs).We find that only very modest edge disorder is sufficient to induce the conduction energy gap inthe otherwise metallic GNRs and to lift any difference in the conductance between nanoribbonsof different edge geometry. We relate the formation of the conduction gap to the pronounced edgedisorder induced Anderson-type localization which leads to the strongly enhanced density of states atthe edges, formation of surface-like states and to blocking of conductive paths through the ribbons.

Place, publisher, year, edition, pages
American Physical Society , 2008. Vol. 78, no 16, 161407- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14778DOI: 10.1103/PhysRevB.78.161407OAI: oai:DiVA.org:liu-14778DiVA: diva2:25251
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2013-06-12Bibliographically approved
In thesis
1. Quantum transport and spin effects in lateral semiconductor nanostructures and graphene
Open this publication in new window or tab >>Quantum transport and spin effects in lateral semiconductor nanostructures and graphene
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies electron spin phenomena in lateral semi-conductor quantum dots/anti-dots and electron conductance in graphene nanoribbons by numerical modelling. In paper I we have investigated spin-dependent transport through open quantum dots, i.e., dots strongly coupled to their leads, within the Hubbard model. Results in this model were found consistent with experimental data and suggest that spin-degeneracy is lifted inside the dot – even at zero magnetic field.

Similar systems were also studied with electron-electron effects incorporated via Density Functional Theory (DFT) in the Local Spin Density Approximation (LSDA) in paper II and III. In paper II we found a significant spin-polarisation in the dot at low electron densities. As the electron density increases the spin polarisation in the dot gradually diminishes. These findings are consistent with available experimental observations. Notably, the polarisation is qualitatively different from the one found in the Hubbard model.

Paper III investigates spin polarisation in a quantum wire with a realistic external potential due to split gates and a random distribution of charged donors. At low electron densities we recover spin polarisation and a metalinsulator transition when electrons are localised to electron lakes due to ragged potential profile from the donors. In paper IV we propose a spin-filter device based on resonant backscattering of edge states against a quantum anti-dot embedded in a quantum wire. A magnetic field is applied and the spin up/spin down states are separated through Zeeman splitting. Their respective resonant states may be tuned so that the device can be used to filter either spin in a controlled way.

Paper V analyses the details of low energy electron transport through a magnetic barrier in a quantum wire. At sufficiently large magnetisation of the barrier the conductance is pinched off completely. Furthermore, if the barrier is sharp we find a resonant reflection close to the pinch off point. This feature is due to interference between a propagating edge state and quasibond state inside the magnetic barrier.

Paper VI adapts an efficient numerical method for computing the surface Green’s function in photonic crystals to graphene nanoribbons (GNR). The method is used to investigate magnetic barriers in GNR. In contrast to quantum wires, magnetic barriers in GNRs cannot pinch-off the lowest propagating state. The method is further applied to study edge dislocation defects for realistically sized GNRs in paper VII. In this study we conclude that even modest edge dislocations are sufficient to explain both the energy gap in narrow GNRs, and the lack of dependance on the edge structure for electronic properties in the GNRs.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 66 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1202
Keyword
Electronic transport, Spin related phenomena, Quantum dots, Quantum wires, Two-dimensional electron gas, 2DEG, Graphene
National Category
Other Physics Topics Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12410 (URN)978-91-7393-835-8 (ISBN)
Public defence
2008-09-19, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-24 Created: 2008-09-03 Last updated: 2009-03-10Bibliographically approved

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Evaldsson, MartinZozoulenko, Igor V.

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