| 1. |
- Evaldsson, Martin, et al.
(författare)
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Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 78:16, s. 161407-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Evaldsson, Martin, et al.
(författare)
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Spin polarization in modulation-doped GaAs quantum wires
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 77:16, s. 165306-1-165306-7
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Tidskriftsartikel (refereegranskat)abstract
- We study spin polarization in a split-gate quantum wire focusing on the effect of a realistic smooth potential due to remote donors. Electron interaction and spin effects are included within the density functional theory in the local spin density approximation. We find that depending on the electron density, the spin polarization exhibits qualitatively different features. For the case of relatively high electron density, when the Fermi energy EF exceeds a characteristic strength of a long-range impurity potential Vdonors, the density spin polarization inside the wire is practically negligible and the wire conductance is spin-degenerate. When the density is decreased such that EF approaches Vdonors, the electron density and conductance quickly become spin polarized. With further decrease of the density the electrons are trapped inside the lakes (droplets) formed by the impurity potential and the wire conductance approaches the pinch-off regime. We discuss the limitations of the density functional theory in the local spin density approximation in this regime and compare the obtained results with available experimental data.
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| 3. |
- Evaldsson, Martin, et al.
(författare)
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Spin polarization in open quantum dots
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:3, s. 035319-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate coherent transport through open lateral quantum dots using recursive Green's function technique, incorporating exchange-correlation effects within the density functional theory (DFT) in the local spin-density approximation. At low electron densities the current is spin polarized and electron density in the dot shows a strong spin polarization. As the electron density increases the spin polarization in the dot gradually diminishes. These findings are consistent with available experimental observations. Results of our DFT-based modeling indicate that utilization of the simplified approaches that use phenomenological parameters and/or model Hamiltonians might not be always reliable for theoretical predictions as well as interpretations of the experiments.
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| 4. |
- Rahachou, Aliaksandr, et al.
(författare)
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Light propagation in nanorod arrays
- 2007
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Ingår i: Journal of optics. A: Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 9:3, s. 265-270
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Tidskriftsartikel (refereegranskat)abstract
- We study the propagation of TM- and TE-polarized light in two-dimensional arrays of silver nanorods of various diameters in a gelatin background. We calculate the transmittance, reflectance and absorption of arranged and disordered nanorod arrays and compare the exact numerical results with the predictions of the Maxwell–Garnett effective-medium theory. We show that interactions between nanorods, multipole contributions and formations of photonic gaps affect strongly the transmittance spectra that cannot be accounted for in terms of the conventional effective-medium theory. We also demonstrate and explain the degradation of the transmittance in arrays with randomly located rods as well as the weak influence of their fluctuating diameter. For TM modes we outline the importance of the skin effect, which causes the full reflection of the incoming light. We then illustrate the possibility of using periodic arrays of nanorods as high-quality polarizers.
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| 5. |
- Rahachou, Aliaksandr, et al.
(författare)
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Waveguiding properties of surface states in photonic crystals
- 2006
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Ingår i: Journal of the optical society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:8, s. 1679-1683
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Tidskriftsartikel (refereegranskat)abstract
- We propose and analyze novel surface-state-based waveguides in bandgap photonic crystals. We discuss the surface-mode band structure, the field localization, and the effect of imperfections on the waveguiding properties of the surface modes. We demonstrate that surface-state-based waveguides can be used to achieve directional emission out of the waveguide. We also discuss the application of the surface-state waveguides as efficient light couplers for conventional photonic crystal waveguides.
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| 6. |
- Tvingstedt, Kristofer, et al.
(författare)
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Surface plasmon increased absorption in polymer photovoltaic cells
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:11, s. 113514 -
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Tidskriftsartikel (refereegranskat)abstract
- The authors demonstrate the triggering of surface plasmons at the interface of a metal grating and a photovoltaic bulk heterojunction blend of alternating polyfluorenes and a fullerene derivative. An increased absorption originating from surface plasmon resonances is confirmed by experimental reflection studies and theoretical modeling. Plasmonic resonances are further confirmed to influence the extracted photocurrent from devices. More current is generated at the wavelength position of the plasmon resonance peak. High conductivity polymer electrodes are used to build inverted sandwich structures with top anode and bottom metal grating, facilitating for triggering and characterization of the surface plasmon effects.
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