Browsing by Author "Lin, M. F."

Now showing 1 - 4 of 4

Coulomb scattering rates of excited carriers in moderate-gap carbon nanotubes
(2006-06-01)
Chiu, C. W.
;
Shyu, F. L.
;
Chang, C. P.
;
Chuu, D. S.
;
Lin, M. F.
Temperature induces some free carriers in moderate-gap carbon nanotubes, which, thus, creates the low-frequency intraband e-h excitations. Such excitations are the effective deexcitation channels for the excited electrons (holes) in conduction (valence) bands, while they are very weak. The Coulomb decay rates of the lowest two conduction bands are sensitive to the changes in wave vector, radius, and temperature. However, those of the band-edge states depend on chirality weakly. These results directly reflect the strong energy dispersions and the temperature-dependent electron distributions. The calculated results are roughly consistent with the experimental measurements from the ultrafast optical spectroscopies.
Electronic structure of a two-dimensional graphene monolayer in a spatially modulated magnetic field: Peierls tight-binding model
(2008-01-01)
Chiu, Y. H.
;
Lai, Y. H.
;
Ho, J. H.
;
Chuu, D. S.
;
Lin, M. F.
Magnetoelectronic properties of a two-dimensional (2D) monolayer graphene are investigated by the Peierls tight-binding model. They are dominated by the period, strength, and direction of a spatially modulated magnetic field. Such a field could induce the reduction in dimensionality, change of energy dispersions, anisotropy at low energy, composite behavior in state degeneracy, extra band-edge states, and asymmetry of energy bands. There are partial flatbands at the Fermi level and one-dimensional parabolic bands at others. These make density of states exhibit delta-function-like structure and asymmetric prominent peaks, respectively. Energies of the extra band-edge states strongly depend on the period, while those of the original band-edge states exhibit little dependence. Both of them grow as the strength increases. The modulated and uniform magnetic fields differ from each other in energy dispersion, state degeneracy, and dimensionality. Important differences between a monolayer graphene and a 2D electron gas also exist.
Magnetic energy bands of a 2D graphite layer in the spatially modulated magnetic field
(2008-04-01)
Chiu, Y. H.
;
Lai, Y. H.
;
Ho, J. H.
;
Chuu, D. S.
;
Lin, M. F.
A 2D graphite layer exists in a spatially modulated magnetic field. The low magnetic energy bands, which are calculated from the Peierls tight-binding model, strongly depend on the period and strength of a modulated magnetic field. There are a lot of I D parabolic bands. Such bands exhibit the double degeneracy, strong energy dispersions, and extra band-edge states. Density of states owns many asymmetric square-root divergent structures, mainly owing to the band-edge states in 1D parabolic bands. The band-edge state energies decrease with the increasing field period, while the opposite is true for the dependence on the field strength. That a modulated magnetic field reduces dimensionality and thus drastically changes electronic properties could be examined by the experimental measurements. (c) 2007 Elsevier B.V. All rights reserved.
The Effects of the Modulated Magnetic Fields on Electronic Structures of Graphene Nanoribbons
(2009-05-01)
Wu, J. Y.
;
Chiu, Y. H.
;
Lien, J. Y.
;
Lin, M. F.
;
物理研究所
The low-energy magnetoelectronic structures of nanographene ribbons under a modulated magnetic field are investigated by the Peierls tight-binding model. They are dominated by the field strength, period, phase, the ribbon width, and edge structure. The modulated magnetic field could add state degeneracy, modify energy dispersions, alter subband spacings, affect carrier-density distributions, create additional band-edge states, and cause semiconductor-metal transitions. The main features of energy bands are directly reflected in density of states, such as the position, height, structure, and number of the prominent peaks. These results immensely differ from those in a uniform magnetic field. Significant differences between a 1D graphene ribbon and a 2D electron gas are also found.