Theoretical Studies on Novel Electronic TransportProperties of Graphene Systems
| Autor: | Ya-Fen Hsu, 許雅芬 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 Graphene is a single atomic layer of graphite with a two-dimensional honeycomb lattice structure. The valence and conduction bands of graphene touch each other at six corner points of the hexagonal Brillouin zone. These six corner points are known as Dirac points. Graphene possesses a linear energy dispersion and chiral eigenstates near each Dirac point. Hence, charge carriers in graphene would exhibit relativistic dynamics even at low energy. Several theoretical as well as experimental works have shown that the Dirac-type fermions may result in many intriguing transport phenomena such as anomalous quantum Hall effect and Klein tunneling.In this thesis, we will report our works on the electronic transport properties in graphene, which could be categorized into three: (i) superconducting transport,(ii) quantum Hall effect (QHE), and (iii) Kondo effect. In work (i), we calculate the tunnelling conductance of graphene ferromagnet-insulatorsuperconductor (FIS) juctions within the Blonder-Tinkham-Klapwijk formalism by solving spin polarized Dirac-Bogoliubov-de-Gennes equation. In the thin-barrier limit, the conductance G of a graphene FIS junction oscillates as a function of barrier strength chi, the same as graphene normal metal-insulator-superconductor junctions. Interestingly, we find a universal phase difference of pi/2 exists between the G − chi curves for exchange energy E_{ex} > E_F (Fermi energy) and E_{ex} < E_F. This research has been published in Phys. Rev. B 81, 045412 (2010). In work (ii), we investigate the quantum Hall effect of AA-stacked bilayer graphene. We calculate the Hall conductivity as well as longitudinal conductivity within linear response Kubo formalism. Interestingly, we find that QHE in AA-stacked bilayer graphene possesses three unique characteristics: the filling factor ar{ u} = 0 Hall plateau, the periodic 8e^2/h-steps, and the strong dependence on magnetic field and chemical potential. This research has been published in Phys. Rev. B 82, 165404 (2010). In work (iii), we study Kondo effect in graphene by solving the graphene Anderson model, using numerical renormalization group (NRG) method. Unlike conventional host metal, for the study on kondo physics in graphene, the two characteristics of graphene, namely chirality and non-constant density of states have to been taken into account. Graphene was shown to exhibit impurity-position-dependent Kondo effcet. Therefore, we investigate the Kondo physics of two diffenent configurations in graphene: (i) an adatom impurity on the top of one carbon atom, and (ii) an adatom impurity at the center of the honeycomb. So far, we have develop a NRG formalism applicable to graphene. We have analytically discretized Hamiltonian and numerically obtained Lanczos coefficiences. In the furture, we will use our NRG formalism to investigate the Kondo effect of iron-impurities in graphene. Nowadays, the origin of magnetic moment and multi-channel Kondo effect in graphene are controversial. We expect our work would contribute to clarify the two issues. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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