Persistent Current And Magnetic Response In Carbon Nanotori Filled With Carbon Atoms And C60 Moleculars

Electronic phase coherence gives rise to a rich variety of peculiar effects in semiconductor and metal samples in mesoscopic scale. The Aharonov-Bohm (AB) flux-induced persistent current flowing around a non-superconducting ring exemplifies such quantum coherence effects. Using the tight-binding formalism and a developed supercell method for numerical simulations, in this thesis, we have explored the electronic structures, persistent currents and magnetic response of a filled mesoscopic toroidal catbon nanotube (TCN). The thesis is organized as follows:In chapter 1, some basic concepts in the realm of mesoscopic physics are illustrated, a brief description of the fundamental theories of AB effect and the induced persistent current is given, and experimental developments about persistent current, which are compared with theory, are summarized.In chapter 2, a toroidal carbon nanowire (TCNW) model device is proposed, consisting of a toroidal carbon nanotube (TCN) and a filled carbon ring, which may in physical existence be an ideal 1D mesoscopic ring. The energy spectra and persistent currents in TCNWs are investigated within the singleπ-orbital tight-binding formalism. It is found that the tube-ring interactions lead to a charge transfer from the inner ring to the outer TCN, and thus the Fermi level rises and the band overlaps in a certain flux range. In zigzag TCNWs with a metallic TCN, the actual magnetic response, the amplitude and the period of persistent current in the primary carbon ring are concealed by those in the resultant TCNW; in zigzag TCNWs with a semiconducting TCN, persistent current exhibits the same behavior as that in their primary carbon rings. The results show that persistent current in the sample ring depends strongly on the surrounding environment and thus a semiconducting or insulating matrix may provide a desired environment for measuring persistent current in mesoscopic rings.In chapter 3, the energy spectra and persistent currents in toroidal carbon nanopeapods (TCNPs), i.e., TCNs with a filled C60 loop-chain, are investigated within the sp3 hybridized orbital tight-binding formalism, in order to obtain a persistent current-induced giant orbital paramagnetism (GOP) in TCNs. It is found that in the presence of mirror symmetry of the TCNP, there exists a level crossing at the Fermi level in the energy spectra, leading to a GOP, in spite of the curvatures and hybridizations of the outer TCN, When the mirror symmetry is broken by rotating the inner C60s, however, two level crossings appear at the Fermi level, and the GOP changes into very small diamagnetic response. The results reveal the GOP effect in a filled TCN, depending on the characteristics of filled materials. In addition, the temperature dependence of the GOP is also discussed.Finally, we give a conclusion of the thesis and some prospects for further studies.