Orbital magnetism in two-dimensional mesoscopic ring systems

Based on the exactly solvable model, various features of orbital magnetism of mesoscopic ring systems with finite width have been studied in various regimes of temperature and magnetic field with special emphasis on the spatial distribution of persistent current and resultant magnetization. When the width is very narrow and only one channel along the ring is occupied, Aharonov-Bohm (AB) oscillation appears due to interference effects at low temperature; its amplitude is, however, seen to be suppressed as the magnetic field increases because of the finite width. When the width is not very narrow and several channels are occupied, AB oscillation is transformed into mesoscopic fluctuations as seen in disc systems. De Haas-van Alphen (dHvA) oscillation also appears in this regime. At high temperature where all of AB oscillation, mesoscopic fluctuations and dHvA oscillation fade away, Landau diamagnetism whose magnitude is proportional to the effective area of the ring appears irrespective of the width of the ring. A wide ring with only a small hole in its center has been also studied and compared with the case of a disc. Phase diagrams in the plane of temperature and magnetic fields are systematically presented both for narrow and wide rings.