First predicted over a half a century ago, one of the most fundamental phenomena in quantum physics is the Aharonov-Bohm effect, which occurs when two beams of charged quantum particles, such as electrons, pass either side of a region containing a magnetic field. The presence of a magnetic flux changes the phase of the electron wave function and therefore influences the interference pattern created by the two beams. For non-simply-connected nanostructures, such as quantum rings or carbon nanotubes pierced by magnetic field, the angular continuity of the wave function together with the magnetic-flux-induced phase change results in modification of the energy spectrum which has periodic flux dependence. For a typical carbon nanotube a full oscillation requires very high magnetic fields. However, a noticeable effect, such as a band gap opening in the terahertz (THz) range in a metallic nanotube can be achieved at experimentally attainable fields.
It has been recently realised that the Aharonov-Bohm effect in semiconductor nanorings also occurs for excitons - neutral composite particles consisting of an electron and a positively charged hole. Due to the spatial extent of its wave function an exciton's energy spectrum and oscillator strength become sensitive to the magnetic flux through the ring.
The proposed PhD research will be devoted to the two problems related to excitons in non-simply-connected nanostructures subjected to a strong magnetic field. Firstly, we will study the influence of electron-hole correlations (excitons) on THz transitions in carbon nanotubes across a magnetic-field-induced band gap. Secondly, we will consider excitons in Aharonov-Bohm quantum rings subjected to an in-plane electric field. A high enough electric field should break the exciton so that the ground state of such a system should be optically inactive (dark). This effect could be used for "light storage" and its release on demand. We will also study transitions in the THz range between the dark and optically active exciton states.