Coulomb-interaction effects on the electronic structure of radially polarized excitons in nanorings

Abstract

The electronic structure of radially polarized excitons in structured nanorings is analyzed, with emphasis in the ground-state properties and their dependence under applied magnetic fields perpendicular to the ring plane. The electron-hole Coulomb attraction has been treated rigorously, through numerical diagonalization of the full exciton Hamiltonian in the non-interacting electronhole pairs basis. Depending on the relative weight of the kinetic energy and Coulomb contributions, the ground-state of polarized excitons has "extended" or "localized" features. In the first case, corresponding to small rings dominated by the kinetic energy, the ground-state shows Aharonov-Bohm (AB) oscillations due to the individual orbits of the building particles of the exciton. In the localized regime, corresponding to large rings dominated by the Coulomb interaction, the only remaining AB oscillations are due to the magnetic flux trapped between the electron and hole orbits. This dependence of the exciton, a neutral excitation, on the flux difference confirms this feature as a signature of Coulomb dominated polarized excitons. Analytical approximations are provided in both regimens, which accurate reproduce the numerical results.

Interband Optical Properties of Concentric Type-I Nanorings in a Normal Magnetic Field

“…This is indeed the case in the analyzed structure, where both the rings radii are larger than the effective Bohr radius, which is approximately equal to 12 nm in GaAs. A rigorous inclusion of the Coulomb interaction demonstrated that the optical excitonic AharonovBohm oscillations are also suppressed in the regime of week interaction [22], which exists in small rings. However, calculation of the exciton states is beyond scope of the present work.…”

Noncircular semiconductor nanorings of types I and II: Emission kinetics in the excitonic Aharonov-Bohm effect

“…This can be achieved by separating electron and hole using a static electric field, 14,15 or going to type II material combinations where electron and hole are confined in different regions. 12,13,16,17 In the original ABE idea, the particle path was assumed to lie in a region with zero magnetic field, which means to concentrate the magnetic flux into the middle of the ring. For a semiconductor nanoring of nanometer size, this is technically very demanding -if not impossible using state-of-the-art techniques.…”

Tunneling and optical control in quantum ring molecules

“…Moreover, quantum rings have a unique magnetic field level dispersion: unlike quantum dots, the ground-state total angular momentum L in quantum rings changes from L =0 to L 0 by the application of a moderate external magnetic field B. [16][17][18][19][20][21] The values of B for which these transitions take place depend on the flux threading each ring, resulting in a different energy dispersion for excitons in QRMs with different ring radii. Thus, charge tunneling between states with distinct angular momentum is strongly suppressed by orbital selection rules.…”