Reading Comprehension - Linear and Nonlinear Susceptibilities of a D System

In nanoscale semiconductor quantum rings, charged carriers are confined in a small region and consequently the Coulomb interaction is enhanced. Compared with nanoscale semiconductor quantum dots, quantum rings belong to another kind of topological structures in which more rich phenomena can be clearly shown. These semiconductor quantum dots and quantum rings are widely applied for fabricating single electron transistors, low threshold laser, optical memories, solar cells, light-emitting diodes, biological markers and so on. On the other hand, the application of a magnetic field leads to the enhancement of the localization of both the electron and the hole in a quantum ring. Under the influence of a magnetic field, some interesting physical phenomena of quantum rings, e.g., persistent currents and Aharonov-Bohm effect¹, can be observed. The electronic and optical properties of quantum rings will occur in the Aharonov-Bohm oscillation² when a variable magnetic field is perpendicularly applied to the plane of the ring. Experimental observation on the Aharonov-Bohm oscillation was reported in quantum rings.

The negative donor (D^-) system is one of the simplest many-body systems in low-dimensional semiconductors. This system is a very interesting occasion to study the electron-electron and electron-impurity interactions in low-dimensional semiconductor systems. On the other hand, the impurity problem is a very useful model for understanding the electronic and optical properties of semiconductor nanostructures, so that topics like confined the (D^-) systems in low-dimensional space have been extensively investigated. Since the existence of (D^-) systems in quantum wells was first reported, many experimental and theoretical investigations and research for (D^-) systems have been carried out in quantum wells, quantum dots with and without magnetic fields. Very recently, some new results have been obtained in the singly ionized double-donor (D^-) and the neutral double-donor (D^-) complexes in quantum rings. The results have shown that the Aharonov-Bohm ground state oscillations are associated with the localization of the electron by the fixed donors in quantum rings.

In low-dimensional semiconductors, intraband nonlinear optics of two-level systems have many interesting properties. Recently, some authors investigated the nonlinear properties of the neutral donor and (D^-) systems in semiconductor quantum dots. The results have shown that the size of quantum dots and the external fields have drastic effects on the nonlinear properties of these systems. In addition, the nonlinear optical properties of two-level systems in semiconductor quantum rings have attracted an enormous interest because they have the potential for device applications in far-infrared laser amplifies, photodetectors, and high-speed electro-optical modulators. The attention has also been attracted by donor impurity-related linear and nonlinear optical properties of semiconductor quantum rings. However, up to now, the study of the size and the magnetic effects on the nonlinear optical properties of a (D^-) system in semiconductor quantum rings is still rare. Very recently, Zeng and co-worker investigated the linear and the nonlinear optical susceptibilities in a laterally coupled quantum-dot-quantum-ring system. They found that the enhancement of the coupling effects between the dot and ring to increase considerably the optical susceptibilities, and redshift drastically the transition energies. In this paper, we will investigate the linear and nonlinear optical behavior of a (D^-) system in semiconductor quantum rings under an external magnetic field. We use the exact diagonalization method and the compact density-matrix approach to calculate the linear and third-order nonlinear susceptibilities of a (D^-) system in semiconductor quantum rings in order to investigate the effects of the external magnetic field and the ring radius.

How Magnetism Impacts (D-) Systems 100 90 80 70 60 Mangetism found in (D-) Systems (By % of System Charged) 50 40 30 20 10 O 10 26 NO Magnetism Force in Parts per Trillion