Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

Abstract

Semiconducting quantum dots -more fancifully dubbed artificial atoms -are quasi-zero dimensional, tiny, manmade systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement -or the lack of any degree of freedom for the electrons (and/or holes) -in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magnetooptical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines' randomphase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level transitions are seen to be forbidden. The spherical quantum dots have an edge over the strictly two-dimensional quantum dots in that the additional (magnetic) quantum number makes the physics richer (but complex). A deeper grasp of the Coulomb blockade, quantum coherence, and entanglement can lead to a better insight into promising applications involving lasers, detectors, storage devices, and quantum computing.

The quantum pinch effect in semiconducting quantum wires: A bird’s-eye view

“…The continued tremendous research interest in these quasi-n-dimensional electron gas [Q-nDEG] systems can now safely be accredited to the discovery of the quantum Hall effects -both integral [20] and fractional [21]. The fundamental issue behind the excitement in these manmade nanostructures lies in the fact that the charge carriers exposed to external probes such as electric and/or magnetic fields can exhibit unprecedented quantal effects that strongly modify their behavior characteristics [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. To what extent these effects can influence the behavior of a quantum wire [or, more realistically, Q-1DEG system] in the cylindrical symmetry, which offers a quantum analogue of the classical structure subjected to investigate the pinch effect in the conventional SSP [or GSP],…”