Quantum Ring Nanostructure Research Articles

Electron energy spectrum and oscillator strengths of quantum transitions in double quantum ring nanostructure driven by electric field

The effect of homogeneous electric field on the energy spectrum, wave functions of electron and oscillator strengths of intra-band quantum transitions in a double cylindrical quantum ring (GaAs/Al$_{x}$Ga$_{1-x}$As) is studied within the approximations of effective mass and rectangular potentials. The calculations are performed using the method of expansion of quasiparticle wave function over a complete set of cylindrical wave functions obtained as exact solutions of Schr\"odinger equation for an electron in a nanostructure without electric field. It is shown that the electric field essentially affects the electron localization in the rings of a nanostructure. Herein, the electron energies and oscillator strengths of intra-band quantum transitions non-monotonously depend on the intensity of electric field.

Fabrication of InAs quantum ring nanostructures on GaSb by droplet epitaxy

In this article, we report the formation of InAs quantum ring nanostructures (QRNs) on GaSb (0 0 1) surface by droplet epitaxy (DE) mode using molecular beam epitaxy. We examined the impact of various growth conditions, including substrate temperature (Ts), As2 beam equivalent pressure (BEP) and surface stoichiometry, on the shape, density and size of the InAs QRNs. We confirmed that the InAs QRNs have better rotational symmetry at relatively high Ts and low As2 BEP. The symmetry of the QRN is due to the isotropic indium (In) out-migration along [1 1 0] and [1 −1 0], controlled via change in stoichiometry (surface As coverage) with temperature and the As2 BEP. These results indicate that we can realize InAs QRN on GaSb surface by DE process.

The Aharonov–Bohm oscillations and energy spectrum in two-dimensional elliptical quantum ring nanostructures

Based on the finite element method, we present a numerical study of the Aharonov–Bohm (AB) oscillations and electronic energy spectrum for the system of a two-dimensional elliptical quantum ring (EQR) nanostructure pierced by a static magnetic flux ϕ in the presence of local charge impurities. Strong changes are observed in the energy spectrum and in the amplitude of the AB oscillations depending on both the geometrical parameters of the EQR and the strengths, locations and screening of impurities embedded in the system. Energy gaps are opened at the integer values of ϕ due to elliptical confinement, while the opening of the gaps at the half-integer values of ϕ depends on the location of impurities. Impurities can shift the low-lying energy levels in various ways depending on their azimuthal locations.

Hydrostatic pressure and electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in InAs Pöschl–Teller quantum ring

We consider the effects of electric and magnetic fields as well as of hydrostatic pressure on the donor binding energy in InAs Pöschl–Teller quantum rings. The ground state energy and the electron wave function are calculated within the effective mass and parabolic band approximations, using the variational method. The binding energy dependencies on the electric field strength and the hydrostatic pressure are reported for different values of quantum ring size and shape, the parameters of the Pöschl–Teller confining potential, and the magnetic field induction. The results show that the binding energy is an increasing or decreasing function of the electric field, depending on the chosen parameters of the confining potential. Also, we have observed that the binding energy is an increasing/decreasing function of hydrostatic pressure/magnetic field induction. Likewise, the impurity binding energy behaves as an increasing/decreasing function of the inner/outer radii of the quantum ring nanostructure.

Ground state and infrared response of triple concentric quantum ring structures

Within local-spin density-functional theory, we study the ground state and infrared response of two-dimensional, triple concentric quantum ring nanostructures. Changes in their physical properties are presented as a function of the number of electrons or the intensity of a perpendicularly applied magnetic field. We discuss the addition spectrum of few-electron triple quantum rings at zero magnetic field, as well as the physical appearance of the ground state and dipole response of selected systems containing up to 50 electrons. We also investigate the ground state, persistent currents, and charge- and spin-density responses of a system made of 30 electrons.

Temperature dependence of time-resolved photoluminescence spectroscopy in InAs/GaAs quantum ring

We present detailed experimental results of the temperature dependence of continuous wave and time-resolved photoluminescence (PL) spectroscopy in self-assembled InAs/GaAs quantum dot and quantum ring nanostructures. A dramatic increase in PL decay time of the excited and ground states is observed in InAs quantum rings at high temperature. We speculate that the longer PL lifetime in quantum rings is due to the interplay among the dark states, ground states, and the reduced wave function overlapping between electrons and holes. A rate equation model is proposed to interpret the observed temperature dependence of the ground state exciton lifetime.

Photon antibunching in double quantum ring structures

We address the question whether a quantum ring nanostructure can be considered as a single-photon emitter by means of intensity time-correlation measurement based on a Hanbury-Brown and Twiss interferometer. The second-order correlation function ${g}^{(2)}$ well characterizes the quantum nature of the emitter by the photon antibunching dip at zero delay. In concentric quantum rings we find evidence that the inner ring satisfies the requirement of single-photon source, while in the outer ring this requirement is relaxed.

Quantal cumulant dynamics III: A quantum confinement under a magnetic field

The quantal cumulant dynamics (QCD) method for multi-dimensional cases is developed in order to simulate the model quantum confinement systems under a magnetic field. We feature the resonant levels in quantum wells as found in the classical mechanics, magnetic-field induced tunneling, and magnetic confinement in a model quantum ring nanostructure. Trajectories and position cumulant variables are analyzed in order to characterize these phenomena. We find that (i) the magnetic confinement originates from resonant level trajectories between cycloid and drift motions and (ii) the position cumulant variables decrease during transitions among the wells, which reflects a tunneling motion.