Search results for "quantum dot"
showing 10 items of 418 documents
Quantitative modeling of spin relaxation in quantum dots
2011
Physics Department, Harvard University, 02138 Cambridge MA, USA(Dated: December 16, 2011)We use numerically exact diagonalization to calculate the spin-orbit and phonon-induced triplet-singlet relaxation rate in a two-electron quantum dot exposed to a tilted magnetic field. Our schemeincludes a three-dimensional description of the quantum dot, the Rashba and the linear and cubicDresselhaus spin-orbit coupling, the ellipticity of the quantum dot, and the full angular descriptionof the magnetic field. We are able to find reasonable agreement with the experimental results ofMeunier et al. [Phys. Rev. Lett. 98, 126601 (2007)] in terms of the singlet-triplet energy splittingand the spin relaxation …
Gaussian quantum dots of type II in in-plane electric field
2007
The growing interest is recently focusing on QDs of type II, which contrary to type I QDs attract electrons and repulse holes (or conversely). In such QDs an electron-hole pair (Xexciton) can still be traped due to electron-hole Coulomb attraction, resulting in significantly more complex structure of excitonic states. We consider an X exciton in QD of type II defined by electrostatic focusing in a narrow quantum well, in the presence of additional external in-plane electric field. The dependence of PL spectrum on dot size and in-plane electric field is analysed within the Hartree approach for model planar Gaussian confinement. The exciton ground state and its energy red-shift are found as a…
Lateral induced dipole moment and polarizability of excitons in a ZnO single quantum disk
2013
The lateral Stark shift of an exciton confined in a single ZnO quantum thin disk of radius R was calculated using a variational approach within the two bands effective mass approximation. It is shown that the exciton has a non negligible induced dipole moment when an external electric field is applied mainly for electron-hole separation below to the 3D excitonic Bohr radius. The behavior of the exciton lateral Stark shift proves the existence of an important correlation between the polarizability and the induced dipole moment.
Resonant Raman scattering in self-assembledGaN∕AlNquantum dots
2006
Self-assembled $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ quantum dots have been investigated by means of Raman scattering. A resonant enhancement of the Raman peaks has been observed when the excitation is tuned above the GaN band-gap energy. The polar mode nature, either quasiconfined or interfacial, has been assigned after comparing with the polar optical modes of spheroidal dots calculated within the framework of the anisotropic dielectric continuum model. The built-in strain of the GaN dots induced a substantial blueshift of the nonpolar ${E}_{2H}$ Raman mode frequency. A theoretical model that analyzes the three-dimensional strain distribution in the quantum dots has been employed …
On the anomalous Stark effect in a thin disc-shaped quantum dot
2010
The effect of a lateral external electric field F on an exciton ground state in an InAs disc-shaped quantum dot has been studied using a variational method within the effective mass approximation. We consider that the radial dimension of the disc is very large compared to its height. This situation leads to separating the excitonic Hamiltonian into two independent parts: the lateral confinement which corresponds to a two-dimensional harmonic oscillator and an infinite square well in the growth direction. Our calculations show that the complete description of the lateral Stark shift requires both the linear and quadratic terms in F which explains that the exciton possess nonzero lateral dipo…
Competition between carrier recombination and tunneling in quantum dots and rings under the action of electric fields
2008
6 páginas, 3 figuras.-- Proceedings of the 7th International Conference on Physics of Light-Matter Coupling in Nanostructures.
Quantum Dots in Magnetic Fields: Phase Diagram and Broken Symmetry at the Maximum-Density-Droplet Edge
1999
Quantum dots in magnetic fields are studied within the current spin-density-functional formalism avoiding any spatial symmetry restrictions of the solutions. We find that the maximum-density droplet reconstructs into states with broken internal symmetry: The Chamon-Wen edge coexists with a modulation of the charge density along the edge. The phase boundaries between the polarization transition, the maximum-density droplet, and its reconstruction are in agreement with recent experimental results.
Spontaneous magnetism of quantum dot lattices.
2003
The magnetism of square lattices of quantum dots with up to 12 electrons per dot is studied using the spin-density functional formalism. At small values of the lattice constant, all lattices are nonmagnetic and gapless. When the lattice constant is increased, the shell structure of the single dots governs the magnetism of the lattice. At closed shells, the lattices are nonmagnetic and have a gap at the Fermi level. At the beginning and at the end of a shell, they become ferromagnetic and stay gapless up to large values of the lattice constant. Antiferromagnetism was observed only at midshell after a band gap was opened.
Tight-Binding Model for Spontaneous Magnetism of Quantum Dot Lattices
2003
We use a simple tight-binding model to study the magnetism of two-dimensional quantum dot lattices with 1 to 12 electrons per dot. The results show that in the middle of an electron shell the lattice favours antiferromagnetism while with nearly empty or full shells ferromagnetism is favoured. The size of the antiferromagnetic region increases with the coordination number of the dot. A one-dimensional dot lattice shows a spin-Peierls transition. The results for a square lattice are in good agreement with density functional calculations of Koskinen et al.
Close packing of clusters: Application toAl100
2003
The lowest energy configurations of close-packed clusters up to N=110 atoms with stacking faults are studied using the Monte Carlo method with Metropolis algorithm. Two types of contact interactions, a pair-potential and a many-atom interaction, are used. Enhanced stability is shown for N=12, 26, 38, 50, 59, 61, 68, 75, 79, 86, 100 and 102, of which only the sizes 38, 75, 79, 86, and 102 are pure FCC clusters, the others having stacking faults. A connection between the model potential and density functional calculations is studied in the case of Al_100. The density functional calculations are consistent with the experimental fact that there exist epitaxially grown FCC clusters starting from…