Hole spin relaxation in InAs/GaAs quantum dot molecules

We calculate the spin-orbit induced hole spin relaxation between Zeeman sublevels of vertically stacked InAs quantum dots. The widely used Luttinger-Kohn Hamiltonian, which considers coupling of heavy- and light-holes, reveals that hole spin lifetimes (T1) of molecular states significantly exceed those of single quantum dot states. However, this effect can be overcome when cubic Dresselhaus spin-orbit interaction is strong. Misalignment of the dots along the stacking direction is also found to be an important source of spin relaxation.

Magnetic field implementation in multiband k⋅p Hamiltonians of holes in semiconductor heterostructures

We propose an implementation of external homogeneous magnetic fields in k⋅p Hamiltonians for holes in heterostructures, in which we make use of the minimal coupling prior to introducing the envelope function approximation. Illustrative calculations for holes in InGaAs quantum dot molecules show that the proposed Hamiltonian outperforms the standard Luttinger model (Luttinger 1956 Phys. Rev. 102 1030) describing the experimentally observed magnetic response. The present implementation culminates our previous proposal (Planelles et al 2010 Phys. Rev. B 82 155307).

Valence band mixing of cubic GaN/AlN quantum dots

We study the spin purity of the hole ground state in nearly axially symmetric GaN/AlN quantum dots (QDs). To this end, we develop a six-band Burt-Foreman Hamiltonian describing the valence band structure of zinc blende nanostructures with cylindrical symmetry and calculate the effects of eccentricity variationally. We show that the aspect ratio is a key factor for spin purity. In typical QDs with small aspect ratio the ground state is essentially a heavy hole (HH) whose spin purity is even higher than that of InGaAs QDs of similar sizes. When the aspect ratio increases, mixing with light-hole (LH) and split-off (SO) subbands becomes important and, additionally, the ground state becomes sensitive to QD anisotropy, which further enhances the mixing. We finally show that, despite the large GaN hole effective mass, an efficient magnetic modulation is feasible in QDs with aspect ratio ~1, which can be used to modify the ground state symmetry and hence the optical spectrum properties.

Dielectric confinement of excitons in type-I and type-II semiconductor nanorods

We theoretically study the effect of the dielectric environment on the exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that insulating environments enhance the exciton recombination rate and blueshift the emission peak by tens of meV. These effects are particularly pronounced for type-II nanorods. In these structures, the dielectric confinement may even modify the spatial distribution of the electron and hole charges. A critical electric field is required to separate electrons from holes, whose value increases with the insulating strength of the surroundings.

Correlation in narrow nanorods: a variational potential-configuration interaction scheme

Full configuration interaction calculations for two electrons in narrow semiconductor nanorods are carried out employing different orbital basis sets. It is shown that the usual configurations built from single-particle states cannot yield a correct singlet-triplet energetic order regardless of the basis size, as they miss the correlation energy. Mean-field optimized orbitals partially correct this drawback. A new approach is introduced, based on a simple variational procedure, which yields robust results.

Antibonding ground states in InAs quantum-dot molecules

Coherent tunneling between two InAs quantum dots forms delocalized molecular states. Using magnetophotoluminescence spectroscopy we show that when holes tunnel through a thin barrier, the lowest energy molecular state has bonding orbital character. However, as the thickness of the barrier increases, the molecular ground state changes character from a bonding orbital to an antibonding orbital, confirming recent theoretical predictions. We explain how the spin-orbit interaction causes this counterintuitive reversal by using a four-band k.p model and atomistic calculations that account for strain.