Quantum Rings in Electromagnetic Fields

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordThis chapter is devoted to optical properties of so-called Aharonov-Bohm quantum rings (quantum rings pierced by a magnetic flux resulting in AharonovBohm oscillations of their electronic spectra) in external electromagnetic fields. It studies two problems. The first problem deals with a single-electron AharonovBohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quanta, a small change in the lateral electric field allows for tuning of the energy levels of the quantum ring into resonance with the microcavity mode, thus providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are discussed for several combinations of the applied magnetic and electric fields

The manifestation of Coulomb gap in photoluminescence of GaAs/AlGaAs quantum wells with positively charged acceptors

We reportresultsofphotoluminescenceandphotoexcitationstudiescarriedoutonGaAs/AlGaAsquantum well structureswithpositivelychargedacceptors.We explaintheobservedspectralpeculiaritiesbyan appearanceoftheCoulombgap.Anotherevidenceofthe CoulombgapisananomalouslylargeStocksshift which hasbeenobservedinourexperiments

Polarization of tunneling-assisted recombination of two-dimensional holes

\u3cp\u3eWe have studied the polarization anisotropy of the radiative recombination of a two-dimensional hole gas (2DHG) confined at the interface of a modulation-doped AlxGa1-xAs/GaAs heterostructure. The observed ''cleaved-side'' luminescence from the heavy-hole ground subband is due to indirect optical transitions in real space and is found to be polarized perpendicular to the plane of the 2DHG. This unexpected behavior is ascribed to the admixture of light-hole states to the heavy-hole ground subband. For increasing in-plane wave vector, the degree of linear polarization decreases due to an enhanced penetration of the heavy-hole states into the bulk GaAs layer. These results can be qualitatively explained by our calculations.\u3c/p\u3

Separate electron-hole confinement in composite InAsyP 1-y/Ga xIn1-xAs quantum wells

Composite double qunatum wells made from materials with a type-II band line-up have been grown to realize separate confinement in real space for electrons and holes. We have observed a substantial blue shift of the lowest energy transition in such composite double quantum wells. The photocurrent measurements demonstrate a linear Stark shift due to the separate confinement in real space for electrons and holes. The charge separation is up to 45 Å in the strain balanced InAs0.42P0.58/Ga0.67In0.33As samples. The experimental results agree very well with calculations in the framework of Bir-Pikus strain Hamiltonian

Dispersion of the electron g factor anisotropy in InAs/InP self-assembled quantum dots

The electron g factor in an ensemble of InAs/InP quantum dots with emission wavelengths around 1.4 μm is measured using time-resolved pump-probe Faraday rotation spectroscopy in different magnetic field orientations. Thereby, we can extend recent single dot photoluminescence measurements significantly towards lower optical transition energies through 0.86 eV. This allows us to obtain detailed insight into the dispersion of the recently discovered g factor anisotropy in these infrared emitting quantum dots. We find with decreasing transition energy over a range of 50 meV a strong enhancement of the g factor difference between magnetic field normal and along the dot growth axis, namely, from 1 to 1.7. We argue that the g factor cannot be solely determined by the confinement energy, but the dot asymmetry underlying this anisotropy therefore has to increase with increasing dot size

Solid-state physics: Spin's lifetime extended

Electrons in semiconductors are subject to forces that make their spins flip. According to new evidence, if an ensemble of spins curls into a helix, the collective spin lifetime can be greatly enhanced