Strain-induced g-factor tuning in single InGaAs/GaAs quantum dots

The tunability of the exciton g factor in InGaAs quantum dots using compressive biaxial stress applied by piezoelectric actuators is investigated. We find a clear relation between the exciton g factor and the applied stress. A linear decrease of the g factor with compressive biaxial strain is observed consistently in all investigated dots. A connection is established between the response of the exciton g factor to the voltage applied to the piezoelectric actuator and the response of the quantum dot emission energy. We employ a numerical model based on eight-band k⋅p theory to calculate the exciton g factor of a typical dot as a function of strain and a good agreement with our experiments is found. Our calculations reveal that the change in exciton g factor is dominated by the contribution of the valence band and originates from increased heavy hole light hole splitting when applying external stress

Active tuning of the g -tensor in InGaAs/GaAs quantum dots via strain

\u3cp\u3eDynamic control over the full g-tensor in individual InGaAs/GaAs self-assembled quantum dots is achieved by inducing external strain via a piezoelectric actuator. The full g-tensor is obtained by measuring in different geometries with different angles between an externally applied magnetic field and the quantum dot growth axes. A large decrease in the out-of-plane hole g-factor with strain is observed, whereas the other components are found to be less sensitive. To further investigate this, a numerical model based on eight-band k.p-theory is used and an excellent agreement with the experimental results is established, both qualitatively and quantitatively. Furthermore, the calculations reveal the origin of the observed large change in the out-of-plane hole g-factor to be the increase in heavy-hole light-hole splitting under compressive stress.\u3c/p\u3

Self-organized quantum rings:physical characterization and theoretical modeling

\u3cp\u3eAn adequate modeling of self-organized quantum rings is possible only on the basis of the modern characterization of those nanostructures. We discuss an atomic-scale analysis of the indium distribution in self-organized InGaAs quantum rings (QRs). The analysis of the shape, size and composition of self-organized InGaAs QRs at the atomic scale reveals that AFM only shows the material coming out of the QDs during the QR formation. The remaining QD material, as observed by Cross-Sectional Scanning Tunneling Microscopy (X-STM), shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and determines the observed ring-like electronic properties of QR structures. A theoretical model of the geometry and materials properties of the self-organized QRs is developed on that basis and the magnetization is calculated as a function of the applied magnetic field. Although the real QR shape differs strongly from an idealized circular-symmetric open-ring structure, Aharonov-Bohm-type oscillations in the magnetization have been predicted to survive. They have been observed using the torsion magnetometry on InGaAs QRs. Large magnetic moments of QRs are shown to originate from dissipationless circulating currents in the ground state of an electron or hole in the QR. Examples of prospective applications of QRs are presented that do and do not utilize the topological properties of QRs.\u3c/p\u3