MODEL CALCULATION OF THE FEMTOSECOND CARRIER DYNAMICS IN AL0.48GA0.52AS

We present a model calculation capable of investigating the dynamics of photoexcited carriers in the Al0.48Ga0.52As indirect gap semiconductor. Nearly resonant excitation at the Gamma point produces low excess energy carriers, so that we use Boltzmann like equations and assume thermalized carrier distributions for each of the conduction valleys. Some aspects of the carrier dynamics are discussed and pump and probe measurements are compared to the calculated saturation bleaching, evidencing a very good agreement between theory and experiment. We obtain a value of 3.5 eV/Angstrom A for the D-Gamma X deformation potential.7663749375

Interacting valence holes in p-type SiGe quantum disks in a magnetic field

The interaction of holes in p-type SiGe quantum disks in a magnetic field is studied. The holes are described by a Luttinger Hamiltonian, with parity replacing spin as a good quantum number. The interaction Hamiltonian separates into charge-charge and parity-parity parts. The effect of parity mediated hole-hole interactions is illustrated by numerical calculations of the energy and capacitance spectra for up to two holes in a quantum disk for parameters corresponding to a SiGe system.5523156941570

Coherent Control of Quantum Dynamics with Sequences of Unitary Phase-Kick Pulses

Coherent optical control schemes exploit the coherence of laser pulses to change the phases of interfering dynamical pathways in order to manipulate dynamical processes. These active control methods are closely related to dynamical decoupling techniques, popularized in the field of Quantum Information. Inspired by Nuclear Magnetic Resonance (NMR) spectroscopy, dynamical decoupling methods apply sequences of unitary operations to modify the interference phenomena responsible for the system dynamics thus also belonging to the general class of coherent control techniques. Here we review related developments in the fields of coherent optical control and dynamical decoupling, with emphasis on control of tunneling and decoherence in general model systems. Considering recent experimental breakthroughs in the demonstration of active control of a variety of systems, we anticipate that the reviewed coherent control scenarios and dynamical decoupling methods should raise significant experimental interest.Comment: 52 pages, 7 figure

Effects of interdot hopping and Coulomb blockade on the thermoelectric properties of serially coupled quantum dots

We have theoretically studied the thermoelectric properties of serially coupled quantum dots (SCQD) embedded in an insulator matrix connected to metallic electrodes. In the framework of Keldysh Green's function technique, the Landauer formula of transmission factor is obtained by using the equation of motion method. Based on such analytical expressions of charge and heat currents, we calculate the electrical conductance, Seebeck coefficient, electron thermal conductance and figure of merit (ZT) of SCQD in the linear response regime. The effects of electron Coulomb interactions on the reduction and enhancement of ZT are analyzed. We demonstrate that ZT is not a monotonic increasing function of interdot electron hopping strength ($t_c$). We also show that in the absence of phonon thermal conductance, SCQD can reach the Carnot efficiency as $t_c$ approaches zero.Comment: corrected some argumenet

Observation of the Smallest Metal Nanotube with Square-cross-section

Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms and helical wires have been produced by the stretching of metal junctions. Here we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation

Interface roughness localization in quantum wells and quantum wires

We studied the effects of interface localization due to microroughness in a sample presenting a quantum well and a quantum wire. We measured the magnetoluminescence at different temperatures and analyzed the results with a model where the average microroughness, the magnetic field, and the excitonic effects are treated within the same level of approximation. We were able to extract a quantitative estimate for the exciton localization due to microroughness. Our results also demonstrate the efficiency of the temperature to detrap excitons from the interface roughness localization. [S0163-1829(98)03439-0].58159876988