Phenomena In Quantum Dots Research Articles

Random-hopping approach to fluctuation phenomena in quantum dots with chiral symmetry.

We propose a numerical approach to study mesoscopic fluctuations in quantum dots with chiral symmetry. Our method involves applying the random-hopping model to a tight-binding Hamiltonian, allowing us to calculate the conductance and shot-noise power distributions for systems belonging to the three chiral symmetry classes of random matrix theory. Furthermore, we demonstrate that the spectral fluctuations of quantum dots belonging to the Wigner-Dyson symmetry classes of random matrix theory can be obtained by applying the random-hopping model to a scattering region that was originally integrable, thus bypassing the need to use the boundaries of chaotic billiards.

The Influence of Photoinduced Processes on a Quantum Dot Surface on the Electron Transfer Efficiency in TiO2 Nanoparticle/Quantum Dot Structures

The influence of photoinduced processes occurring on the surfaces of CdSe/ZnS quantum dots is considered in relation to the functional characteristics of hybrid TiO2 nanostructure/quantum dot systems. Preirradiation of quantum dots is shown to achieve a threefold increase in electron transfer efficiency within these structures. Photoinduced processes are found to impact both the efficiency of nonradiative phenomena in quantum dots and the electron transfer in the indicated systems.

On the Absence of Detectable Carrier Multiplication in a Transient Absorption Study of InAs/CdSe/ZnSe Core/Shell1/Shell2 Quantum Dots

Tunable femtosecond pump-near IR probe measurements on InAs/CdSe/ZnSe core/shell1/shell2 nanocrystal quantum dots were conducted to quantify spontaneous carrier multiplication previously reported in this system. Experimental conditions were chosen to eliminate the need for determining absolute wavelength dependent cross sections of the nanocrystals and allow direct comparison of band edge absorption bleach kinetics for different excitation energies up to 3.7 times the band gap. Results for two sample sizes show no signs of carrier multiplication within that range. This result is discussed in light of reports describing occurrence of this novel phenomenon in quantum dots based on this as well as numerous other semiconductor materials.

Influence of many-particle interactions on slow light phenomena in quantum dots

We investigate the impact of many-particle interactions on group-velocity slowdown achieved via Electromagnetically Induced Transparency (EIT) in quantum dots. Using a ladder scheme we find in the steady-state an increase in maximum slow-down as compared to the non-interacting case, which can be attributed to Coulomb interaction effects. The necessary pump power at which maximum slow down is obtained EIT remains, however.

Kondo resonance in a single-molecule transistor.

When an individual molecule, nanocrystal, nanotube or lithographically defined quantum dot is attached to metallic electrodes via tunnel barriers, electron transport is dominated by single-electron charging and energy-level quantization. As the coupling to the electrodes increases, higher-order tunnelling and correlated electron motion give rise to new phenomena, including the Kondo resonance. To date, all of the studies of Kondo phenomena in quantum dots have been performed on systems where precise control over the spin degrees of freedom is difficult. Molecules incorporating transition-metal atoms provide powerful new systems in this regard, because the spin and orbital degrees of freedom can be controlled through well-defined chemistry. Here we report the observation of the Kondo effect in single-molecule transistors, where an individual divanadium molecule serves as a spin impurity. We find that the Kondo resonance can be tuned reversibly using the gate voltage to alter the charge and spin state of the molecule. The resonance persists at temperatures up to 30 K and when the energy separation between the molecular state and the Fermi level of the metal exceeds 100 meV.

Quantum chaos and transport phenomena in quantum dots

This paper discusses some of the issues related to quantum dots that were raised during the first session on transport phenomena at the Nobel Symposium.

The statistical theory of quantum dots

A quantum dot is a sub-micron-scale conducting device containing up to several thousand electrons. Transport through a quantum dot at low temperatures is a quantum-coherent process. This review focuses on dots in which the electron's dynamics are chaotic or diffusive, giving rise to statistical properties that reflect the interplay between one-body chaos, quantum interference, and electron-electron interactions. The conductance through such dots displays mesoscopic fluctuations as a function of gate voltage, magnetic field, and shape deformation. The techniques used to describe these fluctuations include semiclassical methods, random-matrix theory, and the supersymmetric nonlinear \ensuremath{\sigma} model. In open dots, the approximation of noninteracting quasiparticles is justified, and electron-electron interactions contribute indirectly through their effect on the dephasing time at finite temperature. In almost-closed dots, where conductance occurs by tunneling, the charge on the dot is quantized, and electron-electron interactions play an important role. Transport is dominated by Coulomb blockade, leading to peaks in the conductance that at low temperatures provide information on the dot's ground-state properties. Several statistical signatures of electron-electron interactions have been identified, most notably in the dot's addition spectrum. The dot's spin, determined partly by exchange interactions, can also influence the fluctuation properties of the conductance. Other mesoscopic phenomena in quantum dots that are affected by the charging energy include the fluctuations of the cotunneling conductance and mesoscopic Coulomb blockade.