Search results for "mesoscopic"
showing 10 items of 709 documents
Far-infrared laser on quantum dots created by electric-field focusing
2003
The new proposal of a far-infrared laser employing intraband transitions in the system of quantum dots is briefly described. The conditions for inversion of population for electrons in the quantum dot matrix created by an electric-field focusing in narrow GaAs/AlGaAs quantum well are discussed. The laser is planned to be pumped by periodically repeated rapid creation and destruction of the quantum dot matrix allowing for repeated filling of the dot levels with electrons from a quantum well. Some major results of the analysis of the kinetics of the electron-photon system are presented.
Incommensurate phases of a bosonic two-leg ladder under a flux
2016
A boson two--leg ladder in the presence of a synthetic magnetic flux is investigated by means of bosonization techniques and Density Matrix Renormalization Group (DMRG). We follow the quantum phase transition from the commensurate Meissner to the incommensurate vortex phase with increasing flux at different fillings. When the applied flux is $\rho \pi$ and close to it, where $\rho$ is the filling per rung, we find a second incommensuration in the vortex state that affects physical observables such as the momentum distribution, the rung-rung correlation function and the spin-spin and charge-charge static structure factors.
Quantum simulation of the cooperative Jahn-Teller transition in 1D Ion crystals
2012
The Jahn-Teller effect explains distortions and nondegenerate energy levels in molecular and solid-state physics via a coupling of effective spins to collective bosons. Here we propose and theoretically analyze the quantum simulation of a many-body Jahn-Teller model with linear ion crystals subjected to magnetic field gradients. We show that the system undergoes a quantum magnetic structural phase transition which leads to a reordering of particle positions and the formation of a spin-phonon quasicondensate in mesoscopic ion chains.
Multidimensional quantum walks: Diabolical points, optical wave-like propagation, and multipartite entanglement
2013
Quantum walks (QWs) are important for quantum information science, but are becoming also interesting for other fields of research as this simple quantum diffusion model finds analogues in diverse physical systems, optical ones in particular. The experimental capabilities regarding QWs have remarkably increased along recent years and several aspects of QWs are now open to experimental research, multidimensional QWs in particular [1].
Exciton recombination dynamics inInAs∕InPself-assembled quantum wires
2005
In this work we investigate the exciton recombination dynamics in InAs/ InP semiconductor self-assembled quantum wires, by means of continuous wave and time resolved photoluminescence. The continuous wave photoluminescence results seem to indicate that the temperature quenching of the emission band seems to be more probably due to unipolar thermal escape of electrons towards the InP barrier. On the other hand, the analysis of time resolved photoluminescence reveals that the temperature dependence of the radiative and nonradiative recombination times is mainly determined by the dynamics of excitons localized by disorder shigh energy tail of the PL bandd and strongly localized slow energy tai…
Mesoscopic gels at low agarose concentration: perturbation effects of ethanol
1997
Aqueous agarose solutions at low concentrations (0.5 g/liter) were temperature quenched below the spinodal line to form mutually disconnected mesoscopic gels. In the presence of 6% ethanol, these solutions, obtained by quenching at the same temperature depth as in pure water, appear much more fluid, as determined by probe diffusion experiments. We show by static and dynamic light scattering that this can be explained by the solvent-mediated effects of ethanol, leading to a globular shape of mesoscopic agarose gels, rather than to an extended rodlike structure observed in pure water. Our findings show the significant effects of solvent perturbations on particle condensation and, therefore, m…
Phonon Cooling of Nanomechanical Beams with Tunnel Junctions
2009
We demonstrate electronic cooling of 1D phonon modes in suspended nanowires for the first time, using normal-metal-insulator-superconductor (N-I-S) tunnel junctions. Simultaneous cooling of both electrons and phonons to a common temperature was achieved. In comparison with nonsuspended devices, better cooling performance is achieved in the whole operating range of bath temperatures between 0.1-0.7 K. The observed low-temperature thermal transport characteristics are consistent with scattering of ballistic phonons at the nanowire-bulk contact as being the mechanism limiting thermal transport. At the lowest bath temperature of the experiment approximately 100 mK, both phonons and electrons in…
Raman study of strain in GaN/AlN quantum dot multilayered structures
2005
Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm–1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant eff…
Raman Spectroscopy and Low-Temperature Transport Measurements of Individual Single-Walled Carbon Nanotubes with Varying Thickness
2009
We have investigated two metallic and one semiconducting individual single-walled carbon nanotubes (SWNT) and one bundle of two semiconducting nanotubes with a diameter range 1.1−2.9 nm with Raman spectroscopy and low-temperature electric transport measurements. With these two methods, we obtain mutually independent measurements on the basic properties of a specific nanotube. In particular, we obtain data on metallic and semiconducting properties. Evidence of a small band gap for one metallic tube was obtained. For the semiconducting SWNTs with diameters of 2.7−2.9 nm, a special resonance condition was observed which causes an anomalous intensity ratio for the two components of the G-band. …
Solvatochromism Unravels the Emission Mechanism of Carbon Nanodots
2016
High quantum yield, photoluminescence tunability, and sensitivity to the environment are hallmarks that make carbon nanodots interesting for fundamental research and applications. Yet, the underlying electronic transitions behind their bright photoluminescence are strongly debated. Despite carbon-dot interactions with their environment should provide valuable insight into the emitting transitions, they have hardly been studied. Here, we investigate these interactions in a wide range of solvents to elucidate the nature of the electronic transitions. We find remarkable and systematic dependence of the emission energy and kinetics on the characteristics of the solvent, with strong response of …