Search results for "Condensed Matter::Superconductivity"
showing 10 items of 632 documents
Investigations of the emission properties of single CdS-nanocrystallites
1997
Semiconductor nanocrystallites (NCs) with a radius in the range of the bulk exciton radius exhibit a strong quantum size effect. We investigated CdS-NCs, that were spin coated on a glass cover slip, with a low temperature confocal microscope. At low coverage we could image the fluorescence light from single NCs. The typical emission spectra of single NCs show four peaks. Besides the main peak related to near bandgap recombination, up to two LO-phonon satellites and one blue shifted peak were observed. It could be shown that the absorption can be polarization dependent. From the images as well as from the intensity autocorrelation function it could be concluded that the fluorescence emission…
Engineering thermal conductance using a two-dimensional phononic crystal
2014
Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature…
Theory and Simulations of Friction between Flat Surfaces Lubricated by Submonolayers
2001
Recent simulations suggest that wearless friction between two solid surfaces can only be obtained if the two surfaces are commensurate or if they are lubricated by a film. Some simple theoretical arguments are given why the presence of a submonolayer film between two solids leads to friction. Possible implications of the symmetry of the confining walls on the tribological properties of the system are then investigated in the presence of a thin film by means of molecular dynamics simulation. Erratic stick-slip motion of the incommensurate system and oscillating friction forces for the commensurate system in the sliding regime are observed.
Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound
2000
Crystal engineering--the planning and construction of crystalline supramolecular architectures from modular building blocks--permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this…
Ab initio simulations on charged interstitial oxygen migration in corundum
2018
We have performed this work within the framework of the EUROfusion Consortium receiving funding from the European grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Authors thank R. Vila, A.I. Popov, A. Luchshik and R.A. Evarestov for fruitful discussions. To carry out large-scale calculations, we have used the HPC supercomputer at Stuttgart University (Germany)
Luminescence Properties of ZnO Nanocrystals and Ceramics
2008
The luminescence excitation spectra, luminescence spectra and the nanosecond-scale decay kinetics were studied. The ZnO and ZnO:Al nanopowders were prepared by vaporization-condensation in a solar furnace using different raw powders: commercial, hydrothermal and those obtained by plasma synthesis. Exciton-phonon as well as exciton-exciton interaction processes in nanopowders, a bulk crystal and ZnO ceramics were studied and compared. The fast decay and low afterglow intensity of ZnO nanopowders and ceramics support these materials for scintillators.
Comparative study of electrical behavior and phase transitions in pure and chromium doped α-LiIO3single crystals
1999
Abstract The polymorphic phase transitions of undoped and chromium doped α-LiIO3 crystals have been investigated by means of DTA experiments at slow heating rates and electrical measurements vs temperature and frequency. Upon heating the well known α ⇔ γ ⇒ β sequence appears to be influenced by the sample's morphology, acidity of the growing solution and doping. Dielectric response at room temperature is close to the type “superposition of d.c. ionic conductivity and dipolar response”. We describe the thermal behavior of conductivity along the c polar axis at three frequencies. Electrical measurements also highlight a higher value of ionic conductivity and a less destructive transition for …
Transient and stable color centers in neutron irradiated MgO
2008
Abstract The transient absorption and luminescence induced by the pulsed electron beam have been investigated in the MgO single crystal containing transition metal ion (Cr, Mn, Fe) impurities and preliminary irradiated by the fast neutrons. It is supposed that the different behavior of the absorption spectra of the MgO samples preliminary irradiated by the different fast neutron fluence is connected with the destruction of the hole centers and with the creation of interstitial protons and the formation of the microphase Mg(OH)2. We assume that the luminescence band at ∼3.2 eV is connected with F+ color centers.
Induced optical absorption and ITS relaxation in LiNbO3
1999
Abstract Electron pulse induced absorption spectra and their decay kinetics have been investigated in LiNbO3 crystals with various Li/Nb ratios rasnging from congruent to stoichiometric composition. It is shown that the absorption spectra, the optical density and the decay kinetics depend on the Li/Nb ratio. The rising front of the induced absorption is too fast to be resolved. The room temperature decay, characterized by the half-lifetime Δt, is faster in the stoichiometric crystal (∼ 750 ns) than in the congrruent crystal (∼ 3.5 μs).
The MESA Experimental Program: A Laboratory for Precision Physics with Electron Scattering at Low Energy
2021
A rich experimental program is currently being prepared at a new laboratory for high-intensity electron scattering at the Mainz Energy recovering Superconducting Accelerator (MESA). The physics pro...