Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe effect of the noncentral impurity-matrix interaction upon the thermal expansion and polyamorphism of solid CO-C60 solutions at low temperatures
125
0
0.0
(
0
)
Added by
Alexander Dolbin V.
Publication date
2008
fields
Physics
and research's language is
English
Authors
A.V. Dolbin
Ask ChatGPT about the research
No Arabic abstract
Orientational glasses with CO molecules occupying 26% and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2.5 - 23 K. At temperatures 4 - 6 K the glasses undergo a first-order phase transition which is evident from the hysteresis of the thermal expansion and the maxima in the temperature dependences of the linear thermal expansion coefficients, and the thermalization times of the samples. The effect of the noncentral CO-C60 interaction upon the thermal expansion and the phase transition in these glasses was clarified by comparing the behavior of the properties of the CO-C60 and N2-C60 solutions.
rate research
Read More
In highly doped uncompensated p-type layers within the central part of GaAs/AlGaAs quantum wells at low temperatures we observed an activated behavior of the conductivity with low activation energies (1-3) meV which can not be ascribed to standard mechanisms. We attribute this behavior to the delocalization of hole states near the maximum of the narrow impurity band in the sense of the Anderson transition. Low temperature conduction $epsilon_4$ is supported by an activation of minority carriers - electrons (resulting from a weak compensation by back-ground defects) - from the Fermi level to the band of delocalized states mentioned above. The corresponding behavior can be specified as virtual Anderson transition. Low temperature transport ($<4$ K) exhibits also strong nonlinearity of a breakdown type characterized in particular by S-shaped I-V curve. The nonlinearity is observed in unexpectedly low fields ($<10$ V/cm). Such a behavior can be explained by a simple model implying an impact ionization of the localized states of the minority carriers mentioned above to the band of Anderson-delocalized states.
We report on extended investigation of the thermal transport and acoustical properties on hard carbon samples obtained by pressurization of C60 fullerene. Structural investigations performed by different techniques on the same samples indicate a very inhomogeneous structure at different scales, based on fractal-like amorphous clusters on the micrometer to submillimetre scale, which act as strong acoustic scatterers, and scarce microcrystallites on the nanometer scale. Ultrasonic experiments show a rapid increase in the attenuation with frequency, corresponding to a decrease in the localization length for vibrations. The data give evidence for a crossover from extended phonon excitations to localized fracton excitations. The thermal conductivity is characterized by a monotonous increase versus temperature, power law T^(1.4), for T ranging from 0.1 to 10 K, without any well-defined plateau, and a strictly linear-in-T variation between 20 and 300K. The latter has to be related to the linear-in-T decrease of the sound velocity between 4 and 100 K, both linear regimes being characteristic of disordered or generally aperiodic structures, which can be analysed by the phonon-fracton hopping model developed for fractal and amorphous structures.
Cryogenic rejuvenation in metallic glasses reported in Ketov et al s experiment (Nature(2015)524,200) has attracted much attention, both in experiments and numerical studies. The atomic mechanism of rejuvenation has been conjectured to be related to the heterogeneity of the glassy state, but the quantitative evidence is still elusive. Here we use molecular dynamics simulations of a model metallic glass to investigate the heterogeneity in the local thermal expansion. We then combine the resulting spatial distribution of thermal expansion with a continuum mechanics calculation to infer the internal stresses caused by a thermal cycle. Comparing the internal stress with the local yield stress, we prove that the heterogeneity in thermomechanical response has the potential to trigger local shear transformations, and therefore to induce rejuvenation during a cryogenic thermal cycling.
The kinetics of sorption and subsequent desorption of argon gas by a C60 powder has been investigated in the temperature interval 58-290 K. The temperature dependence of the coefficients of Ar diffusion in fullerite has been obtained using the measured characteristic times of sorption. The diffusion coefficients of Ar decrease monotonically with lowering temperature in the whole range of the investigated temperatures, which corresponds to the thermally activated diffusion of Ar atoms in fullerite. The glass transition in fullerite induces an order-of-magnitude decrease in the activation energy of Ar diffusion in fullerite. Most likely this is because new directions may appear due to the glass transition in which the barriers separating the interstitial voids in the C60 lattice are significantly lower
The electronic structure of a prototype Kondo system, a cobalt impurity in a copper host is calculated with accurate taking into account of correlation effects on the Co atom. Using the recently developed continuous-time QMC technique, it is possible to describe the Kondo resonance with a complete four-index Coulomb interaction matrix. This opens a way for completely first-principle calculations of the Kondo temperature. We have demonstrated that a standard practice of using a truncated Hubbard Hamiltonian to consider the Kondo physics can be quantitatively inadequate.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
