V. I. Kozub

Ioffe-Regel criterion and diffusion of vibrations in random lattices

We consider diffusion of vibrations in 3d harmonic lattices with strong force-constant disorder. Above some frequency w_IR, corresponding to the Ioffe-Regel crossover, notion of phonons becomes ill defined. They cannot propagate through the system and transfer energy. Nevertheless most of the vibrations in this range are not localized. We show that they are similar to diffusons introduced by Allen, Feldman et al., Phil. Mag. B 79, 1715 (1999) to describe heat transport in glasses. The crossover frequency w_IR is close to the position of the boson peak. Changing strength of disorder we can vary w_IR from zero value (when rigidity is zero and there are no phonons in the lattice) up to a typical frequency in the system. Above w_IR the energy in the lattice is transferred by means of diffusion of vibrational excitations. We calculated the diffusivity of the modes D(w) using both the direct numerical solution of Newton equations and the formula of Edwards and Thouless. It is nearly a constant above w_IR and goes to zero at the localization threshold. We show that apart from the diffusion of energy, the diffusion of particle displacements in the lattice takes place as well. Above w_IR a displacement structure factor S(q,w) coincides well with a structure factor of random walk on the lattice. As a result the vibrational line width Gamma(q)=D_u q^2 where D_u is a diffusion coefficient of particle displacements. Our findings may have important consequence for the interpretation of experimental data on inelastic x-ray scattering and mechanisms of heat transfer in glasses.

Many electron theory of1∕fnoise in hopping conductivity

We show that

Electron transport in monodisperse metal nanostructures

1∕f

Anomalous electron transport in doped uncompensated p-GaAs/AlGaAs quantum wells: evidence of virtual Anderson transition

noise in the variable-range hopping regime is related to transitions of many-electrons clusters (fluctuators) between two almost-degenerate states. Giant fluctuation times necessary for

Low-temperature hopping conduction over the upper Hubbard band in p-GaAs/AlGaAs multilayered structures

1∕f

Structure and transport properties of nanocarbon films prepared by sublimation on a 6H-SiC surface

noise are provided by a slow rate of simultaneous tunneling of many localized electrons and by large activation barriers for their consecutive rearrangements. The Hooge constant steeply grows with decreasing temperature because it is easier to find a slow fluctuator at lower temperatures. Our conclusions qualitatively agree with the low-temperature observations of

Interference mechanism of magnetoresistance in variable-range hopping conduction: The effect of paramagnetic electron spins and continuous spectrum of scatterer energies

1∕f

Transition from strong to weak localization in the split-off impurity band in two-dimensional p-GaAs/AlGaAs structures

noise in

Suppression of the Virtual Anderson Transition in the Impurity Band of Doped Quantum Well Structures

p

Metal-insulator transition in n-3C-SiC epitaxial films

-type silicon and GaAs.