V. I. Grishaev

Effect of defects on the quasiparticle spectra of graphite and graphene

It is shown that in graphite the spectral density of phonons polarized along the c axis has a V shaped feature similar to the so-called Dirac singularity characteristic of the electron density of states in graphene. The formation of quasilocal states, which increase the occupation of the quasiparticle levels near this feature, is analyzed from a unified standpoint for the phonon spectrum of metal-intercalated graphite and the electronic spectrum of graphene with vacancies. It is determined that in the electronic spectrum of graphene with an isolated vacancy quasilocal states are characteristic only of atoms belonging to the sublattice that does not contain this vacancy.

Ioffe–Regel’ crossover and boson peaks in disordered solid solutions and similar anomalies in heterogeneous crystalline structures

Low-frequency features of the phonon spectra of disordered solid solutions and heterogeneous crystalline structures are analyzed at the microscopic level. It is shown that boson-peak type excitations can arise in disordered solid solutions whose sites have only translational degrees of freedom. Thus it is established that such excitations appear mainly because of the additional positional dispersion of sound waves which is due to the disordering. The influence of boson-peak excitations on the low-temperature specific heat is investigated. It is found that in a number of cases the specific heat is more sensitive to excitations of this kind than the low-frequency density of states is. It is shown that anomalies similar to Ioffe–Regel’ crossover and boson peaks can also arise in disordered heterogeneous crystalline structures with a complicated lattice.

Vibrational dynamic and thermodynamic characteristics of metal–hydrogen superlattices

The phonon spectra and vibrational thermodynamic characteristics of Pd–H superlattices are investigated. Our calculations show that the neutron scattering and calorimetric data are consistent with one another and make it possible to explain for such systems the atomic mean-square amplitudes and the correlations between them.

Evolution of discrete local levels into an impurity band in solidified inert gas solution

The density of states g(ω) of disordered solutions of solidified inert gases are calculated using the Jacobian matrix method. The transformation of a discrete vibrational level into an impurity band at a growing concentration of light impurity atoms is investigated. It is shown that a 1-10% change in the impurity concentration leads to smearing the local discrete level into an impurity band. As this occurs, additional resonance levels appear which carry important information about the impurity-impurity and impurity-basic lattice force interactions in such solutions.

Oscillations localized near an interface in the strongly anisotropic layered crystal

Abstract The spectrum of oscillations localized near an interface between two identical infinite layered crystals is studied. It is shown that some important characteristics of oscillations polarized normally to the layers in layered crystals are almost completely defined by the value of interatomic anisotropy. Quasi-one-dimensional character of oscillations localized near an interface and polarized normally to it is demonstrated.

On the conditions for the existence of 1D magnetic solitons with frequency characteristics falling in the continuous spectrum

Solutions of a modified (with higher-order dispersion taken into account) sine-Gordon equation in the form of a double soliton (4π kink) and a pair of spatially separated bound kinks are investigated. An analytical condition for the absence of radiation from the soliton at large distances is formulated. The previous finding of the existence of a discrete set of nonradiative composite solitons is confirmed. The physical meaning of this result is that at certain distances between kinks the radiation generated by one of the kinks completely quenches the field of the other kink outside the soliton as a result of ordinary interference of waves in antiphase.

Phonon heat capacity of graphene nanofilms and nanotubes

Based on calculations conducted on a microscopic level, the phonon heat capacity of ultrathin graphene nanofilms such as bigraphene and trigraphene, and single-wall graphene nanotubes, is quantitatively described. The nature of the flexural stiffness of graphene monolayers is analyzed, and the temperature intervals at which the shape of the temperature dependence of heat capacity is determined by contributions made by flexural vibrations are identified. The contribution to the phonon heat capacity derived from graphene nanotube flexural waves that propagate along the surface thereof is analyzed, as are the bending vibrations of the tube as a whole one-dimensional object, and the contribution from torsional vibrations.

Specific features of the transformation of local levels into an impurity band of Ag1−p Al p disordered solid solutions

The phonon densities of states in disordered solid solutions of aluminum in silver are determined using the Jacobi matrix method. The transformation of discrete vibrational levels (local vibrational modes) into an impurity band with increasing concentration of impurity atoms is investigated. The formation of discrete vibrational levels is associated with the presence of individual aluminum impurity atoms in the lattice. It is demonstrated that, at relatively low (approximately 5–15%) aluminum concentrations, the broadening of the main local level is accompanied by the appearance of additional resonance peaks, which contain important information on the interatomic interactions in these solid solutions.

Oscillatory Spectra of Surface Atoms in Layered Crystal (Quasi-1D Behavior)

Vibrations localized near the surface have been analyzed by the Jacobian matrix method taking into account discreteness of the lattice. It has been shown that localized surface vibrations in layered crystals with the complex lattice have quasi-one-dimensional character and their properties are described by exact solutions obtained in the framework of the one-dimensional model.