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Laser ablation in liquid (LAL) is important technique used for formation of nanoparticles (NP). The LAL processes cover logarithmically wide range of spatiotemporal scales and is not fully understood. The NP produced by LAL are rather expensive, thus optimization of involved processes is valuable. As the first step to such optimizations more deep understanding is necessary. We employ physical models and computer simulations by thermodynamic, hydrodynamic, and molecular dynamics codes in this direction. Absorbing light metal expanding into transparent solid or liquid dielectrics is considered. We analyze an interplay between diffusion, hydrodynamic instability, and decrease of surface tension down to zero value caused by strong heating and compression transferring matter into state of overcritical fluids. The primary NPs appear during expansion and cooling of diffusion zone when pressure in this zone drops below critical pressure for a metal. Long evolution from the overcritical states to states below a critical point for a metal and down to critical point of liquid and deeply down to surrounding pressure of 1 bar is followed. Conductive heating of liquid from hot metal is significant.

We consider expansion, break off, and flight of 10 nm molybdenum film deposited onto glass support. These events are initiated by action of subpicosecond laser pulse onto film. Approximations for two-temperature equation of state and electron--ion coupling parameter are developed. Heat conduction is unimportant because film is ultrathin and because radius of a laser beam is rather large $\sim 10$ $\mu$m (thus lateral thermal spreading is insignificant at the considered time scale). We use two-temperature one-dimensional hydrodynamic code to follow evolution of laser induced flow. Additional code for treating transmission and reflection of a monochromatic electromagnetic wave is developed. It is applied to describe interference between transmitted and reflected waves in the layered structure appearing thanks to laser induced expansion and separation of a film., Comment: XXXIII International Conference on Equations of State for Matter, Accepted to Jourmal of Physics: Conference Series

The cold curves for energy and pressure of Copper, Iron, and Tantalum were obtained using methods of the density functional theory. We consider hydrostatic and uniaxial deformations in the range from double compression of the initial volume per atom to double stretching. The presence of allotropic transformation from $\alpha$ - phase of Iron to the hexaferrum with the growth of pressure is observed. In the case of hydrostatic deformations we also have obtained analogous cold curves, but with non-zero electronic temperatures in the range up to 5 eV. The similar volume and electronic temperature ranges have been considered recently. The behavior of electronic internal energy, pressure, and density of states was investigated in the volume and temperature ranges called above. The maximum hydrostatic strains and the types of lattice instabilities were theoretically predicted for the considered metals. The influence of high electronic temperature on the electronic heat conductivity and electric resistivity has been provided for d-band metals by the approach based on the solution of Boltzmann kinetic equation in $\tau$-approximation. This data is compared with the results of quantum molecular dynamics for Gold.

There are two types of intrinsic surface states in solids. The first type is formed on the surface of topological insulators. Recently, transport of massless Dirac fermions in the band of "topological" states has been demonstrated. States of the second type were predicted by Tamm and Shockley long ago. They do not have a topological background and are therefore strongly dependent on the properties of the surface. We study the problem of the conductivity of Tamm-Shockley edge states through direct transport experiments. Aharonov-Bohm magneto-oscillations of resistance are found on graphene samples that contain a single nanohole. The effect is explained by the conductivity of the massless Dirac fermions in the edge states cycling around the nanohole. The results demonstrate the deep connection between topological and non-topological edge states in 2D systems of massless Dirac fermions., Comment: Strongly revised version of arXiv:1310.0991: new title, abstract, introduction, conclusions, and updated figures. New corresponding author

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO$_2$ substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of the Fermi level through an equidistant ladder of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions., Comment: 7 pages, 5 figures

The effect of irradiation by 30-keV Ga+ and 35-keV He+ ions (in relatively small doses) on the excitonic reflectivity spectra of single InGaAs/GaAs quantum-well structures is studied. It is found that the irradiation results in decreasing intensity and broadening of the excitonic resonances in the reflectivity spectra for all the doses. It is shown that these changes are not related to a decrease of the exciton transition oscillator strength and, therefore, to the irradiation-induced destruction of the excitonic states, but can be rather ascribed to a common cause, namely, to inhomogeneous broadening of the excitonic resonances proportional to the exposure dose.A tentative model of the irradiation-induced broadening is considered, with the mechanism of the process being a consequence of scat-tering of the 2D excitons by structural defects associated with Ga(In) and As vacancies arising upon collisions of the high-energy ions with regular atoms of the crystal structure. The model is used to compare experimental dependence of efficiency of the Ga+-ion-induced broad-ening on distance of the quantum well from the irradiated surface with a similar dependence calculated using the Monte-Carlo technique. A discrepancy between the results of simulation and experimental data is discussed.

Graphene is a stable single atomic layer material exhibiting two-dimensional electron gas of massless Dirac fermions of high mobility. One of the intriguing properties of graphene is a possibility of realization of the Tamm-type edge states. These states differ from the usual surface states caused by defects, impurities and other imperfections at the edge of the system, as well as they differ from the magnetic edge states caused by skipping cyclotron orbits. The Tamm states result from breaking of periodic crystal potential at the edge, they can exist even at zero magnetic field and form a conducting band. Until recently those states have been observed in graphene only by local STM technique and there were no direct experiments on their contribution to transport measurements. Here we present the experiments on Aharonov-Bohm (AB) oscillations of resistance in a single-nanohole graphite and graphene structures, it indicates the presence of conducting edge states cycling around nanohole. An estimation show the penetration depth of the edge states to be as short as about 2 nm. The oscillations persist up to temperature T=115 K and the T-range of their existence increases with a decrease of the nanohole diameter. The proposed mechanism of the AB oscillations based on the resonant intervalley backscattering of the Dirac fermions by the nanohole via the Tamm states. The experimental results are consistent with such a scenario. Our findings show a way towards interference devices operating at high temperatures on the edge states in graphene, Comment: 11 pages, 4 figures

The effect of geometrical shape of eroding absolutely rigid particles on the threshold rate of failure has been studied. The Shtaerman-Kilchevsky theory of quasi-static blunt impact, which generalizes Hertz's classical impact theory, is used for modeling the frictionless contact interaction of an axially-symmetric particle with an elastic half-space. The incubation time fracture criterion is applied for predicting surface fracture. It is shown that there exist a critical value of the particle shape parameter such that for all its lower values the fracture energy possesses a nonzero minimal value., Comment: 13 pages, 3 figures

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration $\tau_L$ is shorter than acoustic relaxation time $t_s$ is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse.

This work was firstly published in 1986 \cite{we}. No real two-dimensional object with the zero-gap quasi-relativistic spectrum was known in that time. Such an object is well known now: this is graphene. That is why we decided to present it again as a e-print in a slightly modified form. A density of the two-dimensional zero-gap electronic states at the quantizing magnetic field in the presence the Gaussian random potential has been calculated. The problem is reduced to zero-dimensional spinor field theory using the holomorphic supersymmetric representation. The calculated density of states in the case of the mass perturbation has a delta function peak in the Dirac point.This peak smears due to the potential perturbation.

The theory and experiments concerned with the electron-ion thermal relaxation and melting of overheated crystal lattice constitute the subject of this paper. The physical model includes two-temperature equation of state, many-body interatomic potential, the electron-ion energy exchange, electron thermal conductivity, and optical properties of solid, liquid, and two phase solid-liquid mixture. Two-temperature hydrodynamics and molecular dynamics codes are used. An experimental setup with pump-probe technique is used to follow evolution of an irradiated target with a short time step 100 fs between the probe femtosecond laser pulses. Accuracy of measurements of reflection coefficient and phase of reflected probe light are ~1% and $\sim 1\un{nm}$, respectively. It is found that, {\it firstly}, the electron-electron collisions make a minor contribution to a light absorbtion in solid Al at moderate intensities; {\it secondly}, the phase shift of a reflected probe results from heating of ion subsystem and kinetics of melting of Al crystal during $0

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress., Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos corrected