Analytical approximations of the Lindhard equations describing radiation effects

Starting from the general Lindhard theory describing the partition of particles energy in materials between ionisation and displacements, analytical approximate solutions have been derived, for media containing one and more atomic species, for particles identical and different to the medium ones. Particular cases, and the limits of these equations at very high energies are discussed.Comment: 10 pages, 5 figures, latex2e, submitted to Nucl. Instr. Meth. in Phys. Res.

Coherent Neutral Current Neutrino-Nucleus Scattering at a Spallation Source; a Valuable Experimental Probe

The coherent contribution of all neutrons in neutrino nucleus scattering due to the neutral current is examined considering the Spallation Neutron Source (SNS) as a source of neutrinos. SNS is a prolific pulsed source of electron and muon neutrinos as well as muon antineutrinos.Comment: 15 LaTex pages, 14 figures, 3 Table

Dispersion in a relativistic degenerate electron gas

Relativistic effects on dispersion in a degenerate electron gas are discussed by comparing known response functions derived relativistically (by Jancovici) and nonrelativistically (by Lindhard). The main distinguishing feature is one-photon pair creation, which leads to logarithmic singularities in the response functions. Dispersion curves for longitudinal waves have a similar tongue-like appearance in the relativistic and nonrelativistic case, with the main relativistic effects being on the Fermi speed and the cutoff frequency. For transverse waves the nonrelativistic treatment has a nonphysical feature near the cutoff frequency for large Fermi momenta, and this is attributed to an incorrect treatment of the electron spin. We find (with two important provisos) that one-photon pair creation is allowed in superdense plasmas, implying relatively strong coupling between transverse waves and pair creation.Comment: 17 pages, 9 figures. Submitted to Physical Review

Energy losses of fast heavy-ion projectiles in dense hydrogen plasmas

It has been recently shown that the Bethe-Larkin formula for the energy losses of fast heavy-ion projectiles in dense hydrogen plasmas is corrected by the electron-ion correlations [Phys. Rev. Lett. \textbf{101}, 075002 (2008)]. We report numerical estimates of this correction based on the values of $g_{ei}(0)$ obtained by numerical simulations in [Phys. Rev. E \textbf{61}, 3470 (2000)]. We also extend this result to the case of projectiles with dicluster charge distribution. We show that the experimental visibility of the electron-ion correlation correction is enhanced in the case of dicluster projectiles with randomly orientated charge centers. Although we consider here the hydrogen plasmas to make the effect physically more clear, the generalization to multispecies plasmas is straightforward.Comment: 5 pages, 1 figure. International Conference on Strongly Coupled Coulomb Systems 2008, Camerino (Italy). To appear in J. Phys.

Polarizational stopping power of heavy-ion diclusters in two-dimensional electron liquids

The in-plane polarizational stopping power of heavy-ion diclusters in a two-dimensional strongly coupled electron liquid is studied. Analytical expressions for the stopping power of both fast and slow projectiles are derived. To go beyond the random-phase approximation we make use of the inverse dielectric function obtained by means of the method of moments and some recent analytical expressions for the static local-field correction factor.Comment: 9 pages, 5 figures. Published in Physical Review B http://link.aps.org/abstract/PRB/v75/e11510

Phase transition and phase diagram at a general filling in the spinless one-dimensional Holstein Model

Among the mechanisms for lattice structural deformation, the electron-phonon interaction mediated Peierls charge-density-wave (CDW) instability in single band low-dimensional systems is perhaps the most ubiquitous. The standard mean-field picture predicts that the CDW transition occurs at all fillings and all values of the electron-phonon coupling $g$ and the adiabaticity parameter $t/\omega_0$. Here, we correct the mean-field expression for the Peierls instability condition by showing that the non-interacting static susceptibility, at twice the Fermi momentum, should be replaced by the dynamic one. We derive the Luttinger liquid (LL) to CDW transition condition, {\it exact to second order in a novel blocked perturbative approach}, for the spinless one-dimensional Holstein model in the adiabatic regime. The small parameter is the ratio $g \omega_0/t$. We present the phase diagram at non-half-filling by obtaining the surprising result that the CDW occurs in a more restrictive region of a two parameter ($g^2 \omega_0/t$ and $t/\omega_0$) space than at half-filling.Comment: Made changes in the appendices and also in notatio

Plasmon-assisted electron-electron collisions at metallic surfaces

We present a theoretical treatment for the ejection of a secondary electron from a clean metallic surface induced by the impact of a fast primary electron. Assuming a direct scattering between the incident, primary electron and the electron in a metal, we calculate the electron-pair energy distributions at the surfaces of Al and Be. Different models for the screening of the electron-electron interaction are examined and the footprints of the surface and the bulk plasmon modes are determined and analyzed. The formulated theoretical approach is compared with the available experimental data on the electron-pair emission from Al.Comment: 30 pages, 9 figure

van der Waals density functionals built upon the electron-gas tradition: Facing the challenge of competing interactions

The theoretical description of sparse matter attracts much interest, in particular for those ground-state properties that can be described by density functional theory (DFT). One proposed approach, the van der Waals density functional (vdW-DF) method, rests on strong physical foundations and offers simple yet accurate and robust functionals. A very recent functional within this method called vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412] stands out in its attempt to use an exchange energy derived from the same plasmon-based theory from which the nonlocal correlation energy was derived. Encouraged by its good performance for solids, layered materials, and aromatic molecules, we apply it to several systems that are characterized by competing interactions. These include the ferroelectric response in PbTiO$_3$, the adsorption of small molecules within metal-organic frameworks (MOFs), the graphite/diamond phase transition, and the adsorption of an aromatic-molecule on the Ag(111) surface. Our results indicate that vdW-DF-cx is overall well suited to tackle these challenging systems. In addition to being a competitive density functional for sparse matter, the vdW-DF-cx construction presents a more robust general purpose functional that could be applied to a range of materials problems with a variety of competing interactions

The influence of initial impurities and irradiation conditions on defect production and annealing in silicon for particle detectors

Silicon detectors in particle physics experiments at the new accelerators or in space missions for physics goals will be exposed to extreme radiation conditions. The principal obstacles to long-term operation in these environments are the changes in detector parameters, consequence of the modifications in material properties after irradiation. The phenomenological model developed in the present paper is able to explain quantitatively, without free parameters, the production of primary defects in silicon after particle irradiation and their evolution toward equilibrium, for a large range of generation rates of primary defects. Vacancy-interstitial annihilation, interstitial migration to sinks, divacancy and vacancy-impurity complex (VP, VO, V2O, CiOi and CiCs) formation are taken into account. The effects of different initial impurity concentrations of phosphorus, oxygen and carbon, as well as of irradiation conditions are systematically studied. The correlation between the rate of defect production, the temperature and the time evolution of defect concentrations is also investigated.Comment: 14 pages, 8 figures, submitted to Nucl. Instrum. Meth. Phys. Res.

Shielding of a moving test charge in a quantum plasma

The linearized potential of a moving test charge in a one-component fully degenerate fermion plasma is studied using the Lindhard dielectric function. The motion is found to greatly enhance the Friedel oscillations behind the charge, especially for velocities larger than a half of the Fermi velocity, in which case the asymptotic behavior of their amplitude changes from 1/r^3 to 1/r^2.5. In the absence of the quantum recoil (tunneling) the potential reduces to a form similar to that in a classical Maxwellian plasma, with a difference being that the plasma oscillations behind the charge at velocities larger than the Fermi velocity are not Landau-damped.Comment: 9 pages, 11 figures. v3: Fixed typo, updated abstrac