No Arabic abstract
We describe arrangements of ions capable of producing short-range attractive interactions between pairs of charged colloidal spheres in the low temperature strongly correlated limit. For particles of radius $R$ with bare charge $Z$ and comparable absorbed charge $-N$ ($N sim Z$), the correlations contribution to the spheres self-energy scales as $N^{3/2}/R$, and as $N/R$ for the interaction energy between two touching spheres. We show that the re-arrangement of charges due to polarization plays an insignificant role in the nature and magnitude of the interaction.
The effective force between two parallel DNA molecules is calculated as a function of their mutual separation for different valencies of counter- and salt ions and different salt concentrations. Computer simulations of the primitive model are used and the shape of the DNA molecules is accurately modelled using different geometrical shapes. We find that multivalent ions induce a significant attraction between the DNA molecules whose strength can be tuned by the averaged valency of the ions. The physical origin of the attraction is traced back either to electrostatics or to entropic contributions. For multivalent counter- and monovalent salt ions, we find a salt-induced stabilization effect: the force is first attractive but gets repulsive for increasing salt concentration. Furthermore, we show that the multivalent-ion-induced attraction does not necessarily correlate with DNA overcharging.
Strongly correlated systems of fermions have a number of exciting collective properties. Among them, the creation of a lattice that is occupied by doublons, i.e. two quantum particles with opposite spins, offers interesting electronic properties. In the past a variety of methods have been proposed to control doublon formation, both, spatially and temporally. Here, a novel mechanism is proposed and verified by exact diagonalization and nonequilibrium Green functions simulations---fermionic doublon creation by the impact of energetic ions. We report the formation of a nonequilibrium steady state with homogeneous doublon distribution. The effect should be observable in strongly correlated solids in contact with a high-pressure plasma and in fermionic atoms in optical lattices.
Using molecular dynamics simulations we examine the effective interactions between two like-charged rods as a function of angle and separation. In particular, we determine how the competing electrostatic repulsions and multivalent-ion-induced attractions depend upon concentrations of simple and multivalent salt. We find that with increasing multivalent salt the stable configuration of two rods evolves from isolated rods to aggregated perpendicular rods to aggregated parallel rods; at sufficiently high concentration, additional multivalent salt reduces the attraction. Monovalent salt enhances the attraction near the onset of aggregation, and reduces it at higher concentration of multivalent salt.
We study the spin excitation spectra and the dynamical exchange coupling between iron adatoms on a Bi bilayer nanoribbon. We show that the topological character of the edge states is preserved in the presence of the magnetic adatoms. Nevertheless, they couple significantly to the edge spin currents, as witnessed by the large and long-ranged dynamical coupling we obtain in our calcula- tions. The large effective magnetocrystalline anisotropy of the magnetic adatoms combined with the transport properties of the topologically protected edge states make this system a strong candidate for implementation of spintronics devices and quantum information and/or computation protocols.
A combined nonequilibrium Green functions-Ehrenfest dynamics approach is developed that allows for a time-dependent study of the energy loss of a charged particle penetrating a strongly correlated system at zero and finite temperature. Numerical results are presented for finite inhomogeneous two-dimensional Fermi-Hubbard models, where the many-electron dynamics in the target are treated fully quantum mechanically and the motion of the projectile is treated classically. The simulations are based on the solution of the two-time Dyson (Keldysh-Kadanoff-Baym) equations using the second-order Born, third-order and T-matrix approximations of the self-energy. As application, we consider protons and helium nuclei with a kinetic energy between 1 and 500 keV/u passing through planar fragments of the two-dimensional honeycomb lattice and, in particular, examine the influence of electron-electron correlations on the energy exchange between projectile and electron system. We investigate the time dependence of the projectiles kinetic energy (stopping power), the electron density, the double occupancy and the photoemission spectrum. Finally, we show that, for a suitable choice of the Hubbard model parameters, the results for the stopping power are in fair agreement with ab-initio simulations for particle irradiation of single-layer graphene.