Rovibrational dynamics of the RbCs molecule in static electric fields. Classical study

We study the classical dynamics of the RbCs molecule in the presence of a static electric field. Under the Born–Oppenheimer approximation, we perform a rovibrational investigation which includes the interaction of the field with the molecular polarizability. The stability of the equilibrium points and the phase space structure of the system are explored in detail. We find that, for strong electric fields or for energies close to the dissociation threshold, the molecular polarizability causes relevant effects on the system dynamics.     

Analysis of magnetic disaccommodation in La-Co-substituted strontium ferrites

M-type strontium ferrites substituted by La³⁺-Co²⁺(Sr_1−xLa_xFe_12−xCo_xO₁₉) were prepared by ceramic process. Effects of the substituted amount of La³⁺ and Co²⁺ on structure and magnetic properties of Sr_1−xLa_xFe_12−xCo_xO₁₉ compounds have systematically been investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and magnetic disaccommodation. In the measurement range from 80 to 500 K, the magnetic disaccommodation is represented by means of isochronal curves. It is well known that magnetic disaccommodation cannot be obviously found in the M-type of pure strontium ferrites. However, three peaks were observed in Sr_1−xLa_xFe_12−xCo_xO₁₉, and this behavior is explained in terms of the presence of Fe²⁺ cation and to the site occupation by the magnetic Co²⁺ ionic within the hexagonal structure.     

Quantum Hall effect, screening, and layer-polarized insulating states in twisted bilayer graphene

We investigate electronic transport in dual-gated twisted-bilayer graphene. Despite the subnanometer proximity between the layers, we identify independent contributions to the magnetoresistance from the graphene Landau level spectrum of each layer. We demonstrate that the filling factor of each layer can be independently controlled via the dual gates, which we use to induce Landau level crossings between the layers. By analyzing the gate dependence of the Landau level crossings, we characterize the finite interlayer screening and extract the capacitance between the atomically spaced layers. At zero filling factor, we observe an insulating state at large displacement fields, which can be explained by the presence of counterpropagating edge states with interlayer coupling.     

On the nuclear curvature energy

The curvature energy coefficient of the nuclear mass formulaa _c is first calculated for the model case of a Fermi gas bounded by an external Woods-Saxon potential. The semiclassical theory of Wigner and Kirkwood is used anda _c is found to be close to zero. It is, however, shown that this low value is due to the lack of selfconsistency of the potential. When available, the results of the model compare very well with quantal values and the extrapolation to the spherical cavity (billiard) checks with the value fora _c known from the Balian-Bloch theory. Second, the selfconsistent case is generalised to finite range forces. No indication is found that this modifies the fact that all theoretical values for a _c are larger than about 7 MeV which is an order of magnitude above the empirical value.     

Theoretical vibrational terms and rotational constants for the 15N substituted isotopologues of N2O calculated using normal hyperspherical coordinates

Variational calculations of the vibrational terms G_v and rotational constants B_v of the ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁵N¹⁵N¹⁶O isotopologues of nitrous oxide are carried out using normal hyperspherical coordinates. The Morse-cosine potential energy surface for N₂O previously determined by the authors by fitting to a set of experimental vibrational frequencies is employed. The G_v and B_v spectroscopic constants calculated for the ¹⁵N substituted isotopologues show an satisfactory agreement with those experimentally observed for a large number of vibrational bands of these isotopologues recently measured. Predicted calculated values of these spectroscopic constants for unobserved vibrational bands of the ¹⁵N substituted isotopologues are given in order to be of help in the identification and characterization of such bands, as a complement to the use of global effective Hamiltonians.     

Morphology and thermal stability of AlF3 thin films grown on Cu(100)

The growth of ultrathin epitaxial layers of aluminum fluoride on Cu(100) has been studied by a combination of surface science techniques. Deposition at room temperature results in step decoration followed by the formation of dendritic two-dimensional islands that coalesce to form porous films. Ultrathin layers (up to 2 monolayers in thickness) are morphologically unstable upon annealing; de-wetting takes place around 430 K with the formation of three-dimensional islands and leaving a large fraction of the Cu surface uncovered. Films several nanometers thick, on the contrary, are stable up to ca. 730 K where desorption in molecular form sets on. The effect of electron irradiation on the AlF₃ has also been characterized by different spectroscopic techniques; we find that even small quantities of stray electrons from rear electron beam heating can provoke significant decomposition of the aluminum fluoride, resulting in the release of molecular fluorine and the formation of deposits of metallic aluminum. These features make AlF₃ an interesting material for spintronic applications.     

Cooperative origin of low-density domains in liquid water

We study clusters formed by water molecules possessing large enough tetrahedrality with respect to their nearest neighbors. Using Monte Carlo simulation of SPC/E water and Voronoi tessellation, we find that regions of lower density than the bulk are formed by accretion of molecules into clusters exceeding a minimum size. Clusters are predominantly linear objects and become less compact as they grow until they reach a size beyond which further accretion is not accompanied by a density decrease. The results suggest that the formation of "icelike" regions in liquid water is cooperative.     

Gravitational and electromagnetic signatures of accretion into a charged black hole

We present the derivation and the solutions to the coupled electromagnetic and gravitational perturbations with sources in a charged black hole background. We work in the so called ghost gauge and consider as source of the perturbations the infall of radial currents. In this way, we study a system in which it is provoked a response involving both, gravitational and electromagnetic waves, which allows us to analyze the dependence between them. We solve numerically the wave equations that describe both signals, characterize the waveforms and study the relation between the input parameters of the infalling matter with those of the gravitational and electromagnetic responses.