Above threshold ionization by few-cycle spatially inhomogeneous fields

We present theoretical studies of above threshold ionization (ATI) produced by spatially inhomogeneous fields. This kind of field appears as a result of the illumination of plasmonic nanostructures and metal nanoparticles with a short laser pulse. We use the time-dependent Schr\"odinger equation (TDSE) in reduced dimensions to understand and characterize the ATI features in these fields. It is demonstrated that the inhomogeneity of the laser electric field plays an important role in the ATI process and it produces appreciable modifications to the energy-resolved photoelectron spectra. In fact, our numerical simulations reveal that high energy electrons can be generated. Specifically, using a linear approximation for the spatial dependence of the enhanced plasmonic field and with a near infrared laser with intensities in the mid- 10^{14} W/cm^{2} range, we show it is possible to drive electrons with energies in the near-keV regime. Furthermore, we study how the carrier envelope phase influences the emission of ATI photoelectrons for few-cycle pulses. Our quantum mechanical calculations are supported by their classical counterparts

High-order harmonic generation from inhomogeneous fields

We present theoretical studies of high-order harmonic generation (HHG) produced by non-homogeneous fields as resulting from the illumination of plasmonic nanostructures with a short laser pulse. We show that both the inhomogeneity of the local fields and the confinement of the electron movement play an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff, more pronounced for the longer wavelengths cases studied. In order to understand and characterize the new HHG features we employ two different approaches: the numerical solution of the time dependent Schr\"odinger equation (TDSE) and the semiclassical approach known as Strong Field Approximation (SFA). Both approaches predict comparable results and show the new features, but using the semiclassical arguments behind the SFA and time-frequency analysis tools, we are able to fully understand the reasons of the cutoff extension.Comment: 25 pages, 12 figure

Exciton trapping in magnetic wire structures

The lateral magnetic confinement of quasi two-dimensional excitons into wire like structures is studied. Spin effects are take into account and two different magnetic field profiles are considered, which experimentally can be created by the deposition of a ferromagnetic stripe on a semiconductor quantum well with magnetization parallel or perpendicular to the grown direction of the well. We find that it is possible to confine excitons into one-dimensional (1D) traps. We show that the dependence of the confinement energy on the exciton wave vector, which is related to its free direction of motion along the wire direction, is very small. Through the application of a background magnetic field it is possible to move the position of the trapping region towards the edge of the ferromagnetic stripe or even underneath the stripe. The exact position of this 1D exciton channel depends on the strength of the background magnetic field and on the magnetic polarisation direction of the ferromagnetic film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte

Equivalence of volume and temperature fluctuations in power-law ensembles

Relativistic particle production often requires the use of Tsallis statistics to account for the apparently power-like behavior of transverse momenta observed in the data even at a few GeV/c. In such an approach this behavior is attributed to some specific intrinsic fluctuations of the temperature $T$ in the hadronizing system and is fully accounted by the nonextensivity parameter $q$. On the other hand, it was recently shown that similar power-law spectra can also be obtained by introducing some specific volume fluctuations, apparently without invoking the introduction of Tsallis statistics. We demonstrate that, in fact, when the total energy is kept constant, these volume fluctuations are equivalent to temperature fluctuations and can be derived from them. In addition, we show that fluctuations leading to multiparticle power-law Tsallis distributions introduce specific correlations between the considered particles. We then propose a possible way to distinguish the fluctuations in each event from those occurring from event-to-event. This could have applications in the analysis of high density events at LHC (and especially in ALICE).Comment: Revised version with new figure, footnotes and references adde

Localization Properties of Quantized Magnetostatic Modes in Nanocubes

We investigate the dynamical properties of a system of interacting magnetic dipoles disposed in sites of an sc lattice and forming a cubic-shaped sample of size determined by the cube edge length (N-1)a (a being the lattice constant, N representing the number of dipolar planes). The dipolar field resulting from the dipole-dipole interactions is calculated numerically in points of the axis connecting opposite cube face centers (central axis) by collecting individual contributions to this field coming from each of the N atomic planes perpendicular to the central axis. The applied magnetic field is assumed to be oriented along the central axis, magnetizing uniformly the whole sample, all the dipoles being aligned parallelly in the direction of the applied field. The frequency spectrum of magnetostatic waves propagating in the direction of the applied field is found numerically by solving the Landau-Lifshitz equation of motion including the local (nonhomogeneous) dipolar field component; the mode amplitude spatial distributions (mode profiles) are depicted as well. It is found that only the two energetically highest modes have bulk-extended character. All the remaining modes are of localized nature; more precisely, the modes forming the lower part of the spectrum are localized in the subsurface region, while the upper-spectrum modes are localized around the sample center. We show that the mode localization regions narrow down as the cube size, N, increases (we investigated the range of N=21 to N=101), and in sufficiently large cubes one obtains practically only center-localized and surface-localized magnetostatic modes.Comment: 20 pages, 9 figures in postscript, useing Revtex4.cl

Heap games, numeration systems and sequences

We propose and analyse a 2-parameter family of 2-player games on two heaps of tokens, and present a strategy based on a class of sequences. The strategy looks easy, but is actually hard. A class of exotic numeration systems is then used, which enables us to decide whether the family has an efficient strategy or not. We introduce yet another class of sequences, and demonstrate its equivalence with the class of sequences defined for the strategy of our games.Comment: To appear in Annals of Combinatoric