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We study analytically an armchair graphene nanoribbon (AGNR) in the presence of a bichromatic light wave, consisting of intense low-frequency and perturbative high frequency modes. The electric fields of both waves are directed parallel to the ribbon axis. The Dirac equation describing the electron-nonstationary field interaction is employed and solved in the resonant approximation. This allows us to calculate in an explicit form the Rabi frequency of the resonant transitions between the hole and electron size-quantized subbands, induced by the weak wave. The dependencies of the Rabi frequency on the parity of the low frequency photon numbers, magnitudes of the electric fields and ribbon width are examined and found to be in line with those obtained by numerical methods. We show that the Rabi frequency associated with the additional weak wave exceeds that generated by only the strong mode. [ABSTRACT FROM AUTHOR]

A unifying description of lattice potentials generated by aperiodic one-dimensional sequences is proposed in terms of their local reflection or parity symmetry properties. We demonstrate that the ranges and axes of local reflection symmetry possess characteristic distributional and dynamical properties, determined here numerically for certain lattice types. A striking aspect of such a property is given by the return maps of sequential spacings of local symmetry axes, which typically traverse few-point symmetry orbits. This local symmetry dynamics allows for a description of inherently different aperiodic lattices according to fundamental symmetry principles. Illustrating the local symmetry distributional and dynamical properties for several representative binary lattices, we further show that the renormalized axis-spacing sequences follow precisely the particular type of underlying aperiodic order, revealing the presence of dynamical self-similarity. Our analysis thus provides evidence that the long-range order of aperiodic lattices can be characterized in a compellingly simple way by its local symmetry dynamics. [ABSTRACT FROM AUTHOR]

We analyze the quantum properties of atoms in a magnetic quadrupole field. The quantum dynamics of ground state atoms in this field configuration is studied firstly. We formulate the Hamiltonian and perform a symmetry analysis. Due to the particular shape of the quadrupole field in general there exist no stable states. We provide resonance energies, lifetimes and calculate the density of states and investigate under what conditions quasi-bound states occur that possess long lifetimes. An effective scalar Schrödinger equation describing such states is derived. As a next step we explore the influence of a high gradient quadrupole field on the electronic structure of excited atoms. An effective one-body approach together with the fixed nucleus approximation is employed in order to derive the electronic Hamiltonian. We present the energy spectrum and discuss peculiar features such as non-trivial spin densities and magnetic field induced electric dipole moments. [ABSTRACT FROM AUTHOR]

We investigate the effects of a magnetic field with low to intermediate strength on several spectroscopic properties of the sodium atom. A model potential is used to describe the core of sodium, reducing the study of the system to an effective one-particle problem. All states with principal quantum numbers n = 3,4,5,6 and 7 are studied and analysed. A grid of twenty values for the field strength in the complete regime B = 0-0.02 a.u. is employed. Ionisation energies, transition wavelengths and their dipole oscillator strengths are presented. [ABSTRACT FROM AUTHOR]

The ground and a few excited states of the beryllium atom in external uniform magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for field strengths ranging from zero up to 2.35×109 T. With changing field strength the ground state of the Be atom undergoes three transitions involving four different electronic configurations which belong to three groups with different spin projections Sz = 0, - 1, - 2. For weak fields the ground state configuration arises from the 1 s22 s2, Sz = 0 configuration. With increasing field strength the ground state evolves into the two Sz = - 1 configurations 1 s22 s2 p-1 and 1 s22 p-13 d-2, followed by the fully spin polarised Sz = - 2 configuration 1 s2 p-13 d-24 f-3. The latter configuration forms the ground state of the beryllium atom in the high field regime γ > 4.567. The analogous calculations for the Be+ ion provide the sequence of the three following ground state configurations: 1s22s and 1 s22 p-1 ( Sz = - 1/2) and 1 s2 p-13 d-2 ( Sz = - 3/2). [ABSTRACT FROM AUTHOR]

We present a theoretical profile of the Lyman line of atomic hydrogen perturbed by collisions with neutral hydrogen atoms and protons. We use a general unified theory in which the electric dipole moment varies during a collision. A collision-induced satellite appears on Lyman , correlated to the asymptotically forbidden transition of H2. As a consequence, the appearance of the line wing between Lyman and Lyman is shown to be sensitive to the relative abundance of hydrogen ions and neutral atoms, and thereby to provide a temperature diagnostic for stellar atmospheres and laboratory plasmas. [ABSTRACT FROM AUTHOR]

What does the center of mass motion of the hydrogen atom in a magnetic field look like? Is it similar to the uniform straight-lined motion of the field-free case or does is perform only tiny vibrations? We show that there is a great variety in the center of mass motion. For regular electronic motion only a bounded range of phase space is available for the center of mass coordinate. There exist many different types of regular center of mass behavior according to the values of the magnetic field strength, energy and angular momentum. At the onset of chaos in the electronic motion a prominent transition to chaos in the center of mass motion is observed. In the fully chaotic regime the trajectories of the center of mass exhibit many properties of a random motion and fill up the unbounded coordinate space. In particular, we obtain a linear diffusion law for the spreading of an ensemble of center of mass trajectories. [ABSTRACT FROM AUTHOR]