arXiv subjects

Peter Schmelcher

Publications and source records attributed to Peter Schmelcher.

249 records · Page 14Linked to original sources

arXiv2003

Magnetically induced anions

The main focus of this review is on magnetically induced anions. Before discussing these new anionic states which exclusively exist in the presence of magnetic fields, we review in some detail the anionic physics without external field. For completeness, we also outline the properties of field-free existing anions when exposed to magnetic fields. The magnetically induced states constitute an infinite manifold assuming that the nucleus of the anion is infinitely heavy. At laboratory field strengths the corresponding binding energies show two different scaling properties belonging to the ground ($\propto B^2$) and the excited ($\propto B^3$) magnetically induced states. We provide a detailed discussion of the physics of the moving anion taking into account the coupling between the anionic centre of mass and its electronic degrees of freedom. A number of field-adapted techniques exploiting exact constants of motion and the adiabatic separation of motions are applied to simplify the Hamiltonian that describes the effective interaction between the centre of mass and the electronic degrees of freedom. Employing classical simulations the autodetachment process of the anions in the field is observed and a rich variety of spectral properties of moving anions is predicted: depending on the parameters, such as the mass and polarizability of the neutral system as well as the field strength, induced bound states, resonances and detaching states of the corresponding anions are to be expected. An outline of an {\it{ab initio}} quantum approach is provided that allows quantum dynamical investigations of the moving anion.

physics.atom-ph↗

arXiv2003

Collinear helium under periodic driving: stabilization of the asymmetric stretch orbit

The collinear eZe configuration of helium, with the electrons on opposite sides of the nucleus, is studied in the presence of an external electromagnetic (laser or microwave) field. We show that the classically unstable "asymmetric stretch" orbit, on which doubly excited intrashell states of helium with maximum interelectronic angle are anchored, can be stabilized by means of a resonant driving where the frequency of the electromagnetic field equals the frequency of Kepler-like oscillations along the orbit. A static magnetic field, oriented parallel to the oscillating electric field of the driving, can be used to enforce the stability of the configuration with respect to deviations from collinearity. Quantum Floquet calculations within a collinear model of the driven two-electron atom reveal the existence of nondispersive wave packets localized on the stabilized asymmetric stretch orbit, for double excitations corresponding to principal quantum numbers of the order of N > 10.

physics.atom-ph↗

arXiv2002

Two-dimensional negative donors in magnetic fields

A finite-difference solution of the Schroedinger equation for negative donor centers D^- in two dimensions is presented. Our approach is of exact nature and allows us to resolve a discrepancy in the literature on the ground state of a negative donor. Detailed calculations of the energies for a number of states show that for field strengths less than γ=0.117 a.u. the donor possesses one bound state, for 0.117<γ<1.68 a.u. there exist two bound states and for field strengths γ>1.68 a.u. the system possesses three bound states. Further relevant characteristics of negative donors in magnetic fields are provided.

cond-mat.mes-hall↗

arXiv2000

Finite-Difference Calculations for Atoms and Diatomic Molecules in Strong Magnetic and Static Electric Fields

Fully numerical mesh solutions of 2D quantum equations of Schroedinger and Hartree-Fock type allow us to work with wavefunctions which possess a very flexible geometry. This flexibility is especially important for calculations of atoms and molecules in strong external fields where neither the external field nor the internal interactions can be considered as a perturbation. The applications of the present approach include calculations of atoms and diatomic molecules in strong static electric and magnetic fields. For the latter we have carried out Hartree-Fock calculations for He, Li, C and several other atoms. This yields in particular the first comprehensive investigation of the ground state configurations of the Li and C atoms in the whole range of magnetic fields (0<B<10000 a.u.) and a study of the ground state electronic configurations of all the atoms with 1<Z<11 and their ions A^+ in the high-field fully spin-polarised regime. The results in a case of a strong electric field relate to single-electron systems including the correct solution of the Schroedinger equation for the H_2^+ ion (energies and decay rates) and the hydrogen atom in strong parallel electric and magnetic fields.

physics.atom-ph↗

arXiv2000

Nonzero angular momentum states of the helium atom in a strong magnetic field

The electronic structure of the helium atom in the magnetic field regime B=0-100a.u. is investigated, using a full configuration interaction approach which is based on a nonlinearly optimized anisotropic Gaussian basis set of one-particle functions. The corresponding generalized eigenvalue problem is solved for the magnetic quantum number M=-1 and for both even and odd z-parity as well as singlet and triplet spin symmetry. Accurate total electronic energies of the ground state and the first four excitations in each subspace as well as their one-electron ionization energies are presented as a function of the magnetic field. Additionally we present energies for electromagnetic transitions within the M=-1 subspace and between the M=-1 subspace and the M=0 subspace treated in a previous work. A complete table of wavelengths and field strengths for the detected stationary points is given.

astro-ph↗

arXiv2000

Excited states of the hydrogen molecule in magnetic fields: The singlet Sigma states of the parallel configuration

Excited states of the hydrogen molecule subject to a homogeneous magnetic field are investigated for the parallel configuration in the complete regime of field strengths B=0-100a.u.. Up to seven excitations are studied for gerade as well as ungerade spin singlet states of Sigma symmetry with a high accuracy. The evolution of the potential energy curves for the individual states with increasing field strength as well as the overall behaviour of the spectrum are discussed in detail. A variety of phenomena like for example the sequence of changes for the dissociation channels of excited states and the resulting formation of outer wells are encountered. Possible applications of the obtained data to the analysis of magnetic white dwarfs

physics.chem-ph↗

arXiv2000

Bound states of negatively charged ions induced by a magnetic field

We analyse the bound states of negatively charged ions which were predicted to exist because of the presence of a magnetic field by Avron et al. We confirm that the number of such states is infinite in the approximation of an infinitely heavy nucleus and provide insight into the underlying physical picture by means of a combined adiabatic and perturbation theoretical approach. We also calculate the corresponding binding energies which are qualitatively different for the states with vanishing and non-vanishing angular momentum. An outlook on the case of including center of mass effects is presented.

physics.atom-ph↗

arXiv2000

Theory and Applications of the Systematic Detection of Unstable Periodic Orbits in Dynamical Systems

A topological approach and understanding to the detection of unstable periodic orbits based on a recently proposed method (PRL 78, 4733 (1997)) is developed. This approach provides a classification of the set of transformations necessary for the finding of the orbits. Applications to the Ikeda and Henon map are performed, allowing a study of the distributions of Lyapunov exponents for high periods. Particularly the properties of the least unstable orbits up to period 36 are investigated and discussed.

nlin.CD↗

arXiv2000

Analysing Lyapunov spectra of chaotic dynamical systems

It is shown that the asymptotic spectra of finite-time Lyapunov exponents of a variety of fully chaotic dynamical systems can be understood in terms of a statistical analysis. Using random matrix theory we derive numerical and in particular analytical results which provide insights into the overall behaviour of the Lyapunov exponents particularly for strange attractors. The corresponding distributions for the unstable periodic orbits are investigated for comparison.

nlin.CD↗

arXiv2000

Quantum energy flow in atomic ions moving in magnetic fields

Using a combination of semiclassical and recently developed wave packet propagation techniques we find the quantum self-ionization process of highly excited ions moving in magnetic fields which has its origin in the energy transfer from the center of mass to the electronic motion. It obeys a time scale by orders of magnitude larger than the corresponding classical process. Importantly a quantum coherence phenomenon leading to the intermittent behaviour of the ionization signal is found and analyzed. Universal properties of the ionization process are established.

physics.atom-ph↗

arXiv2000

Ground and excited states of the hydrogen negative ion in strong magnetic fields

The lowest bound states of the hydrogen negative ion and negative donor systems in a homogeneous magnetic field are investigated theoretically via a full configuration interaction approach with an anisotropic Gaussian basis set. The broad magnetic field regime γ=0.0008 - 4000 is covered. Nonrelativistic total energies, electron detachment energies and transition wavelengths are presented assuming an infinite nuclear mass. The binding mechanisms are discussed in detail. The accuracy for the energies is enhanced significantly compared to previously published data.

physics.atom-ph↗

arXiv1999

Magnetic Field Induced Two-Body Phenomena in Atoms

We report on a number of recently discovered phenomena which arise due to the interaction of the collective (CM) and internal motion of atoms moving in magnetic fields. For neutral atoms the properties of the so-called giant dipole states are discussed and their experimental preparation is outlined. For ions moving in magnetic fields the energy flow between the collective and electronic motions is studied. For low CM velocities this results in a crossover from localization to delocalization with respect to the spreading of the mixing of the CM and internal motion in quantum number space. Large CM velocities induce for both the classical as well as quantum ion the self-ionization process. Future perspectives for both multi-electron atoms as well as molecules are drawn.

physics.atom-ph↗

arXiv1999

Magnetic Field Stimulated Transitions of Excited States in Fast Muonic Helium Ions

It is shown that one can stimulate, by using the present-day laboratory magnetic fields, transitions between the $lm$ sub-levels of fast $μHe^+$ ions formating in muon catalyzed fusion. Strong fields also cause the self-ionization from highly excited states of such muonic ions. Both effects are the consequence of the interaction of the bound muon with the oscillating field of the Stark term coupling the center-of-mass and muon motions of the $μHe^+$ ion due to the non-separability of the collective and internal variables in this system. The performed calculations show a possibility to drive the population of the $lm$ sub-levels by applying a field of a few $Tesla$, which affects the reactivation rate and is especially important to the $Kα$ $x$-ray production in muon catalyzed fusion. It is also shown that the $2s-2p$ splitting in $μHe^+$ due to the vacuum polarization slightly decreases the stimulated transition rates.

physics.atom-ph↗

arXiv1998

Systematic Computation of the Least Unstable Periodic Orbits in Chaotic Attractors

We show that a recently proposed numerical technique for the calculation of unstable periodic orbits in chaotic attractors is capable of finding the least unstable periodic orbits of any given order. This is achieved by introducing a modified dynamical system which has the same set of periodic orbits as the original chaotic system, but with a tuning parameter which is used to stabilize the orbits selectively. This technique is central for calculations using the stability criterion for the truncation of cycle expansions, which provide highly improved convergence of calculations of dynamical averages in generic chaotic attractors. The approach is demonstrated for the Henon attractor.

chao-dyn↗

arXiv1998

Mesoscopic motion of atomic ions in magnetic fields

We introduce a semiclassical model for moving highly excited atomic ions in a magnetic field which allows us to describe the mixing of the Landau orbitals of the center of mass in terms of the electronic excitation and magnetic field. The extent of quantum energy flow in the ion is investigated and a crossover from localization to delocalization with increasing center of mass energy is detected. It turns out that our model of the moving ion in a magnetic field is closely connected to models for transport in disordered finite-size wires.

physics.atom-ph↗