arXiv subjects

Lorenz S. Cederbaum

Publications and source records attributed to Lorenz S. Cederbaum.

121 records · Page 7Linked to original sources

arXiv2004

Ground state fragmentation of repulsive BEC in double-trap potentials

The fragmentation of the ground state of a repulsive condensate immersed into a double-trap potential is found to be a general and critical phenomenon. It takes place for a given number of bosons if their scattering length is larger than some critical value or for a given value of the scattering length if the number of bosons is above some critical number. We demonstrate that the geometry of the inner trap determines these critical parameters while the number of the fragments and the fraction of bosons in the various fragments can be manipulated by the outer trap. There is also a maximal number of bosons for which the ground state is fragmented. If this number is exceeded, the fragmented state becomes a very low-lying excited state of the condensate. This maximal number of bosons can be substantially manipulated by varying the inner and outer traps. To study three-fold fragmentation we have chosen a potential well with two barriers as the inner trap and embedded by two types of outer ones. A many-fold fragmentation is also addressed.

cond-mat.other↗

arXiv2004

On interacting fermions and bosons with definite total momentum

Any {\it exact} eigenstate with a definite momentum of a many-body Hamiltonian can be written as an integral over a {\it symmetry-broken} function $Φ$. For two particles, we solve the problem {\it exactly} for all energy levels and any inter-particle interaction. Especially for the ground-state, $Φ$ is given by the simple Hartree-Fock/Hartree ansatz for fermions/bosons. Implications for several and many particles as well as a numerical example are provided.

quant-ph↗

arXiv2004

Tunneling lifetime of trapped condensates

Using the complex scaling transformation we calculate the tunneling lifetime of a condensate inside a magnetic/optical trap. We show that by varying the scattering length, the external potential acts like a 'selective membrane' which controls the direction of the flux of the cold atoms through the barriers and thereby controls the size of the stable condensate inside the trap.

cond-mat.other↗

arXiv2004

Impact of Interatomic Electronic Decay Processes on Xe 4d Hole Decay in the Xenon Fluorides

A hole in a 4d orbital of atomic xenon relaxes through Auger decay after a lifetime of 3 fs. Adding electronegative fluorine ligands to form xenon fluoride molecules, results in withdrawal of valence-electron density from Xe. Thus, within the one-center picture of Auger decay, a lowered Xe 4d Auger width would be expected, in contradiction, however, with experiment. Employing extensive ab initio calculations within the framework of many-body Green's functions, we determine all available decay channels in XeFn and characterize these channels by means of a two-hole population analysis. We derive a relation between two-hole population numbers and partial Auger widths. On this basis, interatomic electronic decay processes are demonstrated to be so strong in the xenon fluorides that they overcompensate the reduction in intra-atomic Auger width and lead to the experimentally observed trend. The nature of the relevant processes is discussed. These processes presumably underlie Auger decay in a variety of systems.

physics.chem-ph↗

arXiv2004

Continuous configuration-interaction for condensates in a ring

A continuous configuration-interaction approach for condensates in a ring is introduced. In its simplest form this approach utilizes for attractive condensates the Gross-Pitaevskii symmetry-broken solution and arrives at a ground-state of correct symmetry. Furthermore, the energy found is {\it lower} than the Gross-Pitaevskii one and, with increasing number of particles and/or strength of inter-particle interaction, is even {\it lower} than that accessed by tractable diagonalization of the many-body Hamiltonian. Implications also to excited states are briefly discussed.

cond-mat.other↗

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

Ionization of the Xenon Fluorides

The noble-gas atom xenon can bind fluorine atoms and form several stable compounds. We study the electronic structure of the xenon fluorides (XeFn, n = 2,4,6) by calculating their ionization spectra using a Green's function method, which allows to treat many-body effects at a high level. Our focus is on the valence region and on the Xe 4d core hole. We observe a sensitive dependence of the spectra on the number of fluorine ligands. Systematic line shifts are uncovered and explained. In the Xe 5s and F 2s inner-valence regimes, from XeF2 to XeF6, the usefulness of the one-particle picture of ionization is found to become progressively worse. Moreover, adding the electronegative fluorine ligands seems to enhance--not suppress--the Auger decay of a Xe 4d core hole.

physics.chem-ph↗

arXiv2003

Coulombic Energy Transfer and Triple Ionization in Clusters

Using neon and its dimer as a specific example, it is shown that excited Auger decay channels that are electronically stable in the isolated monomer can relax in a cluster by electron emission. The decay mechanism, leading to the formation of a tricationic cluster, is based on an efficient energy-transfer process from the excited, dicationic monomer to a neighbor. The decay is ultrafast and expected to be relevant to numerous physical phenomena involving core holes in clusters and other forms of spatially extended atomic and molecular matter.

physics.atm-clus↗

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↗

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

The dynamical Green's function and an exact optical potential for electron-molecule scattering including nuclear dynamics

We derive a rigorous optical potential for electron-molecule scattering including the effects of nuclear dynamics by extending the common many-body Green's function approach to optical potentials beyond the fixed-nuclei limit for molecular targets. Our formalism treats the projectile electron and the nuclear motion of the target molecule on the same footing whereby the dynamical optical potential rigorously accounts for the complex many-body nature of the scattering target. One central result of the present work is that the common fixed-nuclei optical potential is a valid adiabatic approximation to the dynamical optical potential even when projectile and nuclear motion are (nonadiabatically) coupled as long as the scattering energy is well below the electronic excitation thresholds of the target. For extremely low projectile velocities, however, when the cross sections are most sensitive to the scattering potential, we expect the influences of the nuclear dynamics on the optical potential to become relevant. For these cases, a systematic way to improve the adiabatic approximation to the dynamical optical potential is presented that yields non-local operators with respect to the nuclear coordinates.

physics.chem-ph↗

arXiv1998

First Order Static Excitation Potential: Scheme for Excitation Energies and Transition Moments

We present an approximation scheme for the calculation of the principal excitation energies and transition moments of finite many-body systems. The scheme is derived from a first order approximation to the self energy of a recently proposed extended particle-hole Green's function. A hermitian eigenvalue problem is encountered of the same size as the well-known Random Phase Approximation (RPA). We find that it yields a size consistent description of the excitation properties and removes an inconsistent treatment of the ground state correlation by the RPA. By presenting a hermitian eigenvalue problem the new scheme avoids the instabilities of the RPA and should be well suited for large scale numerical calculations. These and additional properties of the new approximation scheme are illuminated by a very simple exactly solvable model.

physics.chem-ph↗

arXiv1996

Extended Two--Particle Green's Functions and Optical Potentials for Two--Particle Scattering by Many--Body Targets

An extension of the fermionic particle--particle propagator is presented, that possesses similar algebraic properties to the single--particle Green's function. In particular, this extended two--particle Green's function satisfies Dyson's equation and its self energy has the same analytic structure as the the self energy of the single--particle Green's function. For the case of a system interacting by one--particle potentials only, the two--particle self energy takes on a particularly simple form, just like the common self energy does. The new two--particle self energy also serves as a well behaved optical potential for the elastic scattering of a two--particle projectile by a many--body target. Due to its analytic structure, the two--particle self energy avoids divergences that appear with effective potentials derived by other means.

chem-ph↗