Fully Self-Consistent RPA Description of the Many Level Pairing Model

The self-consistent RPA (SCRPA) equations in the particle-particle channel are solved without any approximation for the picket fence model. The results are in excellent agreement with the exact solutions found with the Richardson method. Particularly interesting features are that screening corrections reverse the sign of the interaction and that SCRPA yields the exact energies in the case of two levels with two particles.     

Die diamagnetische Suszeptibilität eines nicht kugelsymmetrischen Systems

The diamagnetic susceptibility of the ground state of a non-spherosymmetric system is calculated, and the eigenfunction used is the exact solution of the problem and can be written in a compact form.

Herrn Professor Dr. F. Hund in Verehrung zum achtzigsten Geburtstag gewidmet.     

A semiclassical density matrix valid beyond the classically allowed region

Zeitschrift für Physik A Hadrons and nuclei - We study semiclassical approximations to the density matrix of a system of Fermions in a one body potential. We derive an expression for the...     

Spurious states in extended RPA theories,part II

Using an extended RPA theory (ERPA) which contains the effects of ground-state correlations and preserves hermiticity, conditions that spurious modes have zero-energy solutions in extended RPA theories are investigated from a general point of view. The single and double excitations of translational motion are considered as illustrative examples.     

A convergence study of Dyson's boson expansion for weak coupling situations in 209Bi

In this paper we study within the Dyson boson expansion (DBE) the particle-vibration coupling in ²⁰⁹Bi as a function of the number of configurations one is taking into account (vertical convergence). We find that the energies converge quite rapidly but that it is somewhat more difficult to achieve convergence also for the transition probabilities. We essentially investigate the well-known septuplet and decuplet in ²⁰⁹Bi and find reasonable agreement with experiment.     

Microscopic formulation of interacting fermion-boson systems

A general fully microscopic theory for interacting fermion—boson systems is presented with an explicit treatment for the single-fermion case. The broken-pair approximation (BPA) is applied to generate correlated fermion pairs. Using these and an odd fermion the boson and the ideal-fermion images are constructed by employing modified Marumori and Dyson mappings. Various problems like the renormalization effects, spurious solutions and the non-hermiticity encountered in practical calculations are discussed. Explicit expressions for calculating the parameters of the hamiltonian of the phenomenological interacting fermion-boson model are derived.     

Hydrodynamics of nanoscopic tubulin rings in dilute solutions

We combine fluorescence correlation spectroscopy and sedimentation velocity measurements to probe the hydrodynamic behavior of tubulin dimers and nanoscopic tubulin rings. The rings are rigid, have circular geometry, and are monodisperse in size. We use the high-precision ratio of the sedimentation coefficients and that of the translational diffusion coefficients to validate theories for calculating the hydrodynamic properties of supramolecular structures.     

Observation of excitons in one-dimensional metallic single-walled carbon nanotubes

Excitons are generally believed not to exist in metals because of strong screening by free carriers. Here we demonstrate that excitonic states can in fact be produced in metallic systems of a one-dimensional character. Using metallic single-walled carbon nanotubes as a model system, we show both experimentally and theoretically that electron-hole pairs form tightly bound excitons. The exciton binding energy of 50 meV, deduced from optical absorption spectra of individual metallic nanotubes, significantly exceeds that of excitons in most bulk semiconductors and agrees well with ab initio theoretical predictions.