Kálmán Varga

The structure of exotic atoms containing positrons and positronium

The structures of a number of exotic atoms with an attached positron or positronium atom are studied using a large-scale variational expansion in terms of a basis of explicitly correlated Gaussian functions. The binding energies and annihilation rates for seven exotic species with electronically stable ground states, namely HPs, , LiPs, , , NaPs and have been predicted. The binding energy for HPs, 0.038 1944 Hartree, is the largest attained so far. Two of the species, and , with approximate binding energies of 0.0024 and 0.0005 Hartree respectively, are seen to have structures best described as a positronium atom orbiting a residual or positively charged core. The atom with an approximate binding energy of 0.0028 Hartree is best characterized as a positron orbiting a polarized Be core. The binding energy of the ground state, 0.014 Hartree, is larger than that of any other positronic atom (a neutral atom with an attached positron). The LiPs and NaPs atoms, with approximate binding energies of 0.012 and 0.0072 Hartree respectively, have structures similar to HPs although the binding energies are smaller and the valence electrons and the positron are found at larger distances from the nucleus.

Magnetic field dependence of the energy of negatively charged excitons in semiconductor quantum wells

We present a variational calculation of the spin-singlet and spin-triplet states of a negatively charged exciton (trion) confined to a single quantum well in the presence of a perpendicular magnetic field. We calculated the probability density and the pair correlation function of the singlet and triplet trion states. The dependence of the energy levels and of the binding energy on the well width and on the magnetic field strength was investigated. We compared our results with the available experimental data on GaAs/AlGaAs quantum wells and find that in the low-magnetic-field region (B 25 T) the dark trion becomes optically inactive and possibly a transition to a bright triplet trion (angular momentum L{sub z}=0) state is observed.

Stability of Few-Charge Systems in Quantum Mechanics

We consider non-relativistic systems in quantum mechanics interacting through the Coulomb potential, and discuss the existence of bound states which are stable against spontaneous dissociation into smaller atoms or ions. We review the studies that have been made of specific mass configurations and also the properties of the domain of stability in the space of masses or inverse masses. These rigorous results are supplemented by numerical investigations using accurate variational methods. A section is devoted to systems of three arbitrary charges and another to molecules in a world with two space dimensions.

Study of light exotic nuclei with a stochastic variational method: Application to lithium isotopes

The stochastic variational method on correlated Gaussian basis was applied to the study of the structure of light exotic nuclei. The halo structure of {sup 11}Li was described in a {sup 9}Li+n+n picture by including the distortion of the {sup 9}Li core as well as the correlation among the core and the neutrons. The treatment was fully microscopic and successfully reproduced virtually all the properties of {sup 11}Li consistently with {sup 9}Li. Two p-wave resonances of {sup 10}Li were predicted around 300-500 keV above the {sup 9}Li+n threshold.

Positively charged magnetoexcitons in a semiconductor quantum well

A variational calculation of the lower singlet and triplet states of positively charged excitons (trions), confined to a single quantum well and in the presence of a perpendicular magnetic field, is presented. All the three particles of the exciton complex are treated within the effective-mass approximation. We study the dependence of the energy levels and of the binding energy on the well width and on the magnetic-field strength. Our results are compared with the available experimental data, and show a good qualitative and quantitative agreement. A singlet-triplet crossing is found which for a

Positively and negatively charged excitons in a semiconductor quantum well

200\ensuremath{-}\AA{}

Theory of trions in quantum wells

-wide GaAs is predicted to occur for

Correlation Energy and Configuration of Biexcitons in Quantum Wells

B=15 \mathrm{T}.

Origin of Colossal Ionic Conductivity in Oxide Multilayers: Interface Induced Sublattice Disorder

The energy levels of negatively and positively charged excitons (also called trions) confined in quantum wells are studied in the presence of a perpendicular magnetic field. The magnetic field dependence of the average inter-particle distance and of the pair correlation function of the singlet and dark triplet states are investigated. A comparison is made with available experimental data on a 200 {angstrom} wide GaAs/AlGaAs quantum well.