Interatomic correlations of valence electrons in metals

Takuma Yamashita, Yasushi Kino

We report a theoretical calculation of the relativistic corrections to the binding energy of positronic alkali-metal atoms. The ground state for the positronic alkali-metal atom is a loosely bound state with the structure of an alkali-metal ion surrounded by a positronium cloud. The correlation between the valence electron and positron in the field of a residual core ion is taken into account using a three-body model. Relativistic corrections to the binding energy for positronic alkali-metal atoms are evaluated based on the Breit-Pauli perturbation theory up to the second order of the fine structure constant. The relativistic corrections caused by the interaction between the valence electron and core ion was evaluated from the decomposed expectation values of the perturbation Hamiltonian. We found that the importance of relativistic corrections to the binding energy, namely the ratio of the net relativistic correction in the total binding energy, is remarkably enhanced in the loosely bound states of positronic alkali-metal atoms, where the charge of the valence electron is screened by the positron as positronium in the outermost region, while the electron is released from the positron near the nucleus. The results imply that positronic atoms with a dominant positronium can serve as an apt testing ground for relativistic quantum mechanics.

Peter Fulde, Y. Kakehashi, Gernot Stollhoff

Jacob Szeftel

D. K. Walter, W. Happer, Thad G Walker

We present a detailed theoretical analysis of the noble-gas nuclear-spin relaxation due to the anisotropic magnetic-dipole hyperfine interaction between the noble-gas nucleus and alkali-metal valence electron vis \`a vis the already well-understood (spin-conserving) isotropic magnetic-dipole hyperfine interaction in alkali-metal--noble-gas systems. We find that, for all pairs in which the noble gas is not helium, the predicted spin-relaxation rate from the anisotropic interaction does not exceed 2.5% of the rate from the isotropic interaction, thereby not appreciably limiting the maximum noble-gas nuclear polarization attainable via spin-exchange collisions with polarized alkali-metal atoms. For alkali-metal--helium pairs, we predict that the anisotropic interaction has a slightly larger relative effect, perhaps limiting the nuclear polarization to $\ensuremath{\sim}95%$ of the electronic polarization in the Rb-${}^{3}\mathrm{He}$ system; however, our confidence in the helium results is limited by a lack of knowledge of the interatomic potentials necessary for the calculation.

K. S. Singwi, Monica Tosi, Alf Sjölander

C. Hoffmeister, Carsten Müller, Alexander B Voitkiv

We consider photoionization in a system of two atoms of different species caused by a laser field. In this process an inner-valence vacancy, created by photoexcitation in one of the atoms, decays not only due to intra- but also interatomic electron-electron correlations with the energy release in the latter case being transferred to the other atom which is ionized. We show that when the intensity of the laser field increases this photoionization process---due to Rabi oscillations and Pauli blocking---may acquire qualitatively new features in its time evolution and the electron emission spectra.