Comparison of atomic quasi-Landau spectrum with semiclassical strong-field-mixing models

Abstract

The authors compare the spectrum of the regularly spaced photoabsorption resonances which appear in the vicinity of the ionization threshold for atoms in a strong magnetic field with predictions of semiclassical strong-mixing models. Quasi-Landau resonance positions are shown to agree well with a two-dimensional WKB semiclassical hydrogenic model which depicts the resonances as bound states of the electron in the combined Coulomb and magnetic fields and which reduces to the Rydberg levels at low excitation. Simpler treatments based on a modified Bohr atomic model are also discussed. The data include observations in the $M=0$ even-parity channels of Bai and Sri with $B=25\ensuremath{-}40$ kG and the $M=\ensuremath{-}1$ odd-parity channel of Bai at $B=47$ kG. A scaling procedure is used to allow field-independent comparison among the various spectra and models. Although fairly successful in predicting energy positions, none of the models attempts to explain the complex resonance profiles or superposed fine structure, thus indicating the need for a comprehensive quantum-mechanical theory of the diamagnetic strong-mixing regime. The appearance of the quasi-Landau resonances in $M=0$ even-parity spectra is consistent with the requirement that the states have even parity with respect to reflection along the direction of the magnetic field in order for the resonances to occur.