Unexpected effects in spin-polarized electron-impact excitation of the(3d104s5s)3S

Topological angular momentum in electron exchange excitation of a single atom

“…The experimental studies with zinc atoms leading to the present paper were reported recently in a brief communication [9] as "unexpected effects," and without explanation, in the spin-polarized excitation (3d 10 4s 2 ) 1 S 0 → (3d 10 4s5s) 3 S 1 process. That paper outlined briefly the relevant apparatus and experimental methods from the viewpoint of traditional polarized electron scattering from a beam of zinc atoms, the observations of photon polarizations, and the deductions of Stokes parameters and their comparison with quantum scattering calculations.…”

“…Recently, Berry recalled [8], instructively, the diversity of fundamental ideas and paths leading to his concept and related geometrical and topological phases. Here we explain our recent observations [9] in terms of a geometric Berry phase [10,11] where, in a free single atom with only two electrons in the outer valence orbits, spin-polarized electron exchange excitation from a singlet S = 0, M S = 0 to a triplet S = 1, M S = 0 state is described essentially as parallel movement of electron spin around a closed path with an inherent phase change of π radians in the wave function. The process causes alignment rather than polarization of the electron charge cloud.…”

Measurement of the Integrated Stokes Parameters for Zn 468 nm Florescence Excited by Polarized-Electron Impact

“…1) of Zn (4 3 P0 -5 3 S1) 468 nm florescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)5 3 S1 state. This work was motivated by similar studies reported several years ago by Pravica et al [1], in which they measured non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)5 3 S1 excitation and the first cascading (4s5p)5 3 PJ threshold. In our experiment, the electrons scattered in the excitation process are not measured (hence the designation of the Stokes parameters as "integrated"), and the fluorescence is observed in the direction of the initial electron spin polarization.…”

“…In the cascade-free range of excitation between 6.7 eV and 7.6 eV, we have measured P2 at 7.0 eV and 7.3 eV and find its values in this range to be consistent with zero and inconsistent with those measured in [1]. Work supported by the USA NSF Award PHY-1505794.…”

“…This assumption is invalid if (a) the excited state producing the fluorescence is not well LS-coupled or (b) the spin of the continuum electron precesses during the collision under the influence of a motional magnetic field, i.e., the electron undergoes Mott scattering. Since both possibilities are ruled out by state-of-the-art theory [3,4], which predicts P2 values of order 10 -4 , the results of reference [1], which are as large as 10 -1 , are remarkable. We used a standard GaAs polarized electron source to produce beams of electrons with a polarization of 0.25(1) and an energy width of ca.…”