We have experimentally studied the effect of the trapping laser linewidth on the number of capped atoms in a magneto-optical trap (MOT). Our data show that a significant number of the atoms can still be trapped in the MOT, even when the trapping laser linewidth is larger than the natural linewidth of the excited state of the driving transition.

Angle-resolved photoemission has been utilized to study the surface electronic structure of 1/3 monolayer of Sn on Ge(lll) in both the room-temperature (root3 x root3)R30 degrees phase and the low-temperature (3 x 3) charge-density-wave phase. The results reveal a gap opening around the (3 x 3) Brillouin zone boundary, suggesting a Peierls-like transition despite the well-documented lack of Fermi nesting, a highly sensitive electronic response to doping by intrinsic surface defects is the cause for this unusual behavior, and a detailed calculation illustrates the origin of the (3 x 3) symmetry.

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Trimer is the smallest cluster that can have a one-dimensional or two-dimensional structure on surfaces, and it can diffuse and transform between these structures. Using first-principles density-functional theory (DFT) calculations, the structural and dynamical behaviors of Al trimer on Al(111) surface have been studied in detail. Al trimer on Al(111) surface has three different kinds of structure conformations (groups with similar configurations): close-packed (compact) triangular trimers, non-compact triangular trimers, and linear trimers. The close-packed triangular trimers are more stable than the non-compact triangular trimers and the linear trimers, while most of the non-compact triangular trimers are as stable as the linear trimers. For the dynamics of Al trimer on Al(111) surface, there are three different kinds of diffusion mechanisms: (1) concerted translations and rotation of compact triangular trimers (the highest energy barrier by DFT calculation

We have observed various Lambda-type electromagnetically induced transparency (EIT) spectra in laser-cooled Rb-87 atoms of different laser polarization configurations. Unexpected profiles occur in the EIT spectra. We have found the degenerate Zeeman sublevels are responsible for these profiles. The experimental data are in good agreement with the results from the theoretical calculation which takes into account all the 13 Zeeman levels in the Lambda system. Our study demonstrates that Zeeman sublevels play important roles in quantum interference phenomena such as EIT and amplification without population inversion (AWI), and should be taken into account in the analysis of these phenomena.

We use ab initio density-functional theory supplemented with the embedded-atom method to study the self-diffusion of small clusters on the (111) surface of eight fee metals. A zigzag motion is found to be important in the dimer and tetramer diffusions. The dimer diffuses by a zigzag and concerted motion. The trimer diffuses by a concerted three-atom motion. The tetramer diffuses through a zigzag motion where only two atoms move simultaneously in each step. Thus, instead of increasing, the migration energy is lowered (or stays constant) for the tetramer as compared to that for the trimer. This novel break of the upwards trend in migration energy is predicted to be a general phenomenon.

We capture Rb-87 atoms from room-temperature background vapor with a magneto-optical trap (MOT). The temperature of the atoms in the MOT is 320 mu K as the result of Doppler cooling. We further employ polarization gradient cooling to lower atom temperature. The factors that can affect the performance of polarization gradient cooling have been systematically studied. An atom temperature of 75 mu K has been reached with the optimized conditions. Temperatures are measured by the release and recapture method and the time of flight method. Such cold atoms are ready for the evaporative cooling which will finally realize the Bose-Einstein condensation.