A first principles approach for spin and angle resolved resonant photoemission is developed within multiple scattering theory and applied to a Cr(110) surface at the 2$p$-3$d$ resonance. The resonant photocurrent from this non ferromagnetic system is
found to be strongly spin polarized by circularly polarized light, in agreement with experiments on antiferromagnetic and magnetically disordered systems. By comparing the antiferromagnetic and Pauli-paramagnetic phases of Cr, we explicitly show that the spin polarization of the photocurrent is independent of the existence of local magnetic moments, solving a long-standing debate on the origin of such polarization. New spin polarization effects are predicted for the paramagnetic phase even with unpolarized light, opening new directions for full mapping of spin interactions in macroscopically non magnetic or nanostructured systems.
Southern Africa has some of the worlds best sites for air Cherenkov telescopes. South Africa has only one viable site, which is south of Sutherland and also close to the Southern African Large Telescope (SALT). This site has very good infrastructure
and is easy to access, but only 47% of the night-time has a cloudless sky usable for observations. Namibia, which already hosts the H.E.S.S telescope, has a number of potential sites with much less cloud coverage. The H.E.S.S. site is one of the highest of these sites at 1840 m a.s.l. with about 64% of the night-time cloudless. It also has very low night sky background levels and is relatively close (about 100 km) to Windhoek. Moving further away from Windhoek to the south, the cloud coverage and artificial night sky brightness becomes even less, with the site at Kuibis (between Keetmanshoop and Luderitz) at 1640 m a.s.l. having clear night skies 73% of the time. Even though this site seems remote (being 660 km from Windhoek by road), it is close to the national B4 highway, a railway line, a power line and an optical fiber line. It is also less than two hours drive away from a harbour and national airports. The Namibian sites also receive very little snow, if any, and the wind speeds are less than 50 km/h for more than 90% of the time with maximum wind speeds of around 100 km/h. Seismically the whole Southern African region is very stable.
We prepare a chemically and thermally one-dimensional (1d) quantum degenerate Bose gas in a single microtrap. We introduce a new interferometric method to distinguish the quasicondensate fraction of the gas from the thermal cloud at finite temperatur
e. We reach temperatures down to $kTapprox 0.5hbaromega_perp$ (transverse oscillator eigenfrequency $omega_perp$) when collisional thermalization slows down as expected in 1d. At the lowest temperatures the transverse momentum distribution exhibits a residual dependence on the line density $n_{1d}$, characteristic for 1d systems. For very low densities the approach to the transverse single particle ground state is linear in $n_{1d}$.
We study the dynamics of matter waves in an effectively one-dimensional Bose-Einstein condensate in a double well potential. We consider in particular the case when one of the double wells confines excited states. Similarly to the known ground state
oscillations, the states can tunnel between the wells experiencing the physics known for electrons in a Josephson junction, or be self-trapped. As the existence of dark solitons in a harmonic trap are continuations of such non-ground state excitations, one can view the Josephson-like oscillations as tunnelings of dark solitons. Numerical existence and stability analysis based on the full equation is performed, where it is shown that such tunneling can be stable. Through a numerical path following method, unstable tunneling is also obtained in different parameter regions. A coupled-mode system is derived and compared to the numerical observations. Regions of (in)stability of Josephson tunneling are discussed and highlighted. Finally, we outline an experimental scheme designed to explore such dark soliton dynamics in the laboratory.
We give a comprehensive overview of the development of micro traps, from the first experiments on guiding atoms using current carrying wires in the early 1990s to the creation of a BEC on an atom chip.
