We use a gray molasses operating on the D 1 atomic transition to produce degenerate quantum gases of 6 Li with a large number of atoms. This sub-Doppler cooling phase allows us to lower the initial temperature of 10 9 atoms from 500 to 40 μK in 2 ms. We observe that D 1 cooling remains effective into a high-intensity infrared dipole trap where two-state mixtures are evaporated to reach the degenerate regime. We produce molecular Bose-Einstein condensates of up to 5 × 10 5 molecules and weakly interacting degenerate Fermi gases of 7 × 10 5 atoms at T /T F < 0.1 with a typical experimental duty cycle of 11 s.

By combining hydrogen and sulfur within diamond-anvil cells we synthesize (H 2 S) 2 H 2 at 5 GPa and 373 K. Through a series of Raman spectroscopy, infrared spectroscopy, and synchrotron x-ray diffraction experiments we have constrained the phase diagram of (H 2 S) 2 H 2 within a wide P-T range. On compression we observe the phase transition sequence of I-II-II-III, where II is a previously unreported phase; at room temperature this sequence spans from 5 to 47 GPa, while the application of low temperatures stabilizes this sequence to 127 GPa (< 80 K). Above these pressures we propose that phase III of (H 2 S) 2 H 2 transforms to a nonmolecular H 3 S network. Our Raman and infrared measurements indicate that the transition from (H 2 S) 2 H 2 to H 3 S is reversible at room temperature. X-ray diffraction reveals that the symmetry of the underlying S lattice of (H 2 S) 2 H 2 and H 3 S is retained along this compression path up to at least 135 GPa.

Angle-dispersive x-ray powder diffraction experiments have been performed on yttrium metal up to 183 GPa. We find that the recently discovered oF 16 structure observed in the high-Z trivalent lanthanides is also adopted by yttrium above 106 GPa, pressures where it has a superconducting temperature of ∼20 K. We have also refined both tetragonal and rhombohedral structures against the diffraction data from the preceding "distorted-fcc" phase and we are unable to state categorically which of these is the true structure of this phase. Finally, analysis of yttrium's equation of state reveals a marked change in the compressibility upon adoption of the oF 16 structure, after which the compression is that of a 'regular' metal. Electronic structure calculations of oF 16-Y confirm its stability over oF 8 structure seen in Nd and Sm, and provide insight into the nature of the shift of orbital character from s to d under compression.

The observation of high-temperature superconductivity in hydride sulfide (HS) at high pressures has generated considerable interest in compressed hydrogen-rich compounds. High-pressure hydrogen selenide (HSe) has also been predicted to be superconducting at high temperatures; however, its behaviour and stability upon compression remains unknown. In this study, we synthesize HSe in situ from elemental Se and molecular H at pressures of 0.4 GPa and temperatures of 473 K. On compression at 300 K, we observe the high-pressure solid phase sequence (I-I'-IV) of HSe through Raman spectroscopy and x-ray diffraction measurements, before dissociation into its constituent elements. Through the compression of HSe in H media, we also observe the formation of a host-guest structure, (HSe)H, which is stable at the same conditions as HSe, with respect to decomposition. These measurements show that the behaviour of HSe is remarkably similar to that of HS and provides further understanding of the hydrogen chalcogenides under pressure.