This year’s Highlights again reflect the broad spectrum of scientific applications within the Dynamics and Extreme Conditions Group, and in particular underline the importance of continuously improving the instrumentation and of developing new concepts and ideas.

The first part of the chapter is dedicated to fundamental phenomena. The detection of superradiance and the collective Lamb shift combine beautifully the unique properties of synchrotron radiation, the X-ray wave guide effect and the 57Fe Mössbauer resonance as a two-level system. This intricate setup enabled the detection of the predicted minute energy shift of 24 neV at 14.4 keV, corresponding to a relative change of ΔE/E = 1.7x10-12! The second contribution reveals that the previously thought “homogeneous” supercritical phase of fluids can be partitioned into a liquid- and a gas-like portion, with the disappearance of the positive sound dispersion at THz frequencies marking the boundary between these two regions. The third contribution provides an important new insight into glass physics. High-resolution inelastic X-ray scattering measurements on hot vitreous silica clearly reveal two distinctly different scattering regimes of phonon-like excitations which are intimately related to the peculiar behaviour of the thermal conductivity and specific heat of glasses at low temperature.

The second part of the chapter focusses on high pressure studies. The first two contributions witness the significant progress made in the study of materials in laser-heated diamond anvil cells (DACs). Very tightly focussed and stable X-ray and laser beams, in conjunction with carefully designed diagnostic tools, are the pre-requisites for reliable and trustworthy results. The work on tantalum puts an end to a long-lasting controversy between previous experimental results and theoretical predictions and sets the standard for future work on the melting of solids. The knowledge of melting curves as a function of pressure is of utmost importance to constrain geochemical models and explains seismological observations. This is nicely demonstrated by the X-ray diffraction work on peridotite. In addition to these “static” measurements, the direct determination of sound velocities by inelastic X-ray scattering provides valuable complementary information, as shown in the highlight on the composition of the Earth’s inner core. The last contribution illustrates that the combination of three experimental techniques – X-ray diffraction, X-ray absorption and conventional Mössbauer spectroscopy – were required to unravel the subtle interplay between structural, electronic, and magnetic degrees of freedom in delafossite, a binary transition metal oxide.

The third part of the chapter is devoted to the study of electronic and magnetic properties. The discovery of strong magnetic circular dichroism in K-edge resonant inelastic X-ray scattering (RIXS) opens exciting new perspectives in the study of magnetic materials, taking full advantage of the bulk-, valence-, and site-sensitivity of hard X-ray RIXS. The study of the spin reorientation transition of epitaxially grown Fe on W(110) illustrates the strength of nuclear resonance scattering to detect magnetisation directions with atomic layer resolution and a precision of a few degrees. “Classical” correlated electron systems such as V2O3 still offer new insights thanks to advanced spectroscopies. A systematic study of the temperature, pressure, and doping dependence across the canonical Mott transition suggests that there might actually be two different mechanisms responsible for the metal-insulator transition. Finally, the X-ray Raman study on tetrahydrofuran clathrate hydrate formation gives a flavour of the kind of studies which will become routine once the IXS upgrade beamline UPBL06 becomes operational.

A significant amount of the experiments conducted on the beamlines rely on the excellent support services. The automatic diamond anvil cell gas loading system, the laser drilling device, and the laser annealing setup were important developments of great benefit to the high-pressure community.

Other science-related activities kept the Dynamics and Extreme Conditions Group busy: ID26 and UPBL6 (inelastic X-ray scattering) were reviewed in Spring 2010, and received very positive feedback. In fact, the technical design report for this upgrade beamline (UPBL) was approved, and purchasing of the key components will start at the beginning of 2011. Finally, the group was involved in the organisation of the 7th International Conference on Inelastic X-ray Scattering which was jointly hosted by ESRF and Politecnico di Milano, and attracted more than 160 participants to Grenoble in October 2010.

M. Krisch