The discovery of superconductivity is more than 100 years old, and the BCS theory, describing the phenomenon in its conventional version, is now 60. Today, the mechanism at the heart of the "high temperature" superconductivity (non BCS), discovered 30 years ago, remains to be identified. In all cases, the superconducting phase is characterized by the opening of a gap between the occupied and unoccupied electronic states, which closes above the critical temperature, in the normal phase.
In a joint project between the LSI, LPS and UPMC, it is observed by time-resolved angular resolved photoemission spectroscopy (TR-ARPES) that upon an ultra-short pulsed laser excitation of the electrons, the superconductor gap can be transiently closed in specific crystallographic directions, during a time in the femtoseconde range. This observation illustrates the potentialities of the method that provides a new way of exploring the mysteries of high temperature superconductivity. The method seems similarly promising in the investigation of the physics of fast electron dynamics of other strongly driven systems, like polaritons and ultracold atoms.
|The chemical bonding in actinide compounds is usually analysed by inspecting the shape and the occupation of the orbitals or by calculating bond orders which are based on orbital overlap and occupation numbers. However, this may not give a definite answer because the choice of the partitioning method may strongly influence the result possibly leading to qualitatively different answers. In this review, we summarized the state-of-the-art of methods dedicated to the theoretical characterisation of bonding including charge, orbital, quantum chemical topology and energy decomposition analyses. This review is not exhaustive but aims to highlight some of the ways opened up by recent methodological developments. Various examples have been chosen to illustrate this progress.
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for biology, allowing structural and chemical analysis of metabolites as well as imagery (MRI). A collaboration of scientists from Nimbe, Neurospin and Bordeaux University, has recently designed a non-invasive online NMR μ-probe for profiling in-vivo metabolic physiological activities with a micro-size NMR detector placed in "close proximity" to a microdialysis sampling probe. Such a device is able to perform real-time diagnostic, deciphering complex metabolic activities.