Contribution Invited Oral
Polarization dependent X-ray spectroscopy: recent advances
Development of the third generation synchrotron radiation sources has boosted X-ray spectroscopy, as illustrated by the discovery of a variety of new experimental techniques associated with the exploitation of the polarisation properties of x-rays. The detection of X-ray magnetic linear and circular dichroism in ferro-, ferri- and paramagnetic systems, the discovery of X-ray natural circular dichroism in gyrotropic single crystals as well as the observation of non-reciprocal X-ray linear dichroism and X-ray magneto-chiral dichroism in magnetoelectric systems are particularly interesting. In combination with sum rules these spectroscopies appear as remarkable tools to study fundamental properties of matter via various order parameters, e.g., spin and orbital moments, electric dipole moment, toroidal moments etc. In this talk we report on advanced instrumentation developments carried out over the past 25 years at the ESRF beamline ID12 which is dedicated to polarization dependent x-ray spectroscopy at photon energies above 2keV. Emphasis is laid on control of the polarization state of the x-ray beam and on the detection systems. We highlight two recent science-driven instrumentation developments initiated by the ID12 team: the first one deals with measurements of x-ray magnetic circular dichroism under multiple extreme conditions (high magnetic field, low temperatures and high pressure); the second examples concerns x-ray detection of optical activity in non-centrosymmetric crystals.