X-ray natural circular dichroism in langasite crystal

Abstract

Optical activity in the X-ray range stems from the electric-dipole–electric-quadrupole interference terms mixing multipoles of opposite parity, and can be observed exclusively in systems with broken inversion symmetry. The gyration tensor formalism is used to describe the X-ray optical activity in langasite La3Ga5SiO14crystal with theP321 space group. An experimental study of the X-ray natural circular dichroism (XNCD) near the GaK-edge in La3Ga5SiO14single crystal was performed at ESRF beamline ID12, both along and perpendicular to the crystal optical axis. The combination of the quantum mechanical calculations and high-quality experimental results has allowed us to separate the contributions into X-ray absorption and XNCD spectra of Ga atoms occupying three distinct Wyckoff positions.