We make use of time-resolved diffraction techniques to investigate both, the structural dynamics of the crystal lattice, and the dynamics of electronic, orbital and spin ordering in complex oxides following their optical excitation.
Resonant soft X-ray diffraction (RSXD) is an extremely powerful tool to investigate element-specific electronic and magnetic ordering phenomena on nanometer length scales. This technique combines X-ray absorption spectroscopy with momentum selective diffraction, and therefore, is particularly attractive for the investigation of complex oxides, in which periodic spatial modulations of the charges, orbitals, spins and the lattice are a key ingredient. We exploit this technique to understand the physical pathway of optically induced phase transitions in the transition metal oxide systems. To this end, we extend RSXD to the time domain, with experiments carried out at the DIAMOND Light Source synchrotron storage ring [I06 BEAMLINE] and the LCLS free electron laser [SXR BEAMLINE]. Pump pulses in the infrared or mid-infrared, synchronized to the soft X-ray probe pulses, allow for stimulating the samples under investigation.
Hard X-ray diffraction (at wavelengths in the 0.5-2 Angstrom range) provides direct access to the atomic arrangement within matter. Correlating the atomic structure to the (functional) macroscopic physical or chemical properties of a solid has been a primary task of this technique over many decades. Further interest in this technique has been raised through the availability of femtosecond X-ray pulses, which enable exploring fundamental processes in nature on their intrinsic time scale given by the motion of atoms. Our specific interest in femtosecond hard X-ray diffraction arises from the eagerness to understand the dynamic interactions between the structural and the electronic/magnetic degrees of freedom in strongly correlated materials. We seek to disclose the structural response that is capable of unbalancing the interplay with charges and spins in order to drive ultrafast phase transitions, particularly following the coherent lattice control by selective phonon excitation.
