Studying ultrafast phase transitions by fs Resonant X-ray Diffraction

Sketch showing the approach to studying photoinduced
phase transitions by pump&probe x-ray diffraction.
Here an optical pump pulse selectively excites the e.g.  orbital degree
of freedom and subsequently e.g. the structural degree of freedom is
selectively probed by x-ray diffraction using fs x-ray pulses. The
timescales the perturbation takes to arrive at the various degrees of
freedom allows concluding on the coupling mechanisms involved in
the phase transition. 

The combination of resonant x-ray diffraction with ultra-short light pulses allows studying phase transitions of correlated materials in an ultrafast fashion. Since different phases in correlated materials usually manifest in altered lattice symmetry or the occurrence, disappearance, or modification of ordering phenomena of charge, orbitals, and spins, (resonant) x-ray diffraction is ideally suited to probe any alternation of the individual degrees of freedom.

The crux of pump&probe x-ray diffraction is to study phase transitions away from thermal equilibrium.  A photo-excitation selectively introduces excitation one or a few particular degrees of freedom (see figure below). The induced dynamics and involved time scales on which the perturbation dissipates towards the remaining degrees of freedom yield valuable information on the coupling between the electronic, magnetic and lattice structure. This is why investigations into the photo-induced dynamics of complex materials are an increasingly important research activity in the field of material and life science research. Here you additionally can watch a movie demonstrating the principle of pump&probe x-ray diffraction as a probe of dynamic pathways on multidimensional landscapes. Animation on “Dynamical Pathways on Multidimensional Landscapes” (4.3 MB wmv).

Pump&probe Resonant X-ray Diffraction (RXD) along with pump&probe XMCD and pump&probe XAS is a time resolved x-ray techniques which we provide for external users at our FemtoSPEX facility. A dedicated ultrafast X-Ray Scattering chamber allows for variable wavelength photoexcitation (260nm-18µm) of solid state samples under UHV conditions at variable temperatures from 10K to 450 K. > fs-diffraction chamber