Resolving CuO chain andCuO2plane contributions to theYBa2Cu3O7−

Surface structure determination by x-ray standing waves at a free-electron laser

“…Time-resolved structural data will enormously contribute to the fundamental understanding of more complex processes in heterogeneous catalysis both on single metal crystals [53] and more exotic layered crystals as perovskites [54], leading eventually to more efficient catalysts. In addition, time-resolved XSW may reveal the structural dynamics at the basis of light-induced superconductivity [55][56][57] by providing element and site specific atomic positions [58][59][60] as a function of the delay from the light pump pulse. This could pave the way to solve the longstanding puzzle of high critical temperature superconductors and indicate the appropriate crystal structure to enhance superconductivity.…”

Element- and momentum-resolved electronic structure of the dilute magnetic semiconductor manganese doped gallium arsenide

“…It has long been realized through various theoretical studies and experimental comparisons that, as the photon energy is increased, the matrix elements and cross sections for valence photoemission are increasingly controlled by the inner spatial regions of each atom involved [23,24,25], thus making the decomposition above a better and better approximation. This sort of superposition has also been used previously to analyze SW spectra in the hard X-ray DOS limit [13,14,15,16,17], but not with momentum resolution, which is unique to this study.…”

“…In the next step, we assume that the SW variation of these components with photon energy will follow the core intensity for a given atom as a function of photon energy, again an assumption that has been used before [13][14][15][16][17]. Each core intensity is normalized to unity away from the Bragg reflection, such that it should represent the fractional variation of a given component of the valence intensity as the SW position moves.…”

“…The purely experimental quantities derivable from Eq. 1 can also, through the same assumptions of prior work [13][14][15][16][17][23][24][25] be related to partial densities of states As and Ga and the differential photoelectric cross sections of the dominant orbitals making up the valence states, here being Ga 4s 2 +4p 1 , As 4s 2 +4p 3 , and Mn 3d 5 +4s 2 , as averaged over the spectrometer detection range:…”

“…In particular, standing-wave excitation from Bragg crystal planes provides a way to differentiate a signal from the specific sites within a single unit cell of a single-crystalline or epitaxial material. This has previously been successfully employed by Woicik et al [13,14], Kim et al [15] and Thiess et al [16,17] to decompose valence-band spectra into site-specific components. However, the momentum information was not accessible in these experiments due to some combination of the lack of angle-resolving capabilities in the energy analyzers used and the momentum-smearing effects of phonon excitations, which significantly lower the fraction of direct transitions in hard X-ray photoemission [7,8,18].…”