Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO.

We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.

Band-Resolved Double Photoemission Spectroscopy on Correlated Valence Electron Pairs in Metals.

Correlated valence electrons in Ag and Cu are investigated using double photoemission spectroscopy driven by a high-order harmonic light source. Electron pairs consisting of two d electrons as well as pairs with one sp and one d electron are resolved in the two-dimensional energy spectrum. Surprisingly, the intensity ratio of sp-d to d-d pairs from Ag is 3 times higher than in the self-convoluted density of states.