Real-space Green's function approach for Diffraction Anomalous Fine Structure at finite temperature

There has been growing interest in understanding the behavior of materials under non- equilibrium and extreme conditions. Such phenomena can now be probed on femtosecond and even attosecond timescales using x-ray free electron lasers (XFELs). Here, we present a real-space Green’s function (RGSF) approach that provides a unified theoretical framework for modeling non-equilibrium x-ray absorption spectra (XAS), encompassing both finite-temperature XAS (1) and diffraction anomalous fine structure (DAFS) (2). In this framework, the real part of the anomalous x-ray scattering amplitude for DAFS is obtained via a Kramers-Kronig transform of the corresponding XAS spectrum. Illustrative calculations at the Zn K-edge of ZnO are in good agreement with recent experimental pump-probe XAS and DAFS data (3). Ultrafast DAFS emerges as a powerful technique for simultaneously tracking changes in unit-cell parameters and in the local electronic and lattice structure near the resonant atom. This approach provides new opportunities for probing ultrafast structural dynamics in photoexcited materials.

(1) T. S. Tan, J. J. Kas, J. J. Rehr, Phys. Rev. B 104, 035144 (2021).

(2) A. L. Ankudinov, J. J. Rehr, Phys. Rev. B 62, 2437 (2000).

(3) T. C. Rossi, L. Qiao, C. P. Dykstra, R. Rodrigues Pela, R. Gnewkow, R. F. Wallick, J. H. Burke, E. Nicholas, A. M. March, G. Doumy, D. B. Buchholz, C. Deparis, J. Zúñiga-Pérez, M. Weise, K. Ellmer, M. Fondell, C. Draxl, R. M. van der Veen, Communications Materials 6, 191 (2025).