Local and Nonlocal Electron and Spin Dynamics of Au/Fe/MgO(001) Analyzed by Pump-Probe Experiments

日時　2023年2月3日　（金）　14：30～15：30
場所　広島大学放射光科学研究センター　2階　セミナー室(オンライン併用)
講師　Uwe Bovensiepen
(Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen)

An excited electron propagates in condensed matter with its momentum k at an energy E(k) and experiences elastic and inelastic scattering processes, which lead to electronic relaxation and energy transfer to microscopic excitations of the lattice and spin systems. Experiments employing femtosecond time-resolved photoelectron spectroscopy exploited so far very successfully the surface sensitivity of the method and probed such scattering processes locally at or near the surface in the time domain [1]. Here, we report on experimental results which analyze the non-local dynamics of excited electrons in two-photon photoemission (2PPE) and demonstrate sensitivity to buried media [2]. In these experiments one photon excites in Au/Fe/MgO(001) heterostructures electrons in Fe. Electron propagation through the layer stack to the Au surface is detected in 2PPE in back side pump – front side probe experiments in a time-of-flight like scheme. We observe pronounced differences between front- and back-side pumping of the heterostructure which are attributed to electron transport contributions through the layer stack. These experiments were extended recently to time-resolved linear photoelectron emission [3] which allowed to analyze the hot electron transport mechanism. A perspective for spin-resolved experiments will be based on time-resolved linear and non-linear optical experiments [4,5] using the back-side vs. front-side pumping geometries and Au/Fe/MgO(001).

[1] U. Bovensiepen, H. Petek, M. Wolf, Dynamics at Solid State Surface and Interfaces, Vol. 1, Wiley-VCH, 2010.
[2] Y. Beyazit J. Beckord, P. Zhou, J. Meyburg, F. Kühne, D. Diesing, M. Ligges, U. Bovensiepen, Phys. Rev. Lett. 125, 076803 (2020).
[3] F. Kühne, Y. Beyazit, B. Sothmann, J. Jayabalan, D. Diesing, P. Zhou, U. Bovensiepen, Phys. Rev. Research 4, 033239 (2022).
[4] A. Melnikov, I. Razdolski, T. O. Wehling, E. Th. Papaioannou, V. Roddatis, P. Fumagalli, O. Aktsipetrov, A. I. Lichtenstein, U. Bovensiepen, Phys. Rev. Lett. 107, 076601 (2011).
[5] I. Razdolski, A. Alekhin1, N. Ilin, J. P. Meyburg, V. Roddatis, D. Diesing, U. Bovensiepen, A. Melnikov, Nature Commun. 8, 15007 (2017).

問合せ先　黒田健太(先進理工系科学研究科)、出田真一郎（放射光科学研究センター）