The 165th AMCP Open Seminar

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Prof.Uwe Bovensiepen

Faculty of Physics and Center for Nanointegration (CENIDE)

University of Duisburg-Essen, Germany

Institute for Solid State Physics, University of Tokyo, Japan

Local and nonlocal electron and spin dynamics in metallic materials

analyzed with time-resolved solid state spectroscopy

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 specific 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 photo-electron emission [3] which allowed to analyze the hot electron transport mechanism. A complementary approach which provides element- and site specificity is soft x-ray absorption spectroscopy [4]. Here, recent experimental results obtained at the synchrotron light source BESSY II using femtosecond slicing [4] and at the SCS endstation of the European X-FEL [5-7] will be discussed.
 

References

[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] N. Rothenbach, M. E. Gruner, K. Ollefs, C. Schmitz-Antoniak, S. Salamon, P. Zhou, R. Li, M. Mo, S. Park, X. Shen, S. Weathersby, J. Yang, X. J. Wang, R. Pentcheva, H. Wende, U. Bovensiepen, K. Sokolowski-Tinten, A. Eschenlohr, Phys. Rev. B 100, 174301 (2019).

[5] T. Lojewski et al., arXiv: 2210.13162.

[6] R. Engel et al., arXiv: 2211.17008.

[7] L. LeGuyader et al., arXiv: 2211.04265.