In this project, we will investigate the ultrafast dynamics of spin-polarized carriers in heterostructures of the ferromagnetic oxide EuO on various (insulating and conducting, para-, ferro-, and antiferromagnetic) substrates, and the spin transport properties across their interfaces. In terms of both basic understanding and potential ultrafast spintronic applications, we will address critical questions, for instance about the influence of the band structure on the spin dynamics, the strength and lifetimes of spin currents, and the interaction of different magnetic states in such heterojunctions.

Epitaxial films of EuO grown by oxide molecular beam epitaxy (MBE) will be investigated with various timeresolved techniques available within the CRC/TRR. Most prominently, extreme ultraviolet (XUV)-based time and angle-resolved photoemission spectroscopy (trARPES) will be used to investigate the dynamics of magnetization-induced changes in band structure (semi-metal-insulator transition, exchange splitting) and the lifetime of excited spin-polarized carriers. In addition, excitation above and below the optical bandgap of the oxide film will be used to study the spin transport properties across the metal-oxide interface and its dependence on spin polarization and magnetic state. Complementary experiments using other techniques available within the CRC (X-ray magnetic circular dichroism, THz spectroscopy, magneto-optical methods) will be used to quantify the transient spin polarization and transport dynamics of both substrate and oxide film.

Publications (1^st Funding Period 2018 - 2021)

• Direct measurement of key exciton properties: Energy, dynamics and spatial distribution of the wave function
  S. Dong, M. Puppin, T. Pincelli, S. Beaulieu, D. Christiansen, H. Hubener, C. W. Nicholson, R. P. Xian, M. Dendzik, Y. Deng, Y. W. Windsor, M. Selig, E. Malic, A. Rubio, A. Knorr, M. Wolf, L. Rettig, and R. Ernstorfer
  Nat. Sci. 1, e10010 (2021)  - DOI: 10.1002/ntls.10010

• Ultrafast dynamical Lifshitz transition 
  S. Beaulieu, S. Dong, N. Tancogne-Dejean, M. Dendzik, T. Pincelli, J. Maklar, R. P. Xian, M. A. Sentef, M. Wolf, A. Rubio, L. Rettig, and R. Ernstorfer 
  Sci. Adv. 7 : eabd9275 (2021)  - DOI: 10.1126/sciadv.abd9275

• Exchange-striction driven ultrafast nonthermal lattice dynamics in NiO  
  Y. W. Windsor, D. Zahn, R. Kamrla, J. Feldl, H. Seiler, C.-T. Chiang, M. Ramsteiner, W. Widdra, R. Ernstorfer, and L. Rettig
  Phys. Rev. Lett. 126, 147202 (2021)  - DOI: 10.1103/PhysRevLett.126.147202

• A quantitative comparison of time-of-flight momentum microscopes and hemispherical analyzers for time- and angle-resolved photoemission spectroscopy experiments 
  J. Maklar, S. Dong, S. Beaulieu, T. Pincelli, M. Dendzik, Y. W. Windsor, R. P. Xian, M. Wolf, R. Ernstorfer, and L. Rettig 
  Rev. Sci. Instrum. 91, 123112 (2020)  - DOI: 10.1063/5.0024493

• An open-source, end-to-end workflow for multidimensional photoemission spectroscopy 
  R. P. Xian, Y. Acremann, S. Y. Agustsson, M. Dendzik, K. Bühlmann, D. Curcio, D. Kutnyakhov, F. Pressacco, M. Heber, S. Dong, T. Pincelli, J. Demsar, W. Wurth, P. Hofmann, M. Wolf, M. Scheidgen, L. Rettig, and R. Ernstorfer 
  Sci. Data 7, 442  (2020)  - DOI: 10.1038/s41597-020-00769-8

• Revealing hidden orbital pseudospin texture with time-reversal dichroism in photoelectron angular distributions 
  S. Beaulieu, J. Schusser, S. Dong, M. Schüler, T. Pincelli, M. Dendzik, J. Maklar, A. Neef, H. Ebert, K. Hricovini, M. Wolf, J. Braun, L. Rettig, J. Minár, and R. Ernstorfer
  Phys. Rev. Lett. 125, 216404 (2020)  - DOI: 10.1103/PhysRevLett.125.216404

• Observation of an excitonic Mott transition through ultrafast core-cum-conduction photoemission spectroscopy 
  M. Dendzik, R. P. Xian, E. Perfetto, D. Sangalli, D. Kutnyakhov, S. Dong, S. Beaulieu, T. Pincelli, F. Pressacco, D. Curcio, S. Y. Agustsson, M. Heber, J. Hauer, W. Wurth, G. Brenner, Y. Acremann, P. Hofmann, M. Wolf, A. Marini, G. Stefanucci, L. Rettig, and R. Ernstorfer 
  Phys. Rev. Lett. 125, 096401 (2020)  - DOI: 10.1103/PhysRevLett.125.096401

• Deterministic control of an antiferromagnetic spin arrangement using ultrafast optical excitation 
  Y. W. Windsor, A. Ernst, K. Kummer, K. Kliemt, Ch. Schüßler-Langeheine, N. Pontius, U. Staub, E. V. Chulkov, C. Krellner, D. V. Vyalikh, and L. Rettig 
  Commun. Phys. 3: 139 (2020)  - DOI: 10.1038/s42005-020-00407-0

• Time- and momentum-resolved photoemission studies using time-of-flight momentum microscopy at a free-electron laser 
  D. Kutnyakhov, R. P. Xian, M. Dendzik, M. Heber, F. Pressacco, S. Y. Agustsson, L. Wenthaus, H. Meyer, S. Gieschen, G. Mercurio, A. Benz, K. Bühlman, S. Däster, R. Gort, D. Curcio, K. Volckaert, M. Bianchi, Ch. Sanders, J. A. Miwa, S. Ulstrup, A. Oelsner, C. Tusche, Y.-J. Chen, D. Vasilyev, K. Medjanik, G. Brenner, S. Dziarzhytski, H. Redlin, B. Manschwetus, S. Dong, J. Hauer, L. Rettig, F. Diekmann, K. Rossnagel, J. Demsar, H.-J. Elmers, Ph. Hofmann, R. Ernstorfer, G. Schönhense, Y. Acremann, and W. Wurth 
  Rev. Sci. Instr. 91, 013109 (2020)  - DOI: 10.1063/1.5118777