The vision of our research is pushing angle-resolved photoemisssion spectroscopy (ARPES) to a new level. Traditionally, ARPES is used to access band-structure information of solids. However, the synergy of unprecedented resolution and state-of-the-art theory allows to trace quantum degrees of freedom, including topological effects.

ARPES can be understood in terms of Fermi's Golden rule, which determines the photoemission intensity from the initial Bloch states, final photoelectron states, and the experimental geometry. The key ingredient containing information on the initial complex-valued wave-function is the photoemission matrix element. Connecting specific features of ARPES to the matrix elements thus allows for extracting wave-function properties. This is enabled by the power of multi-dimensional ARPES: recording spectra with additional degrees of freedom.

Combining state-of-the-art theory and experiments, we have already made some steps into this exciting field. In collaboration with the group of Angel Rubio (MPSD Hamburg) we unraveled the distinct signatures of momentum-resolved Berry curvature in paradigmatic 2D materials from circular dichroism. In collaboration with Samuel Beaulieu and Ralph Ernstorfer (FHI Berlin) we showed how properties of the orbital pseudospin – a measure of interference of the relevant orbitals – can be obtained from time-reversal dichroism. We pushed this idea even further to multi-dimensional ARPES, where the extra dimension is the continuously tunable light polarization.

Relevant publications:

  1. Polarization-Modulated Angle-Resolved Photoemission Spectroscopy: Towards Circular Dichroism without Circular Photons and Bloch Wavefunction Reconstruction
    M. Schüler, T. Pincelli, S. Dong, T. P. Devereaux, M. Wolf, L. Rettig, R. Ernstorfer, S. Beaulieu
    arXiv:2103.17168 (2021)

  2. Unveiling the Orbital Texture of 1T-TiTe2 using Intrinsic Linear Dichroism in Multidimensional Photoemission Spectroscopy
    S. Beaulieu, M. Schüler, J. Schusser, S. Dong, T. Pincelli, J. Maklar, A. Neef, F. Reinert, M. Wolf, L. Rettig, J. Minár, R. Ernstorfer
    arXiv:2107.07158 (2021), in print in NPJ Quantum Materials

  3. 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, R. Ernstorfer
    Phys. Rev. Lett. 125, 216404 (2020)

  4. How Circular Dichroism in Time- and Angle-Resolved Photoemission Can Be Used to Spectroscopically Detect Transient Topological States in Graphene
    M. Schüler, U. De Giovannini, H. Hübener, A. Rubio, M. A. Sentef, T. P. Devereaux, P. Werner
    Phys. Rev. X 10, 041013 (2020)

  5. Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials
    M. Schüler, U. d. Giovannini, H. Hübener, A. Rubio, M. A. Sentef, P. Werner
    Sci. Adv. 6, eaay2730 (2020)