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Speaker: Michael Schüler
Tracking topological signatures by time- and angle-resolved photoemission spectroscopy
Angle-resolved photoemission spectroscopy (ARPES) is one of the most powerful tools to study the electronic properties of solids. Besides providing a wealth of information on the momentum-dependent band structure, the impressive progress in high-resolution and multi-dimensional ARPES allows insights into the nature of the quantum states in the solid itself. In this talk, we will discuss how topological properties like Berry curvature and orbital angular momentum are manifest in circular dichroism in ARPES. Based on an intuitive wave-packet description and corroborated by state-of-the-art first-principle calculations, we demonstrate how momentum-resolved Berry curvature can be mapped out for prototypical two-dimensional materials.
Furthermore, topological properties can be induced by tailored light. In particular, graphene pumped by circularly polarized light is the paradigmatic example of such a Floquet-Chern insulator. However, realizing the induced Floquet-Chern insulator state and tracing clear experimental manifestions has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic nonequilibrium Green’s functions (NEGF) calculations including realistic electron-electron and electron-phonon scattering. This allows us to study the stability of the Floquet features due to dephasing and thermalization effects. Combining our nonequilibrium calculations with an accurate one-step theory of photoemission allows us to establish a direct link between the build-up of the topological state and the dichroic pump-probe photoemission signal.
References:
[1] M. Schüler, U. De Giovannini, H. Hübener, A. Rubio, M. Sentef, P. Werner, Sci. Adv. 6, eaay2730 (2020)
[2] M. Schüler, U. De Giovannini, H. Hübener, A. Rubio, M. Sentef, T. Devereaux, P. Werner, arXiv:2003.11621 [cond-mat] (2020)