How Circular Dichroism in time- and angle-resolved photoemission can be used to spectroscopically detect transient topological states in graphene

(submitted), (2020)

How Circular Dichroism in time- and angle-resolved photoemission can be used to spectroscopically detect transient topological states in graphene

Michael Schüler, Umberto De Giovannini,Hannes Hübener,Angel Rubio,Michael A. Sentef, Thomas P. Devereaux, Philipp Werner

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. 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 quantum kinetic calculations including realistic electron-electron and electron-phonon scattering. Our theory provides a direct link to the build-up of the Floquet-Chern insulator state in light-driven graphene and its detection in time- and angle-resolved photoemission spectroscopy (ARPES). This allows us to study the stability of the Floquet features due to dephasing and thermalization effects. We also discuss the ultrafast Hall response in the laser-heated state. Furthermore, the induced pseudospin texture and the associated Berry curvature gives rise to momentum-dependent orbital magnetization, which is reflected in circular dichroism in ARPES (CD-ARPES). 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. The characteristic features in CD-ARPES are further corroborated to be stable against heating and dephasing effects. Thus, tracing circular dichroism in time-resolve photoemission provides new insights into transient topological properties.

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arxiv
http://arxiv.org/abs/2003.11621
Notes
We acknowledge helpful discussion with Shunsuke A. Sato.M. S. and T. P. D. acknowledge financial support from the U. S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under contract no. DE-AC02-76SF00515. Furthermore, this work was supported by the Swiss National Science Foundation via NCCR MARVEL and the European Research Council via ERC-2015-AdG-694097 and ERC Consolidator Grant No. 724103. The Flatiron Institute is a division of the Simons Foundation. M. S. thanks the Alexander von Humboldt Foundation for its support with a Feodor Lynen scholarship and the Department. M. A. S. acknowledges financial support by the DFG through the Emmy Noether program (SE 2558/2-1).

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