How Circular Dichroism in Time- and Angle-Resolved Photoemission Can Be Used to Spectroscopically Detect Transient Topological States in Graphene

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature has been a challenge, and it has become clear that scattering effects p...

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Bibliographic Details
Published in:Physical review. X 2020-10, Vol.10 (4), p.041013, Article 041013
Main Authors: Schüler, Michael, De Giovannini, Umberto, Hübener, Hannes, Rubio, Angel, Sentef, Michael A., Devereaux, Thomas P., Werner, Philipp
Format: Article
Language:English
Subjects:
Accumulation
Angle-resolved photoemission spectroscopy
Circular polarization
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Dichroism
Electronic structure
Electrons
Fault tolerance
Floquet systems
Graphene
Laser beam heating
Lasers
Mathematical analysis
Nonequilibrium Green's function
Photoelectric emission
Photoelectron spectroscopy
Playgrounds
Polarized light
Quantum computing
Quantum phenomena
Scattering
Spectrum analysis
Thermalization (energy absorption)
Topological insulators
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Summary:Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature 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 approach allows us to study the robustness of the Floquet features against 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 give 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 shown to be stable against heating and dephasing effects. Thus, tracing circular dichroism in time-resolved photoemission provides new insights into transient topological properties.
ISSN:2160-3308
2160-3308
DOI:10.1103/PhysRevX.10.041013