Abstract
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.
Highlights
Topological properties play an important role in a wide range of phenomena in condensed matter systems
The simple physical picture based on the effective Brillouin-Wigner Hamiltonian provides a simple description of the opening of the effective bands but fails to take dynamical processes into account
We presented a detailed investigation of the topological properties of graphene pumped with circularly polarized light under realistic conditions
Summary
Topological properties play an important role in a wide range of phenomena in condensed matter systems. As an alternative technique for detecting the induced topological state, time-resolved transport experiments on graphene show a pump-induced Hall response [27] In these experiments, a pump-induced population imbalance plays a role [28,29], and disentangling such effects from those of the induced Berry curvature is a nontrivial task. The associated heating and dephasing effects compete with the coherence required for a Floquet state [30,31], it is not clear yet which scattering mechanism is most important We address this challenge in the present work by considering the pump-induced dynamics in graphene including both electron-electron (e-e) and electron-phonon (e-ph) scattering. All details on the methods can be found in Appendix C
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