AQP Seminar: Floquet moiré engineering

Aalto Quantum Physics Seminars (Zoom). Speaker: Dr Gabriel E. Topp (Aalto University, Department of Applied Physics)



Mediated by ultrafast light-matter interactions, precisely tunable laser sources nowadays allow for the tailored engineering of material properties on demand [1]. In my research, I apply the ideas of ultrafast control to the newly thriving field of twistronics [2] - the twist-angle-controlled moiré potential engineering of stacked 2D van der Waals heterostructures.

Motivated by the measurement of light-induced Hall currents in graphene [3], I will first discuss the topological properties of intermediate-angle twisted bilayer graphene (TBG). Employing a full moiré-unit-cell tight-binding model, I will present how circularly polarized light can induce a controllable transition to a topologically nontrivial Floquet band structure [4]. By revealing a surprisingly strong light-matter response for smaller twist angles and associated strongly quenched band velocities, I will slightly switch gears to light-matter couplings (LMCs) in flat-band systems for the second half of my talk.

By pointing out fundamental relations between LMCs and quantum geometry in a generic multiband setting, I will show how the nontrivial properties of the electronic wavefunction sustain a finite light-matter response in flat electronic bands despite a diverging effective mass. Finally, I will employ these conceptual findings to discuss the static and dynamic light-matter response for magic-angle TBG [5].

The presented results provide an essential step towards ultrafast switching protocols and the future integration of moiré materials into optoelectronic devices.



[1] A. de la Torre, D. M. Kennes, M. Claassen, S. Gerber, J. W. McIver, and M. A. Sentef “Nonthermal pathways to ultrafast control in quantum materials”. In: arXiv:2103.14888 (2021).

[2] S. Carr, D. Massatt, S. Fang, P. Cazeaux, M. Luskin, and E. Kaxiras “Twistronics: Manipulating the electronic properties of two-dimensional layered structures through their twist angle”. In: Phys. Rev. B 95, 075420 (2017).

[3] J. W. McIver, B. Schulte, F.-U. Stein, T. Matsuyama, G. Jotzu, G. Meier, and A. Cavalleri “Light-induced anomalous Hall effect in graphene”. In: Nature Physics 16, 38-41 (2020).

[4] G. E. Topp, G. Jotzu, J. W. McIver, L. Xian, A. Rubio, and M. A. Sentef “Topological Floquet engineering of twisted bilayer graphene”. In: Phys. Rev. Research 1, 023031 (2019).

[5] G. E. Topp, C. J. Eckhardt, D. M. Kennes, M. A. Sentef, and P. Törmä “Light-matter coupling and quantum geometry in moiré materials”. In: arXiv:2103.04967 (2021).




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