Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 36: Poster III

HL 36.16: Poster

Wednesday, March 20, 2024, 18:00–20:30, Poster E

Nonlinear optical observation of time-reversal symmetry breaking in graphene — •Nele Tornow, Omid Ghaebi, and Giancarlo Soavi — Institute of Solid State Physics, Friedrich Schiller University Jena, Jena, Germany

Monolayer graphene (MLG) provides the ideal platform to study the interplay between space inversion symmetry (IS), time-reversal symmetry (TRS), and topology [1]. The development of new ultrafast and non-perturbative all-optical spectroscopy methods could provide invaluable insights in this context, and nonlinear optics (NLO) is a promising approach thanks to its sensitivity to crystal symmetries.

In this work, we use NLO spectroscopy to investigate breaking of TRS in MLG, while preserving IS. To this end, we excite a MLG field-effect transistor with elliptically polarized light, i.e. with perfectly time and space superimposed and degenerate circular (pump) and linear (probe) beams. The circular pump breaks TRS, while the linear component probes the new terms generated in the NLO susceptibility, which result in a rotation of the emitted third-harmonic (TH) signal, in analogy with the valley nonlinear Kerr rotation observed in transition metal dichalcogenides [2]. Preliminary results further show a rotation of the TH signal as a function of both doping and excitation power.

Our results demonstrate a new method for all-optical generation and detection of broken TRS in MLG and thus a new powerful tool to explore topology in centro-symmetric crystals.

[1] McIver, J. W. et al., Nat. Phys. 16, 38-41 (2020)

[2] Herrmann, P. et al., Small 19, e2301126 (2023)

Keywords: Nonlinear optical spectroscopy; Graphene; Time-reversal symmetry; Symmetry breaking