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HL: Fachverband Halbleiterphysik
HL 2: 2D Semiconductors and van der Waals Heterostructures I
HL 2.9: Vortrag
Montag, 17. März 2025, 11:45–12:00, H15
Universal and ultrafast probe of broken time-reversal symmetry — •Florentine Friedrich1, Paul Herrmann1, Sebastian Klimmer1, Zdeněk Sofer2, Shridhar Sanjay Shanbhag3, Jan Wilhelm3, and Giancarlo Soavi1 — 1Institute of Solid State Physics, University of Jena, Germany — 2Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Czech Republic — 3Institute of Theoretical Physics and Regensburg Center for Ultrafast Nanoscopy, University of Regensburg, Germany
Time-reversal symmetry (TRS) defines some of the most fundamental properties of condensed matter, such as the relation between energy, spin and Berry curvature, therefore influencing features like topology or non-trivial spin textures. Two-dimensional transition metal dichalcogenides (TMDs) offer the possibility to engineer TRS and space-inversion symmetry independently, rendering them excellent model systems. TRS in TMDs can be lifted via, e.g. valley-selective bandgap opening. Nonlinear optics (NLO) as a probe of TRS is non-invasive and ultrafast; however, detection via second harmonic generation is limited to non-centrosymmetric systems. In this work, we make the nonlinear all-optical probe of broken TRS universal by utilizing polarization-resolved third harmonic generation (THG), which is always present also in centro-symmetric crystals. As a proof of principle, we probe broken TRS in a TMD monolayer, by using elliptically polarized light, leading to valley and spin asymmetric gap opening. We then test our method on a TMD bilayer, probing broken TRS in a centrosymmetric system with THG for the first time.
Keywords: Time-reversal symmetry; Transition metal dichalcogenides; Nonlinear optics; Two-dimensional materials