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HL: Fachverband Halbleiterphysik

HL 2: 2D Materials and Heterostructures: Photonic Aspects

HL 2.1: Talk

Monday, March 18, 2024, 09:30–09:45, EW 201

Measuring the complex valley polarization nonlinear susceptibility in monolayer WSe₂ — •Paul Herrmann, Sebastian Klimmer, Till Weickhardt, and Giancarlo Soavi — Institute of Solid State Physics, Friedrich Schiller University Jena, Jena, Germany

Valleytronics suffers from the lack of an ideal method to probe the valley degree of freedom. Both state of the art methods, namely polarized photoluminescence and Kerr rotation, are insensitive to the complex nature of valley polarization (VP). More generally, one can view measuring VP as probing broken time-reversal (TR) symmetry. As second harmonic generation (SHG) is sensitive to symmetry, it was proposed as a probe of VP. However, said method of probing the rotation in the SHG pattern of elliptically polarized pulses [1] suffers from limited valley adressability and also disregards the complex nature of VP. In this work we overcome both aforementioned problems [2]. We develop and demonstrate a new method that probes the interference between electric-dipole and VP in the SHG signal when we directly excite at ±K resonance with circularly polarized light. We show that such interference can only be explained by taking into consideration the complex nature of VP, in analogy to the magnetic- to electric-dipole interference observed in bulk magnets [3]. Our work provides a new method for detection of VP and we argue that it could be extended to probe broken TR symmetry in other crystal classes.
[1] Herrmann, P. et al.: small 2023 19:2301126
[2] Herrmann, P. et al.: arXiv 2023 2310.16549
[3] Fiebig, M. et al.: PRL 1994 15(73)

Keywords: Nonlinear optics; Valleytronics; Two-dimensional materials; Time-reversal symmetry