Előadó: Vámos Lénárd (Institute of Photonic Sciences (ICFO), vendéglátó: Dombi, Péter)
Előadásának címe: Investigating bulk TMDC materials by high-harmonic spectroscopy
Dátum: 2026. május 12. kedd, 10 óra
Helyszín: 1-es épület tanácsterem
Összefoglaló:
The emergence of valley polarization in monolayers of layered transition metal dichalcogenides (TMDCs) and charge-density-wave (CDW) order in their bulk phases are key research areas in modern condensed matter physics. In my talk, building on two recent experimental–theoretical works, I will demonstrate how high-harmonic spectroscopy (HHG) can be applied to probe the electronic topology and hidden order parameters of these materials, even in the case of bulk crystals.
First, focusing on bulk MoS₂, I will show how optical control pulses carrying spin angular momentum with a polarization more complex than circular, resembling a propeller, can be used to transiently break time-space inversion symmetry. This universal, non-resonant method enables all-optical, ultrafast switching of valley polarization without the need for monolayer structures. The phenomenon was verified by generating the second-harmonic of a non-resonant probe beam [1].
Second, I will investigate the CDW phase of TiSe₂ using high-harmonic generation. The asymmetry in the intensity of high harmonics as a function of the incident laser polarization angle directly reflects the anisotropic CDW order in the low-temperature phase. Using a phenomenological mean-field model, we successfully reproduced the experimental observations, opening new perspectives for optically probing the nature of CDW order [2].
Our results suggest that, contrary to conventional wisdom, bulk TMDC materials may provide a platform for ultrafast valleytronics and topological phase transitions just as viable as their thin-layer counterparts.
References:
[1] I. Tyulnev, Á. Jiménez-Galán, J. Poborska, L. Vamos, P. St. J. Russell, F. Tani, O. Smirnova, M. Ivanov, R. E. F. Silva and J. Biegert, Valleytronics in bulk MoS₂ with a topologic optical field, Nature 628(8009), 746–751 (2024)
[2] L. Zhang, I. Tyulnev, L. Vamos, J. Poborska, U. Bhattacharya, R. W. Chhajlany, T. Grass, J. Biegert and M. Lewenstein, Revealing the anisotropic charge-density-wave order of TiSe₂ through high harmonic generation, Physical Review B 112, 085147 (2025)
