ELFT HÍRADÓ

[Szeminárium koordinátor <szfi-seminar AT wigner.hun-ren.hu>]

Dear Colleagues,
Please find the updated invitation for the upcoming seminar below. This 
version includes the corrected start time as well as the missing title and 
abstract.
I am sorry for any confusion caused by the previous message.
Best regards,
Tamás PusztaiSZFI Seminar
Vámos, Lénárd
(Institute of Photonic Sciences (ICFO), host: Dombi, Péter)
Investigating bulk TMDC materials by high-harmonic spectroscopy
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)Tuesday, 12 May 2026, 10:00
Wigner FK SZFI, Bldg. 1, 2nd floor auditorium
Language of the talk: English
All interested are welcome!
Attila Nagyszfi-seminar AT wigner.hun-ren.hu