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SUMMARY:Nonlinear all-optical control and detection of ultrafast bandgap e
 ngineering
DTSTART:20250717T141500Z
DTEND:20250717T153000Z
DTSTAMP:20261017T153300Z
UID:indico-event-539@indico.physik.uni-siegen.de
CONTACT:stefan.nimmrichter@uni-siegen.de
DESCRIPTION:Speakers: Giancarlo Soavi (Institute of Solid State Physics\, 
 Friedrich Schiller University Jena)\n\nLayered materials\, such as graphen
 e and transition metal dichalcogenides (TMDs)\, possess unique nonlinear o
 ptical (NLO) properties [1]\, which allow a full control over the intensit
 y [2\,3]\, polarization [4] and orbital angular momentum [5] of the light 
 emitted via perturbative harmonic generation processes. Furthermore\, TMD
 s have emerged as the ideal platform to study the interplay between space-
 inversion and time-reversal symmetries\, which can be independently engine
 ered in by tuning the number of layers (space-inversion) and via excitatio
 n with circularly polarized light (time-reversal). In this talk\, I will d
 iscuss our recently developed approaches to modulate the bandgap in TMDs u
 sing ultrafast and off-resonant excitation\, and the possibility to subseq
 uently detect broken time-reversal symmetry using second [6\,7] and third 
 harmonic generation. In particular\, all-optical bandgap modulation can be
  achieved via the coherent optical Stark and Bloch-Siegert effects\, with 
 the additional degree of freedom to create either a symmetric or asymmetri
 c bandgap opening in the ±K valleys\, depending on the number of layers o
 f the sample and the polarization state of the excitation beam. In monolay
 er TMDs\, a valley asymmetric bandgap modulation effectively corresponds t
 o breaking of time-reversal symmetry. In bilayer TMDs\, broken time-revers
 al symmetry manifests itself as a valley symmetric bandgap modulation\, wh
 ich lifts the spin degeneracy. Subsequently\, both symmetric and asymmetri
 c all-optical bandgap modulation can be probed via polarization and intens
 ity dependent measurements of perturbative nonlinear optics.\nReferences\n
 \n\nDogadov\, O. et al.\, “Parametric Nonlinear Optics with Layered Mate
 rials and Related Heterostructures”\, Laser & Photon. Rev.\, Vol. 16\, N
 o. 9\, 2100726\, 2022\n\n\nSoavi\, G. et al.\, “Broadband\, electrically
  tunable third-harmonic generation in graphene”\, Nat. Nanotechnol.\, Vo
 l. 13\, 583-588\, 2018 \n\n\nGhaebi\, O. et al.\, “Ultrafast Opto-Electr
 onic and Thermal Tuning of Third-Harmonic Generation in a Graphene Field E
 ffect Transistor”\, Adv. Science\, Vol. 11\, No. 31\, 2401840\, 2024\n\n
 \nKlimmer\, S. et al.\, “All-optical polarization and amplitude modulati
 on of second-harmonic generation in atomically thin semiconductors”\, Na
 t. Photon.\, Vol. 15\, 837-842\, 2021\n\n\nSinelnik\, A. et al.\, “Ultra
 fast all-optical second harmonic wavefront shaping”\, Nat. Comms.\, Vol.
  15\, 2507\, 2024\n\n\nHerrmann\, P. et al.\, “Nonlinear valley selectio
 n rules and all-optical probe of broken time-reversal symmetry in monolaye
 r WSe2”\, Nat. Photon.\, Vol. 19\, 300-306\, 2025\n\n\nHerrmann\, P. et 
 al.\, “Nonlinear All-Optical Coherent Generation and Read-Out of Valleys
  in Atomically Thin Semiconductors”\, Small\, Vol. 19\, No.37\, 2301126\
 , 2023\n\n\n \n\nhttps://indico.physik.uni-siegen.de/event/539/
LOCATION:ENC-D114 (ENC)
URL:https://indico.physik.uni-siegen.de/event/539/
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