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SUMMARY:Shift current response in 2D materials – A study in moiré graph
 ene systems and Janus transition-metal dichalcogenides - Dr Yuncheng Mao (
 Aix-Marseille Université)
DTSTART:20260326T140000Z
DTEND:20260326T151500Z
UID:TALK244111@talks.cam.ac.uk
CONTACT:Bo Peng
DESCRIPTION:The Bulk photovoltaic effect (BPVE) has long been believed to 
 hold enormous potential for the designing of the  next-generation solar ce
 ll components of ultra-high light energy conversion efficiency. Different 
 from the conventional photovoltaic effect\, BPVE does not depend on the in
 ternally built electric field created by the PN-junction of two semiconduc
 tors. With its nature being non-linear response to light excitation\, theo
 retical study of BPVE falls into a special case of second-harmonic generat
 ion (SHG) where the alternating external field outputs a DC current respon
 se. The lack of centrosymmetry lies at the center of the onset mechanism o
 f BPVE. Here I will focus on one type of BPVE current called shift current
 . Two types of approaches of studying shift current were applied to moiré
  twisted multilayer graphene layers and Janus transition-metal dichalcogen
 ides\, respectively. The moiré systems are shown to have a special moiré
  amplification effect where the amplitude of shift current response is exp
 ected to be inversely proportional to the square of the twist angle. The r
 esponse to light is limited to infrared regime\, with giant and various re
 sponses to far infrared light and stable large response to mid-infrared ex
 citations. In the Janus TMD system\, steady shift current response to vis-
 UV light was confirmed via TDDFT/MPBT calculations. Through comparative st
 udying by different treatment of interactions in the system\, it is shown 
 that interaction and correlation have substantial influences on the shift 
 current response\, where we remark particularly the importance of excitoni
 c states.
LOCATION:Seminar Room 3\, RDC.
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