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SUMMARY:Optical properties of 2D semiconductors in van der Waals heterostr
 uctures
DTSTART:20170616T151500
DTSTAMP:20260506T004118Z
UID:ab46ad30d537b6e543a46085466ee1da443116c29ed71648419d7046
CATEGORIES:Conferences - Seminars
DESCRIPTION:Bernhard Urbaszek CNRS – Toulouse University\, France\nTrans
 ition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 are layered mate
 rials that are semiconductors with a direct bandgap when thinned down to o
 ne monolayer. The current research effort on TMDC structures for optoelect
 ronics and spintronics\, often based on monolayer samples obtained by simp
 le exfoliation using adhesive tape\, is motivated by several remarkable pr
 operties : First\, TMDC monolayers strongly interact with light in the vis
 ible region of the optical spectrum. The optically generated electrons and
  holes form excitons with high binding energy (several hundred meV) and hi
 gh oscillator strength\, resulting in optical absorption up to 20 % per mo
 nolayer. Second\, the valence and conduction spin states are split in ener
 gy by a strong Spin Orbit interaction. Third\, interband optical selection
  rules are polarization selective (chiral). This allows addressing non-equ
 ivalent valleys in momentum space with polarized lasers for optical spin a
 nd valley index manipulation.\nTo address the intrinsic optical properties
  of these materials we investigate TMDC monolayers ‘sandwiched’ betwee
 n ultrathin insulating layers of hexagonal boron nitride (hBN) in van der 
 Waals heterostructures. The optical emission of these encapsulated monolay
 ers is spectrally narrow (down to 1 nm FWHM) comparable to emission from I
 II-V quantum well structures used in today’s optoelectronic devices and 
 approaching the homogenous limit. This allows accessing the optical and sp
 in properties of these materials with unprecedented detail for neutral and
  charged excitons (trions). As important examples\, we are able to compare
  exciton resonances with transition dipoles in-plane and out-of the monola
 yer plane\, determining the bright-dark exciton splitting.  First signatu
 res of boson scattering for excitons are presented and Valley polarization
  and coherence measurements are discussed.\n \nExamples of recent results
  and collaborations:\narXiv 1701.05800\, 1702.00323\, 1704.05341\, 1704.05
 448
LOCATION:auditorium CE5
STATUS:CONFIRMED
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