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SUMMARY:Excitons and Symmetry: Studying Structural Effects on Complex Exci
 ted-State Phenomena in 2D and Molecular Crystals  - Sivan Refaely-Abramson
 \; Weizmann Institute of Science
DTSTART:20190503T143000Z
DTEND:20190503T150000Z
UID:TALK123853@talks.cam.ac.uk
CONTACT:Elizabeth Tennyson
DESCRIPTION:New developments in the theory of excited-state phenomena can 
 lead to better understanding of the involved nanoscale mechanisms and to p
 redictions of new materials hosting such phenomena. In this talk\, I will 
 present recent studies using first-principles computational methods to mod
 el and understand such mechanisms in extended materials. Specifically\, I 
 will discuss the effect of point defects on excited-state properties and s
 election rules in monolayer transition metal dichalcogenides. These impuri
 ties can give rise to localized states\, introduce strongly-bound excitons
  below the absorption edge\, and reduce the valley-selective circular dich
 roism\, suggesting a novel pathway to tune spin-valley polarization and ot
 her optical properties through defect engineering. Additionally\, I will p
 resent a new approach to explore multi-exciton generation in solids from f
 irst principles and describe an application of this approach to singlet fi
 ssion\, a multi-exciton generation process in organic crystals. Focusing o
 n crystalline acenes\, I will discuss a newly discovered exciton—bi-exci
 ton coupling channel\, revealing selection rules for singlet fission that 
 are associated with the crystal symmetry and structure. 
LOCATION:Rayleigh Seminar Room\, Maxwell Centre\, Cavendish Laboratory
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