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SUMMARY:Ultrafast Photoexcited Carrier Dynamics in   Low Dimensional Syste
 ms by Time Resolved Terahertz Spectroscopy - Dr. Srabani Kar\, Department 
 of Engineering\, University of Cambridge
DTSTART:20190515T130000Z
DTEND:20190515T140000Z
UID:TALK125149@talks.cam.ac.uk
CONTACT:Dr Kaveh Delfanazari
DESCRIPTION:This talk will discuss the photoexcited carrier dynamics of on
 e and two-dimensional nanomaterials studied by using time resolved optical
  pump-terahertz spectroscopy. The studies include the carrier dynamics of 
 single layer and bilayer graphene\, single walled and double walled carbon
  nanotubes and transition metal di-chalcogenides. In single layer graphene
 \, the real part of terahertz photoconductivity\, was found to be negative
  at high doping and positive at low doping throughout the spectral range 0
 .5-2.5 THz. In contrast\, for moderately doped bilayer graphene\, real par
 t of photoconductivity was negative at low frequency and positive on high 
 frequency part of the spectra. In addition\, opening a gap across the Dira
 c point through hydrogen doping results in the sign change of photoconduct
 ivity from negative to positive. The role of short-range scattering arisin
 g from charge neutral defects such as ripples\, grain boundaries etc\, lon
 g-range Coulomb scattering due to charged defects from underlying substrat
 e\, acoustic phonon\, and surface-optical phonon scattering all are evalua
 ted quantitatively to explain the photoinduced terahertz conductivity spec
 tra for all these cases. The measured photo-conductivities for single wall
  and double wall carbon nanotubes were found to be different by their sign
  and spectral responses which were also described quantitatively by Boltzm
 ann transport model of electrical conductivity. In transition metal di-cha
 lcogenides\, the carrier relaxation was faster at higher pump fluence whic
 h was understood by rate equation model incorporating defect-mediated elec
 trons\, holes\, and excitons capture and recombination rates.
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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