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SUMMARY:Graphene: from point defects to tunable twins - Prof Pilar Ariza\,
  University of Sevilla
DTSTART:20220506T130000Z
DTEND:20220506T140000Z
UID:TALK173339@talks.cam.ac.uk
CONTACT:46601
DESCRIPTION:I will begin with a brief account of the computational methodo
 logy used in calculations. We divide calculations into three main steps: a
  first harmonic step aimed at building a pattern of defects into the latti
 ce followed by a fully-nonlinear relaxation\, and as a final step we inves
 tigate charge-carrier transmission across the structures that spontaneousl
 y arise in the graphene layer. Then\, I will evaluate a number of point de
 fect configurations in monolayer graphene and document different accommoda
 tion mechanisms. Finally\, I will show that the transport gap of twinned g
 raphene can be tuned through the application of a uniaxial strain in the d
 irection normal to the twin band. Remarkably\, we find that the transport 
 gap Egap bears a square-root dependence on the control parameter εx −ε
 c\, where εx is the applied uniaxial strain and εc ∼ 19% is a critical
  strain. We interpret this dependence as evidence of criticality underlyin
 g a continuous phase transition\, with εx−εc playing the role of contr
 ol parameter and the transport gap Egap playing the role of order paramete
 r. For εx < εc\, the transport gap is non-zero and the material is semic
 onductor\, whereas for εx > εc the transport gap closes to zero and the 
 material becomes conductor\, which evinces a semiconductor-to-conductor ph
 ase transition. The computed critical exponent of 1/2 places the transitio
 n in the meanfield universality class\, which enables far-reaching analogi
 es with other systems in the same class.
LOCATION:LR5\, Baker Building\, CUED
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