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SUMMARY:Topological electronic properties of silicon - Prof. Claudio Chamo
 n\, Boston University
DTSTART:20171005T131500Z
DTEND:20171005T141500Z
UID:TALK83581@talks.cam.ac.uk
CONTACT:Bartomeu Monserrat
DESCRIPTION:The central role that materials play in human history is exemp
 lified by the three-age division of prehistory into the stone\, bronze\, a
 nd iron ages. References to our present time as the information age or sil
 icon age epitomizes the important role that this semiconducting material c
 ame to play in the development of computers and devices that permeate our 
 daily lives. Remarkably\, silicon has been left out of the explosion of re
 search activity on topological materials. On the surface\, this omission i
 s the result of a boundary-centric classification of undoped\nsilicon as a
  “trivial insulator”. Here we show that the electronic states in silic
 on have nontrivial topological structures that are captured by a network o
 f Berry flux lines that link at points of high symmetry in the Brillouin z
 one. This complex network has ice-nodal points where fluxes satisfy ice ru
 les. Fixing the longitudinal momentum parallel to such flux lines yields a
  two-dimensional Dirac Hamiltonian for the transverse degrees of freedom. 
 This complex Berry-flux network implies a topologically stable two-fold de
 generacy along the X-W\ndirection in all of silicon bands\, a fact that is
  supported by crystal symmetry arguments as well as direct inspection of t
 he vast literature on silicon band structures.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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