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SUMMARY:Spin Scattering in Graphene: Impurity Characterization and  Birefr
 ingent Electron Optics  - Professor Sergio Ulloa \, Department of Physics 
 and Astronomy\, Ohio University\, Athens\, Ohio\, USA  and Dahlem Center f
 or Complex Quantum Systems\, Freie Universität Berlin\, Germany
DTSTART:20130510T130000Z
DTEND:20130510T141500Z
UID:TALK45228@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:An important element on the dynamics of spins in materials is 
 the spin-orbit interaction (SOI)\, which reflects/arises from intrinsic la
 ck of inversion symmetry in the lattice structure\, or via broken symmetri
 es in the system due to external or interfacial fields (Rashba interaction
 ).  Although intrinsic SOI is weak in graphene\, the Rashba SOI can in fac
 t be large due to strong local hybridizations by impurities of defects or 
 by manipulation of substrates or applied gates [1]. We have studied electr
 on/hole transport in graphene under sizeable SOI and address theoretically
  some of the anticipated observables due to this effect.\n\nWe have develo
 ped analytical spinor solutions of the Dirac equation that include spin de
 pendent observables\, and use these to examine the role of SOI on scatteri
 ng cross sections. By calculating the ratio of total to transport cross se
 ction at low energy we are able to probe the degree of isotropy of the sca
 ttering processes\, and consequently probe the nature of the impurities an
 d defects present in the graphene sample. This suggests then a sample spec
 ific measurement of the important effective size of the SOI\, especially i
 f one is to consider spin transport.\n\nWe also show that Rashba SOI in gr
 aphene gives rise to optical birefringence in electron optics\, which in e
 ssence reflects the intrinsic crystal structure even at long electronic wa
 velengths. This effect requires the presence of Rashba SOI\, where differe
 nt group velocities depend on the chirality of the electronic states\, mim
 icking the light polarization dependence of the group velocities in optica
 l birefringent materials. In circular “Veselago lenses”  the birefring
 ence would be evident by the doubling of caustics and cusps produced\, whi
 ch could be probed in scanning probe experiments. \n\n[1] D. Marchenko et 
 al.\, Nature Commun. 3\, 1232 (2012).\n[2] M. M. Asmar and S. E. Ulloa\, P
 hys. Rev. B 87\, 075420 (2013).\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory\, Department of Physics
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