Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 77: Graphene V
O 77.6: Vortrag
Donnerstag, 17. März 2011, 16:15–16:30, WIL B321
Epitaxial graphene on Ir(111): How it forms mountains and how it gets a Rashba surface state out into the fresh air — •Andrei Varykhalov — Helmholtz-Zentrum Berlin, 12489 Berlin
A new phase of epitaxial graphene on Ir(111) is discovered. It occurs as a periodic array of pyramids with giant height corrugation of 3.5Å, is free of carbide, and can be easily recognized by its unique LEED pattern. The corrugation is 10× larger than for the known Moiré-type phases of graphene/Ir [1] which suggests that a novel formation mechanism is at work. STM, XPS, ARPES, as well as LEED simulations of pyramid-shaped graphene and Moiré-type control samples indicate that the pyramids occur by relief of lateral strain from a chiral dislocation network which renders them a prospective playground for quasi-Landau quantization of Dirac fermions in giant pseudomagnetic fields [2]. The bare Ir(111) harbors fascinating electronic and spin properties as well. By spin-ARPES we reveal a previously unobserved giant (αR of the order of 10−10 eVm) Rashba-type spin splitting of a prominent Ir surface state. It will be shown that this spin-orbit split surface state is not affected when Ir(111) is epitaxially covered with graphene. Moreover, it will be demonstrated that graphene itself protects the Ir surface so efficiently that the surface state remains stable in ambient atmosphere. This behavior is explained based on topological properties of this surface state.
[1] A. T. N’Diaye et al., Phys. Rev. Lett. 97, 215501 (2006) and refs. therein; [2] F. Guinea et al., Nat. Phys. 6, 30 (2010); N. Levy et al., Science 329, 544 (2010).