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HL: Fachverband Halbleiterphysik

HL 31: Focus Session: Dirac fermions in solid-state systems (HL, jointly with TT)

HL 31.1: Topical Talk

Dienstag, 12. März 2013, 09:30–10:00, H2

Localization at graphene system and topological insulator edges — •Markus Buttiker — University of Geneva, Dept. of Theoretical Phys., 24 Quai E. Ansermet, 1211 Geneva, Switzerland

Graphene systems share a number of features with topological insulators. We investigate localization phenomena at the edges of these two systems [1,2]. In bilayer graphene subject to a strong perpendicular electric field we have found that in the presence of a strongly disordered edge a sequence of localized states appears. Interestingly the localization length depends only on the size of the bulk gap but is otherwise universal, i.e. independent of the type and strength of the disorder [1]. The appearance of these localized states reflects the marginal topological properties of bilayer graphene, a bipartite square lattice with similarly disordered edges does not show edge states localized at the edge.

In two-dimensional topological insulators such as HgTe/CdTe there exists a pair of helical edge states which are protected against non-magnetic disorder. However, if time-reversal symmetry is removed by the application of a magnetic field the protection is removed and these states localize. We investigate the divergence of the localization length as the magnetic field tends to zero and find that the localization length saturates at higher fields [2].

[1] Jian Li, Ivar Martin, Markus Buttiker, Alberto F. Morpurgo, Nat. Phys. 7, 38-42 (2011); Phys. Scr. Physica Scripta T146, 014021 (2012).

[2] Pierre Delplace, Jian Li, Markus Büttiker , Phys. Rev. Lett. 109. 246803 (2012).