Topological invariants and boundary states in normal and superconducting carbon nanotubes

Thursday, May 25, 2017 - 12:00
Place: 
Donostia International Physics Center
Who: 
Dr. Magdalena Marganska-Lyzniak, Universität Regensburg, Germany
Source Name: 
DIPC

Carbon nanotubes, like their parent graphene, are an
excellent host for a variety of topological phases. The chiral symmetry of
their Hamiltonian gives rise to end states, similar in their nature to the
zigzag end states of graphene. Their number is determined by the topological
invariant associated with the chiral symmetry, the winding number. When placed
in contact with a superconductor, nanotubes can inherit its Cooper pairing
mechanism via the proximity effect. Under the influence of perpendicular
magnetic field another type of boundary states arises, this time not a Dirac,
but a Majorana fermion. Their presence depends on the value of another
topological invariant, a Pfaffian. I shall discuss the topological phase
diagram generated with the Pfaffian, the limits of its usability and the
feasibility of inducing the Majorana states experimentally.

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