"Topological invariants and boundary states in normal and superconducting carbon nanotubes"

Who: Dr. Magdalena Marganska-Lyzniak, Universitšt Regensburg, Germany

Place: Donostia International Physics Center

Date: Thursday, 25 May 2017, 12:00

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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