Séminaire RQMP: Ben Levitan
Date : 23 July 2020 10:30
Type : Institut Quantique
Higher-ordertopological insulators under strong magnetic fields
Benjamin A. Levitan,
supervised by Tami Pereg-Barnea
Vidéoconférence, Zomm #: 892019835 (Zoom link)
Lorsque demandé, indiquer 'zéro zéro deux quatre sept deux' en chiffre.
The family tree of topological insulators has blossomed vigorously since theirinitial prediction and discovery in the 2000s. Higher-order topologicalinsulators are the youngest branch on this tree. Like their more familiar(first-order) cousins, these materials are fully-gapped insulators in the bulk.Their “higher-order” topological nature is reflected in their bulk-boundarycorrespondence: in D spatial dimensions, an n-th order topological insulatorwill have in-gap states localized to (D - n)-dimensional pieces of itsboundary, protected by a combination of symmetry and topology.
We study the response of a three-dimensional second-order topological insulator(with one-dimensional chiral metallic “hinge” modes) to an applied magneticfield. We derive an effective surface theory which accurately captures severalkey qualitative features of its underlying bulk lattice model, including massiveDirac fermions, Landau levels, and chiral hinge modes. We find that the fulllattice model predicts a lowest Landau level closer to zero energy than wouldbe expected from the surface theory. As a result, within the surface gap, thereexist different regions of energy, within which either one or two chiral hingemodes propagate in either direction. This directly leads to an observablemagnetotransport signature: as one scans across the surface gap, thedifferential conductance of a rectangular nanowire steps between one and twoconductance quanta.
Ref: B.A. Levitan and T. Pereg-Barnea, arXiv:2004.05652 [cond-mat.mes-hall],2020 (with referees @ PRR)