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Spin helical transport in normal and superconducting topological insulators.

19/11/2013 Ewelina Hankiewicz (Institut für Theoretische Physik, Université de Würzburg, Germany)


Topological insulators (TIs) have a bulk energy gap that separates the highest occupied band from the lowest unoccupied band like in ordinary insulators. However, the edge (for 2D TIs) or the surface (for 3D TIs) of a topological insulator exhibits gapless electronic states that are protected by time reversal symmetry [1,2].

In this talk I will focus on transport properties of topological insulators when the Fermi energy probes the helical edge states (counter-propagating gapless spin edge states) or gapless surface states where a spin follows a momentum. In particular I will discuss how the helical edge states merge to the metal and how they can be detected through the electrical response [3]. Later I will talk about the magnetotransport of the helical edge channels and surface states; in particular I will analyze the transition between topological insulator and quantum Hall regimes [4]. Further, I will show that the helicity of edge states leads to new phenomena when superconducting (SC) proximity gap is induced in TI. As an example I will discuss the spatial separation of the crossed Andreev reflection and the electron cotunneling in 2D TI/ SC /2D TI junctions [5], and the superconducting Klein tunneling in 3D TIs [2].


[1] M. Z. Hasan and C. L. Kane Rev. Mod. Phys. 82, 3045 (2010).

[2] G. Tkachov and E. M. Hankiewicz, topical review in Phys. Status Solidi B 250, 215 (2013). 

[3] C. Brüne, A. Roth, H. Buhmann, E. M. Hankiewicz, L. W. Molenkamp, J. Maciejko, X.-L. Qi and S.-C. Zhang, Nature Physics 8, 486 (2012).

[4] G. Tkachov and E. M. Hankiewicz Phys. Rev. Lett. 104, 166803 (2010).

[5] R. W. Reinthaler, P. Recher, and E. M. Hankiewicz, Phys. Rev. Lett. 110, 226802 (2013).