Condensed Matter Seminar - Michael Fuhrer, University of Maryland - "Surface Conduction of Topological Dirac Electrons in Bulk Insulating Bi2Se3"
The three dimensional strong topological insulator (STI) is a new phase of electronic matter which is distinct from ordinary insulators in that it supports on its surface a conducting two-dimensional surface state whose existence is guaranteed by topology. I will discuss experiments on the STI material Bi2Se3, which has a bulk bandgap of 300 meV, much greater than room temperature, and a single topological surface state with a massless Dirac dispersion. Field effect transistors consisting of thin (3-20 nm) Bi2Se3 are fabricated from mechanically exfoliated from single crystals, and electrochemical and/or chemical gating methods are used to move the Fermi energy into the bulk bandgap, revealing the ambipolar gapless nature of transport in the Bi2Se3 surface states. The minimum conductivity of the topological surface state is understood within the self-consistent theory of Dirac electrons in the presence of charged impurities. The intrinsic finite-temperature resistivity of the topological surface state due to electron-acoustic phonon scattering is measured to be 60 times larger than that of graphene largely due to the smaller Fermi and sound velocities in Bi2Se3[2], which will have implications for topological electronic devices operating at room temperature. In the thinnest Bi2Se3 samples (~3 nm) we observe the opening of a bandgap due to coupling of the top and bottom surfaces which hybridize to form a conventional two-dimensional insulator[3], and by controllably thinning regions of Bi2Se3 samples we achieve quantum dots with gate-tunable insulating barriers[4].
[1] D. Kim et al., Nature Physics 8, 460 (2012).
[2] D. Kim et al., Phys. Rev. Lett. 109, 166801 (2012).
[3] S. Cho et al., Nano Letters 11, 1925 (2011).
[4] S. Cho et al., Nano Letters 12, 469 (2012).
Location: PCTS Seminar Room
Date/Time: 11/19/12 at 1:15 pm - 11/19/12 at 2:30 pm
Category: Condensed Matter Seminar
Department: