A New State of Matter In topological insulators

A New State of Matter In topological insulators, quantum effects are macroscopically observable. Macroscopic topological insulators (TIs) • First identified at the ALS in 2007 (M. Zahid Hasan group, Princeton) • Electrical conductivity is weak inside bulk, strong at surface • "2 nd generation" of TIs retain properties well above room temp. • Test bed for studies of exotic high-energy physics particles ARPES (angle-resolved photoemission spectroscopy) • ALS Beamlines 12. 0. 1 and 10. 0. 1, SSRL Beamline 5 -4 • Identify new classes of topological insulator materials • Establish key traits of their unique electronic environment Studies of Bi 2 Se 3: largest bulk band gap, TI state up to 1310°F • Surface electrons behave as if they have no mass • Surface conduction states are spin polarized Spin polarization of surface states • Means that there is no backscattering from impurities or defects • Backscattering obstacle to device engineering at nanometer scale • No backscattering advances in spintronics and quantum computing These results uncover an exciting macroscopic quantum environment in which new physical rules create a new realm of phenomenological possibilities. Band structure of the topological insulator, bismuth selenide (Bi 2 Se 3). The red areas represent surface states. The vertical space between the yellow areas is the bulk band gap. Because the surface states cross the band gap, this "insulator" conducts electricity on its surface. Inset: 3 D schematic of the cone-shaped surface band structure. The spin states (yellow arrows) indicate that the electrons on the surface won't backscatter from disorder and impurities. (Image courtesy of David Hsieh, Yuqi Xia, and Andrew Wray, Princeton University). D. Hsieh, Y. Xia, Y. L. Chen, P. Roushan et al. , Nature, Science, PRL, 2008– 2009 (see notes page) www-als. lbl. gov/index. php/science-highlights/481