Topological Insulators

Three-dimensional topological insulators represent an exciting new phase of matter that includes bulk insulator properties with metallic surface states. Though these materials do not conduct electricity in the bulk, electrons are able to move around freely on the surface of the material in a manner that is protected from defect scattering: it is difficult to destroy these states.

Moreover, these topological surface states show spin-momentum locking. All electrons traveling in a given direction must have their spins pointing the same way, or conversely, all electrons with the same spin component must be moving in the same direction. The resulting possibility of moving spins around the material by passing current has generated considerable interest in potential spintronics applications. Still, much work remains to be done to understand the properties of these materials, which include Bi2Se3, Bi2Te3, Sb2Te3, and others.

The one-of-a-kind spin-ARPES spectrometer built in the Lanzara group (see Spin-ARPES) is ideal for studying topological insulators as it measures electronsí spin polarization as a function of their momentum. It has already been used to show the highest ever observed spin polarization from these topological surface states as well as the persistence of these spin polarizations at room temperature. That these properties exist well above cryogenic temperatures will be crucial for any device applications.

Finally, the spin-ARPES system has been used with our laboratory laser to show that photoemitted electronsí spins can be twisted and turned by manipulating the polarization of light from the laser. As a result, these topological insulators could potentially be used as a source of spins of any arbitrary orientation.

Selected Publications

(Please see Journal Articles for a more complete list.)

Photoelectron spin-flipping and texture manipulation in a topological insulator
Chris Jozwiak, Cheol-Hwan Park, Kenneth Gotlieb, Choongyu Hwang, Dung-Hai Lee, Steven G. Louie, Jonathan D. Denlinger, Costel R. Rotundu, Robert J. Birgeneau, Zahid Hussain, and Alessandra Lanzara
Nature Physics, in press (2013)

Widespread spin polarization effects in photoemission from topological insulators
C. Jozwiak, Y. L. Chen, A. V. Fedorov, J. G. Analytis, C. R. Rotundu, A. K. Schmid, J. D. Denlinger, Y.-D. Chuang, D.-H. Lee, I. R. Fisher, R. J. Birgeneau, Z.-X. Shen, Z. Hussain, and A. Lanzara
Phys. Rev. B 84, 165113 (2011)