"Shining Light on Topological Insulators"

Colloquium by Nuh Gedik
PHYSICS DEPARTMENT COLLOQUIUM

Shining Light on Topological Insulators

Nuh Gedik
MIT, Boston, USA

Topological insulators (TIs) are novel materials that do not conduct electricity in their
bulk yet possess exceptional conducting electronic states on their surface. These surface
electrons have a number of highly unusual characteristics: (i) they behave like massless
relativistic particles with a linear energy-momentum dispersion relation (ii) their spin is
locked perpendicular to their momentum and (iii) this state is robust against moderate
disorder. Understanding and characterizing unique properties of these materials can lead to
novel applications such as current induced magnetization or extremely robust quantum memory
bits. In this talk, I will give an overview of this field and discuss recent experiments in
which we used ultrafast laser pulses to probe the fascinating properties of these materials.
In particular, I will present measurements in which we simultaneously mapped all three
components of spin over the entire energy momentum phase space by using circularly polarized
ultrafast laser pulses to perform novel angle-resolved photoelectron spectroscopy. I will
show that an idealized spin-momentum locking is only present within a small energy window
about the Dirac point, beyond which strong textural deformations occur. I will also describe
our experiments in which we directly visualized the coupling of topological surface electrons
to other excitations by recording 3D movies of electronic band structure after
photoexcitation by an ultrashort laser pulse.

Date: March 27, 2013 (Wednesday)
Time: 16:00-17:00
Place: EE01