Topological insulators are a newly discovered class of materials characterized by having an insulating bulk band gap with gapless edge/surface states. The surface states exhibit linear dispersion with a single Dirac cone, and are protected against backscattering by all time-reversal invariant (e.g. non-magnetic) defects within the bulk. 3D topological insulators have recently been predicted and confirmed experimentally by angular resolved photoemission spectroscopy (ARPES), including Bi2Te3, Bi2Se3, and Sb2Te3. Unfortunately, transport measurements lack sensitivity to spin polarization and time-resolved dynamics of these surface states. Optoelectronic measurements offer a unique way of probing these states with a combination of ultrafast spectroscopy and electrical transport techniques. These integrated techniques enable the use of photon polarization to detect and manipulate helical spin texture as well as femtosecond time resolution of spin and charge dynamics using pump-probe optical spectroscopy. In addition, we can use advanced electrostatic gating geometries (e.g. top and bottom gates) to overcome intrinsic doping of the bulk by independently controlling the Fermi level of the top and bottom surface states. The goal of this research is to understand the fundamental properties of this exotic new class of quantum materials to further applications in novel topological insulator based electronics/photonics.
TEM image of a Bi2Se3 nanoribbon (left), with its corresponding diffraction pattern (right).
SEM image of a Bi2Se3 nanoplatelet, and a Bi2Se3 nanoribbon device.