Femtosecond study of A1g phonons in the strong 3D topological insulators: From pump-probe to coherent control

Fully symmetric A(1g) phonons are expected to play a dominant role in electron scattering in strong topological insulators (TIs), thus limiting the ballistic transport of future electronic devices. Here, we report on femtosecond time-resolved observation of a pair of A(1g) coherent phonons and their optical control in two strong 3D TIs, Bi2Te3 and Bi2Se3, by using a second pump pulse in ultrafast spectroscopy measurements. Along with well- defined phonon properties such as frequency and lifetime, an obvious phonon chirp has been observed, implying a strong coupling between photocarriers and lattices. The coherent phonon manipulation, on the other hand, allows us to change the phonon amplitude selectively but does not affect either the frequency or coherence lifetime of the chosen mode. Published by AIP Publishing.