Ultrafast surface Dirac fermion dynamics of Sb2Te3-based topological insulators

Abstract Topological insulators (TIs) characterized by gapless and spin-polarized conical band dispersion on their surfaces have been extensively studied over the last decade. This article reviews our recent works on ultrafast carrier dynamics of Sb2Te3-based nonmagnetic and magnetic TIs by utilizing state-of-the-art femtosecond time- and angle-resolved photoelectron spectroscopy. We have demonstrated that the electronic recovery time elongated from a few ps to > 400 ps in case that the Dirac point was close to the Fermi energy in the series of ( Sb 1 - x Bi x )2Te3. We also investigated how the magnetic-impurity affects the carrier dynamics in ferromagnetic Sb 2 - y V y Te3. It was found that the electronic recovery time drastically shortened from a few ps to 500 fs with increasing vanadium concentration. Since the lifetime of the nonequilibrated surface Dirac fermions can range from femto- to nano-second, Sb2Te3-based TIs would be promising for ultrafast spin switching and spin-polarized current generation device applications.