Photoinduced terahertz dynamics in BizSes topological insulator

Plasmons are collective charge density waves in a conductive material, which show remarkable electromagnetic properties and have great potential for photonics from terahertz to the ultraviolet. Besides the conventional plasmonic excitations in metals and in semiconductors, 2-dimensional (2D) plasmons of massless Dirac electrons have been observed in graphene and at the surface of topological insulators (TIs). TIs are quantum electronic materials with an insulating gap in the bulk originated by a strong spin-orbit coupling and Dirac metallic states at their interfaces. Among the various TIs, Bi2Se₃ is one of the most promising material due to its large band gap Eg~300 meV. Recently, it has been shown that the low energy single particle and collective (plasmons) electrodynamics response are dominated by surface Dirac electrons in Bi2Se3 in steady state regime [1]. The relaxation dynamics show that an excess of electrons are continuously injected from bulk to the surface through surface states-bulk phonon scattering channel [2,3]. In this work we study the time resolved photoinduced THz dynamics of plasmonic response in micro-ribbons patterned Bi2Se3 thin film by means of optical-pump/THz-probe spectroscopy.