Dynamic Opening of a Gap in Dirac Surface States of the Thin-Film 3D Topological Insulator Bi2Se3 Driven by the Dynamic Rashba Effect.

Optical control of Dirac surface states (SS) in topological insulators (TI) remains one of the most challenging problems governing their potential applications in novel electronic and spintronic devices. Here, using visible-range transient absorption spectroscopy exploiting ∼340 nm (∼3.65 eV) pumping, we provide evidence for dynamic opening of a gap in the Dirac SS of the thin-film 3D TI Bi2Se3, which has been induced by the dynamic Rashba effect occurring in the film bulk with increasing optical pumping power (photoexcited carrier density). The observed effect appears through the transient absorption band associated with inverse-bremsstrahlung-type free carrier absorption in the gapped Dirac SS. We have also recognized experimental signatures of the existence of the higher energy Dirac SS in the 3D TI Bi2Se3 (in addition to those known as SS1 and SS2) with energies of ∼2.7 and ∼3.9 eV (SS3 and SS4). It is evidenced that the dynamic gap opening has the same effect on the Dirac SS occurring at any energy.