Selective scattering between Floquet–Bloch and Volkov states in a topological insulator

• Published in: Nature physics Vol. 12; no. 4; pp. 306 - 310
• Main Authors: Mahmood, Fahad, Chan, Ching-Kit, Alpichshev, Zhanybek, Gardner, Dillon, Lee, Young, Lee, Patrick A., Gedik, Nuh
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-04-2016; Nature Publishing Group
• Subjects: 140/125; 140/146; 639/766/119/2792; 639/766/119/995; 639/766/483/3925; Atomic; Classical and Continuum Physics; Coherence; Complex Systems; Condensed Matter Physics; Coupling; Insulators; Lasers; letter; Mathematical and Computational Physics; Molecular; Nonlinear optics; Optical and Plasma Physics; Optics; Phases; Physics; Quantum physics; Semiconductors; Solids; Spectroscopy; Theoretical; Topology
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys3609

Time- and angle-resolved photoelectron spectroscopy experiments are used to monitor the transition between Floquet–Bloch and Volkov states in the topological insulator Bi
2
Se
3
.
The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter
1
,
2
,
3
,
4
,
5
. The strong time-periodic potential of intense laser light can be used to generate hybrid photon–electron states. Interaction of light with Bloch states leads to Floquet–Bloch states, which are essential in realizing new photo-induced quantum phases
6
,
7
,
8
. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors
9
. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi
2
Se
3
. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet–Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light–matter interaction.