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Séminaire « Propriétés optiques et électroniques des nanostructures » de l’INSP

Out-of-equilibrium electron dynamics in topological matter - Evangelos Papalazarou - Mardi 24 janvier 2017 à 11 h

INSP - UPMC - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Evangelos Papalazarou - Laboratoire de Physique des Solides, Université Paris-sud


In the recent years, the topological phases of matter have been in focus of intense theoretical and experimental studies. The generic features of these phases are : they possess topologically protected surface states and their order can be described by topological invariants that are insensitive to smooth changes in the system parameters. Among these phases three-dimensional topological insulators exhibit a great attention because they possess a band gap in the bulk and conducting surface states. Carriers occupying these surface states are highly protected by time-reversal symmetry leading to a substantial suppression of back-scattering and to a robust helical spin texture. With such unique properties three-dimensional topological insulators have considered as milestones towards novel applications spanning from spin-based field-effect transistors to ultrafast optrospintronic devices, whose performance depends strongly on the dynamics of excited carriers Using femtosecond time- and angle-resolved photoelectron spectroscopy we reveal the out-of-equilibrium electron dynamics of the binary, Bi2Te3, and the ternary, Bi2Te2Se, topological insulator [1,2]. We demonstrate that the interplay of surface and bulk transient carrier dynamics in a photo-excited topological insulator compound may alter the charge balance between electrons and holes in Dirac surface states. This results to an unusually long-lived population of hot massless Dirac fermions with an out-of-equilibrium lifetime exceeding 100 picoseconds. This transient hot electron population shifts the surface chemical potential and generates a sizeable energy barrier between bulk and surface.

[1] M. Hajlaoui et al. Nano Lett., 12, 3532 (2012).
[2] M. Hajlaoui et al. Nature Comm. 5, 3003 (2014).