Ultrafast surface carrier dynamics in topological insulators: Bi 2 Te 3 Marino Marsi Laboratoire de Physique des Solides CNRS UMR 8502 - Université Paris-Sud IMPACT, Orsay, September 2012
Outline Topological Insulators 3D Topological Insulators ARPES Non equilibrium 3D TI s pump-probe ARPES Bi 2 Te 3 interband scattering (sub-ps) non-equilibrium Dirac cone Slow relaxation of surface states Weak electron-phonon coupling Conclusions, perspectives
Topological Insulators Novel state of matter Insulating bulk, but gapless edge or surface states Combined action of spin-orbit coupling and time reversal symmetry (QSH effect) Unique transport properties: topologically protected states, immune to defects, perturbations Info on empty electronic states, interband scattering rates, hot electron properties? Hasan and Kane, RMP 2010 Qi and Zhang, RMP 2011
3D Topological Insulators: Bi 2 Te 3 Bi 1-x Sb x, Bi 2 Te 3, Bi 2 Se 3,Sb 2 Te 3 Non trivial topology band inversion driven by strong S-O coupling Single Dirac cone on surface Zhang et al., Nat. Phys. 2009
3D Topological Insulators ARPES (Hsieh et al., Nature 2008; Chen et al., Science 2009; ) Dirac cone studied by ARPES : Spin in surface plane, perpendicular to k
FemtoARPES Faure et al., Rev. Sci. Instrum. (2012)
FemtoARPES
FemtoARPES
FemtoARPES Rep rate: 0.25 MHz pump: 1.5 ev, 6 mj, 35 fs Probe: 6.28 ev 40 pj, 65 fs 10 13 photons/s Low energy ARPES L. Perfetti Friday
Bi 2 Te 3 low energy ARPES n-type Bi 2 Te 3 gap = 0.3 ev e probe: hν = 6.28 ev pump: hν = 1.5 ev Yazyev and al, PRL 105, 266806
Bi 2 Te 3 pump-probe ARPES n-type Bi 2 Te 3 gap = 0.3 ev probe: hν = 6.28 ev pump: hν = 1.5 ev Yazyev and al, PRL 105, 266806
Transient electronic structure
Transient electronic structure
Transient electronic structure
Transient electronic structure
Transient band populations 0.8 0.6 B 1 * E-E F (ev) 0.4 0.2 0.0 B 2 * S* -0.2-0.4 700 fs -0.1 0.0 0.1 k // (1/Å) Excitation VB to B 1 * scattering B1* S* and B 2 * Relaxation of S* slow weak e-phonon coupling Hajlaoui et al., Nano Lett. 12, 3532 (2012)
EDC s from transient Dirac cone states Energy Distribution Curves of hot electrons in the Dirac cone electron thermalization: ps scale influenced by interband scattering Hajlaoui et al., Nano Lett. 12, 3532 (2012)
Conclusions Time resolved ARPES hot «Dirac cone» electrons in 3D TI s Direct visualisation of interband (sub-ps) and intraband processes Information on (slow) electron relaxation Weak electron-phonon coupling for edge states, consistent with: - Pump-proble ARPES on Bi 2 Se 3 (Sobota et al., PRL 2012) - Analysis of ARPES lineshapes - Theoretical calculations Perspectives: tuning the position of the Dirac point with respect to E F Extension to other 3D TI s, thin films
Thanks to: M. Hajlaoui E. Papalazarou J. Mauchain G. Lantz L. Perfetti A. Taleb-Ibrahimi D. Boschetto N. Moisan I. Miotkowski Y.P. Chen Z. Jiang
Rate equations
Time resolved ARPES on TI s Bi 2 Se 3 Sobota et al., PRL 2012
Optical pump-probe reflectivity
The «Paris-Saclay» campus «Triangle de la Physique», the «Physics Triangle» Paris (30 km) Saclay (SOLEIL) Orsay (Université Paris-Sud) Palaiseau (Ecole Polytechnique)
Mott-Hubbard transition Correlation-induced metal to insulator transition (MIT) in strongly correlated materials : E E F Competition d band U p band U charge gap Kinetic energy (t) e e interaction (U) no change in the crystal structure no change in the long range magnetic order Isostructural MIT in Cr-doped V 2 0 3 : textbook example of Mott-Hubbard transition
Ultrafast lasers condensed matter e-e interaction T e >> T lattice Femtosecond laser excitation e-phonon scattering T e T lattice Thermalisation T e T lattice Photons interact with electrons in sample
Ultrafast lasers condensed matter Pump-probe spectroscopy signal Excited electronic states Photoinduced phase transitions Coherent lattice oscillations
Ultrafast pump-probe reflectivity signal Lab. Optique Appliquée Palaiseau λ = 800 nm, 50 fs, 1 khz