Ultrafast Electron-Electron Dynamics in Graphene Daniele Brida

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1 Ultrafast Electron-Electron Dynamics in Graphene

2 Ultrafast Spectroscopy Light-matter interaction on timescale of fundamental physical processes: electron scattering, phonon emission, energy transfer D. Brida et al., J. Opt 12, (2010).

3 Electron Thermalization in Graphene First: how it happens in metals E E E E Thermalization Cooling E F E F E F E F f(e) f(e) f(e) f(e) Beyond two-temperature model G. Della Valle et al., PRB, (2012).

4 Electron Thermalization in Graphene E +hν/2 Conduction band hν k y EF k x -hν/2 Valence band

5 Electron Thermalization in Graphene E k y k x

6 Electron Thermalization in Graphene E 1 ev k y 2.3 ev k x -1 ev T = 300 K T >> 300 K

7 Electron Thermalization in Graphene E 1 ev k y 2.3 ev k x -1 ev T = 300 K T el >> 300 K

8 Electron Thermalization in Graphene E 1 ev k y 2.3 ev k x -1 ev T = 300 K T el >> 300 K

9 Ultrafast Spectroscopy E PUMP PROBE hν k x k y PUMP pulse impulsevely excite an out-of-equilibrium electron/hole distribution A photobleaching signal (Pauli blocking) appears in the PROBE spectral window when electrons reach hv/2 above Fermi energy.

10 Ultrafast Spectroscopy Ultrashort tunable pulses from OPAs Wavelength (nm) Intensity (a arb. un.) PUMP 8 fs Photon energy (ev) D. Brida et al. IEEE J. Sel. Top. Quant. El. 18, 329 (2012)

11 Ultrafast Spectroscopy Ultrashort tunable pulses from OPAs Wavelength (nm) Intensity (a arb. un.) PROBE 1 13 fs 8 fs PUMP Photon energy (ev) D. Brida et al. IEEE J. Sel. Top. Quant. El. 18, 329 (2012)

12 Ultrafast Spectroscopy Sample: single layer graphene growth by CVD Graphene layer growth by CVD on a copper substrate A polymer is spin-coated on top of the sample Copper is selectively etched away The polymer is then dissolved with acetone The graphene layer is moved to a SiO2 substrate

13 Experimental Results PUMP Visible - PROBE NIR Wavele ength (nm) T/T Wavelength: 960 nm 900 nm 840 nm Time (fs) Time (fs)

14 Experimental Results PUMP Visible - PROBE NIR Wavele ength (nm) T/T Wavelength: 960 nm 900 nm 840 nm Time (fs) Time (fs) τ fs τ 2 > 1 ps

15 Experimental Results PUMP Visible - PROBE NIR Wavelength: 960 nm 900 nm 840 nm

16 Theoretical model Delay: 0 fs f(e E) E

17 Theoretical model Delay: 0 fs 10 fs f(e E) E

18 Theoretical model Delay: 0 fs 10 fs 22 fs f(e E) E

19 Theoretical model f(e E) Delay: 0 fs 10 fs 22 fs 88 fs E

20 Theoretical model PUMP Visible - PROBE NIR Wavele ength (nm) Time (fs)

21 Theoretical model PUMP Visible - PROBE NIR Wavelength (nm) Wavele ength (nm) T/T(x x10-2 ) Spectra: 10 fs Time (fs) Probe photon energy/2 (ev)

22 Theoretical model PUMP Visible - PROBE NIR Wavelength (nm) Wavele ength (nm) T/T(x x10-2 ) Spectra: 10 fs 22 fs Time (fs) Probe photon energy/2 (ev)

23 Theoretical model PUMP Visible - PROBE NIR Wavelength (nm) Wavele ength (nm) T/T(x x10-2 ) Spectra: 10 fs 22 fs 88 fs Time (fs) Probe photon energy/2 (ev)

24 Experiments/Simulations Wavelength (nm) T/T(x10-2 ) Delay Probe photon energy/2 (ev) f(e) Delay: 0 fs 10 fs 22 fs 88 fs E

25 Theoretical model f(e E) Delay: 0 fs 10 fs 22 fs 88 fs E

26 Ultrafast Spectroscopy Ultrashort tunable pulses from OPAs Wavelength (nm) Intensity (a arb. un.) PROBE PUMP 2 PROBE 1 9 fs 13 fs 8 fs Photon energy (ev) D. Brida et al. IEEE J. Sel. Top. Quant. El. 18, 329 (2012)

27 Experimental Results PUMP Visible - PROBE IR 70 fs

28 Theoretical model: Auger recombination

29 Theoretical model Carrier Multiplication and Auger Recombination into play

30 Theoretical model Vs Koppens, Nat. Phys. (2013)

31 CONCLUSIONS Delay: 0 fs 10 fs 22 fs 88 fs ultrafast non-thermal dynamics of elctrons in graphene e-e scattering occurs in the 10 fs timescale and dominates early thermalization events Wavelength (nm) Auger recombination unveiled T/T(x10-2 ) Delay Probe photon energy/2 (ev) D. Brida et al., submitted.

32 Collaborations Politecnico di Milano: Cristian Manzoni Giulio Cerullo NEST Scuola normale di Pisa Andrea Tomadin Marco Polini Cambridge University: Antonio Lombardo Silvia Milana Andrea C. Ferrari Manchester University: Yong-Jin Kim Rahul R. Nair Kostya S. Novoselov

33 Ultrafast Electron-Electron Dynamics in Graphene