Probing electronic and nuclear dynamics of solids - Workshop on "Attosecond to Few-Femtosecond Ultrafast Science at Future FELs"
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Workshop on “Attosecond to Few-Femtosecond Ultrafast Science at Future FELs”
Probing electronic and nuclear dynamics of solids
and at surfaces on their intrinsic timescales
Martin Wolf
Fritz Haber Institute of the Max Planck Society, Berlin, Germany
Motivation:
Elementary molecular
interactions in movie
solids
► The „holy grail“ of stuctural dynamics: Mapping the time-evolution of a
quantum system (molecular or solid state) as function of its atom positions.
molecular target
photoexcitation
snapshot probe
Key question (so far):
© MPIbpc; © DESY Photon Science
How do the atoms move?
http://photon-science.desy.de/research
X-ray free electron laser
Beyond the
Elementary molecular in
interactions movie…
solids
► The „holy grail“ of stuctural dynamics: Mapping the time-evolution of a
quantum system (molecular or solid state) as function of its atom positions.
molecular target
How to access intrinsic time-scales
photoexcitation
of electron-nuclear
snapshotdynamics?
probe
Electron-nuclear coupling is
key in chemical dynamics
© MPIbpc; © DESY Photon Science
- Reactions at surfaces
- Phase http://photon-science.desy.de/research
transitions in solids
X-ray free electron laser
Surface femtochemistry
rate-limiting step in catalysis:
dissociative adsorption associative desorption
hv
“detailed
ABgas ABgas
balance”
Aads Bads Aads Bads
ABgas D
DEE
Ea
Aads+Bads
Femtochemistry at metal surfaces: Nonadiabatic coupling to electronic excitations
fs-laser pulse
monolayer is optical thin
substrate-mediated
excitations dominate
Review: Ch. Frischkorn and M. Wolf, Chem. Rev. 106, 4207 (2006)
fs-laser-induced CO oxidation probed by trXAS
A. Nilsson & coworker (trXAS) (400 nm)
Science 347, 978 (2015) CO2
O + CO
O + CO → CO2 / Ru(001)
Ru(001)
Appearance of new
XAS contrast
electronic states in
O K-edge XAS
fs-laser-induced CO oxidation probed by trXAS
Science 347, 978 (2015)
Appearance of new electronic states: Formation of transient CO─O species
Transients: Rapid increase of O 2p* in 280 fs, CO 2p* shift occurs in 500 fs
and new electronic states appear on 800 fs timescale
fs-laser-induced CO oxidation probed by trXAS
Science 347, 978 (2015)
Time evolution
“smeared out”
by electron
dynamics in the
metal substrate
Appearance of new electronic states: Formation of transient CO─O species
Faster trigger required to access intrinsic
Transients: Rapid increase of O 2p* in 280 fs, CO 2p* shift occurs in 500 fs
time-scale of
and new electron-nuclear
electronic
H. Öström states
et al., appear
Science on 800
347, 978 fsdynamics
(2015) timescale !
Ultrafast photoinduced phase
transition in quasi-1D atomic
nanowires on Si(111)
ARPES probe
e-
pump pulse
C. Nicholson et al, Science 362, 821 (2018)
The In/Si(111) (4 x 1) to (8 x 2) phase transition
LEED Surface structure
§ In(4x1)/Si(111) is a quasi 1D metallic nanowire system
§ Structural phase transition into (8x2) upon cooling
below Tc ~130 K
In(4 x 1)/Si111 In(8 x 2)/Si111
metallic phase insulating CDW phase
highly anisotropic periodicity doubling
conductivity
‚high T‘ (>140 K) ‚low T‘ (
Structural dynamics: ultrafast trRHEED vs trARPES
Ultrafast photoinduced phase transition: (8 x 2)In/Si → (4 x 1)In/Si
M. Horn von Hoegen et al (trRHEED) M. Wolf et al (trARPES)
Nature 544, 207 (2017) Science 362, 821 (2018)
In/Si(111) 500 fs
(8 x 2) phase
700 fs
~1 ps
200 fs
200
Delay (ps) Delay (fs)
§ Structural transition < 1 ps § Sequence of time scales:
(with t ~ 350 fs) (gap closing, band edge shift
& structral transition)
UED is only
trARPES sensitve
reveals todistinct
three structural changes
time scalesUltrafast phase transition in In/Si
► trARPES yields deep insight into sequential steps 500 fs
of the band structure dynamics 700 fs
► Scenario: All unit cells switch coherently together
200 fs
(8 x 2) (4 x 1)
700 fs
phase phase
► Structural dynamics driven by transiently enhanced electron temperature
Tel /1000 K
Science 362, 821 (2018)
Delay (fs)Ultrafast phase transition in In/Si
► trARPES yields deep insight into sequential steps 500 fs
of the band structure dynamics 700 fs
► Scenario: All unit cells switch coherently together
200 fs
(8 x 2) (4 x 1)
700 fs
phase phase
► Structural dynamics driven by transiently enhanced electron temperature
► Mechanism of photoinduced transition ?
A simple Peierls picture is insufficient (gap closes
before the structural transition is completed)
Photoinduced chemical reaction driven
by the transient electron temperature
Example for pronounced e-ph coupling
Science 362, 821 (2018)Light-induced Lifshitz transition
in MoTe2 driven by
ultrafast change of Hubbard U
Fermi surface U = 2 eV Fermi surface U ~ 0 eV
ARPES probe
e-
pump pulse
Abrupt change in Fermi surface topologyUltrafast non-equilibrium Lifshitz transition: MoTe2 XUV based trARPES employing the k-space microscope (METIS)
Ultrafast modification of Hubbard U
TDDFT + U (A. Rubio)
g
Beaulieu et al., Science Advances 7, eabd9275 (2021)Ultrafast modification of Hubbard U
TDDFT + U (A. Rubio)
Ultrafast change
of electronic correlations
(pulse width limited)
g
Beaulieu et al., Science Advances 7, eabd9275 (2021)Challenges and future directions
► Coupled electron-nuclear dynamics is key in ultrafast surface reactions
and various photoinduced phase transitions.
► Implementing few femtoscond time-resolution is great, but….
► Access to intrisic timescale is hinderd by lack of real ultrafast triggers:
Estabished excitation mechanisms often „smear out“ the dynamics.
► Need for further research:
Search for direct excitation (as-pulses)
Tel /1000 K
or light field driven processes (not
dominated by hot electron dynamics in solid).
► Promising systems:
- Photo-catalysis on oxide surfaces
Delay (fs)
- Ultrafast light-induced changes of screeing
and/or electron correlation (e.g Mott transitions)Challenges and future directions
► How to probe electron-nuclear coupling in chemical dynamics?
- Photoemission at as/few fs FELs is limited by space charge effects
and modest energy resolution (DtDE)
- Photon-in/photon-out techniques (XAS, XES, trRIXS) enable high
spectral resolution of chemical shifts (reaction intermediates)
► Competition for future FEL experiments: Lab setups for transient XAS
with attosecond time resolution in soft X-ray regime (up to 600 eV)
will be competitive (beam time,
reasonable photon flux)
see e.g.
J. Biegert & coworkers,
PRX 7, 041030 (2017)
200 300 400 500 600
Photon energy (eV)
► Future FEL experiments: Focus on XAS, XES, trRIXS with few fs
time resolution for chemical dynamics.Acknowledgements LCLS collaboration: Toyli Anniyev, Martin Beye, Ryan Coffee, Martina Dell'Angela, Alexander Foehlisch, Jorgen Gladh, Tetsuo Katayama, Sarp Kaya, Oleg Krupin, Jerry LaRue, Andreas Møgelhøj, Anders Nilsson, Dennis Nordlund, Jens Norskov, Hirohito Ogasawara, Henrik Öberg, Henrik Ostrom, , Frank Abild-Pedersen, Lars GM Pettersson, William F Schlotter, Jonas A Sellberg, Florian Sorgenfrei, Joshua J Turner, Wilfried Wurth, Honglian Xin University of Hamburg and DESY, Stockholm University, Helmholtz-Zentrum Berlin, Fritz Haber Institute, SLAC (LCLS, SIMES, SSRL, SUNCAT)
Acknowledgements J. Makler, S. Dong, M. Puppin, C. Monney, T. Pincelli P. Xian, HHG-based S. Beaulieu, L. Rettig & R. Ernstorfer trARPES Fritz-Haber-Institut der MPG, Berlin & METIS C. Nicholson, L. Rettig & R. Ernstorfer In/Si(111) Fritz-Haber-Institut der MPG, Berlin D. Christiansen, E. Malic, A. Knorr theory exciton Technische Universität Berlin dynamics WSe2 A. Lücke and W.G. Schmidt ab initio MD Universität Paderborn In/Si(111) N. Tancogne-Dejean, M. Sentef & A. Rubio TDDFT, DFT+U MPI for Structure and Dynamics of Matter, Hamburg MoTe2
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