Ultrafast and Fast Structural Dynamics

of Photoinduced Transformations in Molecular Materials

Outline 1 – Structural Dynamics and Photo-InducedTransformations in Materials 2 – Tracking the Time Evolution of Molecular Switching in the Solid State 3 – Capturing Precursors of a Photo- Induced Transformation in a Material

Outline 1 – Structural Dynamics and Photo-InducedTransformations in Materials 2 – Tracking the Time Evolution of Molecular Switching in the Solid State 3 – Capturing Precursors of a Photo- Induced Transformation in a Material

Not only to observe matter, on ever smallest scale, but also to direct its functionality at the relevant lenght, time and energy scales

ADVENT OF CONTROL SCIENCE

from BESAC report

Nanometric

Ground State

Transient state

Lattice Relaxation

False Ground State

New Lattice

Structure and

Electronic Order

cooperativity

from K.

Nasu Light pulse may direct the functionality of a material through collective and/or cooperative photoinduced phenomena. Due to interactions between photo-excited constituents, positive feedback can trigger the non-equilibrium transformation of the material towards another macroscopic state of different electronic and/or structural order.

« More is Different » (P. Anderson) response

Cooperativity Nonlinearity

Coherence Far away from Equilibrium

time

perturbation

configuration

system

feedback

Multiscale dynamical processes

In a given time scale, typical for the dynamics of certain degrees of freedom (for instance atomic motions), some other degrees of freedom are faster and acts by their quantum or statistical average, while other ones are slower and then frozen. This leads to decoupling effects and steps in the physical picture of the transformation. Therefore, there is not an unique dynamical description valid at every time scales (not an unique equation to describethe time evolution, not an unique potential energy landscape).

Shock wave Srain propagation

Electronic motion

1 s

10-3 s

10-6 s

10-15 s

days

Atomic motion Optical phonon

Different time-scales

10-9 s

10-12 s

10-15 s

Laser pump and X-ray probe

Watching how material

transforms

from K. Nelson Science (1999)

from 100 ps

to 100 fs

New avenue in structural dynamics

Bragg peaks : long range order position : lattice shape : size and shape of blocks intensity : average cell structure

Diffuse scattering : short range order position : local periodic fluctuation shape : spatial extend of correlation intensity : fluctuation amplitude

The instantaneous density of a given cell may again be decom- posed between an average over all cells in the crystal and its deviation ρn(r,t) = ρcell(r,t) + ∆ρn(r,t) scattering = Bragg + diffuse

Density and scattering

Outline 1 – Structural Dynamics and Photo-InducedTransformations in Materials 2 – Tracking the Time Evolution of Molecular Switching in the Solid State 3 – Capturing Precursors of a Photo- Induced Transformation in a Material

Spin transition

Spin crossover crystals are the proto-type of molecular bistabilityin the solid state. Molecules can cooperatively switch between two states, here from LS to HS under various external sollici-tations, at thermal equilibrium and out of equilibrium (for instance light irrradia-tion). In general, the phase transition are isostructural, i.e. without change of symmetry - no symmetry breaking. The situation is similar to the gas-liquid phase transition.

• C

P

T

LS HS

Structural dynamics of molecular switching in a Fe (III) compound

weakly cooperative

cf. Poster P2 M. L. Boillot et al.

Ultra-fast molecular relaxation

similar to molecules in solution

Watching swithching dynamics

3 main steps :

i) sub-ps molecular switching ii) unit cell volume expansion

on 10 ns time scale iii) significant thermal effect on µs time scale

Phys. Rev. Letters 103, 028301 (2009) Acta Crys. A 66, 189 (2010)

M. Lorenc et al., PRL 103, 028301 (2009)

1 s

10-3 s

10-6 s

10-9 s

10-12 s

10-15 s

Days

atomic motions optical phonons

acoustic phonons domain wall

motions

Electronic motions

ultra-fast molecular switching (local)

thermalization of lattice at constant volume (isolated)

volume expansion (adiabatic τ ≈ l/vs )

thermal molecular switching and heat diffusion

recovery of thermal equilibrium (τ ≈ C/K)

From the molecular to material scale Consecutive different dynamic processes at different length and time-scales

fs

ps

ns

µs

ms

Non-equilibrium (thermo)dynamics

Q W

H. Cailleau et al., Acta Cryst. A 66, 189 (2010)

<Fhkl(dt)> = XHS(dt) FhklHS(dt)

+ [1-XHS(dt)] FhklLS(dt)

Reorganisation and macroscopic homogeneity

E. Collet et al.,

Chem. Eur. J. 18, 2051 (2012)

X-ray

Light

Molecular switching triggered by volume expansion

M. Lorenc et al., PR B 85, 054302 (2012)

.

10µm / 100nm

Propagating and diffusive phenomena: size and

environment

Monocrystal vs Nanocrystals

MONO NANO .

R.Bertoni et al., Angew. Chem. Int. (2012) and in preparation.

Coherent collective dynamics

Bobsleigh effect

A. Martino, unpublished

Outline 1 – Structural Dynamics and Photo-InducedTransformations in Materials 2 – Tracking the Time Evolution of Molecular Switching in the Solid State 3 – Capturing Precursors of a Photo- Induced Transformation in a Material

from K. Nasu

1D exciton-strings in TTF-CA: detection by diffuse scattering

… A° D° A° (D+ A-) (D+ A-) (D+ A-) D° A° D°...

E. Collet et al, ERL 57(1) 67 (2002) M. Buron et al, PRL 96, 205503 (2006)

Diffuse scattering is very weak

Diffuse Scattering at thermal equilibrium

100 ps experiment at KEK (Japan) The intensity of the diffuse scattering signal increases just after the laser excitation

Time-resolved diffuse scattering

L. Guerin et al. PRL 105, 246101

(2010)

Concluding remarks

Very far to draw a global picture We need : - to extend existing theoretical approaches to new regimes and probably to develop fundamentally new concepts, - to perform challenging experiments using the great potential from advanced probes

IPR Rennes : Roman Bertoni, Hiroshi Watanabe, Ciro D’Amico, Wawrzeniec Kaszub, Andrea Marino,, Marina Servol, Marco Cammarata, Maciej Lorenc, Loic Toupet, Marylise Buron, Eric Collet ICMMO Orsay Marie-Laure Boillot ICMCB Bordeaux Jean-François Létard

ESRF, France Michael Wulff, Laurent Guérin

TITech & KEK Japan Shin-ichi Adachi, Shin-ya Koshihara

Synchrotron Soleil Claire Laulhe, Sylvain Ravy

APS Argonne USA Tim Graber

LCLS Stanford USA Henrik Lemke

Team, Collaborations, Funds

Thank you!