Ultrafast Structural Dynamics in Solids Klaus Sokolowski-Tinten

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1 Ultrafast Structural Dynamics in Solids Klaus Sokolowski-Tinten Institut für Experimentelle Physik STI Round-Table Meeting, Hamburg, Juni 2004

2 Outline motivation: why short pulses and the XFEL are important current status: - what has been done/achieved with fs X-rays - why not more - example other topics & issues

3 Relaxation in Optically Excited Solids _ carrier-carrier scattering: T e-h >> T L carrier-phonon scattering: T e-h fl, T L T e-h» T L phonon-phonon scattering heat diffusion thermal melting ablation Time [s]

4 Previous Ultrafast X-ray Experiments Desintegration of a LB-film Rischel et al., Nature 390, 490 (1997) few ps- to fs-range Coherent Acoustic Phonons Rose-Petruck et al. Nature 407, (1999) Lindenberg et al., PRL 84, 111 (2000). Cavalleri et al., PRL 85, 586 (2000). Cavalleri et al., PRB 63, (2001). Larsson et al., APA 75, 467 (2002). Insulator Metal Transition in VO 2 Cavalleri et al., PRL 87, (2001). Cavalleri et al., (in prep., 2004). Ultrafast Melting Chin et al., PRL. 83, 336 (1999) Siders et al., Science 286, 1340 (1999) Rousse et al., Nature 410, 65 (2001) Sokolowski-Tinten et al., PRL 87, (2001) Feurer et al., PRE 65, (2002) Lindenberg, Larsson, Sokolowski-Tinten & SPPS Collab., (in prep., 2004). Coherent Optical Phonons in Bi Sokolowski-Tinten et al., Nature 422, 287 (2003) Common Features: Femtosecond Resolution with Laser-Plasma-Sources (situation is changing slicing source, SPPS) Bragg Diffraction from Single Crystalline Samples There is a flux problem!!!

5 Non-Thermal Melting of Semiconductors Non-thermal melting: (i) disordering induced by electronic excitation (ii) faster than energy relaxation P. Stampfli et al., PRB 49, 7299 (1994) lattice destabilization

6 Previous Ultrafast X-ray Experiments Desintegration of a LB-film Rischel et al., Nature 390, 490 (1997) Ultrafast Melting Coherent Acoustic Phonons Rose-Petruck et al. Nature 407, (1999) Lindenberg et al., PRL 84, 111 (2000). Cavalleri et al., PRL 85, 586 (2000). Cavalleri et al., PRB 63, (2001). Larsson et al., APA 75, 467 (2002). Insulator Metal Transition in VO 2 Cavalleri et al., PRL 87, (2001). Cavalleri et al., (in prep., 2004). Ultrafast Melting Chin et al., PRL. 83, 336 (1999) Siders et al., Science 286, 1340 (1999) Rousse et al., Nature 410, 65 (2001) Sokolowski-Tinten et al., PRL 87, (2001) Feurer et al., PRE 65, (2002) Lindenberg, Larsson, Sokolowski-Tinten & SPPS Collab., (in prep., 2004). Chin et al., PRL. 83, 336 (1999) Siders et al., Science 286, 1340 (1999) Rousse et al., Nature 410, 65 (2001) Sokolowski-Tinten et al., PRL 87, (2001) Coherent Optical Phonons in Bi Feurer et al., PRE 65, (2002) Lindenberg, Larsson, Sokolowski-Tinten & SPPS Collab., (in prep., 2004). Sokolowski-Tinten et al., Nature 422, 287 (2003) Common Features: Femtosecond Resolution with Laser-Plasma-Sources (situation is changing slicing source, SPPS) Bragg Diffraction from Single Crystalline Samples There is a flux problem!!!

7 State-of-the-Art: Experiments at SPPS incident X-ray beam laser InSb diffracted beam crossed beams: space-time mapping grazing incidence: matching pump and probe depths before laser illumination during laser illumination laser-excited area time

8 Single-Shot Experiment Jitter:» 1 ps FWHM measured with streakcamera (A. MacPhee et al.)

9 Disordering of InSb» 200 fs! first femtosecond (111) & (220)! diffraction fastest havedisordering been experiment measured observed at analysis accelerator-based so far under! way source!

10 What do we really know? Not much!!! Decay of one (or two) diffraction order(s) is compatible with disordering We do not know what is the pathway of disordering which phonon modes areinvolved what is the structure of the liquid The XFEL will allow to look for multiple Bragg-peaks diffuse/off-bragg scattering forbidden reflections Sponatenous emission absorption (EXAFS/NEXAFS) What is needed (for scattering experiments): a lot of photons!! < kev < 100fs synchronization w optical laser and/or timing information single 10 Hz rep. rate diffractometer for large samples & with sample translation normalization (intensity & beam profile monitor) detectors: photodiode CCD

11 Ultrafast Structural Dynamics in Solids: Other Topics & Issues single crystals (quasi-)disordered systems large samples small samples to overcome material restrictions materials: strong coupling fs-excitation: impulsive & strong drive UV MIR (HG, OPG/OPA, DFG) fs; µj mj coherent phonons phase transitions (non-equilibrium, role of phonons/soft modes) magnetic materials superconductors CDW-materials surfaces & buried interfaces nanostructures (nano-particles & heterostructures