1. Systematic electron-phonon interaction strength measurements in high- temperature superconductors with femtosecond spectroscopy Christoph Gadermaier Department of Complex Matter Jožef Štefan Insitute Ljubljana, Slovenia

2. What is the role of EPI in high-Tc? Conventional superconductivity Electron-phonon interaction Image courtesy of B. Valenzuela BCS: Isotope effect:

3. Determine electron phonon interaction from electron energy relaxation Image courtesy of G. Cerullo

4. The two-temperature model P.B. Allen, Phys. Rev. Lett. 59, 1460 (1987).

5. Validity of the TTM P.B. Allen, Phys. Rev. Lett. 59, 1460 (1987):

6. The non-equilibrium model V.V Kabanov and A. S. Alexandrov, Phys. Rev. B. 78, 174514 (2008).

7. e-e thermalisation is not faster than e-ph energy relaxation C. Gadermaier et al., Phys. Rev. Lett. 105, 257001 (2010). Metal data from S. D. Brorson et al., Phys. Rev. Lett. 64, 2172 (1990).

8. Electron distribution during relaxation in Bi 2 Sr 2 CaCu 2 O 8+  L. Perfetti et al., Phys. Rev. Lett. 99, 197001 (2007).

9. Compare predictions of TTM and NEM TTM NEM low fluence high fluence all fluences T e undefined

10. Temperature dependent relaxation time We need to measure well above the pseudogap temperature T. Mertelj et al., Phys. Rev. B 81, 224504 (2010).

11. Intensity independent dynamics in La 1.85 Sr 0.15 CuO 4 400K < “T e ” < 800 K C. Gadermaier et al., Phys. Rev. Lett. 105, 257001 (2010).

12. Arguments for the non-equilibrium model textbook knowledge comparison of measured e-ph relaxation and estimated e-e thermalisation times time-dependent electron distribution from ARPES intensity independent dynamics

13. Determination of EPI strength in La 1.85 Sr 0.15 CuO 4 C. Gadermaier et al., Phys. Rev. Lett. 105, 257001 (2010).

14. Determination of EPI strength in YBa 2 Cu 3 O 6.5 C. Gadermaier et al., Phys. Rev. Lett. 105, 257001 (2010).

15. The role of e-ph interaction in high-Tc Unpublished material removed. Please contact christoph.gadermaier@ijs.si

16. Electron correlation T. Nakano et al., J. Phys. Soc. Jap. 67, 2622 (1998). J.-H. Chu, Phys. Rev. B. 79, 014506 (2009).

17. Collaborative electron-electron and electron- phonon Unpublished material removed. Please contact christoph.gadermaier@ijs.si

18. Bipolarons A. S. Alexandrov, Phys. Rev. B. 38, 925 (1988). Basic theory derived already in A. S. Alexandrov, Zh. Fi. Khim. 57, 273 (1983) before the discovery of high Tc

19. Stripes and other textures T. Mertelj, V.V. Kabanov, and D. Mihailovic, Phys. Rev. Lett. 94, 147003 (2005).

20. Conclusion electron-phonon interaction is determined from electron energy relaxation electron energy relaxation is described by the non- equilibrium model, qualitatively even for non-Fermi liquids → T L /  e-ph is a good measure of electron-phonon interaction almost universal dependence of T c of optimally doped compounds on T L /  e-ph, sharp maximum at 5 K/fs → high T c is a collaborative effect of electron-phonon interaction and electron correlation

21. Acknowledgements Primož Kušar, Viktor Kabanov, Tomaž Mertelj, Ljupka Stojchevska, Yasunori Toda, Dragan Mihailović Sasha Alexandrov Cristian Manzoni, Daniele Brida, Dario Polli, Giulio Cerullo grazas pola súa atención