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

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

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

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

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

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

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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).

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

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

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

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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).

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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

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

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

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The role of e-ph interaction in high-Tc Unpublished material removed.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

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

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

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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

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

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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

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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

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