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Time-resolved Boson Emission in the Excitation Spectrum of Bi2Sr2CaCu2O8+δ


Sentef,  Michael A.
Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for Free Electron Laser Science, 22761 Hamburg, Germany;
HISKP, University of Bonn, 53115 Bonn, Germany;

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Rameau, J. D., Freutel, S., Sentef, M. A., Kemper, A. F., Freericks, J. K., Avigo, I., et al. (in preparation). Time-resolved Boson Emission in the Excitation Spectrum of Bi2Sr2CaCu2O8+δ.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0028-4EB1-C
Using femtosecond time- and angle-resolved photoemission spectroscopy we analyze the complex unoccupied electronic structure of optimally doped Bi2Sr2CaCu2O8+δ after optical excitation. Electronic relaxation is characterized by a 250 fs relaxation time below and <20 fs above a single boson energy of ~75 meV above the Fermi energy EF which represents the unoccupied counterpart of the kink observed below EF and Tc. With increasing optical excitation density this sharp energy-dependent step in the relaxation time is found to vanish, in good agreement with self-energy and time-dependent Keldysh Green's function calculations, due to redistribution of electrons within the relaxation phase space. These findings have implications regarding the origin of the primary nodal kink in the electronic structure and for the mechanism behind high Tc superconductivity in the cuprates.