One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive as electronic correlations are expected to greatly accelerate the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and frequency range of transient reflectivity measurements up to an unprecedented level, enabling us to directly observe the ∼16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.
Bibliographical noteFunding Information:
We thank F. Cilento, G. Coslovich, D. Fausti, F. Parmigiani, D. Mihailović, P. Prelovšek, V.V. Kabanov, U. Bovensiepen, M. Eckstein, A. Avella, D. van der Marel, L. Boeri, L. de’ Medici, A. Cavalleri, D. Manske, B. Keimer and D.J. Scalapino for useful and fruitful discussions. We gratefully acknowledge D. Bonn and B. Keimer for support in the development of the MPI-UBC Tl2201OD research effort. The research activities of S.D.C., F.B, G.F., M.C. and C.G. received funding from the European Union, Seventh Framework Programme (FP7 2007-2013), under Grant No. 280555 (GO FAST). S.D.C. received financial support from Futuro through Ricerca grant No. RBFR12SW0J of the Italian Ministry of Education, University and Research. L.V. is supported by the Alexander von Humboldt Foundation. M.M. acknowledges support from the DEC-2013/09/B/ST3/01659 project of the Polish National Science Center. The Y-Bi2212UD crystal growth work was performed in M.G.’s previous laboratory at Stanford University, Stanford, CA 94305, USA, and supported by the US Department of Energy, Office of Basic Energy Sciences. The work at UBC was supported by the Max Planck—UBC Centre for Quantum Materials, the Killam, A. P. Sloan, Alexander von Humboldt, and NSERC’s Steacie Memorial Fellowships (A.D.), the Canada Research Chairs Program (A.D.), NSERC, CFI, and CIFAR Quantum Materials. M.C. is financed by the European Research Council through FP7/ERC Starting Grant SUPERBAD, Grant Agreement 240524. J.B. acknowledges support by the P1-0044 of ARRS, Slovenia and Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences user facility. G.C. acknowledges support by the EC under Graphene Flagship (contract no. CNECT-ICT-604391). N.D.Z. acknowledges support from the NCCR project ‘Materials with Novel Electronic Properties’ and appreciates expert collaboration with J. Karpinski.