A major challenge in understanding the cuprate superconductors is to clarify the nature of the fundamental electronic correlations that lead to the pseudogap phenomenon. Here we use ultrashort light pulses to prepare a non-thermal distribution of excitations and capture novel properties that are hidden at equilibrium. Using a broadband (0.5-2 eV) probe, we are able to track the dynamics of the dielectric function and unveil an anomalous decrease in the scattering rate of the charge carriers in a pseudogap-like region of the temperature (T) and hole-doping (p) phase diagram. In this region, delimited by a well-defined T* neq (p) line, the photoexcitation process triggers the evolution of antinodal excitations from gapped (localized) to delocalized quasiparticles characterized by a longer lifetime. The novel concept of photo-enhanced antinodal conductivity is naturally explained within the single-band Hubbard model, in which the short-range Coulomb repulsion leads to a k-space differentiation between nodal quasiparticles and antinodal excitations.
Bibliographical noteFunding Information:
We thank D. Fausti, G. Zgrablic, G. Sordi, E. Gull, P. Werner, A. Avella, M. Fabrizio, A. Cavalleri, D. Manske, G. Ghiringhelli, B. Keimer, D. Mihailovic for the useful discussions and comments and for their support. The research activities of C.G., S.D.C., N.M., S.M., F.B., G.F., M.C., F.P. and U.B. have received funding from the European Union, Seventh Framework Programme (FP7 2007-2013), under Grant No. 280555 (GO FAST). F.C., G.C., and F.P. acknowledge the support of the Italian Ministry of University and Research under Grant No. FIRB-RBAP045JF2 and FIRB-RBAP06AWK3. M.C. is financed by European Research Council through FP7/ERC Starting Grant SUPERBAD, Grant Agreement 240524. L. R. and U. B. acknowledge support by the Mercator Research Center Ruhr (MERCUR). The YBi2212 crystal growth work was performed in M.G.’s prior laboratory at Stanford University, Stanford, CA 94305, USA, and supported by DOE-BES. The Hg1201 crystal growth work at the University of Minnesota was supported by DOE-BES Award DESC0006858. The work at UBC was supported by the Killam, Alfred 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. D.v.d.M. acknowledges the support of the Swiss National Science Foundation under Grant No. 200020-140761 and MaNEP. The Open Access has been funded by Università Cattolica del Sacro Cuore and Elettra-Sincrotrone Trieste S.C.p.A.