Abstract
The quest for a pairing boson in cuprate high-temperature superconductors is one of the outstanding tasks of solid-state physics. Numerous time-resolved studies of pair breaking, related to pairing by time-reversal symmetry, have been performed using femtosecond optical pulses. By considering energy relaxation pathways between charge, spin, and lattice degrees of freedom, evidence for both phonon and antiferromagnetic fluctuation-mediated pairing has been obtained. Here we present a study of the superconducting-state depletion process in an electron-doped cuprate , where the superconducting gap is smaller than the energy of relevant bosonic excitations. When pumping with above-gap terahertz pulses, we find that the absorbed energy density required to deplete superconductivity, , matches the thermodynamic condensation energy. On the contrary, by near-infrared pumping, is an order of magnitude higher, as in the case of hole-doped, large-gap cuprates. These results imply that only a small subset of bosons, which are generated during the relaxation of optically excited carriers, contributes to pairing. This observation implies that, contrary to the common assumptions, electron-boson coupling in cuprates is strongly energy dependent.
- Received 20 October 2016
- Revised 18 January 2017
DOI:https://doi.org/10.1103/PhysRevB.95.085106
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