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Science 21 January 2000:
Vol. 287. no. 5452, pp. 470 - 473
DOI: 10.1126/science.287.5452.470
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Reports

Ultrafast Mid-Infrared Response of YBa2Cu3O7-delta

R. A. Kaindl, 1 M. Woerner, 1 T. Elsaesser, 1* D. C. Smith, 2 J. F. Ryan, 2 G. A. Farnan, 3 M. P. McCurry, 3 D. G. Walmsley 3

Optical spectra of high-transition-temperature superconductors in the mid-infrared display a gap of in-plane conductivity whose role for superconductivity remains unresolved. Femtosecond measurements of the mid-infrared reflectivity of YBa2Cu3O7-delta after nonequilibrium optical excitation are used to demonstrate the ultrafast fill-in of this gap and reveal two gap constituents: a picosecond recovery of the superconducting condensate in underdoped and optimally doped material and, in underdoped YBa2Cu3O7-delta , an additional subpicosecond component related to pseudogap correlations. The temperature-dependent amplitudes of both contributions correlate with the antiferromagnetic 41-millielectronvolt peak in neutron scattering, supporting the coupling between charges and spin excitations.

1 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin, Germany.
2 Department of Physics, Clarendon Laboratory, Oxford University, Oxford OX1 3PU, UK.
3 Department of Pure and Applied Physics, Queen's University of Belfast, Belfast BT7 1NN, UK.
*   To whom correspondence should be addressed.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)