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Published April 20, 2007 | public
Journal Article

Nonequilibrium Phase Transitions in Cuprates Observed by Ultrafast Electron Crystallography


Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Δc) on fluence (F), with Δc/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at ∼0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity.

Additional Information

© 2007 American Association for the Advancement of Science. Received 14 December 2006; accepted 19 March 2007. This work was supported at Caltech by the Gordon and Betty Moore Foundation and NSF and at BNL by the U.S. Department of Energy (contract number MA-509-MACA). We thank P. Baum in the UEC laboratory and P. Cao in J. Heath's group at Caltech for AFM imaging; V. Butko, C. Deville-Cavelin, and L. Howald at BNL for XRD, AFM, and transport measurements; and Z. Radovic and N. Bozovic at BNL for the cohesive energy calculations.

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