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Single-quasiparticle stability and quasiparticle-pair decay in YBa2Cu3O6.5 (Ortho II)

N. Gedik·P. Blake·R. C. Spitzer·J. Orenstein·Ruixing Liang·D. A. Bonn·W. N. Hardy
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Abstract

We report results and analysis of time-resolved photoinduced reflectivity experiments on the cuprate superconductor YBa2Cu3O6.5. The sample, which has Tc=45 K, was characterized by a high degree of purity and Ortho II ordering. The change in reflectivity (Delta R) was induced and probed using pulses of 100 femtosecond duration and photon energy 1.55 eV from a Ti:Sapphire laser. We provide a detailed picture of the decay rate (gamma) of Delta R as a function of temperature T and pump intensity I. At low T, gamma decreases linearly with decreasing I, extrapolating to nearly zero in the limit that I tends to zero. At higher temperatures gamma has the same linear dependence, but with nonzero limit as I goes to zero. In the interpretation of these results we assume that Delta R is proportional to the nonequilibrium quasiparticle density created by the laser. From an analysis of the gamma vs. I we estimate beta, the coefficient of proportionality relating the quasiparticle decay rate to the density. The intercept of gamma vs. I yields the thermal equilibrium quasiparticle decay rate. In a discussion section, we argue that the quasiparticles induced by the laser occupy primarily states near the antinodal regions of the Brillouin zone. We explain the divergence of the lifetime as T and I both tend to zero as a consequence of momentum and energy conservation in electron-electron scattering. We discuss the significance of the measured value of beta (approximately 0.1 cm2/s) in terms of the electron-phonon interactions.

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N. Gedik, P. Blake, R. C. Spitzer, J. Orenstein, Ruixing Liang, D. A. Bonn, W. N. Hardy. 2003-09-04. Single-quasiparticle stability and quasiparticle-pair decay in YBa2Cu3O6.5 (Ortho II). https://doi.org/10.1103/physrevb.70.014504

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