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The superconducting gap Δ_{c}, the pseudogap Δ_{p} and pair fluctuations above Tc in overdoped YCaBaCuO from femtosecond time-domain spectroscopy

J. Demsar·B. Podobnik·V. V. Kabanov·D. Mihailovic·Th. Wolf
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Abstract

The low-energy electronic excitation spectrum and gap structure in optimally doped and overdoped Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-δ} single crystals are investigated by real-time measurements of the quasiparticle relaxation dynamics with femtosecond optical spectroscopy. From the amplitude of the photoinduced reflectivity as a function of time, temperature and doping x we find clear evidence for the coexistence of two distinct gaps in the entire overdoped phase. One is a temperature-independent pseudogap $Δ_{p}$ and the other is a T-dependent collective gap $Δ_{c}(T)$ which has a BCS-like T-dependence closing at Tc. From quasiparticle relaxation time measurements above Tc we ascertain that fluctuations associated with the collective gap $Δ_{c}(T)$ are limited to a few K, consistent with time-dependent Ginzburg-Landau theory and are distinct from the pseudogap whose presence is apparent well above Tc for all x.

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J. Demsar, B. Podobnik, V. V. Kabanov, D. Mihailovic, Th. Wolf. 1999-05-03. The superconducting gap Δ_{c}, the pseudogap Δ_{p} and pair fluctuations above Tc in overdoped YCaBaCuO from femtosecond time-domain spectroscopy. https://doi.org/10.1103/physrevlett.82.4918

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