SC fluctuations not so strong as previously thought

Here is a wonderful Letter [Nature Physics, 7:298(2011)] which, in a sense, denies the pseudogap as precursor of SC in cuprate. These authors probes LSCO, a very typical p-type high Tc, by Terahertz spectroscopy. They found that, such SC fluctuations persist up to 16 K above Tc, much weaker than former speculations. This is actually quite consistent with a latest work with ARPES [see my yesterday's entry].

The nature of the underdoped pseudogap regime of the high-temperature copper oxide superconductors has been a matter of long-term debate^{1, 2, 3}. On quite general grounds, we expect that, owing to their low superfluid densities and short correlation lengths, superconducting fluctuations will be significant for transport and thermodynamic properties in this part of the phase diagram^{4, 5}. Although there is ample experimental evidence for such correlations, there has been disagreement about how high in temperature they may persist, their role in the phenomenology of the pseudogap and their significance for understanding high-temperature superconductivity^{6, 7, 8, 9, 10}. Here we use THz time-domain spectroscopy to probe the temporal fluctuations of superconductivity above the critical temperature (T_c) in La_2−xSr_xCuO₄ (LSCO) thin films over a doping range that spans almost the entire superconducting dome (x=0.09–0.25). Signatures of the fluctuations persist in the conductivity in a comparatively narrow temperature range, at most 16 K above T_c. Our measurements show that superconducting correlations do not make an appreciable contribution to the charge-transport anomalies of the pseudogap in LSCO at temperatures well above T_c.