Temporal correlations of superconductivity above the transition temperature in La2−xSrxCuO4 probed by terahertz spectroscopy

摘要

The nature of the underdoped pseudogap regime of the high-temperaturesuperconductors has been a matter of long-term debate. On quite generalgrounds, one expects that due to their low superfluid densities and shortcorrelation lengths, superconducting fluctuations will be significant fortransport and thermodynamic properties in this part of the phase diagram.Although there is ample experimental evidence for such correlations, there hasbeen disagreement about how high in temperature they may persist, their role inthe phenomenology of the pseudogap, and their significance for understandinghigh-temperature superconductivity. In this work we use THz time-domainspectroscopy (TTDS) to probe the temporal fluctuations of superconductivityabove the critical temperature (T$_c$) in La$_{2-x}$Sr$_x$CuO$_4$ thin filmsover a doping range that spans almost the entire superconducting dome (x = 0.09to 0.25). Signatures of the fluctuations persist in the conductivity in acomparatively narrow temperature range, at most 16 K above Tc. Our measurementsshow that superconducting correlations do not make an appreciable contributionto the charge transport anomalies of the pseudogap in LSCO at temperatures wellabove T$_c$.