Temporal correlations of superconductivity above the transition temperature in La$_{2-x}$Sr$_x$CuO$_4$ probed by terahertz spectroscopy

TL;DR

This study uses terahertz spectroscopy to investigate superconducting fluctuations above the critical temperature in La$_{2-x}$Sr$_x$CuO$_4$, finding they persist only within 16 K of T$_c$ and do not significantly affect pseudogap transport anomalies.

Contribution

It provides direct temporal measurements of superconducting fluctuations above T$_c$ across a wide doping range in LSCO, clarifying their limited temperature range and role.

Findings

Superconducting fluctuations persist up to 16 K above T$_c$.

Fluctuations do not significantly influence pseudogap charge transport.

Superconducting correlations are confined to a narrow temperature window.

Abstract

The nature of the underdoped pseudogap regime of the high-temperature superconductors has been a matter of long-term debate. On quite general grounds, one expects that due 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. 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. In this work we use THz time-domain spectroscopy (TTDS) to probe the temporal fluctuations of superconductivity above the critical temperature (T$_c$) in La$_{2-x}$Sr$_x$CuO$_4$ thin films over a doping range that spans almost the entire superconducting dome (x = 0.09 to 0.25). Signatures of the fluctuations persist in the conductivity in a comparatively narrow temperature range, at most 16 K above Tc. 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$_c$.