Pairing and the phase diagram of the normal coherence length ${\xi }_N(T,x)$ above $T_c$ of $L{a}_{2-x}S{r}_{x}Cu{O}_4$ thin films probed by the Josephson effect

Abstract

Critical currents $I_c$ were measured in Superconducting - normal - superconducting SNS c-axis junctions, where S was optimally doped $YB{a}_{2}C{u}_3{O}_{7-\delta }$ below $T_c$ (90 K) and N was $L{a}_{2-x}S{r}_{x}Cu{O}_4$ above its $T_c$ ($<$25 K) but in the pseudogap regime. $I_c$ was measured versus temperature T in junctions with various N-barrier thicknesses $d$ and doping levels $x$. From the proximity effect relation $I_c(T)\propto exp[-d/{\xi }_N(T)]$, the normal coherence length ${\xi }_N(T)$ of N was extracted and plotted versus T. Besides finding a long range proximity effect as reported also by others, we found a crossing at about 55 K above which ${\xi }_N(x=0.1)>{\xi }_N(x=0.18)]$. This unexpected result where junctions with lower carrier density in the barrier have higher conductance, is attributed to the presence of pre-formed pairs in the pseudogap regime of the cuprate barrier. Our data yields a new phase diagram of ${\xi }_N(T,x)$ whose contours of constant ${\xi }_N$ follow the trend of the superconducting dome of $L{a}_{2-x}S{r}_{x}Cu{O}_4$ above its $T_c$, with ${\xi }_N$ enhancement in the underdoped regime above 55 K.

Tal Kirzhner passed away on October 3 2013 in Haifa, at the young age of 29, from lung cancer. This study was supposed to be the main part of his PhD thesis. In this revised version, a supplementary part is included, and a correction to the x=0.24 doping level data of Fig. 5 is made (see details in the supplementary)

References in corpus (8)

• Scanning tunneling spectroscopy of high-temperature superconductors
• Magnetic order in the pseudogap phase of high-$T_C$ superconductors
• Polar Kerr Effect Measurements of YBa2Cu3O6+x: Evidence for Broken Symmetry Near the Pseudogap Temperature
• Distinct Fermi-Momentum Dependent Energy Gaps in Deeply Underdoped Bi2212
• Kerr effect as evidence of gyrotropic order in the cuprates
• Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase of cuprates
• Giant proximity effect in a phase-fluctuating superconductor
• Interface effects in d-wave superconductor-ferromagnet junctions

Cited by in corpus (6)

• Observation of two distinct pairs fluctuation lifetimes and supercurrents in the pseudogap regime of cuprate junctions
• Spatial competition of the ground states in 1111 iron pnictides
• From Cooper-pair glass to unconventional superconductivity: a unified approach to cuprates and pnictides
• Proximity effects and pair currents in cuprate junctions
• Fluctuation conductivity due to the preformed local pairs
• Quasiparticle states driven by a scattering on the preformed electron pairs