In cuprates that exhibit high-temperature superconductivity (HTS), as the doping level $p$ is increased beyond the optimal value, the superfluid density $n_{s0}$ decreases and eventually vanishes, closely tracking the critical temperature $T_c$. This has been interpreted using a dirty-$d$-wave extension of the Bardeen-Cooper-Schrieffer theory, assuming that $T_c$ and $n_{s0}$ decrease with increasing disorder and pair breaking. To test this hypothesis, we tuned the doping level in overdoped ${\mathrm{La}}_{2\text{-x}}{\mathrm{Sr}}_{\mathrm{x}}{\mathrm{CuO}}_{4\text{−}\delta }$ films by electrolyte gating, measured several parameters used to quantify the level of disorder (the residual resistivity ratio $\mathrm{RRR}$, the mean free path $l_0$, and the electron mobility $\mu$), and studied how $T_c$ and $n_{s0}$ scale with these. The experimentally measured dependence turned out to be the opposite of the expected—$T_c$ and $n_{s0}$ increased with increasing disorder. This brings the question of the true origin of the demise of $T_c$ and $n_{s0}$ with overdoping back to the center stage of the quest to decipher the HTS enigma.

Close

PrevNext

View figure in article

• Superconductivity
• Superfluid density
• High-temperature superconductors
• Atomic force microscopy
• Deep level transient spectroscopy
• Epitaxy
• Liquid helium cooling
• Resistivity measurements
• Sample preparation
• Susceptibility measurements