(Ir)Relevance of Disorder for Superconductivity in Cuprates

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 La_{2-x}Sr_{x}CuO_{4-δ} films by electrolyte gating, measured several parameters used to quantify the level of disorder (the residual resistivity ratio RRR, the mean free path l_{0}, and the electron mobility μ), 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.