Correlation between unconventional superconductivity and strange metallicity revealed by operando superfluid density measurements

TL;DR

This study reveals a direct correlation between strange-metal behavior and unconventional superconductivity through operando superfluid density measurements in ion-gated FeSe films, highlighting a universal principle across different superconductors.

Contribution

It demonstrates a linear scaling between superfluid density and strange-metal resistivity, linking superconducting condensation to carrier scattering in strange metals, supported by theoretical modeling.

Findings

Linear scaling between superfluid density and resistivity coefficient.

Synchronization of superconducting and strange-metal phases with doping.

Universal correlation observed across different superconductor families.

Abstract

Strange-metal behavior has been observed in superconductors ranging from cuprates to pressurized nickelates, but its relationship to unconventional superconductivity remains elusive. Here, we perform operando superfluid density measurements on ion-gated FeSe films. We observe for the first time a synchronized evolution of superconducting condensate and the strange-metal phase with electron doping. A linear scaling between zero-temperature superfluid density and the strange-metal resistivity coefficient is further established, which nails down a direct link between the formation of superfluid in the superconducting state and the scattering of carriers in the strange-metal normal state. Remarkably, the scaling also applies for different iron-based and cuprate superconductors despite their distinct electronic structures and pairing symmetries. Such a correlation can be reproduced in a theoretical calculation on the two-dimensional Yukawa-Sachdev-Ye-Kitaev model by considering a cooperative effect of quantum critical fluctuation and disorder. These findings indicate a fundamental principle governing superconducting condensation and strange-metal scattering in unconventional superconductors.