Singular spin fluctuations in the strange-metal phase of La2-xSrxCuO4

TL;DR

This study shows that spin fluctuations in overdoped La2-xSrxCuO4 increase continuously at low temperatures, indicating quantum-critical behavior and spatial inhomogeneity, which may underlie strange-metal properties.

Contribution

The paper provides evidence of quantum-critical spin fluctuations and nanoscale inhomogeneity in the overdoped regime, expanding understanding of strange-metal behavior in cuprates.

Findings

Spin susceptibility increases continuously down to low temperatures.

Spin dynamics are spatially inhomogeneous.

Behavior observed beyond the spin-stripe critical doping.

Abstract

Although spin fluctuations are central to the physics of high-Tc cuprates, their relevance to strange-metal behavior in the overdoped regime remains unclear. Here, we use high magnetic fields to suppress superconductivity and an NMR protocol tailored to electronic inhomogeneity to show that the low-energy limit of the dynamical spin susceptibility \chi''(q,omega) at x=0.25 in La2-xSrxCuO4 increases continuously down to our lowest temperatures. This behavior is suggestive of quantum-critical fluctuations, a leading candidate mechanism for strange-metal transport, yet is observed well beyond the spin-stripe critical doping x=0.19. Our data further reveal that the spin dynamics are spatially inhomogeneous, suggesting that nanoscale electronic inhomogeneity may underlie this apparent paradox. These observations provide new insight into the electronic state from which strange-metal behavior emerges.