Strange metal from spin fluctuations in a cuprate superconductor

TL;DR

This study reveals that magnetic fluctuations in a cuprate superconductor's strange metal phase significantly influence charge transport, with a field-induced spin glass state causing resistivity upturns and defining the strange metal's behavior.

Contribution

It demonstrates that magnetic fluctuations and spin glass states are key to understanding the strange metal phase in cuprates, a novel insight into their transport properties.

Findings

Magnetic fields above 80 T enhance magnetoresistance in La$_{2-x}$Sr$_x$CuO$_4$.

Spin glass states cause insulating-like resistivity upturns in the pseudogap phase.

The strange metal phase exists where magnetic moments fluctuate and vanishes when they freeze.

Abstract

Strange metals challenge our understanding of charge transport in metals. Here, we investigate how the strange metal phase of La$_{2-x}$Sr$_x$CuO$_4$ is impacted by a field-induced glassy antiferromagnetic state. Using magnetic fields above 80 T, we discover a strong enhancement of the normal state magnetoresistance when entering the spin glass phase. We demonstrate that the spin glass causes insulating-like upturns in the resistivity inside the pseudogap phase, which resolves the origin of the ''metal-insulator'' crossover. In addition the strange metal phase appears at low temperatures over an extended range of magnetic fields where magnetic moments fluctuate, and disappears when these moments freeze out. We conclude that the transport properties of the strange metal phase are controlled by magnetic fluctuations persisting at the lowest temperatures.