Spin-glass state of vortices in YBa2Cu3Oy and La2-xSrxCuO4 below the metal-to-insulator crossover

TL;DR

This study reveals disordered magnetism confined to vortices in high-Tc superconductors near the metal-insulator crossover, supporting a quantum phase transition theory involving magnetic and superconducting order competition.

Contribution

It provides experimental evidence of disordered vortex magnetism and clarifies the nature of the metal-insulator crossover in high-Tc superconductors.

Findings

Disordered magnetism confined to vortices detected by muon spin rotation.

Magnetism near the quantum phase transition is not ordered.

Normal state governed by a magnetic quantum critical point.

Abstract

Highly disordered magnetism confined to individual weakly interacting vortices is detected by muon spin rotation in two different families of high-transition-temperature superconductors, but only in samples on the low-doping side of the low-temperature normal state metal-to-insulator crossover (MIC). The results support an extended quantum phase transition (QPT) theory of competing magnetic and superconducting orders that incorporates the coupling between CuO2 planes. Contrary to what has been inferred from previous experiments, the static magnetism that coexists with superconductivity near the field-induced QPT is not ordered. Our findings unravel the mystery of the MIC and establish that the normal state of high-temperature superconductors is ubiquitously governed by a magnetic quantum critical point in the superconducting phase.