NMR evidence for two-step phase-separation in Nd_{1.85}Ce_{0.15}CuO_{4-delta}

TL;DR

This study uses Cu NMR to investigate the spin and charge structures in Nd_{2-x}Ce_{x}CuO_{4-delta}, revealing a two-step phase separation process involving charge droplets and antiferromagnetic order, highlighting competition with superconductivity.

Contribution

It provides direct NMR evidence for a two-step phase separation in Nd_{1.85}Ce_{0.15}CuO_{4-delta}, showing the evolution from charge droplets to antiferromagnetic order with reoxygenation.

Findings

Identification of charge droplet ('Blob') phase at low reoxygenation.

Transition to antiferromagnetic order after prolonged reoxygenation.

Evidence of competition between superconductivity and Mott-insulating state.

Abstract

By Cu NMR we studied the spin and charge structure in Nd_{2-x}Ce_{x}CuO_{4-delta}. For x=0.15, starting from a superconducting sample, the low temperature magnetic order in the sample reoxygenated under 1 bar oxygen at 900^0 C, reveals a peculiar modulation of the internal field, indicative for a phase characterized by large charge droplets ('Blob'-phase). By prolonged reoxygenation at 4 bar the blobs brake up and the spin structure changes to that of an ordered antiferromagnet (AF). We conclude that the superconductivity in the n-type systems competes with a genuine type I Mott-insulating state.