Strong correlation between field-induced magnetism and superconductivity in Pr$_{0.89}$LaCe$_{0.11}$CuO$_{4}$

TL;DR

This study reveals a strong link between field-induced magnetism and superconductivity in an electron-doped cuprate, showing how local magnetic responses change with applied field and coexist with superconductivity.

Contribution

It demonstrates the field-dependent enhancement and sign change of the muon Knight shift linked to Pr ion polarization in a superconductor, highlighting coexistence of magnetism and superconductivity.

Findings

Muon Knight shift is proportional to in-plane susceptibility in the paramagnetic state.

Superconductivity enhances the muon Knight shift and causes it to change sign.

Weak Pr ion polarization due to superexchange interacts with the Cu sublattice.

Abstract

We report the local magnetic response of an electron-doped cuprate superconductor, Pr$_{0.89}$LaCe$_{0.11}$CuO$_{4}$ ($T_c\simeq26$ K), studied by muon spin rotation (\msr) over a field range from 200 Oe to 50 kOe. In the paramagnetic state, the muon Knight shift along the crystal c-axis ($K_\mu^z$) is proportional to the in-plane susceptibility $\chi_{ab}$. More surprisingly, $K_\mu^z$ is strongly enhanced by the occurrence of superconductivity (below $\sim$40 kOe), changing its sign from positive to negative around $\sim1$ kOe with increasing field. This finding can be understood by considering the weak polarization of Pr ions due to superexchange interaction with the antiferromagnetic Cu sublattice, which coexists with superconductivity.