Magnetic properties of the overdoped superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ with and without Zn impurities

TL;DR

This study investigates how Zn impurities affect the magnetic properties of overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$ superconductors, revealing induced paramagnetism, suppression of $T_c$, and enhanced magnetic scattering, suggesting a competitive relationship between magnetism and superconductivity.

Contribution

It provides new insights into the effects of Zn substitution on magnetic behavior and superconductivity in overdoped cuprates, supported by magnetization and neutron scattering data.

Findings

Zn induces local paramagnetic moments in overdoped samples.

Zn substitution suppresses the superconducting transition temperature $T_c$.

Zn enhances inelastic magnetic scattering around $( ext{pi}, ext{pi})$ at 7 meV.

Abstract

The magnetic properties of the Zn-substituted overdoped high-$T_c$ superconductor La$_{2-x}$Sr$_{x}$Cu$_{1-y}$Zn$_{y}$O$_{4}$ have been studied by magnetization measurements and neutron scattering. Magnetization measurements reveal that for Zn-free samples with $x \geq 0.22$ a Curie term is induced in the temperature dependence of the magnetic susceptibility implying the existence of local paramagnetic moments. The induced Curie constant corresponds to a moment of 0.5 $\mu_B$ per additional Sr$^{2+}$ ion that exceeds $x=0.22$. Zn-substitution in the overdoped \lsco also induces a Curie term that corresponds to 1.2 $\mu_B$ per Zn$^{2+}$ ion, simultaneously suppressing $T_c$. The relationship between $T_c$ and the magnitude of the Curie term for Zn-free \lsco with $x \geq 0.22$ and for Zn-substituted \lsco with $x = 0.22$ are closely similar. This signifies a general competitive relationship between the superconductivity and the induced paramagnetic moment. Neutron scattering measurements show that Zn-substitution in overdoped \lsco anomalously enhances the inelastic magnetic scattering spectra around the $(\pi, \pi)$ position, peaking at $\omega \sim 7$ meV. These facts are discussed on the basis of a "swiss-cheese" model of Zn-substituted systems as well as a microscopic phase separation scenario in the overdoped region indicated by muon-spin-relaxation measurements.