Superconducting Volume Fraction in Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for Phase Separation from Magnetic-Susceptibility Measurement

TL;DR

This study investigates the overdoped regime of La_2-x_Sr_x_CuO_4_ using magnetic susceptibility measurements, revealing phase separation into superconducting and normal regions as doping increases.

Contribution

It provides direct evidence of phase separation in overdoped La_2-x_Sr_x_CuO_4_ through systematic magnetic susceptibility analysis across different doping levels.

Findings

Superconducting volume fraction decreases with increased Sr doping.

Phase separation occurs into superconducting and normal regions in the overdoped regime.

Superconducting transition temperature correlates with the superconducting volume fraction.

Abstract

We have grown a single crystal of La_2-x_Sr_x_CuO_4_ in which the Sr concentration, x, continuously changes from 0.24 to 0.29 in the overdoped regime and obtained many pieces of single crystals with different x values by slicing the single crystal. From detailed measurements of the magnetic susceptibility, chi, of each piece, it has been found that the absolute value of chi at the measured lowest temperature 2 K, |chi_2K_|, on field cooling rapidly decreases with increasing x as well as the superconducting (SC) transition temperature. As the value of |chi_2K_| is regarded as corresponding to the SC volume fraction in a sample, it has been concluded that a phase separation into SC and normal-state regions occurs in a sample of La_2-x_Sr_x_CuO_4_ in the overdoped regime.