Magnetic-susceptibility and specific-heat studies on the inhomogeneity of superconductivity in the underdoped La_2-x_Sr_x_CuO_4_

TL;DR

This study uses magnetic susceptibility and specific heat measurements on La_2-x_Sr_x_CuO_4_ single crystals to provide evidence of phase separation between superconducting and normal regions in underdoped and overdoped regimes.

Contribution

It is the first experimental work to strongly suggest phase separation in the inhomogeneity of superconductivity in LSCO across doping levels.

Findings

Superconducting volume fraction varies with hole concentration.

Density of states at the Fermi level depends on doping.

Evidence of phase separation in underdoped and overdoped regimes.

Abstract

The possible inhomogeneity of superconductivity has been investigated by means of bulk-sensitive probes, using La_2-x_Sr_x_CuO_4_ (LSCO) single crystals from the underdoped to optimally doped regime. Measurements of the magnetic susceptibility, chi, on field cooling and specific heat have revealed that both the absolute value of chi at 2 K, regarded as corresponding to the superconducting (SC) volume fraction in a sample, and the Sommerfeld constant, reflecting the density of states of quasiparticles at the Fermi level, exhibit significant dependence on x, namely, on the hole concentration. This is the first experimental work strongly suggesting that a phase separation into SC and normal-state regions takes place in the underodped regime of LSCO as well as in the overdoped regime.