Strong electron correlation behind the superconductivity in Ce-free and Ce-underdoped high-Tc T'-cuprates

TL;DR

This study reveals that Ce-free and Ce-underdoped T'-cuprates exhibit strong electron correlations, with short-range magnetic order coexisting with superconductivity, challenging conventional understanding of their electronic states.

Contribution

It demonstrates that Ce-free and Ce-underdoped T'-cuprates are strongly correlated electron systems with coexisting magnetic order and superconductivity, based on muSR and specific-heat measurements.

Findings

Short-range magnetic order coexists with superconductivity.

Excess oxygen induces magnetic order.

Strong electron correlations are present in these materials.

Abstract

In order to investigate the electronic state of Ce-free and Ce-underdoped high-Tc cuprates with the so-called T' structure, we have performed muon-spin-relaxation (muSR) and specific-heat measurements of Ce-free T'-La_1.8_Eu_0.2_CuO_4+d_ (T'-LECO) polycrystals and Ce-underdoped T'-Pr_1.3-x_La_0.7_Ce_x_CuO_4+d_ (T'-PLCCO) single crystals with x=0.10. The muSR spectra of the reduced superconducting samples of both T'-LECO with Tc=15K and T'-PLCCO with x=0.10 and Tc=27K have revealed that a short-range magnetic order coexists with the superconductivity in the ground state. The formation of a short-range magnetic order due to a tiny amount of excess oxygen in the reduced superconducting samples strongly suggest that the Ce-free and Ce-underdoped T'-cuprates are regarded as strongly correlated electron systems.