Strong Electron Correlation behind the Superconductivity in Ce-Free and Ce-Underdoped High-<i>T</i>_c T′-Cuprates

Abstract

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