Antiferromagnetism and high- superconductivity in F-substituted four-layered cuprates probed by Cu-NMR

Abstract We report on the onset of antiferromagnetism in F-substituted four-layered high- T c compounds Ba 2 Ca 3 Cu 4 O 8 ( O 1 - y F y ) 2 ( 2 y = 1.2 , 1.4 , 1.6 and 2.0) which are composed of two types of CuO 2 planes in a unit cell; three inner planes (IPs) and two outer planes (OPs). The Cu-NMR study has revealed that the hole density at the OPs are slightly larger than that at the IPs, and a total carrier density decreases as F content increases. The observation of zero-field Cu-NMR spectra over a broad frequency range has demonstrated that antiferromagnetically ordered phases emerges at low temperatures for all compounds. This result is similar to the case for the five-layered cuprates HgBa 2 Ca 4 Cu 5 O y where the optimally doped OP undergoes a superconducting (SC) transition, whereas the three underdoped IPs do an antiferromagnetic (AFM) transition [H. Kotegawa, et al., Phys. Rev. B 64 (2001) 064515; H. Mukuda, et al., Phys. Rev. Lett. 96 (2006) 087001]. The present result gives evidence for a coexistence of antiferromagnetism and superconductivity in four-layered high- T c cuprates.