### Abstract

We report extensive measurements of the Knight shift K, the nuclear spin-lattice relaxation rate 1/(Formula presented), and the Gaussian spin-echo decay rate 1/(Formula presented) of (Formula presented) in overdoped (Formula presented)(Formula presented)(Formula presented) (Tl1212) with (Formula presented) = 70 K, 52 K, and 10 K, in order to elucidate the origin of the reduction in (Formula presented) with increasing holes and to identify the symmetry of the order parameter. In the normal state, it is shown that 1/(Formula presented)T obeys the Curie-Weiss law, pointing to the presence of the antiferromagnetic (AF) spin correlation. From the analyses of 1/(Formula presented) and 1/(Formula presented), it is found that the increase of the hole content in Tl1212 compounds makes the characteristic energy of the AF spin fluctuation around a zone boundary, Q=(π/a,π/a), (Formula presented), transfer to a higher-energy region and concomitantly reduces the magnetic correlation length (Formula presented) significantly. The AF spin correlation is concluded to become less distinct in going from the optimum-doped to the overdoped regime. In the superconducting state, the T dependences of K and 1/(Formula presented) have revealed that the superconductivity is in the gapless regime with a finite density of states at the Fermi level. The NMR results are consistently interpreted in the d-wave model in which the impurity scattering is incorporated in terms of the unitarity limit as demonstrated in most of the high-(Formula presented) cuprates so far. Eventually, the reduction in (Formula presented) from 70 K to 52 K in Tl1212 is concluded to be not due to the impurity effect associated with the oxygen content. In the previous works, the enhancement of (Formula presented) from 93 K in (Formula presented)(Formula presented)(Formula presented) with double (Formula presented) layers to 115-135 K in (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented)(Formula presented) with triple (Formula presented) layers was shown to be due to the increase in (Formula presented) with (Formula presented) unchanged appreciably. This finding was compatible with the relationship of (Formula presented)∝(Formula presented)(Formula presented)exp(-1/λ) based on the spin-fluctuation-induced mechanism for the d-wave superconductivity. Within the same scheme, the origin of the marked decrease in (Formula presented) irrespective of increasing (Formula presented) in Tl1212 is proposed to be due to the significant reduction in (Formula presented) which makes the pairing interaction weaken and λ in the above formula reduced.

Original language | English |
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Pages (from-to) | 10131-10142 |

Number of pages | 12 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 54 |

Issue number | 14 |

DOIs | |

Publication status | Published - Jan 1 1996 |

Externally published | Yes |

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics

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## Cite this

*Physical Review B - Condensed Matter and Materials Physics*,

*54*(14), 10131-10142. https://doi.org/10.1103/PhysRevB.54.10131