K. Tokiwa

Coexistence of superconductivity and antiferromagnetism in multilayered high-Tc superconductor HgBa2Ca4Cu 5Oy: Cu-NMR study

We report a coexistence of superconductivity and antiferromagnetism in five-layered compound HgBa 2 (Ta 4 Cu 5 O y (Hg-1245) with T c = 108 K, which is 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 optimally doped OP undergoes a superconducting (SC) transition at T c = 108 K, whereas the three underdoped IPs do an antiferromagnetic (AF) transition below T N ∼60 K with the Cu moments of ∼(0.3-0.4)μ B . Thus bulk superconductivity with a high value of T c =108 K and a static AF ordering at T N =60 K are realized in the alternating AF and SC layers. The AF-spin polarization at the IP is found to induce the Cu moments of ∼0.02μ B at the SC OP, which is the AF proximity effect into the SC OP.

Spin Correlation in High-T c Cuprate HgBa2Ca2Cu3O8+δ with T c=133 K –An Origin of T c-Enhancement Evidenced by 63Cu-NMR Study–

The Knight shift, the nuclear spin-lattice relaxation rate, 1/ T 1 , and the transverse relaxation rate, 1/ T 2G , of 63 Cu have been separately measured for the square and the pyramidal CuO 2 planes in HgBa 2 Ca 2 Cu 3 O 8+δ (Hg1223) with the highest transition temperature, T c =133 K to date. From the quantitative analysis of 1/ T 1 and 1/ T 2G , it is shown that the product of the staggered susceptibility and the characteristic energy of spin fluctuations around a zone boundary, χ Q Γ Q , for the square CuO 2 plane site is larger than that for YBa 2 Cu 3 O 7 (YBCO 7 ), although that for the pyramidal CuO 2 plane site is almost the same. This enhancement of χ Q Γ Q for the square site is considered to be responsible for the higher T c in Hg1223 than in YBCO 7 .

63Cu-NMR Study in High-Tc Superconductor HgBa2Ca2Cu3O8 + δ

Abstract The 63Cu nuclear transverse relaxation rates have been measured in the normal state on both square and pyramidal CuO2 planes in HgBa2Ca2Cu3O8 + δ with Tc = 133K. The Gaussian component of the spin-echo decay rate, 63(1/T2G), for both sites increases with decreasing temperature, followed by a peak around T* ~ 150 K, indicating that the spin correlation becomes stronger with decreasing temperature. Also, it is found that the magnitude of 63(1/T2G) for a square site is larger than that for a pyramidal one, suggesting that the spin correlation in the square plane is stronger than that in the pyramidal one.