Anisotropy of the antiferromagnetic spin correlations in the superconducting state of YBa_2Cu_3O_7 and YBa_2Cu_4O_8

Abstract

We present evidence that the antiferromagnetic spin correlations in optimally doped YBa_2Cu_3O_7 and underdoped YBa_2Cu_4O_8 develop a surprisingly strong anisotropy in the superconducting state. Comparing the ratio of the nuclear spin-lattice relaxation rates of the planar copper and oxygen, measured at the lowest and highest temperatures as well as at T_c, we conclude that the antiferromagnetic in-plane correlations vanish as the temperature goes to zero. This observation is corroborated by the measurement of the copper linewidth in YBa_2Cu_4O_8. In contrast, the out-of-plane correlations do not change appreciably between T=T_c and T=0. Within a model of fluctuating fields this extreme anisotropy of the antiferromagnetic correlations also explains the observed temperature dependence of the anisotropy of the copper relaxation measured in a low external magnetic field.

arXiv commentMinor revisions. Accepted for publication in J. Phys.: Condens. Matter as a Letter

References in corpus (3)

• Spin pseudo-gap and interplane coupling in Y_2Ba_4Cu_7O_{15}: a ^{63}Cu nuclear spin-spin relaxation study
• Analysis of NMR Spin-Lattice Relaxation Rates in Cuprates
• Oxygen Isotope Effect of the Plane-Copper NQR Frequency in YBa_2Cu_4O_8

Cited by in corpus (3)

• Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba_0.7K_0.3Fe_2As_2: NMR in a single crystal
• The spin anisotropy of the magnetic excitations in the normal and superconducting states of optimally doped YBa2Cu3O6.9 studied by polarized neutron spectroscopy
• Analysis of NMR Spin-Lattice Relaxation Rates in Cuprates