Normal state spin susceptibility in YBa sub(2)Cu sub(3)O sub(6.92) single crystal from super(63)Cu and super(89)Y nuclear magnetic resonance

• Published in: Physica. C, Superconductivity Superconductivity, 1999-02, Vol.313 (3-4), p.255-270
• Main Authors: Auler, T, Horvatic, M, Gillet, J A, Berthier, C, Berthier, Y, Carretta, P, Kitaoka, Y, Segransan, P, Henry, J Y
• Format: Article
• Language: English
• ISSN: 0921-4534

We present an extensive nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) study of the normal state (T > T sub(c)) of an YBa sub(1.93)Sr sub(0.07)Cu sub(3)O sub(6.92) single crystal (T sub(c) identical with 90 K). The NMR data is interpreted using a model for the imaginary part of the dynamical electron spin susceptibility Chi double prime (q, omega ) that is consistent with the inelastic neutron scattering (INS) experiments (carried out on the same sample investigated here): the q-dependence is assumed to be Gaussian (commensurate), with short and T independent coherence length xi . This model enabled us to perform a quantitative analysis of the planar copper spin-lattice and spin-spin relaxation rates which evidenced that a spin pseudogap starts to open at T* approximately 130 K, confirming the INS results. Moreover, we show that the AF fluctuations contribution to yttrium relaxation is not negligible due to the dipolar coupling of the yttrium with the neighboring copper spins. The main signature of this feature is that a relation K sub( alpha alpha )T sub(1)T identical with const does not hold for the yttrium site at higher temperatures. Our main conclusion is that, in order to explain the yttrium (and the planar oxygen) relaxation coherently with the INS results and the widely accepted one-band picture, the characteristic energy Gamma sub(0) of the spin dynamics near q identical with 0 must be strongly T dependent, otherwise the one-band description is not feasible. All the NMR results are interpreted within the ionic model of the hyperfine Hamiltonian taking into account the anisotropy of the g-factor and the static spin susceptibility Chi sub(s).