Magnetic correlations and spin dynamics

In this Section we try to understand the INS and NMR experiments on the basis of the SRI SB mean-field theory. Using a generalized RPA expression for the spin susceptibility and assuming that the AFM correlations are spatially filtered by various -dependent hyperfine form factors, we focus, in particular, on the spin dynamical properties in the paraphase of the t-t -J model. Our starting point is an RPA-like form for the exchange-enhanced spin susceptibility [5, 6, 65] 

Once the dynamic spin susceptibility has been obtained both, fNS measurements and NMR experiments, can be explored. Probed by INS from the fluctuation-dissipation theorem the -dependent and co-dependent spin structure factor is related to the dynamical susceptibility by 

On the other hand, the nuclear spin-lattice relaxation rate r7a(a = -L, ), e.g. for a field applied parallel to the c-axis, given by [66] 

4 co = Innip [co = 2m + denote the fermionic [bosonic] Matsubara frequencies. 

Together with the anisotropy of the Cu relaxation rates the measurements of the 

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Rigamonti, A., F. Borsa, M. Corti, T. Rega, J. Ziolo and F. Waldner, 1990, Magnetic correlations and spin dynamics in La2 Sr Cu04 from NQR relaxation, in Springer Series in Solid State Sciences, Vol. 90, eds J.G. Bednorz and K.A. MUller (Springer, Heidelberg) pp. 441-466. 

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