Theory of nuclear spin-lattice relaxation in YBa2Cu3O7

Within the framework of the t-J model, we have calculated the temperature dependence of the nuclear spin-lattice relaxation rate, 1/T1, of 63Cu, 17O, and 89Y in the normal state of the superconductor YBa2Cu3O7. The main contribution to the Cu rate arises from strong short-range antiferromagnetic correlations between copper spins; the 17O and 89Y rates are dominated by spin fluctuations of longer wavelength. The theory is able to reproduce the main features of the temperature dependence of 1/T1 as observed experimentally

Orientation relaxation of a water molecule

A new interpretation of the low frequency (up to 1 THz) dielectric spectra of water based on the angular velocity autocorrelation function. is proposed. We use Mori method to derive kinetic: equations for the angular velocity autocorrelation function and obtain the angular velocity correlation time from the comparison of the theoretical result with the inelastic: neutron scattering experiment. Using Hubbard relation we show that beside collective orientation relaxation, i.e. macroscopic dielectric relaxation, there is a single molecule orientation relaxation. It is much faster than the collective one and is displayed at the high frequency tail of the principal dielectric relaxation band. The analysis of the time dependence of the angular velocity autocorrelation function provides the evidence that the single-molecule relaxation is related to the molecules with partially broken H-bonds. © 2003 Elsevier Science B.V. All rights reserved

Spin dynamics in the one-dimensional S = 1/2 Heisenberg antiferromagnet CuGeO3

The temperature dependences of 1/T1 and 1/T2G in the uniform state of the spin-Peierls compound CuGeO3 are investigated using the Green's function method. This study is conducted within the framework of the S = 1/2 one-dimensional Heisenberg model with a next-nearest-neighbor competing interaction. The results reproduce the main features of the observed experimental behavior

Theory of the copper nuclear spin-lattice relaxation in CuGeO3

Within the framework of the one-dimensional S=1/2 Heisenberg model with a next-nearest-neghbor antiferromagnetic interaction, a theory of the copper spin-lattice relaxation in the uniform state of the spin-Peierls compound CuGeO3 is presented. The main contribution to the relaxation rate at intermediate and high temperatures is due to the spin diffusive long-wave processes. A comparison of our results with experimental data shows that the theory is able to reproduce the main features of the temperature dependence of the copper relaxation rate. ©2000 The American Physical Society

Theory of the plane copper nuclear spin-lattice relaxation in La2-xSrxCuO4 and YBa2Cu3O7-y

Within the framework of the t-J model, a microscopical theory of the copper spin-lattice relaxation in the normal state of the superconductors La2-xSrxCuO4 and YBa2Cu3O7-y compounds is presented. The main contribution to the relaxation rate arises from strong short-range antiferromagnetic correlations between copper spins. The theory is able to reproduce the main features of both the doping and the temperature dependence of the copper relaxation rate as observed experimentally. The results for the doping dependence of both the spin-spin correlation function and the width of the conducting band are in agreement with Monte Carlo and exact diagonalization calculations within the t-J model. ©2000 The American Physical Society

Deformations of rocks in periodic regimes of filtration

The authors present results of experimental investigations of deformations of rocks that occur in nonstationary filtration of a liquid in thin deep-lying cracked-porous strata. Equations for description of lateral displacements and deformations that satisfactorily describe the data of the experiments are obtained

The effect of clay morphology on water relaxation

The frequency dependence of the permittivity of water in calcium kaolinite (clay) is measured. It is shown that two mechanisms contribute to dipole relaxation of water. One refers to water in the free volume of pores in the clay. The other is associated with bound water covering the porous surface. Experimental data are treated in terms of a fractal model of the medium. The frequency dependence of the permittivity in a wide range of water content in the clay is accounted for theoretically. © 2001 MAIK "Nauka/Interperiodica"

Dynamical charge susceptibility in layered cuprates: the influence of screened inter-site Coulomb repulsion

The analytical expression for dynamical charge susceptibility in layered cuprates has been derived in the frame of singlet-correlated band model beyond random-phase-approximation (RPA) scheme. Our calculations performed near optimal doping regime show that there is a peak in real part of the charge susceptibility $\chi({\bf q},\omega)$ at {\bf Q} = ($\pi$, $\pi$) at strong enough inter-site Coulomb repulsion. Together with the strong maximum in the Im $\chi({\bf Q},\omega)$ at 15 meV it confirms the formation of low-energetic plasmons or charge fluctuations. This provides a jsutification that these excitations are important and together with a spin flcutuations can contribute to the Cooper pairing in layered cuprates. Analysing the charge susceptibilitiy with respect to an instability we obtain a new plasmon branch, $\omega_{\bf q}$, along the Brillouin Zone. In particular, we have found that it goes to zero near {\bf Q}$_{CDW} \approx (2\pi/3, 2\pi/3)$

Orientation relaxation of a water molecule

A new interpretation of the low frequency (up to 1 THz) dielectric spectra of water based on the angular velocity autocorrelation function. is proposed. We use Mori method to derive kinetic: equations for the angular velocity autocorrelation function and obtain the angular velocity correlation time from the comparison of the theoretical result with the inelastic: neutron scattering experiment. Using Hubbard relation we show that beside collective orientation relaxation, i.e. macroscopic dielectric relaxation, there is a single molecule orientation relaxation. It is much faster than the collective one and is displayed at the high frequency tail of the principal dielectric relaxation band. The analysis of the time dependence of the angular velocity autocorrelation function provides the evidence that the single-molecule relaxation is related to the molecules with partially broken H-bonds. © 2003 Elsevier Science B.V. All rights reserved