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We report /sup 63,65/Cu NMR spectra and nuclear spin-lattice relaxation data for YBa/sub 2/Cu/sub 3/O/sub 7/(T/sub c/ = 91 K) and YBa/sub 2/Cu/sub 3/O/sub 6.75/(T/sub c/ = 5/sub 7/ K) single crystals between 45 and 300 K. An analysis of the spin-lattice relaxation rates gives evidence for localized electronic spins on the planar Cu(2) sites. In YBa/sub 2/Cu/sub 3/O/sub 6.75/ both fourfold and twofold oxygen-coordinated Cu(1) are observed; the latter experience the same quadrupolar coupling (..nu../sub Q/approx. =31.5 MHz) as the Cu(2) sites but a nearly zero magnetic hyperfine shift and a much slower relaxation rate (d/sup 10/ configuration).

Current-voltage characteristics, voltage oscillations and NMR on the same Rb0.30MoO3 crystal at 77 K are presented. The 1/2,-1/2; transition at V0=80 MHz of 87Rb nuclei broadened by the CDW modulation is motionally narrowed for bias currents exceeding threshold for non-linear conduction. Calculation of the lineshapes, assuming a partial depinning of the sample, leads to excellent agreement with experiment. An estimate of the ratio of the average current density and voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. A CDW phase correlation time of single domains is deduced to be τ=200 μS.

We have performed 17O NMR in YBa2Cu3O7 oriented powder samples in the temperature range 10–360 K for the orientation H0∥c and H0⊥c. The Electric Field Gradient (EFG) and Magnetic Hyperfine Shift (MHS) tensors have been determined for the four oxygen sites in the structure. The isotropic (axial) part of the MHS tensor were found to be equal to 0.21 (0.08)% for the O(2,3) site in the CuO2 plane and to 0.04(0.05)% for the bridging oxygen O(4). Both were found temperature independent in the normal state. Below Tc, they vanish to zero and the data for the MHS Kcc[O(2,3)] show that this decrease is faster than expected from BCS theory. The coupling between the localized spins at the Cu (2) sites and the mobile oxygen p-holes is discussed in the light of these results.

We report on EPR measurements on (TMTTF) 2 PF 6 which address the evolution of the spin-Peierls transition temperature T c as a function of pressure. The line intensity was used as a probe of the magnetic susceptibility, and therefore of the density of states at the Fermi level. This density drops in the spin-Peierls regime. The extrapolated onset of the gap is used as a measurement of T c . Using these results and previous NMR data on the antiferromagnetic transition temperature, a complete phase diagram is presented. It will be explained using a model involving an interacting electron gas coupled to acoustic phonons. The various parameters are obtained from available experimental results while their pressure and temperature dependence is suggested as a theoretical model. The interchain interactions (exchange and charge) are deduced from a fit of the transition temperature at 0 and 13 kbar. A very satisfactory phase diagram is deduced.

To determine the velocity of the charge density wave, voltage noise and 87 Rb NMR spectra at an electric field of about 15 E T were measured together with I–V characteristics on a Rb 0.3 MoO 3 crystal between 40 and 60K. NMR spectra are reproduced by use of a velocity distribution determined by the noise spectrum, showing that all the electrons condensed below the Peierls gap participate to the Frohlich mode. A detailed study of NMR sidebands as well as the oscillatory behaviour of the spin echo amplitude demonstrates that the winding rate of the phase ν d = ( 1 2 π) d φ( R )/ dt is equal to the noise frequency ν n and gives evidence for the coherence of the CDW sliding motion. This coherence, as well as the stochastic fluctuations of the phase are discussed in the light of spin-spin relaxation time measurements as a function of the applied electric field (E/E T in the range 3–20) between 40 and 90 K. Comparison of voltage noise and NMR spectra between 60 and 90 K indicates that at moderate E/E T ratios large phase fluctuations occur in parts of the crystal which do not contribute to jCDW.

Current-voltage characteristics, voltage oscillations and NMR on the same Rb0.3MoO3 crystal at 77 K are presented. The 1 2 , − 1 2 transition at ν0=80 MHz of 87Rb nuclei broadened by the CDW modulation is motionallu narrowed for bias currents exceeding threshold for non-linear conduction. Calculation of the lineshapes, assuming a partial depinning of the sample, leads to excellent agreement with experiment. An estimate of the ratio of the average current density and voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. A CDW phase correlation time of single domain is deduced to be τ=200 μS.

We present NMR spin-lattice relaxation measurements of La, obtained at 32.9 MHz in the compound ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$Cu${\mathrm{O}}_{4}$ over the temperature range 12-300 K. Although conductivity and acsusceptibility measurements on a piece of the same pellet indicate an onset of the superconducting transition at 37 and 32 K, respectively, an anomaly in the spin-lattice relaxation rate is observed around $T=52$ K, which can be attributed either to a weak structural phase transition or to precursory magnetic fluctuations. Below the superconducting transition down to 12 K, ${T}_{1}$ stays constant and equal to 530\ifmmode\pm\else\textpm\fi{}10 ms.

We have studied the 93Nb NMR in single crystals of (NbSe4)10/3I (1.8 mg) and (NbSe4)3I (20 mg). In the first compound, the onset of the CDW has been followed through the temperature dependence of the (1/2,−1/2) transition. Using computer simulation of the lineshapes, we have determined the temperature dependence of the order parameter. Comparison of the spin-lattice relaxation rate in (NbSe4)3I and (NbSe4)10/3I, indicate the fluctuations of the the pinned CDW are the dominant mechanism.

We report 63 Cu NMR nuclear spin-lattice relaxation rates (NSLRR) and magnetic hyperfine shift (K cc ) of copper Cu(2) in the CuO 2 planes of YBa 2 Cu 3 O 7−δ as a function of temperature and δ. The independence of K cc and NSLRR (above 120 K) on δ associated with the existence of localized Cu(3d) holes. We comment on the difference in the NSLRR between the δ = 0 and δ ≠ 0 samples which appear below 120 K. It is interpreted as an indirect consequence of the changes in the oxygen 2p electronic band caused by the introduction of oxygen vacancies in the system.

We present the temperature dependence of the Magnetic Hyperfine Shift tensors of 17 O nuclei for the sites within the CuO 2 plane (site O(I)) and in the BaO, LaO, SrO plane (O(II) site) in the compounds YBa 2 Cu 3 O 7 , YBa 2 Cu 3 O 6.65 , La 1.85 Sr 0.15 CuO 4 and Bi 2 Sr 2 CaCu 2 O 8 . For O(I) sites, the isotropic part of the tensor reflects the polarisation of the Oxygen 2s orbitals by the neigboring Cu d-holes and the temperature dependence of the susceptibility. We show that in YBa 2 Cu 3 O 6.65 , the spins of the oxygen p-holes have their own degree of freedom above 120 K.