Nuclear magnetic resonance measurements are reported for liquid Na-NaBr, Cs-CsCl, and Cs-Csl solutions containing less than 10 mole% metal. Correlation of the resonance shifts, relaxation rates, and dc electrical conductivity shows that the electronic mobility is independent of concentration in Na-NaBr, in sharp contrast with the cesium solutions. The results provide an explanation for the apparently anomalous electronic conductivity observed in liquid-sodium-sodium-halide solutions.

We report 63 Cu nuclear spin-lattice relaxation data for Ba2YCu307-<5 in the superconducting state obtained by nuclear quadrupole resonance in zero applied magnetic field. The temperature dependences of the relaxation rates reveal striking differences in the excitation spectra for quasiparticles on the chainforming Cu(l) and planar Cu(2) lattice sites, corresponding to substantially different pairing energies for electrons on the planes and chains. Values of the gap ratio 2A/kT c of 8.3 and 2.4 are obtained for the Cu(l) and Cu(2) sites, respectively.PACS numbers: 74.30.Gn, 76.60.-k Despite rapid recent progress in understanding the properties of the high-T c superconductor Ba2YCu307-5 , there remain fundamental questions concerning the mechanism of superconductivity in this fascinating material. The validity of the BCS theory as a general framework for a microscopic description is still at issue, as are the respective roles of the planar [Cu(2)] and chain-forming [Cu(l)] Cu sites in the crystal structure. Nuclear spin-lattice relaxation offers a powerful local probe of the dynamics of excitations (quasiparticles) in the superconducting state and such measurements have yielded important insight into the microscopic properties of superconductors. ] For example, the classic work of Hebel and Slichter 2 on Al provided one of the earliest confirmations of the BCS theory. In this Letter we present data for the spin-lattice relaxation rates of 63 Cu at the Cu(l) and Cu(2) sites in Ba2YCu 3 07-5 obtained by nuclear quadrupole resonance (NQR) in zero applied magnetic field. The NQR lines for the two Cu sites in Ba 2 YCu30 7 -< 5 are well separated 3 so that in addition to the obvious advantage of permitting study in the absence of an externally applied magnetic field, NQR permits separate relaxation measurements for the Cu(l) and Cu(2) sites. We have found strikingly different relaxation behavior for Cu(l) and Cu(2) in the superconducting state. The relaxation rates for the two sites are comparable just above T c , but as the temperature is lowered below T c , the rate for the Cu(2) sites decreases somewhat more slowly than the weak-coupling BCS prediction while for the Cu(l) sites, a much more rapid decrease occurs. This indicates a substantially larger energy for quasiparticle formation (pair breaking) on the chains. Neither site exhibits the peak in relaxation rate just below T c which is characteristic of BCS superconductors having small or moderate anisotropy of the energy gap. 1,2 As we reported previously, 4 there are also differences in the normal state where relaxation at the Cu(2) sites approximates conventional Korringa behavior while that at the Cu(l) sites shows anomalously weak temperature dependence.The samples used for these experiments were prepared by standard solid-state reaction in the form of pressed ceramic pellets. We subsequently powdered the pellets to improve penetration of the radio-frequency fields into the sample material. To prevent changes in sample characteristics due to oxygen loss or rea...

Extensive high-field galvanomagnetic data for high-purity single crystals of copper are reported and analyzed in terms of current theory. Special attention is given to the study and identification of the higher order open orbits, commonly called "whiskers," and to an understanding of their presence and extent. Accurate measurements of the Hall constant for the field orientations (111) and (100) were made and values significantly different from those reported earlier were obtained. Our experimental results are in good agreement with theoretical predictions based on Roafs best phenomenological Fermi-surface model (CU VI).