The nature of the superconducting state in quasi-one-dimensional organic conductors has remained controversial since its discovery. Here we present results of (77)Se NMR Knight shift (K(s)) experiments in (TMTSF)(2)PF(6) under 7 kbar of pressure with a magnetic field aligned along the most conducting a axis. We find no noticeable shift in K(s) upon cooling through the superconducting transition. Since K(s) directly probes the spin susceptibility chi(s), the fact that chi(s) remains unchanged through the superconducting transition strongly suggests spin-triplet superconductivity.

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A novel method of Fourier transform spectroscopy of the transient signals from wide, inhomogeneously broadened magnetic resonance spectra is described and analyzed. It has the advantages of high resolution, high sensitivity, and freedom from the distortions introduced by the finite amplitude of the pulsed rf magnetic field and the finite bandwidth of the receiving system. It consists of recording the transient signal at a series of magnetic fields, shifting the frequency of the transient by the corresponding field step for each point, and summing the corresponding Fourier transformed signals. Although the primary emphasis is on pulsed NMR, the analysis also applies to pulsed ESR. Criteria for the range and step interval of the magnetic field variation are discussed. The accuracy and sensitivity of the method are compared with earlier methods of spin echo spectroscopy. A description of the corresponding measurement of NQR, NMR, and ESR spectra obtained by stepping the frequency of the spectrometer is also presented.

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The description of a complete pulsed nuclear resonance spectrometer suitable for experiments in solids is given. Its major features are the ability to operate at any frequency between 2 and 30 Mc, an rf pulse output power of 5 kW over most of this range, a receiving system recovery time of 5–10 μsec at 10 Mc, a sensitivity usually limited by thermal noise in the receiver coil, use of phase coherent detection, the availability of a wide variety of pulse sequences, and good long and short term stability of the entire system. Brief instructions for operating the apparatus are included. A method of using the ``boxcar'' integrator to record directly the steady-state absorption (χ″) or dispersion (χ′) is explained.

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