To date, there has been no evidence for the macroscopic structural phase transition to the low temperature tetragonal structure (LTT) with a space group P4 2 /ncm in high-T C cuprate of rare earth-free La 2−x Sr x CuO 4 (LSCO). By investigating Cu-NMR on single crystals, we have found that spatially incoherent LTT structure emerges below 50 K in the sample with x=0.12. This incoherent structure is considered to play a key role for the slight depression of the superconductivity around x=1/8.

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The vortex state in a single crystal of the layered organic superconductor κ-(BEDT-TTF 2 Cu(NCS) 2 , where BEDT-TTF (or ET) is bis(ethylenedithio)tetrathiafulvalene, was studied by 1 H-NMR. Under a low field region around 0.75 T, the vortex glass-liquid transition was demonstrated by a diverging of the longitudinal nuclear spin relaxation rate and peak-broadening in spectra. Under a high field region near the upper critical field H c2 (0) ≃7 T, the curvature of nuclear spin relaxation curves showed a drastic change at the temperature where the emergence of the quantum vortex slush state was reported. The mechanism in this curvature change was discussed in terms of the fluctuating field produced by fragments of vortex glass.

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