We have measured nuclear quadrupole resonance (NQR) for Cu-63 nuclei under high pressure up to 4.8 GPa. A linear increase in NQR frequency (63)nu(Q) of Cu-63 nuclei was observed below 3 GPa. However, (63)nu(Q) deviates gradually from the linear relation above 3.5 GPa. The downward deviation is associated with a change of valence and consistent with the results of band calculations with the structural parameters under pressure. Antiferromagnetic (AFM) spin fluctuations are drastically suppressed with increasing pressure, whereas T-c increases from 0.7 K at ambient pressure to 1.64K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level.
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These are indenter pressure cells for NQR measurements. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim