Number of CuO2 layers dependence of magnetic quantum criticality in homogeneously doped high-[formula omitted] copper oxides: A 63Cu-NMR study on four-layered high-[formula omitted] compounds HgBa2Ca3Cu4O8+y

Abstract

We report 63Cu-NMR/NQR studies on Hg-based four-layered compounds HgBa2Ca3Cu4 O8+y (Hg-1234) with Tc=123, 110, and 95K. The 63Cu Knight shift measurements have revealed that the carrier density (Nh) monotonously decreases with decreasing Tc. Although static magnetic order was not observed at Nh=0.15 for the IP with Tc=95K, it was revealed that antiferromagnetic correlations critically develop, preventing from observing the NMR spectrum below ∼200K far above Tc. Thus, we deduce that a magnetic quantum critical point, where an AFM order collapses, may exist at slightly less than Nh∼0.15 in the Hg-based four-layered compounds, which is lower than that in Hg-based five-layered compounds, Nh∼0.17. This result suggests that a magnetic interlayer coupling, which stabilizes an AFM order, becomes weaker in the four-layered compounds than in five-layered compounds.