Spin dynamics near a putative antiferromagnetic quantum critical point
in Cu substituted BaFe2As2 and its relation to high-temperature
superconductivity
We present the results of elastic and inelastic neutron scattering
measurements on non-superconducting
Ba(Fe0.957Cu0.043)2As2, a composition close to a
quantum critical point between AFM ordered and paramagnetic phases. By
comparing these results with the spin fluctuations in the low Cu composition as
well as the parent compound BaFe2As2 and superconducting
Ba(Fe1−xNix)2As2 compounds, we demonstrate that paramagnon-like
spin fluctuations are evident in the antiferromagnetically ordered state of
Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like
spin fluctuations in the superconducting compounds. Our observations suggest
that Cu substitution decouples the interaction between quasiparticles and the
spin fluctuations. We also show that the spin-spin correlation length,
ξ(T), increases rapidly as the temperature is lowered and find
ω/T scaling behavior, the hallmark of quantum criticality, at an
antiferromagnetic quantum critical point.Comment: 10 pages, 7 figure