Quantum criticality in a uranium heavy fermion system revealed with NMR spin-spin relaxation

In order to clarify quantum criticality in heavy fermion systems, we propose to use the Gaussian spin-echo decay rate 1/T_2G of the NMR spin-spin relaxation. In contrast to the spin-lattice relaxation rate 1/T₁, which is connected with the dynamical susceptibility Im_χ(q,ω), I/T_2G is driven by the static susceptibility Reχ(q,0) at finite q for an antiferromagnet. The combined quantity T₁T/T²_2G is found to provide key information in determining the nature of quantum criticality. The T-dependence of T₁T/T²_2G for the Sn site in the heavy fermion compound USn₃ is presented as an example.