Reentrant superconductivity driven by quantum tricritical fluctuations in URhGe: Evidence from Co 59 NMR in URh0.9Co0.1Ge

Our measurements of the Co59 NMR spin-spin relaxation in URh0.9Co0.1Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at HR≈13T, around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the (Hb,Hc) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field HR as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.