Yb2Sn2O7: A magnetic Coulomb liquid at a quantum critical point

We report neutron scattering and ac susceptibility measurements on the pyrochlore Yb2Sn2O7. The appearance of magnetic diffuse scattering, low-energy spin excitations, and a nearly temperature-independent relaxation time are signatures that the system enters a short-range-ordered regime with quantum dynamics beneath 2 K. ac susceptibility data further suggest that Yb2Sn2O7 enters a long-range magnetically ordered state below 0.11 K. These results suggest that Yb2Sn2O7 is a ferromagnet with persistent spin dynamics down to 0.05 K. Referencing the phase diagram for Yb pyrochlores, Yb2Sn2O7 is approaching a quantum phase transition near the ferromagnetic ordered critical point.