Gapless quantum excitations from an icelike splayed ferromagnetic ground state in stoichiometric Yb2Ti2O7

The ground state of the quantum spin ice candidate magnet Yb2Ti2O7 is known to be sensitive to weak disorder at the ∼1% level which occurs in single crystals grown from the melt. Powders produced by solid state synthesis tend to be stoichiometric and display large and sharp heat capacity anomalies at relatively high temperatures, TC∼0.26 K. We have carried out neutron elastic and inelastic measurements on well characterized and equilibrated …