The Magnetic Excitations in the Ground State of Yb${}_2$Ti${}_2$O${}_7$

The nature of the zero-field ground state of Yb${}_2$Ti${}_2$O${}_7$ remains an enigma within the pyrochlore titanate series. The disparate results are attributed to subtle changes in the sample stoichiometry, which seems to tune the magnetic order of different samples across a phase boundary. We report a study on the zero-field ground state of a powder sample of this pyrochlore. A sharp heat capacity anomaly at T${}_c$ = 280 mK is accompanied by a quasicollinear ferromagnetic order with a magnetic moment of 0.87(2) ${\mu }_B$. Our high-resolution inelastic neutron scattering measurements show that, upon cooling, an inelastic continuum of excitations at $\sim$ 0.6 is observed to persist from at least 2.5 K down to the lowest reached temperatures. Below T${}_c$, the coexistence of sharp gapped low-energy magnetic excitations with a remnant quasielastic contribution evidences that spin fluctuations persist despite the long-range magnetic order.