We report an extensive study on the zero field ground state of a powder sample of the pyrochlore Yb2Ti2O7. A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic order develops below Tc with a magnetic moment of 0.87(2)μB. High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at ∼0.6 meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.
@article{arxiv.1709.01013,
title = {Magnetic Excitations in the Ground State of $\mathrm{Yb_2Ti_2O_7}$},
author = {Viviane Pecanha-Antonio and Erxi Feng and Yixi Su and Vladimir Pomjakushin and Franz Demmel and Lieh-Jeng Chang and Robert J. Aldus and Yinguo Xiao and Martin R. Lees and Thomas Brückel},
journal= {arXiv preprint arXiv:1709.01013},
year = {2017}
}