Single-crystal versus polycrystalline samples of magnetically frustrated Yb2Ti2O7: Specific heat results

Zero-field specific heat C-p measurements carried out between 0.07 and similar to 4 K for single crystal and powder samples of the pyrochlore Yb2Ti2O7 display striking qualitative differences. While the powder sample has a sharp C-p anomaly at similar to 0.25 K, the data for the single crystals do not exhibit any sharp structure in C-p (T). These results call for a cautious interpretation of microscopic results, such as those obtained by single crystal neutron scattering.