Single-crystal versus polycrystalline samples of magnetically frustrated Yb${}_2$Ti${}_2$O${}_7$: Specific heat results

Zero-field specific heat $C_p$ measurements carried out between 0.07 and $\sim 4$ K for single crystal and powder samples of the pyrochlore Yb${}_2$Ti${}_2$O${}_7$ display striking qualitative differences. While the powder sample has a sharp $C_p$ anomaly at $\sim 0.25$ K, the data for the single crystals do not exhibit any sharp structure in $C_p\left(T\right)$. These results call for a cautious interpretation of microscopic results, such as those obtained by single crystal neutron scattering.

Figure 1

Temperature dependence of the specific heat for four samples of Yb${}_2$Ti${}_2$O${}_7$ measured with a dilution refrigerator using a dynamic adiabatic technique. While the powder sample exhibits a sharp anomaly at about 0.25 K (Ref. 25), no such anomaly is present for the two as-grown crystals (#1 and #2), as well as heat treated crystal #2.

Figure 2

The environment of a given rare-earth atom in the pyrochlore lattice structure. We picture a rare-earth atom with the largest symbol, the oxygen atom with the smallest, and the $M$ atom with an intermediate symbol size.