Sample quality dependence of the specific heat peak in solid $^{4}$He

We reported a broad peak in specific heat of solid $^{4}$He[1] at a temperature near the onset of Non-Classical Rotational Inertia (NCRI). This peak is likely to be a thermodynamic signature of the supersolid phase. Since it was found that the supersolid fraction is dependent upon the sample quality[2,3], we are motivated to study the sample quality influence on solid $^{4}$He specific heat. In our recent measurements, we have confirmed the presence of a broad peak in the specific heat of solid $^{4}$He below $\sim $200mK in addition to the phonon contribution. We also show how the excess specific heat peak changes with sample quality. 1 X. Lin, A. C. Clark, and M. H. W. Chan, Nature 449, 1025 (2007). 2 A. S. C. Rittner and J. D. Reppy, Phys. Rev. Lett. 98, 175302 (2007). 3 A. C. Clark, J. T. West and M. H. W. Chan, Phys. Rev. Lett. 99, 135302 (2007).