Probable heat capacity signature of the supersolid transition*

We report our heat capacity measurements [1] of solid $^{4}$He down to 40mK, well into the apparent supersolid region of the phase diagram. We observed a broad peak in the specific heat centered near 75mK in $^{4}$He samples containing 1ppb, 0.3ppm, and 10ppm $^{3}$He impurities. In addition, our measurements of samples containing 10ppm and 30ppm of $^{3}$He have revealed a temperature-independent contribution to the heat capacity that scales with the number of isotopic impurities. New measurements with higher resolution are in progress. \newline [1] Nature (London) 449, 1025 (2007).