Heat Capacity Peak in Solid 4He: Effects of Disorder and 3He Impurities

Heat capacity measurements with significantly improved resolution find the presence of a peak in a solid He-4 sample in coexistence with liquid. With improved crystallinity, the peak decreases in height and moves to lower temperature. A hysteretic heat capacity signature consistent with He-3-He-4 phase separation, not detected in an earlier work is clearly observed.