Effect of $^{3}$He impurity on the supersolid transition of $^{4}$He

The supersolid phase of $^{4}$He was revealed by a series of torsional oscillator experiments.[1] One of the most intriguing features of the supersolid transition is the broadening of the transition and the enhancement of T$_{c}$ by the addition of extremely small amount of $^{3}$He impurity. This effect is very different from that in superfluid film and that in `bulk' superfluid helium. We have investigated the$^{ }$influence of $^{3}$He on the supersolid transition by systematically diluting isotopically-pure $^{4}$He ($^{3}$He impurity less than 0.3ppb) with $^{3}$He. [1] E. Kim and M. H. W. Chan, \textit{Science} \textbf{305}, 1941 (2004); \textit{Nature} \textbf{425}, 227 (2004); \textit{J. Low Temp. Phys.} \textbf{138}, 859 (2005)