| Abstract: | The existence of a supersolid phase in solid helium 4, where superflow of mass can take place, has been thought to be discovered and then to not exist several times during the past decade. The very small signals, alongside the large effects from the elastic contribution of the solid helium, make it hard to distinguish the possible supersolid signature from other effects. We constructed experiments designed to distinguish between the different contributions and to reduce other unwanted effects. Using multiple frequency torsional oscillators we discovered a frequency-independent contribution to the signal, on the order of 1 part in 10^4 of the moment of inertia of the solid helium itself. The same number appeared for both double and triple mode oscillators using both open cylinders and annular cells, and agrees with past theoretical predictions. Lacking an alternative explanation, the results of our carefully designed experiments indicate that a small fraction of solid helium 4 is indeed supersolid. |
