Exploration of solid helium 4 at multiple frequencies using a compound torsional oscillator

Apparent but controversial evidence of supersolidity, a coexistence of crystalline and superfluid states, was observed in 2004. Samples of solid 4He were grown, in a chamber, inside a torsion oscillator (TO). The samples showed evidence of apparent decoupling from their container in the form of a resonant frequency increase of the TO as the temperature was lowered. We have developed a Compound torsion oscillator (CTO), with two resonant modes, that allows us to observe a single solid helium sample at two frequencies simultaneously. This thesis will cover the first comprehensive study on the frequency dependence of the apparent supersolid effect. This includes a study of the effect of varying 3He concentrations (x3) on the frequency dependence. Additionally a study on how changes in x3 affect the dissipation, which previous studies of x3 dependence have not explored. Also studied is how varying x3 affected the hysteresis first observed by Aoki et al. The CTO has allowed the exploration of the amplitude dependent effects in new ways. By exciting the sample at both frequencies simultaneously and varying the driving amplitude of one mode one can see how excitations at one mode affect what is observed at the other.;The studies of the effects of varying x3 show results that are consistent with the dislocation movement model proposed by Iwasa. The collected data was not consistent with the simple supersolid model initially proposed. The studies of hysteresis show that the onset of hysteresis was dependent on x3 but was not frequency dependent. This lends credit to the hysteresis being due to the pinning and unpinning of 3He impurities. The studies of the effect of amplitude dependent effects show an asymmetry between the two frequencies. The higher frequency has a larger effect on the lower frequency than the lower frequency has on the higher. This is also inconsistent with the initial simple supersolid model.