Study of rotation effect in solid ⁴He by an elasticity-sensitive torsional oscillator

Solid ⁴He shows unusual mechanical properties caused by interaction between dislocations and ³He impurities, both of which are highly mobile due to quantum nature of helium. Applying rotation to solid ⁴He changes its elasticity due to the change in motion of ³He impurities by centrifugal and Coriolis forces. We have examined the effect of steady rotation on the elastic properties of solid ⁴He using a “floating core” torsional oscillator (TO), in which multiple resonant modes are highly sensitive to change in shear modulus of solid ⁴He sample located between the side wall of inner cylindrical core and the wall of cavity. Two torsional resonant modes observed at 839 and 6280 Hz changed about 0.15 and 25 Hz, respectively, between 20 and 500 mK, by the change in solid’s shear modulus. Despite of such large frequency shifts due to shear stiffening, the decrement of shear modulus by rotation was observed only in the intermediate temperature range, 50 ≤ T ≤ 200 mK, when the TO was unidirectionally rotated up to 4 rad=s. This observation is inconsistent with other results in previous TO experiments and a direct shear modulus measurement under rotation. Possible mechanisms for the rotation effects are discussed.