Effect Of Rotation On The Elastic Moduli Of Solid He-4

We report measurements of elastic moduli of hcp solid He-4 down to 15 mK when the samples are rotated unidirectionally. Recent investigations have revealed that the elastic behavior of solid He-4 is dominated by gliding of dislocations and pinning of them by He-3 impurities, which move in the solidlike Bloch waves (impuritons). Motivated by the recent controversy of torsional oscillator studies, we have performed direct measurements of shear and Young's moduli of annular solid He-4 using pairs of quarter-circle-shape piezoelectric transducers (PZTs) while the whole apparatus is rotated with angular velocity Omega up to 4 rad/s. We have found that shear modulus mu is suppressed by rotation below 80 mK, when shear strain applied by PZT exceeds a critical value, above which mu decreases because the shear strain unbinds dislocations from He-3 impurities. The rotation-induced decrement of mu at Omega = 4 rad/s is about 14.7(12.3)% of the total change of temperature dependent mu for solid samples of pressure 3.6(5.4) MPa. The decrements indicate that the probability of pinning of He-3 on dislocation segment G decreases by several orders of magnitude. We propose that the motion of He-3 impuritons under rotation becomes strongly anisotropic by the Coriolis force, resulting a decrease in G for dislocation lines aligning parallel to the rotation axis.