Dislocation Mobility and Anomalous Shear Modulus Effect in 4 He Crystals

We calculate the dislocation glide mobility in solid He within a model that assumes the existence of a superfluid field associated with dislocation lines. Prompted by the results of this mobility calculation, we study within this model the role that such a superfluid field may play in the motion of the dislocation line when a stress is applied to the crystal. To do this, we relate the damping of dislocation motion, calculated in the presence of the assumed superfluid field, to the shear modulus of the crystal. As the temperature increases, we find that a sharp drop in the shear modulus will occur at the temperature where the superfluid field disappears. We compare the drop in shear modulus of the crystal arising from the temperature dependence of the damping contribution due to the superfluid field, to the experimental observation of the same phenomena in solid He and find quantitative agreement. Our results indicate that such a superfluid field plays an important role in dislocation pinning in a clean solid He at low temperatures and in this regime may provide an alternative source for the unusual elastic phenomena observed in solid He. Abdul N. Malmi-Kakkada · Oriol T. Valls School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 E-mail: [email protected] Present address: of Abdul N. Malmi-Kakkada Dept. of Chemistry, University of Texas at Austin, 105 E 24th St, Austin, TX 78712 Chandan Dasgupta Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560012, India 2 Abdul N. Malmi-Kakkada et al.