Plasticity induced superclimb in solid ${}^4\mathrm{He}$: Direct and inverse effects

Experimental evidence that the mass supertransport through solid ${}^4\mathrm{He}$ and the anomalously large matter accumulation in the bulk—the giant isochoric compressibility (also known as the syringe effect)—are both supported by a network of dislocations with a superfluid core is getting stronger since a decade ago. However, a structure of this network, as well as its relation to the basal (nonsuperfluid) dislocations which are responsible for plasticity, remain unclear. Here it is shown that superclimbing and basal edge dislocations can form bound pairs. This implies that plastic deformation should produce the syringe effect and vice versa. The experimental test is proposed. While the strength of the effect depends on the average orientation of the paired dislocations, there is a feature unique to the superfluid dislocation scenario: the supercurrents flow in the direction perpendicular to the plastic deformation.

Figure 1

Stable equilibrium positions (dashed lines) of basal gliding dislocation (red) bound to superclimbing one (blue). Each bound pair in (a)–(d) cases is characterized by specific orientations of the Burgers vectors $\pm \vec{b}$ and $\pm {\vec{b}}_c$. The cores are aligned with the $Y$ axis (into the page) of the basal plane. Arrows indicate orientations of the Burgers vectors and the solid lines attached to them outline the half-planes of extra atoms. Motion of the cores can only occur along the $X$ axis, while the superflow occurs along the $Y$ axis.

Figure 2

Schematics of the transverse supershear effect. The view is along $Z$ axis. The upper and lower horizontal lines represent the basal (in red) and the superclimbing (in blue) dislocations, respectively. The directions of their Burgers vector, $b,b_c$, as well as the applied force $f_x$ and the resulting displacement $\xi$ are also shown. Two ellipses labeled as SFR represent reservoirs with superfluid, with the arrows along the core indicating supercurrents driven from the reservoirs by either the external force $f_x=f^{\left(\mathrm{ex}\right)}\sim {\sigma }_{xz}$ applied to the basal dislocations or by the chemical potential bias $\delta \mu$ of the reservoirs. In the latter case, the force $f_x\propto \delta \mu$ will be produced on the basal dislocation.