Figure 1
Illustration: Adapted from [3]

Figure 1: According to Syshchenko et al. [4], the binding of dislocations to 3He impurities is the mechanism that controls the change in shear modulus of solid helium at the temperature where it becomes supersolid. With mobile dislocations (left panel), the crystal is softer than if dislocations are pinned by 3He impurities (right panel). Syshchenko et al. prove that the transition is a broad crossover because the distribution of binding energies is very wide. But the mobility of dislocation lines is due to the existence of kinks, which are mobile along the lines. As a consequence, one interesting question remains: Is it possible that, even in the absence of 3He impurities, the dislocations become smooth and fixed straight lines without kinks at low temperature, due to the periodic potential of the crystal lattice? This is what Aleinikava et al. [10] proposed and this now needs to be checked.