An Ordered State of Dislocations in Solid Helium

An ordered state of dislocations, see e.g. [1], is disclosed from neutron inelastic scattering data taken from solid helium at 40mK and a pressure of about 30bar. A characteristic feature is the phonon gap at the origin of about 0.15 meV, which reveals the non-equilibrium state of stressed helium created by rapid cooling with the blocked-capillary method. Energy gain scattering starts to appear at a temperature of 0.5 K that underlines the non-equilibrium state of stressed helium and the non-applicability of the detailed balance. The increasing thermal occupation of phonon-states observed as increasing intensity in energy gain scattering builds to a phase transition close to 1.4K. The creation of a helium single crystal with hcp-structure in thermal equilibrium [2] is observed at this temperature. This phase transition is in agreement with the vanishing quasi two-dimensional superfluid helium in solid helium confined in aerogel around 1.3K [3]. The event of the ``supersolid'' transition around 100mK is not observed in the two neutron scattering experiments.\\[4pt] [1] G. S\"{o}yler, et. al., Phys. Rev. Lett. {\bf 103}, 175301 (2009)\\[0pt] [2] E. Blackburn, et. al., PRAMANA {\bf 71}, 673 (2008)\\[0pt] [3] H.Lauter, et. al., Phys. Rev. Lett. {\bf 107}, 265301 (2011)