Impact of dislocations on the structure of solid helium*

Uncommon phonon spectra were obtained from solid helium below 1.3K and at pressures near 30 bar. Rapid cooling using the blocked capillary method created stressed solid helium in non-equilibrium state. Using inelastic neutron scattering, we disclosed the absence of Bragg-scattering combined with the presence of a phonon-gap, a phenomenon revealing the absence of long-range crystalline order. The energy of the gap is close to the value of a thermal activation energy measured by ultrasonic attenuation in unstrained solid 4He [1] crystals. The dispersion of the phonons shows point-like intensities interpreted as signature of finite-length edge dislocations. The range and shape of the strain field perpendicular to the dislocation line was identified discerning excitations related to the fluttering mechanism [2]. These finding give new input to the discussion of a dislocation network in view of the shear modulus in distorted solid 4He [3,4]. \\{4pt}[1] G.A. Lengua, J.M. Goodkind, J. Low Temp. Phys. {\bf 79}, 251 (1990) \\{0pt}[2] T. Ninomiya, J. Phys. Soc. Jpn. {\bf 36}, 399 (1974) \\{0pt}[3] J. Day, J. Beamish, Nature {\bf 450}, 853 (2007) \\{0pt}[4] A. Haziot, et.al., Phys. Rev. Lett. {\bf 110}, 35301 (2013)