A glassy contribution to the heat capacity of hcp ${}^4$He solids

Abstract

We model the low-temperature specific heat of solid ${}^4$He in the hexagonal closed packed structure by invoking two-level tunneling states in addition to the usual phonon contribution of a Debye crystal for temperatures far below the Debye temperature, $T<{\Theta }_D/50$. By introducing a cutoff energy in the two-level tunneling density of states, we can describe the excess specific heat observed in solid hcp ${}^4$He, as well as the low-temperature linear term in the specific heat. Agreement is found with recent measurements of the temperature behavior of both specific heat and pressure. These results suggest the presence of a very small fraction, at the parts-per-million (ppm) level, of two-level tunneling systems in solid ${}^4$He, irrespective of the existence of supersolidity.

11 pages, 4 figures

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Cited by in corpus (2)

• The glassy response of double torsion oscillators in solid Helium-4
• Saga of Superfluid Solids