  We report a first attempt to produce metastable hcp solid helium below its
melting pressure. A focused sound pulse is emitted along the c-axis of a
mono-domain hcp helium-4 crystal starting from a static pressure just above the
melting pressure. The sound pulse is made as simple as possible with one
negative and one positive swing only. Density at focus is monitored by an
optical interferometric method. Performed numerical simulations show that the
crystal anisotropy splits the focused wave into two separate pulses,
corresponding to a longitudinal wave along the c-axis and a radial one
perpendicular to it. The amplification factor due to focusing remains
nevertheless important. Negative pressure swings up to 0.9 bar have been
produced, crossing the static melting pressure limit. Improvements in the
detection method and in the focusing amplification are proposed.
