  It was predicted that solid metallic hydrogen can be obtained if solid
molecular hydrogen is pressured to high pressure at low temperature about 80
years ago. Furthermore, the solid metallic hydrogen was theoretically predicted
to show superconductivity at room temperature. In addition, surprising
prediction was made that the solid metallic hydrogen is a metastable metal with
a potential barrier of 1 eV. This prediction implies that the solid metallic
hydrogen remains in the metallic solid phase state even after it is released
from high pressure. Shock compression synthesized liquid metallic hydrogen so
far. However, to obtain metallic hydrogen under ambient pressure at room
temperature, it is necessary to synthesize solid metallic hydrogen. It is
theoretically predicted that an ultrahigh pressure of ~500 GPa is required to
produce solid metallic hydrogen. This pressure is close to the limit of the
high pressure that can be generated by the diamond anvil cell (DAC). Therefore,
it is difficult to synthesize metallic hydrogen by using DAC. Shock compression
methods can generate a sufficiently high pressure to synthesize metallic
hydrogen. But it is impossible to synthesize solid metallic hydrogen by these
methods because these accompany generation of high temperature. There is
currently no definitive way to synthesize solid metallic hydrogen.
  Here we report a new dynamic high-pressure apparatus which aims for synthesis
of solid metallic hydrogen. We show that by using this apparatus, it is
possible to generate a high pressure of 1 TPa, the pressure maintaining time is
103 to 106 times longer than the conventional dynamic compression method.
Furthermore, we show that this apparatus is not accompanied by the generation
of high temperature unlike the conventional dynamic compression method and then
it is possible that solid metallic hydrogen might be synthesized by this
apparatus.
