We know about extremely strong materials such as carbon nanotubes. However, this is only in tension. What are some high strength-to-weight materials (both available and hypothetical) in uniaxial compression?
Such a material would be useful in supertall structures and vacuum airships.
Of my research, PVC pipe seems to be a good bet at 100MPa and only 1.3 g/cm^3. However, this is still inadequate for a vacuum airship.
Beryllium is also a likely candidate as it is 1400MPa and only 1.85 c/cm^3, making it doable in a vacuum airship. However, it is very toxic to work with (I don't know if bulk beryllium is safe) and expensive.