Vacuum Airship

The ultimate "lifting gas" for an airship would be vacuum, which
weighs nothing. So far, it hasn't been used for the very good reason
that a "vacuum tank" is destroyed by the outside air pressure, unless
the tank is beefed up to the point that it becomes so heavy as to
eliminate the weightlessness of vacuum.

In a story I read in my teens and will be reading again in the near
future, such a vehicle is made of a metal called "harbenite," a close
relative of unobtainium. It was stronger than steel but as light as
cork, thus allowing the construction of vacuum tanks light enough to
be useful. Ah, harbenite. Wouldn't it be nice to have harbenite?

So, shouldn't we be close to producing something in our big industrial
laboratories than can do the same job as harbinite? How close are we
to vacuum airships? Sure won't be any hydrogen risks there, and the
expense of helium can be done away with.

Nanotube? Some Kevlar-successor? Come on folks, there's gotta be
something!