Which kind?

ABAB

Do you remember the physicist we all adore?
Not Aage, the son, who got a Nobel too.
It was Niels the Dane who got there before,
and showed the world how the bomb blew.

AABBA

There is a man named Hawking, who’s tied to a chair.
A body too weak, but a mind to whom none can compare.
He’ll speak of microscopic black holes.
And tell you how they evaporate at their poles.
Till after a while the whole hole isn’t there.