  We show that spectral form factors of unconventional gapped superconductors
have singularities occurring periodically in time. These are the
superconductors whose gap function vanishes somewhere in momentum space
(Brillouin zone) but whose fermionic excitation spectrum is fully gapped. Many,
although not all, of these superconductors are topologically nontrivial. In
contrast, conventional fully gapped superconductors have featureless spectral
form factors which are analytic in time. Some gapless superconductors may also
have singularities in their spectral form factors, but they are not as
ubiquitous and their appearance may depend on the details of the interactions
among fermionic particles which form the superconductor and on the underlying
lattice where the particles move. This work builds on the prior publication [1]
where Loschmidt echo of topological superconductors, related but not identical
to spectral form factors, was studied. It follows that spectral form factors
could be used as a test of the structure of the superconducting gap functions.
