  New results on the superdeformed $^{196}$Bi nucleus a re reported. We have
observed with the EUROBALL IV $\gamma$-ray spectrometer array a superdeformed
trans ition of 124 keV which is the lowest observed energy $\gamma$-ray in any
superdeformed nucleus. We have de velopped microscopic cranked
Hartree-Fock-Bogoliubov calculations using the SLy4 effective force and a
realistic surface p airing which strongly support the
$K^\pi=2^-$($\pi$[651]1/2$\otimes \nu$[752]5/2) assignment of this su
perdeformed band.
