System with time-reversal symmetry breaking.

We consider a system composed of ferromagnetically aligned localized spins embedded in a simple metal with a spiral spin-density wave. The localized spins and the spins of the extended electrons interact via an exchange interaction. The mean-field Hamiltonian is not invariant under any symmetry operation containing time reversal. There is no spontaneous current, although it is allowed by symmetry. The ultrasonic attenuation in the superconducting phase does not have the usual exponential temperature dependence and might have a peak just below T c , as observed in several heavy-fermion compounds