  We demonstrate that a weakly disordered metal with short-range interactions
exhibits a transition in the quantum chaotic dynamics when changing the
temperature or the interaction strength. For weak interactions, the system
displays exponential growth of the out-of-time-ordered correlator (OTOC) of the
current operator. The Lyapunov exponent of this growth is
temperature-independent in the limit of vanishing interaction. With increasing
the temperature or the interaction strength, the system undergoes a transition
to a non-chaotic behaviour, for which the exponential growth of the OTOC is
absent. We conjecture that the transition manifests itself in the quasiparticle
energy-level statistics and also discuss ways of its explicit observation in
cold-atom setups.
