  We consider the generation of magnetic field by the flow of a fluid for which
the electrical conductivity is nonuniform. A new amplification mechanism is
found which leads to dynamo action for flows much simpler than those considered
so far. In particular, the fluctuations of the electrical conductivity provide
a way to bypass anti-dynamo theorems. For astrophysical objects, we show
through three-dimensional global numerical simulations that the
temperature-driven fluctuations of the electrical conductivity can amplify an
otherwise decaying large scale equatorial dipolar field. This effect could play
a role for the generation of the unusually tilted magnetic field of the iced
giants Neptune and Uranus.
