  In recent work we formulated a new set of electrodynamic equations for
superconductors as an alternative to the conventional London equations,
compatible with the prediction of the theory of hole superconductivity that
superconductors expel negative charge from the interior towards the surface.
Charge expulsion results in a macroscopically inhomogeneous charge distribution
and an electric field in the interior, and because of this a spin current is
expected to exist. Furthermore, we have recently shown that a dynamical
explanation of the Meissner effect in superconductors leads to the prediction
that a spontaneous spin current exists near the surface of superconductors. In
this paper we extend the electrodynamic equations proposed earlier for the
charge density and charge current to describe also the space and time
dependence of the spin density and spin current. This allows us to determine
the magnitude of the expelled negative charge and interior electric field as
well as of the spin current in terms of other measurable properties of
superconductors. We also provide a 'geometric' interpretation of the difference
between type I and type II superconductors, discuss the relationship between
our model and Slater's seminal work on superconductivity, and discuss the
magnitude of the expected novel effects for elemental and other
superconductors.
