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.
dynamical explanation of the Meissner effect in superconductors
leads to the
prediction that a spontaneous
spin current exists near the surface of superconductors
(spin Meissner effect).
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.