  A conventional superconductor is described by a single complex order
parameter field which has two fundamental length scales, the magnetic field
penetration depth \lambda and the coherence length \xi. Their ratio \kappa
determines the response of a superconductor to an external field, sorting them
into two categories as follows; type-I when \kappa <1/\sqrt{2} and type-II when
\kappa >1/\sqrt{2} . We overview here multicomponent systems which can possess
three or more fundamental length scales and allow a separate "type-1.5"
superconducting state when, e.g. in two-component case
\xi_1<\sqrt{2}\lambda<\xi_2. In that state, as a consequence of the extra
fundamental length scale, vortices attract one another at long range but repel
at shorter ranges. As a consequence the system should form an additional
Semi-Meissner state which properties we discuss below. In that state vortices
form clusters in low magnetic fields. Inside the cluster one of the component
is depleted and the superconductor-to-normal interface has negative energy. In
contrast the current in second component is mostly concentrated on the
cluster's boundary, making the energy of this interface positive. Here we
briefly overview recent developments in Ginzburg-Landau and microscopic
descriptions of this state.
