  Phases analogous to supersolids can be realized in spin systems. Here we
obtain the phase diagram of a frustrated dimer spin-1/2 system on a square
lattice and study the collective excitation spectra, focusing on the supersolid
state (SS). In the phase diagram on a parameter space of the exchange
interaction and magnetic field, we find, on top of the SS phase, a phase that
has no counterpart in the Bose Hubbard model and this state becomes dominant at
the region where the enhancement of SS occurs in the bose Hubbard model. We
then investigate the excitation spectrum and spin- spin correlation, which can
be detected by neutron scattering experiments. We obtain an analytic expression
for the spin wave velocity, which agrees with hydrodynamic relations. The
intensity of excitation modes in the spin-spin correlation function is
calculated and their change in the supersolid and superfluid states is
discussed.

Strongly Correlated Electrons