  New scientific investigations of artificially structured materials and
experiments have exhibit wave manipulation to the extreme. In particular, zero
refractive index metamaterials have been on the front line of wave physics
research for their unique wave manipulation properties and application
potentials. Remarkably, in such exotic materials, time-harmonic fields have
infinite wavelength and do not exhibit any spatial variations in their phase
distribution. This unique feature can be achieved by forcing a Dirac cone to
the center of the Brillouin zone ( point), as previously predicted and
experimentally demonstrated in time-invariant metamaterials by means of
accidental degeneracy between three different modes. In this article, we
propose a different approach that enables true conical dispersion at with
twofold degeneracy, and generates zero index properties. We break time-reversal
symmetry and exploit a space-time modulation scheme to demonstrate a
time-Floquet acoustic metamaterial with zero refractive index. This behavior,
predicted using stroboscopic analysis, is confirmed by fullwave finite elements
simulations. Our results establish the relevance of space-time metamaterials as
a novel reconfigurable platform for wave control.
